The Integrated Aqua-Vegeculture System, or iAVs, is a carefully designed method for growing food sustainably. It is based on many years of strict scientific study, controlled tests, and checks by other experts.

Think of iAVs not just as different parts working together, but as a precise ecosystem. In this system, every part is crucial for being very efficient, simple, and productive. Just like a high-performance car is built for top function, the iAVs is a system adjusted for best results. Why? Because every detail in its design, from the fish tank’s shape to the exact amounts of each part, has a clear reason.

This handbook is made to help anyone interested in iAVs. It’s for beginners, experienced researchers, or people running a business. To help everyone, this book has two main parts. The first part is about actually building, setting up, and running a successful iAVs. It gives clear steps and the basic information you need to start and maintain a system well. This part focuses on what’s useful and easy to grasp, using less technical terms. The second part goes deeper into the science and harder topics behind iAVs. This part is for those who want to know more about how nutrients move, the microbes involved, making the system better, and the solid research that proves the iAVs method works. It offers the scientific background and specific details helpful for researchers, teachers, and anyone wanting to optimize iAVs.

The Importance of Adhering to the Design

Throughout this handbook, you will find detailed recommendations for system design and operation. It is crucial to understand that these guidelines are not arbitrary suggestions; they are the result of extensive scientific investigation aimed at optimizing nutrient cycling, water quality, waste management, and overall system stability. Following the established methods presented here is the most reliable path to achieving the full potential of iAVs: sustainable, high-yield food production with minimal inputs and environmental impact.

Key Design Elements and Why They Matter

The iAVs methodology is proven and robust, but its success relies on respecting the integrated nature of its design. Altering individual components without a thorough understanding of their contribution to the whole system is akin to modifying a high-performance engine without appreciating the engineering principles involved – the result is often a significant reduction in efficiency, or even outright failure. Small changes can cascade into larger problems, undermining the system’s finely tuned balance and sustainability. Key examples include:

Component Ratios: The specific volume-to-volume (V:V) and volume-to-area (V:A) ratios between the fish tank and the sand biofilter are fundamental. These ratios ensure the biofilter has the capacity to process the nutrients generated by the fish and support healthy plant growth. Deviating from these scientifically established ratios can compromise water quality, create nutrient imbalances, reduce productivity, and destabilize the entire system. While minor adjustments may be possible for experienced users targeting specific outcomes, beginners are strongly advised to adhere strictly to the standard ratios for predictable success.
Fish Tank Geometry: The recommended shape and dimensions of the fish tank are integral to efficient waste management and water circulation. Altering these features without understanding their hydraulic and biological implications can disrupt the system’s natural flow and hinder performance.
The Slit Drain: The recommended slit drain design is not interchangeable with other drainage methods like bulkhead fittings common in traditional aquaponics. The slit drain’s specific design facilitates rapid, complete drainage, which is essential for creating the powerful suction effect that draws vital atmospheric oxygen deep into the sand biofilter – a process critical for microbial health and nutrient cycling. Substituting a less efficient drain compromises this core function.
Sand Specifications: The type and depth of sand used are critical. Modifying these parameters without evidence-based validation can lead to complications like clogging, poor drainage, anaerobic conditions, increased costs, and reduced yields.

Innovation and Validation

While innovation is always encouraged, any proposed modifications should be approached with caution, rigorously tested, and validated through controlled experiments before wider implementation. This ensures that the system’s core attributes – sustainability, efficiency, and ecological balance – are preserved, and that any changes are based on empirical evidence rather than speculation.

OUR GOALS AND PURPOSE

Beyond the technical specifications, the development and dissemination of iAVs are driven by a clear set of core principles and objectives:

TEACH PEOPLE IN NEED TO FEED THEMSELVES AND THEIR COMMUNITIES.

Prime Directive (motive): To effect the timely development of sustainable food production capability for people of absolute existing need. Promote and establish food security, health and vitality in regions constrained by and within increasingly diminished environments globally.

PLEASE HELP YOURSELF AND OTHERS BY HELPING US TO DO THAT (#1). ADVICE, ACTION, EFFORT AND SUPPORT IS REQUIRED.

Desire A: To stimulate and participate in informed, actionable discussions on how to most effectively implement environmentally responsible and ultra-efficient resource application in food production capability for the greatest critical benefit and most immediate result.

STAY CURIOUS, GET INVOLVED, AND BE FACTUAL. ACCEPT ONLY EVIDENCE.

Desire B: To encourage and support empirical investigations in intentional ecosystem food production (efficacy, methods, utility) – as both biosystematics research and sustainable human development disciplines – subject to valid modes of inquiry and elucidation via the scientific method.

2. Introduction to iAVs

2.1. Background

The future of food hinges on our ability to innovate, balancing nutrition, health, and environmental responsibility (Galanakis 2024) in the face of mounting global pressure. This strain stems from a growing population, the escalating impacts of climate change, and the intense resource demands of agricultural expansion and urbanization (Tilman 2011; Boyaci-Gunduz 2021). Conventional agriculture contributes significantly to water use and pollution, while traditional aquaculture can also have environmental drawbacks, necessitating a shift towards more sustainable and resilient food production methods.

In recent years, these chronic challenges have been dangerously compounded by a condensed period of multiple crises, including geopolitical conflicts, pandemics, and severe economic shocks (Galanakis 2021; 2023). This has deepened inequalities and continues to threaten global food security; today, over 40% of the world’s population—some 3.1 billion people—cannot afford a healthy diet (FAO 2024). This fragile situation was laid bare by the war in Ukraine, a conflict whose impacts have rippled through the entire global food system. The war has impacted every dimension of food security—availability, access, utilization, and stability—by driving up food prices and inflation, which erodes purchasing power. It has also disrupted global supply chains and damaged critical infrastructure, affecting physical access to food and creating deep uncertainty about future supplies (El Bilali & Ben Hassen, 2024).

Beyond immediate access, the conflict has highlighted the deep interconnectedness of food security, geopolitics, and sustainability. The economic hardship generated by the war threatens to exacerbate political instability and stall progress towards key Sustainable Development Goals (SDGs), particularly those aimed at eliminating poverty and hunger (El Bilali & Ben Hassen, 2024). In response, there is an urgent and growing call to build more resilient and sustainable food systems that can better withstand such shocks (Tilman 2011; Boyaci-Gunduz 2021). It is in this context—one of chronic stress compounded by acute crisis—that innovative solutions are most needed.

There has also been an increased trend that consumers demand for vegetables with high nutritional values and safe characteristics (Zhang 2019).

The Integrated Aqua-Vegeculture System (iAVs) offers a scientifically validated solution to many of these challenges. It is a powerful method that combines aquaculture (raising fish) with horticulture (growing plants) in a closed-loop, symbiotic relationship. The genius of iAVs lies in its use of a deep sand bed, which acts simultaneously as a physical support for plants, a mechanical filter for solid waste, and a biological engine. Over time, as fish waste introduces organic matter and a thriving microbial community develops, the sand bed is transformed. It becomes a true, living soil—a dynamic ecosystem containing the four essential components: minerals (sand), organic matter, water, and air. The result is a low-energy, high-yield, and low-maintenance system designed to empower communities to grow wholesome food sustainably, even in the most challenging environments.

2.2. What is iAVs

iAVs, an acronym for the Integrated Aqua-Vegeculture System, designed for the sustainable production of highly nutritious food. It uniquely combines aquaculture (raising fish for protein) with soil-based horticulture, enabling the cultivation of a wide variety of crops, including fruiting crops, leafy greens and vegetable crops, herbs, and even root crops, within a closed-loop, resource-efficient system. Developed through rigorous research, iAVs utilizes sand not only as the growing medium but also as the system’s primary mechanical and biological filter.

The operational principle of iAVs mimics the natural cycles of freshwater tidal wetlands. It employs an intermittent irrigation regime where nutrient-rich water from the fish tank periodically saturates the sand beds before draining completely. This cyclical process fosters a dynamic interaction between plant roots and the microbial communities thriving within the sand, creating a biologically active, soil-like environment.

Fundamentally, iAVs is engineered to be a low-energy, high-yield, and low-maintenance system. Its primary goal is to empower individuals and communities to grow a diverse range of wholesome food sustainably, even in challenging environments.

An example of a tidal wetland. Joe Mabel, CC BY-SA 4.0, via Wikimedia Commons

2.3. How Does iAVs Work?

iAVs at a Glance: The Basic Cycle

At its simplest, a functioning iAVs consists of four essential physical components:

The Fish Tank: This holds the fish and acts as the primary water reservoir.
The Sand Biofilter(s): These are filled with carefully selected sand. They serve both as the growing area for your plants and as the system’s natural filter.
A Water Pump: Moves water from the fish tank to the sand biofilter(s).
A Timer: Controls when and for how long the water pump runs.

The Basic Cycle (How it Works):

Imagine a simple cycle, powered by nature and a little electricity:

Nutrient Generation: You feed the fish in the fish tank. The fish eat and produce nutrient rich ‘waste’ (effluent).
Irrigation: The timer turns on the water pump for a set period (e.g., 15-20 minutes). The pump moves the nutrient-rich water from the bottom of the fish tank up to the sand biofilter(s).
Filtration & Feeding: The water flows into furrows on the surface of the sand bed and percolates down through the sand. As it does:
1. The sand mechanically filters out solid waste particles.
2. Beneficial microbes living on the sand grains biologically process the dissolved waste/effluent components, converting them into forms plants can use.
3. Plant roots growing in the sand absorb these readily available nutrients. In this role, the plants act as biological filters, absorbing nutrients from the fish farming waste for their growth, which in turn results in cleaner water for the fish (Andriani & Zahidah, 2019).
Return Flow: The now-filtered, cleaner water drains out from the bottom-side of the sand biofilter and flows, by gravity, back into the fish tank.
Drain & Aerate: The timer turns the pump off for a longer period (e.g., 95 minutes). During this time, the sand bed drains completely. This crucial step pulls fresh air (oxygen) deep into the sand, which is vital for healthy plant roots and the beneficial microbes.
Repeat: This intermittent cycle repeats automatically throughout the daylight hours.

In essence: The fish provide the fertilizer, the sand acts as the filter and growing medium, and the plants clean the water while producing food. It’s a highly efficient, integrated ecosystem.

Figure shows an example of furrow irrigation in an iAVs biofilter. Nutrient-rich water flows through the furrows, while plants are grown on the elevated ridges to keep their crowns dry and ensure root access to both water/nutrients and air. Photo courtesy of USDA NRCS.

3. Quick Guide: iAVs in 10 Simple Steps

Select a Suitable Location & Plan the Layout
Excavate a hole for the Fish Tank
Build the Biofilter twice the volume of the Fish Tank
Install a liner in the Tank and the Biofilter, setup Slit Drain
Setup the Water & Air Pumps, Air Stones & Timer
Fill Biofilter with inert Sand with no fines, silt or clay
Shape the surface of the sand into furrows and ridges
Fill the fish tank with Potable Water at a pH of 6.4
Add Plants, 50/50 Fruit and Vegetables/Leafy Greens
& Fish, Feed twice per day

4. Site Selection

Selecting the right site is crucial for the long-term success, stability, and efficiency of your iAVs.

Careful consideration of several factors is essential:

4.1. Utilities and Ease of Accessibility

Reliable Utilities: Access to a dependable water source (municipal supply or rainwater harvesting) and electricity (120/240-volt) for pumps and timers is ideal. For off-grid setups or areas with unreliable power, consider renewable energy sources like solar or wind power with battery backup.
Accessibility: Choose a location with convenient daily access for monitoring, feeding, planting, harvesting, and maintenance, considering proximity to your home or business and ease of access in all weather conditions.

4.2. Ground Stability and Flood Prevention

The stability of the ground is paramount to long-term functionality. An iAVs holds significant weight due to water, sand (approx. 1.5 metric tons/m³), and plant biomass. Unstable, uneven, or poorly prepared ground can cause sinking, tilting, or collapse, leading to operational failure and potential flooding.

4.2.1. Site Preparation for Stability:

Level Ground: Select a site with stable, compacted soil and ensure the ground is level to evenly distribute the weight of the system components. Use tools like a spirit level or laser level to verify accuracy.
Reinforcement: For areas with loose or sandy soils, consider adding a reinforced base, such as a concrete pad or compacted gravel layer, to provide additional support. The size and thickness of the base should be determined by the expected weight of the system and the soil conditions.

4.2.2. Flood Prevention:

Avoid Flood-Prone Areas: Ensure the iAVs is located in an area that is not susceptible to flooding during heavy rainfall or extreme weather events. Consult local flood maps and historical data to assess the risk before selecting a site.
Adequate Drainage: Install drainage channels or grade the site so that water naturally flows away from critical components like the fish tank, biofilter, and sand beds. This prevents pooling water that could lead to waterlogging or erosion. Consider the natural slope of the land and design the drainage system accordingly.
Elevated Placement: In regions prone to heavy rainfall or water accumulation, consider slightly elevating the system components above ground level using platforms or raised foundations. Ensure the foundations are stable and can withstand the weight of the system.

By carefully selecting and preparing the installation site with attention to stability and drainage, you can safeguard the iAVs against structural issues and environmental hazards, ensuring reliable operation over time.

4.3. Protection from Extreme Weather

Site selection should account for prevailing weather patterns. Choosing a location with natural windbreaks (e.g., existing structures or terrain features) can be advantageous.

Where natural protection is insufficient, plan for the installation of structures like greenhouses, hoop houses, or shade cloths (discussed further in the “climate” chapter) to mitigate risks from wind, hail, excessive rain, extreme heat, or freezing temperatures.

4.4. Security Measures

Security is an important consideration for any iAVs installation. While this section provides general guidelines, remember that specific security needs will vary depending on your location and circumstances.

For more detailed information, consult local law enforcement or security professionals.

Basic Physical Security:
- Fencing: A fence can deter casual theft and vandalism. Consider local regulations regarding fence height and materials.
- Lighting: Motion-sensor lights can illuminate the area and deter intruders.
- Locks: Secure access points to your iAVs with appropriate locks.
Surveillance:
- Surveillance Cameras: Consider installing surveillance cameras to monitor activity around your iAVs.
Community Awareness:
- Engage with Neighbors: Building relationships with neighbors can increase awareness and provide an extra layer of security.

4.5. Aesthetics: Visual Appeal and Practical Benefits

Aesthetics in iAVs refers to the visual appeal and overall design harmony of the system. A thoughtfully designed iAVs can seamlessly integrate into residential, community, or commercial settings, significantly enhancing its acceptance and adoption. By proactively addressing aesthetic considerations, system designers can mitigate concerns about visual impact and potential effects on property values, thereby making the system more appealing to both users and the surrounding community.

Cleanliness and organization not only improve functionality but also enhance the system’s visual attractiveness. The location of the system also plays a crucial role in its aesthetic impact. Placing the iAVs in a way that complements the surrounding environment can enhance its integration into the landscape and minimize visual intrusion.

For educational or commercial purposes, strategic visibility can also be important, allowing the system to serve as a showcase for sustainable practices and attract attention.

By prioritizing aesthetics during planning and construction, iAVs can effectively balance functionality with visual appeal, fostering wider acceptance, promoting sustainable agricultural practices, and creating a positive impact on the surrounding environment.

5. Climate

Once a suitable site has been selected, understanding and adapting to the local climate is paramount for the successful operation of an iAVs.

Climate encompasses various factors, including prevailing weather patterns, temperature, sunlight availability, humidity, and day-length, all of which significantly influence fish health, plant growth, system design, and overall productivity.

This section explores these key climatic variables and their implications for managing an iAVs in different environmental settings.

5.1. Weather Considerations

To mitigate the effects of potential weather events, natural or artificial windbreaks can be installed around the iAVs to reduce wind speed, protect plants from physical damage, conserve moisture, and reduce evaporation.

In regions with significant rainfall, a greenhouse or protective cover may be necessary to shield the system from direct rain impacts. These covers can also be adapted seasonally for shading purposes. Excessive rainfall can promote fungal growth and oversaturate the soil, stunting plant development.

An additional advantage of using a greenhouse is that it makes it possible to reuse the carbon dioxide emitted by the fish to feed the plants. Thanks to this supplementation with CO2, not only is a higher yield obtained but the carbon footprint of fish production is also reduced (Sas-Paszt 2023).

In hot climates, shading techniques such as shade cloths or reflective materials can prevent overheating and sunburn in plants. In colder climates, insulating fish tanks and biofilters or using covers during cold nights can help maintain water temperature and protect plants from frost damage.

5.2. Sunlight and Shade

To optimize sunlight exposure for iAVs, consider the following guidelines:

Select a Sunny Location: Ensure the system is placed in an area that receives at least 6 hours of direct sunlight per day, with 12 hours being ideal for most crops. While plants generally thrive in full sun, shade structures may be necessary in extremely hot climates to prevent plant overheating and sunburn.
Consider Solar Power: For off-grid systems or those aiming for greater sustainability, solar panels can power pumps and other equipment. Solar energy is a reliable option in sunny regions, reducing reliance on grid electricity.
Avoid Tree Proximity: Do not place the iAVs under trees, as falling leaves and debris can clog the sand biofilter, disrupting water flow.
Monitor Shadows and Seasonal Changes: Be aware of shadows from trees, buildings, or other structures that may reduce sunlight. Seasonal changes in sun angles can also affect light availability. In winter or regions with shorter daylight hours, supplemental lighting or adjusting plant varieties to those suited for lower light conditions may be needed. Adjusting plant spacing or reorienting shade structures can further optimize sunlight throughout the year.

5.3. Temperature

Temperature directly affects both plant growth and fish health. Maintaining optimal temperature ranges is essential to ensure system stability and productivity.

High Temperatures: In hot climates, elevated temperatures can lead to excessive water evaporation, resulting in significant water loss and increased stress for both plants and fish. To mitigate these effects, shading techniques such as the use of shade cloths, reflective materials, or strategically placed structures can help reduce heat exposure and maintain a balanced environment.
Low Temperatures: In colder climates, low temperatures can slow plant growth and reduce fish metabolism, potentially compromising system performance. Insulating fish tanks, or using protective covers during cold nights, can help maintain stable water temperatures and protect the system from extreme cold.

5.3.1. Temperature Requirements for Freshwater Fish

Fish can die if the water temperature decreases or increases beyond its tolerance limit. This is because fish are very susceptible to drastic changes in temperature (Domingues 2012: Brito 2013).

Freshwater fish species used in iAVs require specific temperature ranges to thrive:

Warm-water species: These species, such as tilapia and jade perch, perform best in temperatures between 25°C and 32°C.

Tilapia fish can grow normally at a temperature range of 14–38°C and spawn naturally at a temperature of 22–37°C. The optimal temperature for the growth of red tilapia fish ranges from 25 to 30°C (Parsono 2021). The growth of red tilapia fish will be disrupted if the water body temperature is lower than 14°C and or higher than 38°C. At temperatures lower than 6°C or higher than 42°C, tilapia fish experience severe stress and die (Sahubawa 2025).

Cold-water species: Species like rainbow trout and brown trout prefer cooler temperatures, typically ranging from 12°C to 17°C.

Deviations from these optimal temperature ranges can lead to stress, reduced feeding activity, slowed growth rates, or even mortality. If environmental conditions consistently fall outside these ranges, implementing heating or cooling solutions may be necessary to stabilize the system and safeguard fish health.

By carefully managing temperature through appropriate design and interventions, iAVs operators can optimize both aquaculture and horticulture components for sustainable food production.

5.4. Humidity

Humidity plays a critical role in both plant health and water management in iAVs.

High Humidity: In tropical or humid environments, reduced evapotranspiration can promote faster plant growth. However, this also raises the likelihood of fungal diseases. To mitigate this risk, proper ventilation and adequate plant spacing are essential.
Low Humidity: In arid or desert climates, low humidity accelerates water evaporation. Strategies such as using shade cloths can help conserve moisture and maintain optimal growing conditions.

5.5. Climate Variations

iAVs is adaptable to diverse climates, but each region presents unique challenges that require tailored strategies for optimal performance.

5.6. Arid/Desert Climates

iAVs was originally developed for arid and semi-arid regions where water scarcity is a significant challenge. Its efficient water management, achieved through sand filtration and moisture retention, makes it particularly suited for these environments.

Water Management: Ensure you have adequate water storage.
Dust and Wind: In desert climates, dust storms and high winds can clog sand filters or damage plants. Windbreaks and protective covers can mitigate these issues.
Shading: High ambient air temperatures cause leafy vegetables to bolt, negatively affecting their growth and quality (Somerville 2014). High temperatures and intense sunlight can stress plants. Shade cloths or reflective materials help prevent overheating and sunburn.

Steel-framed greenhouse under construction in Egypt, showcasing two biofilters (sand-filled biofilters) lined and prepared for use.

5.7. Temperate Climates

Temperate climates experience moderate rainfall and distinct seasonal changes. While iAVs can perform well in these regions, adjustments may be needed to address temperature fluctuations and seasonal variations.

Frost Protection: During colder months, frost can harm plants and fish. Insulating fish tanks and biofilters, and using protective covers during cold nights, helps maintain stable temperatures.
Seasonal Adjustments: In winter, shorter daylight hours may require switching to crops suited for lower light conditions or using supplemental lighting.

5.8. Tropical/Monsoon Climates

In tropical regions with high temperatures and humidity year-round, growers may face challenges related to excess moisture during the wet season causing high humidity levels.

Drainage and Waterlogging Prevention: Excessive rainfall can cause waterlogging in the sand biofilter, thereby reducing oxygen availability for plant roots. Covering the biofilter during heavy rain can prevent this. Heavy rainfall can flatten out the ridges.
Flooding Prevention: Flooding near the fish tank can introduce debris or pollutants, potentially damaging system components. Proper site selection with good drainage is essential to avoid localized flooding.
Humidity Management: High humidity accelerates plant growth but also increases the risk of fungal diseases. Adequate ventilation and proper plant spacing help reduce disease risk.
Rainwater Harvesting: Monsoon seasons offer an opportunity to collect rainwater for use during drier periods.

6. Light

SavidgeMichael, CC BY 4.0, via Wikimedia Commons

Beyond providing the fundamental energy source for photosynthesis, light quality, intensity, and duration regulate numerous plant functions and developmental processes (Li et al., 2012).

Natural light availability is essential, with most species requiring adequate daily exposure.

6.1. Sunlight

Sunlight, with its broad spectrum of wavelengths including ultraviolet (UV), visible, and infrared (IR) light, is arguably the most critical environmental factor influencing plant production in any agricultural system, including iAVs. Sunlight is essential for plant development, promoting stronger structures, aiding in the synthesis of essential compounds, and enhancing plant resilience against pests and diseases. UV light enhances the production of secondary metabolites, such as flavonoids and anthocyanins, which contribute to plant defense and nutritional quality. Blue light promotes vegetative growth, while red light supports flowering and fruiting.

Plants are exposed to low levels of UV-B radiation, which is a component of sunlight. Research shows that UV-B radiation can trigger stress responses in plants, leading to the production of protective compounds like antioxidants, which improve both plant resilience and nutritional value.

6.2. Orientation

Arranging plants in rows can lead to shading between the rows and within the rows themselves, impacting how light spreads and changes during the day (Trentacoste et al. 2016; Campos et al. 2017).

To maximize sunlight exposure, align crop rows or the greenhouse’s long axis along the North-South (N/S) axis. This orientation minimizes shading from adjacent plants or structures. Rows planted in a north-south direction absorb sunlight more evenly compared to rows planted in an east-west direction (Van Der Meer 2021).

Optimal North/South (N/S) orientation of crop rows or greenhouse layout to maximize sunlight exposure throughout the day, particularly important in regions far from the equator.

The positioning of crop rows or greenhouses along a north-south axis is key for optimizing sunlight capture. This orientation becomes especially important as you move further from the equator. Here, the sun’s path across the sky changes more dramatically with the seasons, unlike the relatively consistent path near the equator. By aligning crops or structures north to south, plants receive sunlight more uniformly throughout the day, promoting even growth and maximizing yield.

Having rows of plants arranged from north to south helps them soak up more sunlight in the summer, especially in regions between 15 and 55 degrees latitude (Mutsaers 1980).

If plants are not planted along the north–south axis, they may not receive sufficient light due to uneven sunlight distribution. For example, in Chinese solar greenhouses, when tomato cultivation shifted from the traditional north–south ridge orientation to an east–west row layout, it caused problems with light exposure. In the east–west arrangement, sunlight distribution became uneven, especially in rows facing north. This reduced photosynthetic efficiency and led to uneven growth and lower yields (Zhang 2024).

6.3. Seasonal Adjustments

When planning for plant growth, it’s important to consider how the amount and quality of sunlight changes with the seasons. Here’s what you need to know:

Light Duration and Intensity: In places where the seasons change a lot, there might not be enough sunlight in winter for plants to grow well.
Light Quality: The color of light changes through the year; for example, there’s more blue light in summer and more red in autumn. These changes can influence how plants grow. By using lights that mimic these seasonal shifts, we can help plants grow consistently throughout the year.

6.4. Staggered Planting

Staggered plant spacing (also known as offset planting) refers to the physical arrangement of plants (e.g., in triangular or hexagonal patterns) to optimize space and resources. Staggered planting can boost crop yield by improving light distribution, allowing more sunlight to reach all parts of the crop and creating favorable conditions for individual plants to grow, even at a standard planting density (Yang 2006).

To ensure plants receive the most sunlight, they should be positioned so that their leaves can capture as much light as possible. This involves arranging the plants in a way that maximizes the exposure of leaf surface area to sunlight. This can be achieved through organized planting rows or support structures like trellises for climbing species.

For low- to moderate-height plants, staggered in-row spacing offers several advantages:

Increases the number of plants per unit area
Reduces shading between adjacent rows during morning and evening
Maximizes leaf surface area for energy capture
Reduces evaporation from the growing media

For example, plants can be spaced 15–30 cm (6–12 inches) apart within rows, with rows spaced 30–60 cm (12–24 inches) apart, depending on species and growth habits.

For tall crops like indeterminate tomatoes, arranging plants closely together in rows can make the most of available sunlight. The top part of the plant, known as the upper canopy, is particularly important because it gets the most sunlight, which helps in photosynthesis and supports the growth of flowers and fruits. Studies have found that improving light exposure in this upper area can increase fruit yield by as much as 20%.

For example, in apple trees, increasing light exposure in the upper canopy has been shown to increase fruit yield by up to 20%. This finding is supported by research on peaches, where fruits positioned at the top of the canopy, which receive more light, exhibit better quality in terms of size, weight, acidity, total sugars, and firmness. Similarly, research on Sanguinelli blood oranges has shown that the upper canopy layer positively impacts total soluble solids content, suggesting a link between light exposure and fruit quality. Additionally, the upper layer of olive trees contributes 60% of the overall production, with fruits having a higher maturity index, less moisture, and more fat content. These results collectively indicate that the strategic placement of fruits within the tree canopy to maximize light exposure can significantly improve fruit yield and quality.

This means that for every 1% increase in how much light the plants can capture, there’s potentially a 1% increase in how much crop you can harvest, assuming water, nutrients, and carbon dioxide levels are also well-managed.

Moreover, by staggering the planting of these tall crops, we not only allow more light to reach the plants but also improve airflow around them. By spacing the planting times of tall crops, we ensure that shorter plants or those in the early stages of growth are not overshadowed. This helps in reducing the chances of diseases like powdery mildew by keeping the plants drier and less prone to fungal infections.

When plants are closer together, the air can become trapped, creating a humid microclimate that fosters fungal growth. By spacing the plants, air circulates more freely, reducing moisture accumulation on the leaves and decreasing the humidity in the plant canopy. This practice significantly lowers the risk of fungal infections, including powdery mildew.

Healthier plants are less susceptible to infections, as their immune systems are not compromised by stress from lack of light or excessive moisture.

Comparison between diagonal/staggered row spacing and traditional row spacing. Staggered spacing reduces shading between plants, improves air circulation, and enhances light interception, leading to better growth and yield.

7. System Size & Layout

Figuring out the right size for your iAVs is a key first step in planning your build. Fortunately, iAVs is designed to be straightforward and scalable.

7.1. Lo-Tech vs Hi-Tech iAVs

iAVs can be implemented using two primary design approaches: lo-tech and hi-tech.

The lo-tech design was intentionally developed to be simple, affordable, and accessible, specifically targeting regions with limited resources and aiming to improve food security. In contrast, the hi-tech design focuses on optimizing efficiency, yield, and profitability through the integration of advanced technologies, typically seen in commercial or research settings where more resources and technical expertise are available.

These versions are not mutually exclusive but rather represent points on a continuum, allowing users to tailor their system to their specific needs, resources, and goals.

7.1.1. Lo-Tech Version

The lo-tech iAVs model is specifically designed for resource-constrained environments, such as Least Developed Countries (LDCs) or other settings where access to technology, capital, and other resources are limited.

This version prioritizes simplicity, affordability, and accessibility, making it particularly valuable in areas where food security is a pressing concern. The lo-tech approach emphasizes resourcefulness and adaptability, leveraging locally available materials and minimizing reliance on external inputs.

While this approach maximizes accessibility and affordability, operators should expect lower maximum yields compared to high-tech systems, which benefit from environmental controls and automation.

Lo-tech systems hold significant potential for addressing food security challenges in areas where land, credit, or technology are not readily accessible, particularly in developing countries (Pantanella, 2010).

Key features of the lo-tech iAVs design include:

In-Ground Construction: The fish tank and biofilter are built directly into the ground, conserving resources, labor, and eliminating the need for costly materials like concrete or prefabricated tanks.
Soil Stabilization: Excavated soil forms the perimeter of the sand biofilter, removing the need for additional materials to stabilize the structure. This also distributes weight across a larger surface area, minimizing the risk of sinking or tilting.
Manual Operation: Manual water transfer methods replace automated systems, reducing reliance on electricity or expensive pumps.
Locally Sourced Materials: Sand biofilters can be constructed from locally sourced materials such as bricks, wood, or other readily available resources.

While lo-tech iAVs may not achieve the same maximum productivity as high-tech systems, it provides a reliable and sustainable source of nutrition in challenging environments, prioritizing functionality and resilience over maximizing yield or profit.

This approach aligns with iAVs’ original goal: to create a low-input, sustainable technology adaptable to diverse contexts. By utilizing locally available resources and minimizing construction complexity, lo-tech iAVs remain affordable and accessible for those who need them most, empowering communities to improve their food security and livelihoods.

7.1.2. Hi-Tech Version

In contrast to its lo-tech counterpart, the hi-tech iAVs model leverages advanced technologies to optimize efficiency, yield, and profitability. Hi-tech iAVs are typically found in commercial settings or research facilities where resources, technical expertise, and capital investment are readily available. These systems represent a significant advancement in controlled environment agriculture, maximizing productivity through precise monitoring and control.

Key features of the hi-tech iAVs design often include:

Automated Monitoring and Control Systems: Real-time monitoring of water quality parameters (pH, temperature, dissolved oxygen), nutrient levels, and environmental conditions, with automated adjustments to maintain optimal conditions.
Precise Irrigation Systems: Digital timers and sensors control precise irrigation schedules, delivering water and nutrients directly to plant roots, minimizing waste and maximizing uptake.
Climate Control Systems: Heating, ventilation, and air conditioning (HVAC) systems maintain optimal temperature and humidity levels, regardless of external weather conditions.
Supplemental Lighting and CO₂ Enrichment: Artificial lighting extends the growing season and enhances plant growth, while CO₂ enrichment further boosts photosynthesis and productivity.

Yields from moderate- to hi-tech iAVs can potentially be two to three times greater per unit area/time compared to lo-tech systems. This significant increase is due to the precisely controlled environment and enhanced inputs that promote optimal growth conditions for both fish and plants.

The choice of which variation to implement depends on the specific context, including available resources, technical expertise, and desired outcomes.

The lo-tech variations emerged as a way to make iAVs more accessible in areas with limited resources, while high-tech variations aim to maximize the potential of the technology in commercial settings. Both variations contribute to the overall goal of iAVs: to provide a sustainable and efficient method for producing food and enhancing food security.

Getting Started

A well-established and recommended starting point, proven through research and practice, combines a 1,000-liter (approx. 264 US gallon) fish tank with 6 square meters (approx. 65 square feet) of sand biofilter growing area.

This standard configuration represents a reliable balance point, ensuring the fish can provide enough nutrients for the plants in the growing area, without overwhelming the system’s natural filtering capacity. Think of this 1000L tank / 6m² grow bed combination as the basic building block.

The beauty of iAVs lies in its modularity. To create a larger system, you simply replicate this standard unit. Need twice the production? Plan for two 1000L tanks and two 6m² grow beds (or one 2000L tank and one 12m² bed). This makes scaling up predictable and manageable.

When planning your space, remember to also factor in adequate room around the fish tank and biofilter(s) for easy access – walking, planting, harvesting, and maintenance are all much easier with clear pathways.

While the specific ratios behind this standard size are based on scientific principles (which we’ll explore later for those interested), focusing on this 1000L tank to 6m² grow bed relationship provides a solid, practical foundation for designing your first iAVs or planning its expansion.

Keep it Simple

Understanding the correct size and proportions for your iAVs components is fundamental. However, the beauty of the iAVs methodology lies in its scientifically validated design. For beginners and most users, the simplest path to success is to strictly follow the standard ratios presented in this chapter (specifically, 1:2 Volume-to-Volume and 1:6 Volume-to-Area). These ratios have been proven through extensive research and practical application to create a balanced and efficient system.

The detailed explanations that follow explore why these ratios work and the potential effects of adjustments. This information is valuable for researchers, advanced users seeking optimization, or those simply curious about the underlying science. However, you do not need to master these details to build and operate a successful iAVs. Simply adhering to the recommended standard ratios is the most straightforward approach.

7.2. Core Ratios: Fish Tank to Biofilter Volume and Area

The scientifically validated ratios of fish tank to biofilter volume (V:V) and area (V:A) are the cornerstone of iAVs design, ensuring optimal system performance. These ratios are to ensure the biofilter has sufficient capacity to process the waste produced by the fish and provide the necessary nutrients for plant growth.

7.2.1. Fish Tank to Biofilter Volume Ratio (V:V): 1:2

The recommended volume ratio of 1:2 (fish tank : biofilter) is essential for providing sufficient biofiltration capacity. For every liter of fish tank volume, two liters of biofilter volume are required. For example, a 1,000-liter fish tank necessitates a 2,000-liter biofilter. This ratio ensures that the sand biofilter has sufficient capacity to handle the nutrient load produced by the fish, providing adequate surface area for microbial activity to convert organic matter into plant-available nutrients.

7.2.2. Fish Tank to Biofilter Area Ratio (V:A): 1:6

Complementing the volume ratio, the surface area ratio of 1:6 (fish tank volume : biofilter area) is equally critical. For every cubic meter of fish tank volume, the biofilter requires six square meters of surface area. This high surface area to volume ratio maximizes the area available for biofilm development, enhancing filtration, nutrient conversion, and oxygenation within the sand biofilter.

7.3. Flexibility in System Layout

While the 1:2 V:V ratio is standard, iAVs design allows for flexibility in layout and some adjustments to ratios to suit specific needs and goals.

The required biofilter volume can be achieved with:

Single Large Bed: One biofilter bed twice the volume of the fish tank.
Multiple Smaller Beds: Several smaller biofilter beds whose combined volume equals twice the fish tank volume.

This modularity allows iAVs to be adapted to various spaces and site constraints without compromising the scientifically validated principles.

Key Takeaway: Standard iAVs Ratios (Essential)

Volume Ratio (V:V): 1 part Fish Tank Volume : 2 parts Biofilter Volume (e.g., 1000L tank needs 2000L biofilter)
Area Ratio (V:A): 1 part Fish Tank Volume (in m³) : 6 parts Biofilter Surface Area (in m²) (e.g., 1 m³ tank needs 6 m² biofilter area)
Why Follow Them? These ratios ensure the biofilter can effectively process fish waste and provide sufficient nutrients for plants. Sticking to these proven standards is the easiest way to achieve a balanced, productive system.
Adjustments (Advanced): Modifying these ratios (discussed earlier) is possible but involves trade-offs and is recommended only for experienced users or researchers aiming for specific outcomes.

7.4. Layout

The physical arrangement, or layout, of the iAVs components – primarily the fish tank(s) and sand biofilter(s) – is a critical design decision influenced by site characteristics, operational goals, and available resources. While the core component ratios (See “System Size”) dictate the relative sizes, the layout determines how these components interact spatially and how water flows between them.

An optimal layout enhances system efficiency, simplifies management, and aligns with the specific constraints and objectives of the installation. In its simplest and often most efficient configuration, an iAVs features an in-ground fish tank receiving water via gravity drain from one or more adjacent sand biofilters, with a single pump lifting water from the tank back to the biofilters. However, various alternative layouts can be successfully implemented.

7.4.1. Key Considerations for Layout Design

Choosing the most appropriate layout requires evaluating several factors:

Site-Specific Constraints: Assess the physical characteristics of the location, including topography (slope), ground surface type (soil, concrete, asphalt), available space, potential flood risks, and prevailing climate conditions.
Operational Goals: Determine priorities such as maximizing production, minimizing cost, ensuring ease of access (ergonomics), or creating an educational display. The intended scale (home vs. commercial) will also heavily influence layout choices.
Budget and Materials: Evaluate the cost and local availability of construction materials needed for different layout options (e.g., excavation vs. building retaining walls or support structures).
Aesthetic Preferences: Consider the desired visual integration of the system within its environment. Should it blend in or serve as a prominent feature?

7.5. Water Circulation Layouts: Gravity-Fed vs. Sump Systems

Two primary configurations govern water circulation between the fish tank and biofilter(s):

7.5.1. Gravity-Fed Layout (Preferred Option)

The gravity-fed layout is the standard and recommended design for iAVs due to its inherent simplicity and efficiency. In this configuration, the sand biofilter(s) are positioned physically higher than the fish tank. Water is pumped from the fish tank up to the biofilter inlet(s). After percolating through the sand, the filtered water drains via gravity directly back into the fish tank.

Advantages:

Simplicity: Requires only one pump, reducing potential points of mechanical failure and simplifying operation and maintenance.
Cost-Effectiveness: Lower initial equipment costs (one pump) and lower energy consumption.
Thermal Stability: Placing the fish tank in-ground leverages the surrounding earth’s thermal mass to buffer water temperature fluctuations, benefiting fish health.

7.5.2. Sump Tank System

A sump tank system is an alternative layout used when a gravity-fed design is not feasible. In this setup, a sump tank (an auxiliary reservoir) is placed at the lowest point, typically below the biofilter drain outlet. Water drains from the biofilter(s) into the sump via gravity. A first pump then lifts water from the sump back to the main fish tank. A second pump moves water from the fish tank up to the biofilter(s) for irrigation.

Advantages:

Flexibility: Allows fish tanks and biofilters to be placed at the same elevation or on impermeable surfaces (e.g., concrete) where excavation is impossible or undesirable.
Flood Mitigation: Can be designed to manage excess water in flood-prone areas, although careful engineering is required.

Disadvantages:

Increased Complexity: Requires two separate pump circuits, additional plumbing, and often level-control mechanisms (like float switches), increasing potential failure points and maintenance needs.
Higher Costs: Increased initial equipment costs (two pumps, sump tank) and higher ongoing energy consumption compared to the gravity-fed system.
Space Requirements: The sump tank occupies additional physical space.
Risk Mitigation: A critical potential failure point is the sump pump. If it fails, the fish tank could be pumped dry while the sump overflows. Installing a reliable low-level float switch in the fish tank, wired to cut power to the fish-tank-to-biofilter pump if the water level drops dangerously low, is an essential safety measure for sump-based systems. Using a dual sump pumps can also increase reliability in case one fails, but a sump pump still increases the risks of failure.

This diagram illustrates a sump system where the biofilters are positioned on-ground. This layout is useful when in-ground biofilters are not feasible, such as on rooftops or in areas with poor soil conditions. The water exits the biofilter via a slit drain and into the pvc pipe, and then into the sump tank and a pump returns the water to the fish tank.

A sump with dual pump setup for better reliability. SuSanA Secretariat, CC BY 2.0 , via Wikimedia Commons. This image shows a sump system with a dual pump setup for increased reliability. This redundancy is particularly important in sump systems to mitigate the risk of pump failure.

7.6. Biofilter Positioning Options

The physical placement of the sand biofilter relative to the ground level impacts cost, accessibility, and thermal performance. There are three primary options:

7.6.1. In-Ground Biofilters (Preferred Option):

The in-ground option is considered the most efficient, durable, and environmentally-friendly choice. In-ground biofilters are cost-effective since they eliminate the need for heavy structural support and are ideal for long-term use in stable environments. This is also the simplest and most economical approach to constructing an iAVs. Additionally, this method offers natural insulation.

7.6.2. On-Ground Biofilters:

The on-ground installation option is more convenient to set up compared to the underground option, as it eliminates the need for excavation. It is more accessible for maintenance and harvesting purposes, although it does necessitate the construction of biofilter walls.

This picture illustrates the ‘on ground’ option.

7.6.3. Above-Ground Biofilters:

Above-ground biofilters are designed at waist height, providing ergonomic access and making them particularly suitable for individuals with mobility challenges, including wheelchair users. Their versatility and accessibility make them an excellent choice for educational and urban settings.

Above-ground biofilters offer convenient access for maintenance and harvesting, but they are also the most costly and intricate to construct due to the need for a robust supporting structure for the biofilter’s weight.

Structural Requirements for On-Ground and Above-Ground Biofilters:

Due to the significant weight of sand (approximately 1.5 metric tons per cubic meter), on-ground and above-ground systems require robust structural support to ensure safety and durability. Materials such as reinforced steel or treated wood are recommended for their strength and longevity. The choice of materials and design should be carefully evaluated based on site conditions, intended use, and available resources.

Safety Tip: Always prioritize safety in construction. Ensure that above-ground biofilters are built with materials capable of handling the substantial weight of sand to prevent structural failure.

7.7. iAVs Layout Options

The following examples illustrate the versatility and adaptability of iAVs layouts, showcasing a range of configurations to suit different needs and scales.

These examples collectively demonstrate that iAVs is not limited to a single rigid design, but rather a flexible framework that can be tailored to meet a wide array of operational goals, spatial constraints, and resource availability.

Higher stocking density tank with proportionally larger filter capacity. Pairs of biofilter with dedicated pumps on alternating (out of sync) schedules. Multiples can be set adjacent (parallel) with an operable walk-way for access above the fish tanks.

These images show the construction of the ‘circle of life’ iAVs, designed by Dr. McMurtry.

Use of this comparative scale was suggested by Dr. H. Douglas Gross (Professor Emeritus, Crop Science at NCSU – Assistant Director, International Programs). The fish tank in the ‘Parking Space’ iAVs layout was one large rectangular plywood tank which spanned one short edge of the sand biofilter. The tank, which was buried in the ground so that the biofilters could drain into it, had a sloping base – so that solids settled to within reach of the pump.

Virtually and shape in plan is possible, circular, ‘organic’, irregular, triangular, oval, etc

8. Fish Tank

The iAVs begins with a fish tank which serves as the aquatic environment for the fish and also acts as a reservoir for the water that circulates throughout the system (McMurtry 1990a).

8.1. Introduction: The Central Role of the Fish Tank

A well-designed fish tank is crucial for maintaining water quality and ensuring efficient waste management, which are essential for the health of both the fish and plants in the system. While specific shapes offer optimal performance, the most critical design feature is ensuring efficient waste removal. For practical purposes, the key is a sloped bottom that directs solid waste towards the pump intake. Focus on the functional requirement – getting waste to the pump – rather than achieving a perfect geometric form if resources or skills are limited.

8.2. Optimal Fish Tank Design: Shape and Geometry

The shape and geometry of the fish tank are key factors in optimizing waste management and water quality in iAVs. The recommended shape is rectangular with rounded corners when viewed from above, and catenary-shaped in vertical cross-section.

Side-view illustration of a catenary-shaped fish tank, designed with an optimal width-to-depth ratio. The diagram highlights the placement of key components, including the water pump, air stones, and optional netting to minimize fish disturbance of solid ‘’waste’’.

8.2.1. The Catenary Shape: Advantages and Creation

A critical design element is the sloped bottom, which directs the flow of water and solid fish waste towards a central collection point. The bottom of the fish tank should have a U-shaped or catenary-shaped contour when viewed from the side. A catenary shape increases the stability of the side walls, reducing the likelihood of collapse.

This slope is essential for efficient waste management and encourages the natural settling of solid ‘waste’, such as fish feces and uneaten feed, toward a central low point, allowing the water pump (or pump intake) to easily draw nutrient-rich effluent and transfer it to the biofilters for plant use (McMurtry 1997a, 1997b; Palm 2019). This feature simplifies maintenance, enhances ‘waste’ management, and ensures efficient operation of the system.

8.2.2. How to Dig and Shape a Hole into a Catenary

To create a functional fish tank with a catenary shape, follow these steps:

Excavation of the Hole: Begin by marking the desired area for the tank. Ensure the dimensions are appropriate for the intended volume of water and fish capacity. Dig a hole with uniform depth, keeping the sides sloped inward as you go deeper. This general slope will serve as the foundation for shaping the catenary curve.
Forming the Catenary Shape: Use a flexible chain or rope to define the catenary curve. Suspend it freely between two fixed points at the desired width of the tank. The natural sagging shape of the chain under its own weight represents a perfect catenary. Place stakes or markers along the ground beneath the chain to trace its curve. Adjust the excavation to match this traced outline, ensuring that the walls of the hole align with the catenary profile.
Refinement: Smooth out irregularities in the walls to maintain consistency with the catenary curve. This step is crucial for structural stability and efficient water flow within the tank. Compact the soil along the walls to prevent erosion or collapse.

By following these steps, you can achieve a durable and cost-effective fish tank shaped like a catenary, leveraging its natural structural advantages.

Construction of a rectangular fish tank with rounded corners (top view) and a catenary-shaped bottom (side view), showcasing an optimal design for structural integrity, efficient water circulation, and effective solid ‘waste’ removal.

Newly installed fish tank in a larger integrated aquaculture system. The tank on the right contains fingerlings acclimating in floating bags to adjust to water conditions. In the background on the left, another fish tank is visible along with its associated sand biofilters. While the biofilters for the fish tank on the right are not shown in this image, they follow the same layout as those on the left. Each fish tank is equipped with multiple strategically placed water pumps to ensure effective removal of fish ‘waste’ and maintain optimal water quality.

Key Design Elements of an iAVs Fish Tank

The optimal iAVs fish tank should be rectangular with rounded corners when viewed from above. This shape maximizes space efficiency and minimizes areas where ‘waste’ can accumulate. The vertical cross-section should follow a catenary or parabolic curve to evenly distribute water pressure and direct ‘waste’ towards the center for easier removal.

Key Design Specifications:

Minimum depth: 60 cm (2 ft)
Width-to-depth ratio: ideally 1:1, maximum 1:1.5
Smooth liner installation without folds or creases
A grate or mesh netting positioned 5–10 cm (2–4 inches) above the ‘waste’ extraction zone to prevent fish from disturbing settled solids

This design promotes efficient ‘waste’ management, optimal water pressure distribution, and ease of maintenance. The rounded corners and curved bottom prevent ‘waste’ buildup, while the grate or mesh netting helps keep solids undisturbed for easier extraction.

8.3. Fish Tank Placement and Practical Considerations

The placement of the fish tank is a critical consideration in iAVs design, as it directly impacts system performance, fish health, and ease of operation. Whether the tank is above ground or buried, proper location and environmental considerations are essential for long-term success.

8.3.1. Fish Tank Placement in an iAVs (In-ground vs. Above-ground)

Advantages of an In-Ground Fish Tank

Placing the fish tank partially or fully in the ground offers several benefits:

Space Efficiency: In-ground tanks save above-ground space, allowing for more efficient use of the surrounding area for biofilters, pathways, or other components.
Improved Aesthetics: A buried or partially buried tank integrates more seamlessly into the environment, creating a cleaner and more visually appealing system.
Temperature Stability: The surrounding soil acts as a natural insulator, reducing temperature fluctuations and helping maintain stable water temperatures – critical for fish health.
UV Protection: The ground shields the tank from direct sunlight, reducing UV exposure that can degrade materials (e.g., plastic liners) and limit algae growth in the water.

While the presence of some light is beneficial for fish health, it is essential to shade fish tanks from excessive indirect, as well as direct sunlight, whether the tank is above ground or in-ground.

Importance of Shading the Fish Tank

Shading the fish tank is essential for all systems – whether the tank is above ground or in-ground:

Prevents Overheating: Direct sunlight can cause water temperatures to rise dangerously high, stressing or even killing fish. Shading helps maintain a safe temperature range.
Reduces Temperature Fluctuations: Consistent shading minimizes temperature swings, which can occur even with in-ground tanks during extreme weather conditions.
Limits Algae Growth: Light exposure promotes algae proliferation (Jiang et al., 2020), which can deplete oxygen levels and reduce water quality. Shading mitigates this risk.

It is equally important that the tank is not completely covered or in continuous darkness. This is because a natural photoperiod and appropriate light intensity are crucial for fish, influencing their biological rhythms, metabolic rates, and feed intake (de Alba et al., 2024; Elsbaay, 2013).

Exposure to a natural photoperiod may contribute to enhanced growth, whereas reduced light levels or continuous darkness disrupt the fish’s biological clock and natural rhythms, which may negatively impact their growth (de Alba et al., 2024; Elsbaay, 2013). Therefore, the optimal approach involves providing sufficient ambient light to support natural biological processes while mitigating the detrimental effects of excessive light exposure.

Accessibility Considerations

Regardless of placement, accessibility must be prioritized to ensure smooth operation:

Feeding: The tank should be easily reachable for daily feeding routines.
Maintenance: Sufficient access is required for cleaning, water quality testing, and equipment adjustments.
Harvesting: Ensure convenient access to fish for harvesting or transferring them.

8.3.2. Protecting Fish Tanks with Netting and Covers

To ensure the health and safety of fish, it is essential to cover the fish tank with appropriate netting or other protective materials. Fish are known to exhibit jumping behavior, particularly when startled, which can lead to their escape from the tank and potential losses.

A fine mesh net placed securely over the tank prevents fish from jumping out while still allowing adequate air exchange and visibility for monitoring. In an outdoor iAVs, additional protective measures may be required to safeguard the tank from pests, predators, and contaminants.

Birds, rodents, and other wildlife can pose significant risks to fish health by introducing stress, predation, or contaminants such as droppings, which may lead to water quality degradation or the spread of diseases. To address these risks, a durable cover or enclosure made from materials such as shade cloth, hardware mesh, or polycarbonate sheeting can be used. These materials not only act as a physical barrier but may also provide shade, reducing water temperature fluctuations and algae growth.

An indoor fish tank equipped with a protective netting to prevent fish from jumping out.

8.3.3. Optimizing Fish Tank Design for iAVs (Summary of Key Design Elements)

The design of the fish tank is crucial for effective ‘waste’ management and maintaining optimal water quality in iAVs. A catenary-shaped tank, with a ‘U’ or ‘V’ profile, offers significant advantages over traditional flat-bottom or sharp-corner tanks by improving ‘waste’ removal efficiency and water circulation. This shape minimizes dead spots where ‘waste’ can accumulate, ensuring continuous water flow.

The curved design naturally directs ‘waste’ toward the lowest point of the tank, facilitating efficient removal through the pump intake and preventing the formation of anaerobic zones that could produce harmful gasses like hydrogen sulfide. Efficient ‘waste’ management is key to maintaining water quality by reducing organic matter in the water, which in turn minimizes oxygen depletion caused by decomposition. Clearer water improves fish visibility for feeding and allows better observation of the aquatic environment.

Additionally, the catenary shape reduces the risk of gill clogging and physical damage to fish from suspended particles.

Cross-sectional view of an ideal iAVs fish tank shape.

9. Biofilter

The biofilter serves as both a biological and mechanical filter:

Container: Use a durable, food-grade container.
Slope & Drainage: Slope the biofilter at a gradient of 2 cm/meter to ensure efficient drainage, with a slit drain at the lowest point.

Getting the Basics Right

While you can build biofilters in various shapes and sizes, a few key dimensions are important for basic function. The most critical aspects are ensuring the sand is deep enough (at least 30cm / 12 inches at the shallowest point) and that the bottom of the bed slopes correctly towards the drain (at the deepest point).

The following sections discuss specific recommendations for length, width, depth, and the crucial bottom slope. While details on aspect ratios or very long beds are provided for advanced users or specific situations, focusing on the minimum depth and the correct bottom slope (2cm drop per meter length / approx. 1/4 inch per foot) will ensure your biofilter drains properly.

Example of a biofilter constructed using wood as the primary material.

9.1. Dimensions

The aspect ratio, or the proportion of width to length, of a biofilter in iAVs are flexible as long as the total volume and depth is at the recommended ratio.

9.1.1. Length

For home systems, biofilters are typically shorter, ranging from 3 to 6 meters (approximately 10 to 20 feet) in length, to facilitate easier maintenance, and grading, for drainage. In comparison, longer beds demand additional effort to ensure proper drainage and structural stability, and they require longer access routes for maintenance.

Biofilters exceeding 6 meters (20 feet) in length are considered long. The increased length may impact water distribution across the biofilter, requiring modifications to ensure complete and timely drainage.

Biofilters over 10 to 12 meters (33 to 39 feet) are classified as very long and require careful planning for efficient drainage. Multiple water input points may be necessary to maintain even water distribution along the entire length of the bed.

Installing multiple drainage exit points with collection piping or channels is also recommended, this is covered in the ‘drainage’ section of this book.

9.1.2. Depth

The biofilter depth suitable for most horticultural purposes typically ranges between 300 mm and 400 mm. To ensure proper functionality, the biofilter bed is sloped to facilitate effective drainage The shallowest side of the sand layer must be at least 30 cm deep.

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Due to the sloped base, the sand will be deeper at the end of the biofilter closest to the fish tank. For example, in a 3-meter-long biofilter bed with a slope of 2 cm per meter, the sand depth would measure 30 cm at the shallow end and 36 cm at the deeper end. To accommodate this slope and allow for some freeboard (space above the sand to prevent overflow during irrigation), the depth of the biofilter structure itself would need to be approximately 40 cm. This design ensures proper containment of the sand, efficient water distribution, and optimal filtration performance.

The term ‘freeboard’ refers to the vertical distance between the top of the sand and the upper edge of the biofilter walls. The iAVs research used a freeboard of 2 inches.

Plants develop root systems proportional to their shoot (aerial) growth to support water and nutrient uptake. Adequate depth is necessary to facilitate efficient nutrient assimilation and provide ample rooting volume for optimal plant growth.

A depth of less than 30cm (12 inches) is not ideal for most crop species. Reducing the sand volume proportionally reduces the habitat available for the microfauna essential for the system’s functioning.

If you are growing very shallow-rooted crops, in theory, you may compensate for a reduced bed depth by increasing the surface area of the sand biofilter. It is also important to note that while shallow beds, such as, 200 mm (8 inches), may be suitable for some plant species, this has not been confirmed through any scientific experiments or testing.

Increasing the depth of the sand could provide additional surface area for rooting space and the beneficial bacteria to grow, potentially improving the efficiency of the biofilter. Increasing the depth of sand can support longer-term crops and vertical crops which both have extensive root systems.

When considering increasing the sand depth beyond the recommended guidelines, it is important to carefully evaluate the potential advantages against the extra costs and effort involved. The effects of deeper sand on productivity have not been conclusively established by either anecdotal accounts or thorough scientific studies.

9.1.3. Width

The width of the biofilter should align with the available space while allowing for easy maintenance access. Standard widths typically range from 900 mm to 1200 mm. The width is intentionally kept to a manageable size to allow an operator to easily reach at least halfway across the bed, ensuring ease of maintenance and planting or harvesting activities.

In cases where biofilters exceed the standard width, it is advisable to incorporate access aisles. These aisles facilitate easy movement around and within the system. In some commercial operations, biofilters can be as wide as 10 meters, with walkways constructed in the sand to provide access to plants.

When working with large sand beds in an iAVs, careful navigation is crucial to maintaining the bed’s structural integrity. Walking directly on the sand can create undesirable surface disruptions, forming indentations and ridges that compromise the bed’s uniformity. To mitigate this issue, it is recommended to establish designated pathways using planks or stepping stones that provide a stable walking surface while minimizing direct contact with the sand.

The sand surface is particularly sensitive to human interaction, and while the sand itself won’t compact in the traditional sense, walking on it will alter its smooth, level profile. By strategically placing walking surfaces across the sand bed, operators can preserve the bed’s critical structural characteristics

Some growers adopt the practice of using specific foam sandals within the greenhouse for traversing the sand beds. This footwear is designed to distribute weight more evenly. These measures ensure the sand bed remains smooth and undisturbed.

This image shows an example of a wide biofilter used in a commercial operation. They use the sand between the plants as walkways and use soft sandals to prevent compaction of the sand.

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In-ground biofilters under construction with walkways between each one.

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9.1.4. Shape

Rectangular biofilters are common due to their practicality and ease of construction. The standard dimensions for these biofilters are approximately 1.2 meters (about 4 feet) in width and range from 1 to 3 meters (approximately 3 to 10 feet) in length.

The biofilter can take on various shapes, provided it meets the functional requirements of effective drainage (by using a sloped bottom and a slit-drain) and maintenance accessibility. The most common and practical shape is a rectangular biofilter. This design is widely used because it allows for efficient water flow, easy access for planting and maintenance and is easiest to build.

This image shows an example of a curved biofilter.

9.2. Slope

The slope of the bottom of the sand biofilter is a crucial design element that ensures complete, and rapid, water drainage after an irrigation cycle, preventing waterlogging and the formation of anaerobic zones.

The bottom of the sand bed is gently sloped (2cm per meter) from the inflow end to the drain end, allowing water to flow efficiently through the sand and exit completely and rapidly at the end of each irrigation cycle.

The biofilters have a sloped bottom with a gradient of 1:200 along the length. This slight slope is designed to facilitate drainage of the water and is crucial for ensuring proper drainage of the water back into the fish tanks after it has percolated through the sand bed. The slope prevents water from pooling in the biofilters, ensuring that the water consistently flowed back to the fish tanks, completing the circulation loop. (McMurtry 1997a, 1997b).

An ideal slope is 1:50, which translates to a vertical drop of 20 mm per meter of bed length. For instance, a 6-meter-long sand bed requires a total slope of 120 mm from one end to the other, while shorter beds, such as those measuring 3 meters, need a slope of 60 mm.

Importantly, the surface of the sand should remain nearly level, as the slope applies only to the bottom of the sand bed. This design ensures that all water drains effectively between irrigation cycles, preventing standing water at the bottom of the bed.

Standing water can lead to anaerobic conditions, which promote harmful microbial activity and root rot. Without a proper slope, water may accumulate in certain areas, creating oxygen-depleted anaerobic zones that foster harmful bacteria and reduce overall system performance.

For longer sand beds exceeding 3 meters or those using less permeable sand, additional drainage provisions may be necessary.

9.3. Materials

A biofilter can be constructed using materials such as wood, metal, or plastic. The frame should be sturdy and capable of supporting the weight of the sand and water.

Wood is a versatile and affordable material. It is easy to work with and can be customized to fit any size or shape. However, wood is susceptible to rot and decay, especially when exposed to moisture. It may also require regular maintenance and replacement over time.

The picture above shows a biofilter frame made from hardwood sleepers.

The picture above shows a biofilter made from bricks.

9.4. Multiple Biofilters per Fish Tank

A common iAVs setup includes one fish tank and a biofilter, but it’s feasible to have multiple biofilters supported by a single fish tank.

An initial volume ratio of 1:2 between the fish tank and biofilter is recommended, given an appropriate stocking density and feed rate. However, the actual implementation will depend on the operator’s circumstances and preferences. This ratio can be increased as the fish biomass density and feed rate grow.

The goal is to maintain a balance between plant uptake and the ‘waste’ produced from a specific feed ration. The larger the daily feed ration, the bigger the biofilter and the more plants will be needed to balance uptake with input.

If you start with a low fish density/feed rate compared to the total biofilter available, you don’t need to use the entire filter volume. You can construct a larger filter than initially needed and gradually increase its usage as the fish grow and the feed rate increases.

To limit the filter volume in use, you can block irrigation channels with sand or insert a temporary barrier into the sand column.

Alternatively, you can add more biofilters as needed to process extra ‘waste’. In this case, staggering the tank withdrawal events will allow for more frequent ‘waste’ extraction.

While the usual iAVs configuration comprised one fish tank and a sand biofilter, there is no reason why a fish tank ought not support several sand beds. Ultimately, the goal is to match biofiltration capacity to the amount of fish food required for sustainable fish production while providing sufficient nutrients to grow a full range of plants.

Key Takeaway: Biofilter Essentials

Minimum Sand Depth: 30 cm (12 inches) at the shallow end.
Bottom Slope: Must slope downwards towards the drain end. Recommended slope: 2 cm drop for every 1 meter of length (approx. 1/4 inch drop per foot). This ensures complete drainage.
Surface Level: The top surface of the sand should be kept level for even water distribution.
Width: Keep it narrow enough to easily reach the middle for planting/harvesting (typically 90-120 cm / 3-4 feet).
Length: Keep beds under 6m.
Shape: Rectangular is easiest, but the shape can be adjusted.

10. Liners

Liners are waterproof materials used to contain water and prevent leakage in fish tanks and biofilters within iAVs. Typically, liners are installed in both the fish tank and the biofilter.

When selecting liners, it is crucial to prioritize durability, food safety, and non-toxicity to protect aquatic life and maintain water quality. Additionally, proper installation and protection from ultraviolet (UV) exposure are necessary to prevent degradation and extend the lifespan of the material.

In some cases, however, liners may not be required. Pre-built fish tanks or sand biofilters that are already watertight can eliminate the need for liners. Similarly, concrete fish tanks do not require a liner if they are properly sealed. It is important to note that unsealed concrete can affect the pH of the water disrupting the system’s balance.

Investing in high-quality liners is a cost-effective decision for iAVs. While the initial expense may be higher, premium liners offer superior durability and resistance to wear and tear, significantly reducing the likelihood of damage, leaks, or failures. This minimizes the need for frequent repairs or replacements, ultimately saving money over time.

10.1. Types of Liners

PVC Liner: PVC liners are commonly used due to their durability and cost-effectiveness. Made from polyvinyl chloride, they come in various thicknesses and sizes and can be welded to create a seamless lining. However, PVC poses environmental concerns, as it is derived from petrochemicals and can release harmful chemicals like dioxins during production and degradation, especially under prolonged UV exposure.
BTL Liner: BTL liners are reinforced PVC with polyester mesh for added puncture resistance. They are durable, cost-effective, and easy to install but share the same environmental drawbacks as standard PVC liners, including potential chemical leaching and reliance on non-renewable resources.
HDPE Liner: High-density polyethylene (HDPE) liners are more durable than PVC and better withstand sunlight and environmental conditions. They are more environmentally friendly due to recyclability and lower chemical leaching risks but still depend on fossil fuels for production. HDPE can become brittle over time if not treated with UV inhibitors and may be harder to install due to its rigidity.
EPDM Liner: Ethylene propylene die

An easier way would have been to reduce the height of the side panel by the size of the gap.

The picture above shows the biofilter, now painted white, with the slit drain (barely visible) across the bottom right of the biofilter.

2. Line the Bed: Proceed to line the bed with your chosen membrane liner as you normally would, ensuring it covers the entire surface area of the containment vessel.

3. Create the Slit: Using a sharp knife, insert the blade into the gap from the exterior of the vessel. Carefully slice the liner from one end to the other. This process should be quick, taking approximately 5 seconds.

4. Reinforce the Slit: To prevent water from infiltrating beneath the liner, or ‘tracking’ back under the biofilter, place a scrap piece of liner underneath the slit. This step should take an additional 10-15 seconds.

Position the strip so that it extends beyond the edge of the biofilter. Use a food safe glue to stick it to the bottom of the biofilter, underneath the liner.

The water that exits the flap that was inserted under the liner at the slit can fall, without any plumbing, directly into the tank, or onto a cascade aerator, or into a semicircular gutter (like a PVC pipe sliced lengthwise, lined wood V, etc.) and directed anywhere PVC tubing back to the fish tank.

5. Add Pea Gravel or Shade cloth: Inside the vessel, place some pea gravel and/or shadecloth (as pictured above) or a non-metal screen over the interior side of the slit. This helps to ensure sand doesn’t exit the bed. Do not use weed mat or cloth, such as geo fabric as it will restrict the drainage and could cause issues with clogging.

This is an ideal time to ensure that all components of the biofilter system are working correctly before proceeding further. Take this opportunity to thoroughly check that the liner is properly sealed, the pump is functioning as it should, and all connections are correctly installed. Conducting these checks as a final precaution before adding sand to the biofilter is highly recommended.

It is also advisable to test the drainage system at this stage. Using a colored liquid, such as food coloring diluted in water, makes it easier to track water movement and identify any issues. If the drainage system has been constructed correctly and the bottom of the biofilter is properly sloped, there should be no stagnant water present. Any water remaining in the biofilter indicates a problem – either with installation or construction – that must be identified and fixed before moving forward. Taking these steps ensures the biofilter operates efficiently and reduces the risk of future issues.

The gravel and shade cloth should be held in place by covering them with sand. This provides a good opportunity to test the sand retention before shaping the sand and adding plants.

A slit drain at the base of the sand biofilter allows water to exit laterally as a wide sheet, rather than being forced through a restricted downward pipe opening. This design reduces the downward force exerted on the sand, which is a common cause of sand exiting the bed. By directing water laterally, the slit drain helps maintain the integrity of the sand layer.

If all the necessary steps have been followed, there should be no sand exiting the biofilter. In certain cases, a small amount may initially exit, but it should cease after a brief period.

If the sand persists in exiting the biofilter, it indicates that something has been improperly installed, and it should be rectified before proceeding further.

Once the sand has been added to the biofilter bed, it is recommended to run the water pump for 15 minutes and then allow the system to drain for 30 minutes. After this, dig down into the bottom of the biofilter to check for any standing water. While this step may not be necessary if all previous instructions were carefully followed, it serves as an excellent final confirmation that the drainage system is working perfectly. If no standing water is found, this verifies that the biofilter is functioning as intended and ready for use.

12. Water

While environmental factors like light and temperature can be artificially regulated, water quality and availability are critical determinants for successful iAVs operations.

Water quality parameters are of primary importance, directly influencing both fish health and plant vitality (Yildiz 2017). Therefore, effective water quality management is paramount for ensuring high production and quality in aquaculture. Degraded water quality negatively impacts fish growth and disease resistance (Sallenave, 2019; Deswati et al., 2022).

Suboptimal water quality parameters can induce physiological stress, hinder growth, and increase disease susceptibility, potentially leading to significant production losses (MacIntyre et al., 2008). Specifically, improper water management can result in oxygen deprivation, eutrophication, and the proliferation of harmful microorganisms, alongside nitrite and ammonia toxicities (Hoang et al., 2020; Cao et al., 2016; Wu et al., 2020; Yang et al., 2015; Gobler et al., 2012; Sin and Lee, 2020; Liu et al., 2020).

12.1. Introduction

A reliable, high-quality water source is essential for the effective operation of iAVs. The water must be free from harmful substances that could negatively impact plant growth or aquatic life, including:

Biological pathogens (e.g., bacteria, viruses)
Chemical contaminants (e.g., pesticides, herbicides)
Heavy metals (e.g., lead, mercury)
Radioactive materials

Ideally, the water should meet potability standards. According to the United Nations, by 2030, global water supply could fall short by up to 40% if current management practices are not improved. This deficit may result in severe water scarcity affecting 1.8 billion people and placing two-thirds of the world’s population under water stress.

For agriculture – and particularly for iAVs – the quality and availability of water are critical. Unlike other environmental factors such as light or temperature that can be artificially controlled, water’s role in iAVs is indispensable.

We recommend conducting a full elemental analysis of your source water through a competent testing agency.

12.2. Water Sources

Rainwater is the preferred water source for iAVs due to its availability and minimal contamination. However, proper collection and storage are essential to prevent environmental contaminants such as bird droppings, rodents, air pollution, and surface runoff.

In arid regions, rainwater supports sustainable agriculture practices and can provide significant volumes. For instance, a 1,000 square foot (93 square meter) surface area can yield approximately 623 gallons (2,360 liters) of water per inch (25 mm) of rainfall.

While rainwater is ideal, other water sources may also be viable for iAVs. Each alternative should be evaluated based on water quality, availability, and any necessary pre-treatment.

12.2.1. Rainwater

For iAVs, rainwater is the ideal choice. This supports sustainable urban farming, as effective rainwater harvesting conserves water and decreases dependence on city supplies (Russo et al., 2014). Because it starts clean, rainwater is desirable. Capturing and using it efficiently promotes healthy plants and lessens environmental harm (Walters, 2018).

It’s an ideal source because it naturally has a neutral or slightly acidic pH, low mineral content (hardness), and no salt (Somerville et al. 2014). You can easily collect rainwater runoff from surfaces like roofs, gutters, or greenhouses (Fernandes et al., 2015) and store it for later use.

However, setting up proper collection and storage systems is essential. Storing the water effectively, perhaps using rain barrels or underground cisterns often equipped with filters (Maliva & Maliva, 2020), ensures you have a steady supply, especially during dry spells (Traboulsi & Traboulsi, 2017). Good storage also helps prevent runoff and soil erosion (Maliva & Maliva, 2020).

It’s crucial to prevent contamination from things like bird droppings, rodents, air pollution, or surface runoff getting into your stored water (Maliva & Maliva, 2020). Water collected from roofs, in particular, often needs treatment first to remove potential bacteria or pathogens.

You also need to consider a few other things:

Your Roof: The material and age matter. Some materials like shingles, cedar, or uncoated galvanized aluminum, especially on new or very old roofs, might leach chemicals or heavy metals into the water (Clark et al. 2008).
Acid Rain: Check if this is common in your area.
Local Laws: Some places have regulations or restrictions on rainwater collection.

By carefully planning your rainwater harvesting system, you not only get a suitable water source for your iAVs but also manage resources wisely and contribute to better water security in urban areas (Verma 2025).

12.2.2. Mains or municipal supply

Municipal tap water is a readily available option for iAVs, but requires pre-treatment. Cities use chlorine or chloramine to disinfect drinking water, but these chemicals harm fish and vital nitrifying bacteria in your system and must be removed (Hager 2021).

Chlorine can be removed by letting the water sit exposed to air (ideally with aeration or sunlight) for 1-3 days. Chloramine, being more stable, requires chemical neutralization (using a water conditioner or Vitamin C – approx. 1g per 1000L) or activated charcoal filtration (Hager 2021).

While very small water top-offs (under 10%) might sometimes be tolerated without treatment, consistently treating all added water is the safest approach (Hager 2021).

Be aware that tap water can also potentially contain other contaminants like lead or trace chemicals. Regular testing and proper treatment are always recommended to ensure your water source is suitable for your iAVs.

12.2.3. Rivers and lakes

Surface water sources such as ponds, lakes, rivers, and streams are another possibility, but they require careful management. They can easily introduce biological contaminants like pathogens, algae, and snails into your system. Furthermore, pollution and agricultural runoff often contaminate these waters, creating potential health risks for the fish and anyone consuming the food produced (Hagar 2021).

To use surface water safely, regular testing for specific pollutants is essential. Based on those test results, you must apply suitable filtration or purification techniques. We strongly advise consulting with local environmental agencies or water quality experts for recommendations tailored to your region.

12.2.4. Wells and ponds

Wells and ponds offer alternative water sources, but they come with potential contamination risks. Things like nearby septic systems, industrial runoff, or natural mineral deposits can increase levels of unwanted substances, especially metals.

If you’re considering well water, pay attention to potential contaminants like heavy metals, iron, and sulfur. The local geology plays a role too; aquifers in limestone bedrock often produce water that is hard and has high alkalinity (due to carbonates, bicarbonates, etc.). This high alkalinity raises the water’s pH level. Water that is too hard or alkaline may require treatment to make it suitable for your needs (Somerville et al. 2014).

Because of these potential issues, it’s crucial to test your water quality comprehensively at least twice annually. We strongly advise consulting with local environmental agencies or water quality experts and implementing any testing or treatment methods they recommend.

12.2.5. Reverse Osmosis (RO)

Reverse Osmosis (RO) uses a semi-permeable membrane to remove dissolved chemicals and biological contaminants from water sources, producing high-quality purified water suitable for iAVs.

Benefits:

Removes dissolved chemicals and suspended particles
Eliminates biological contaminants like bacteria

Considerations:

Requires additional equipment
Increases operational time and costs

When considering RO for iAVs, weigh the benefits of high-quality water against the added costs and operational complexity.

12.3. Water Use

Water evaporation in iAVs is influenced by several factors, including:

Climate
Greenhouse design
Temperature
Sunlight exposure (insolation)
Relative humidity (RH)
Surface area and type of crops grown

Research from 1986 highlights the water efficiency of iAVs, with daily evaporation rates ranging from 1% to 3% of system capacity. On an annual basis, an iAVs requires approximately 11 cubic meters (2,906 US gallons) of water for every cubic meter (35.3 cubic feet) of system capacity, assuming a 3% daily loss rate.

13. Managing pH in iAVs

For most operators, frequent pH testing and chemical adjustments are unnecessary once the system matures. The primary task is to check your source water pH and adjust it if needed before adding it to the system. Occasional monitoring (e.g., weekly or monthly, or if problems arise) is prudent, especially during startup.

This diagram illustrates the pH scale, which measures the concentration of hydrogen ions (H⁺) to determine whether a solution is acidic, neutral, or alkaline. The optimal pH range for iAVs is 6.4 (±0.4), which supports healthy soil microbiology, plant growth, and fish welfare.

In iAVs, pH management is strategically prioritized to optimize plant health and nutrient availability, recognizing the interconnectedness of the system’s components.

Unlike traditional aquaponic systems that aim for a compromise pH suitable for fish, bacteria, and plants, iAVs prioritizes the needs of the plants, setting the pH to be optimal for their growth and nutrient uptake. This approach acknowledges that the fish, while important, represent the lowest value component in the system and are selected for their tolerance of the plant-optimized pH.

In iAVs, priorities for managing pH are as follows:

Soil microbiology
Plants
Fish

The pH preferences for soil microbiology and plants generally overlap within a certain range, though specific species may have unique requirements. In an iAVs, maintaining a balanced pH is crucial for the health of both plants and fish. Many fish species used in aquaculture can tolerate a range of pH levels, but extremes should be avoided to ensure the well-being of both fish and beneficial microorganisms.

At a water pH of 7.0 or higher, ammonia (NH3) becomes more toxic due to its conversion into un-ionized ammonia (NH₃), which is highly harmful to fish (Collins 1975; Esteves 1998). However, as the pH decreases, ammonia converts to ammonium (NH4+), which is less toxic.

The conversion of ammonia (NH₃) to ammonium (NH₄⁺) occurs through a chemical equilibrium that is directly influenced by pH and temperature, and does not require nitrification or any biological processes.

13.1. Ideal pH for iAVs

In iAVs, the pH of the water is a critical factor directly affecting plant nutrient availability and microbial activity. Generally, plants exhibit high nutrient absorption within a pH range of 5.8 to 6.5 (Rakocy et al., 2006). While macronutrients can often be absorbed across a varied pH range, the availability of many essential elements is highly pH-dependent. Research specific to iAVs by Dr. Mark McMurtry and the iAVs research group at North Carolina State University (NCSU) identified an ideal operational pH of 6.4 (± 0.4). This slightly acidic range, falling within the broader essential range of 5.5 to 6.8, optimizes nutrient uptake by plants and supports essential microbial processes like nitrification.

Phosphorus availability, for instance, is significantly influenced by pH. While fluctuations within an acceptable range occur, phosphorus uptake can be hindered when pH rises above 6.8, even if abundant in the water, because its solubility decreases (Yildiz et al. 2017). Specifically, at pH above 7.0 in aqueous solution, dissolved phosphorus can react with calcium to form unavailable calcium phosphate (Sahubawa 2025), or co-precipitate with metallic compounds like iron and manganese hydroxides (Esteves). Consequently, phosphorus deficiency, often resulting from high pH, can significantly reduce plant growth (Sultenfuss and Doyle 1999). Iron commonly precipitates as hydrous ferric oxide at pH levels above 6.5 (Alt, 1980) .

Furthermore, pH levels above 6.5 can reduce the availability of essential micronutrients such as iron, copper, zinc, boron, and manganese (Trejo-Téllez 2012). Iron (Fe), for example, is best absorbed at a pH between 5.5 and 6.0; its absorption decreases significantly at pH levels above 7.0, an issue particularly evident in traditional aquaponic systems where pH tends to be higher (Lennard and Goddek, 2019; Maucieri et al., 2019b).

A well-maintained iAVs typically stabilizes around a pH of 6.4, ensuring optimal nutrient availability for both macro- and micronutrients, alongside robust microbial activity, which promotes healthy plant growth and overall system performance.

Effect of pH on the root availability of the essential elements in soil. Blue denotes the ideal soil pH for the majority of plants (slightly acidic) , which aligns with the recommended pH for iAVs (slightly acidic). Inspired by an illustration from the North Carolina Extension Gardener Handbook. CoolKoon, CC BY 4.0, via Wikimedia Commons. Maintaining this range ensures plants can efficiently absorb nutrients.

13.2. Temperature

When temperature rises, water molecules move more, leading to more hydrogen ions being present, so the pH number drops and as temperature decreases, pH reading increases (the water appears more alkaline).

Roughly, for every 10°C increase, pH drops by about 0.3 units. For example, from winter (10°C) to summer (30°C), the pH reading could drop by about 0.6 units.

You should be aware that pH readings change with temperature, but you do not need to panic about small pH shifts caused by temperature alone. With a target pH is 6.4 and system temperature ranging between 20°C and 30°C, the natural pH shift caused by temperature will be minor – about 0.3 units at most across that range. This is well within the normal “buffer zone” for systems.

If you want to be extra precise, you can use a pH meter with automatic temperature compensation.

13.3. Monitoring pH Levels in iAVs

Regular monitoring of pH is essential for maintaining balance in an iAVs. In mature systems, minor pH fluctuations are typically self-regulating due to natural processes, reducing the need for frequent adjustments. However, it is still recommended to check and record pH at least weekly using a reliable digital pH meter or test kit. Newly established systems or those experiencing instability may require more frequent monitoring until they stabilize.

Tracking pH trends over time helps identify potential issues early and supports informed decision-making for system management.

13.4. Testing & Adjusting Source Water pH in iAVs

Ensuring the source water has an appropriate pH before introducing it into an iAVs is essential for maintaining a balance between plant health and fish welfare. The pH adjustment process should be approached with care. Begin by preparing small batches of a dilute solution to gradually adjust the pH of your top-up water storage until it reaches a pH of 6.4, with an acceptable range of plus or minus 0.41. Once adjusted, this water can be used to replenish your iAVs as needed.

Practical Method for Managing pH: Set Up a Top-Up Barrel: Establish a barrel (or barrels) where you can adjust the water’s pH in advance. This ensures that appropriately balanced water is readily available whenever you need to top up your fish tank.

Safety Guidelines for Handling Acids and Alkaline Substances

Personal Protective Equipment (PPE): Always wear appropriate PPE, including gloves, goggles, and long sleeves, when handling acids or alkaline substances to prevent skin irritation and injury.
Mixing Protocol: When mixing acids or bases with water, always add the acid or base to the water to prevent dangerous reactions. Never add water to acids or bases, as this can cause violent reactions.
Ventilation: Work in a well-ventilated area to avoid inhaling fumes or dust from these substances.
Spill Management: In case of acid spills, neutralize them with baking soda before cleaning up with water.

By following these safety precautions, you can minimize the risk of injury while handling potentially hazardous materials.

13.4.1. Testing pH of Source Water

Materials Needed:

Digital pH meter or test kit
Clean container for water sample
Calibration solutions (for digital meters)

Procedure:

Collect a Water Sample: Use a clean container to collect the source water, ensuring it’s free from contaminants.
Calibrate the pH Meter: If using a digital meter, calibrate it according to the manufacturer’s instructions with standard buffer solutions (pH 4, 7, and 10).
Measure the pH: Submerge the probe or test strip into the water sample and wait for a stable reading.
Interpret Results: Compare the reading to the desired range (6.4 ± 0.08). If outside this range, adjustments are necessary.

13.4.2. Adjusting pH Levels

We advise against adding anything with Sodium as a constituent element when adjusting pH.

13.4.2.1. Lowering pH

Materials Needed:

Acidic solution (e.g., phosphoric acid or sulfuric acid)
Stirring rod or spoon

Procedure:

Add Acid: Introduce a small amount of the acidic solution into a separate container of source water.
Mix: Stir the mixture gently to ensure thorough mixing.
Test pH: Re-test the pH after each addition until it stabilizes within the desired range

Important Considerations:

Sand Bed Impurities: If your sand bed raises the pH, it may contain carbonate impurities instead of inert silica (SiO₂). Small amounts of carbonate can be neutralized with weak acids like phosphoric or sulfuric acid. However, if the carbonate content is high, consider using different sand.
Phosphoric Acid (H₃PO₄): This mild acid can lower pH and is available in food-grade quality from hydroponic or agricultural supply stores. While phosphorus is an essential macronutrient for plants, overuse can lead to toxic phosphorus concentrations.
Sulfuric Acid (H₂SO₄): Suitable for extremely hard and basic source water (high KH, high pH), but due to its corrosiveness and danger, beginners should avoid using it.
Nitric Acid (HNO₃): A relatively neutral acid option.
Citric Acid: Avoid using citric acid as it is antimicrobial and can harm beneficial bacteria in biofilters.
Safety Precautions: Concentrated acids are hazardous. Always use safety goggles and gloves. Remember to add acid to water, not water to acid, to prevent dangerous reactions

13.4.2.2. Raising pH

Materials Needed:

Alkaline solution: Options include potassium bicarbonate, potassium hydroxide, calcium carbonate, or calcium hydroxide (also known as builder’s lime).
Stirring rod or spoon

Procedure:

Add Alkaline Solution: Begin by adding a small amount of the chosen alkaline solution to a separate container of the source water.
Mix Thoroughly: Stir the solution gently to ensure thorough mixing.
Monitor pH: Re-test the pH after each addition of the alkaline solution. Continue this process until the pH stabilizes within the desired range.

Caution: Add alkaline solutions gradually in small increments to avoid overshooting the target pH.

Important Notes:

Preferred Bases: Common bases include potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)₂), which are strong and should be added slowly, similar to acids.
Safer Alternatives: Calcium carbonate (CaCO₃) or potassium carbonate (K₂CO₃) are safer alternatives that increase both carbonate hardness (KH) and pH.

Choosing Bases Based on Plant Needs

The selection of bases and buffers should consider the type of plants in the system, as each compound provides essential macronutrients:

Calcium Bases for Leafy Vegetables: Using calcium-based compounds can help prevent tip burn on leaves.
Potassium for Fruit Plants: Potassium is beneficial for flowering, fruit setting, and optimal ripening in fruit plants.
Caution: Sodium bicarbonate is sometimes used to increase carbonate hardness but should be avoided in iAVs due to its potential to increase sodium levels, which can harm plants. Sodium is not considered an essential element for plant growth. Even at low concentrations, sodium can have negative effects on soil quality and plant development. Sodium (salt) can accumulate to phytotoxic levels, and Na can interfere with the uptake of K and Ca at subphytotoxic levels (Douglas 1985).

Excessive sodium in the soil can lead to salinity issues, which impair the plant’s ability to absorb water and nutrients, ultimately hindering growth and development.

13.5. Stabilizing pH Before Adding to Fish Tank

After adjusting the source water’s pH, allow it to sit for several hours to ensure stability before introducing it into the fish tank. Conduct a final check of the pH before adding the water.

Key Takeaway: Practical pH Management in iAVs

Target pH: Aim for 6.4 (acceptable range ~6.0 to 6.8).
Natural Stability: Mature iAVs systems are generally self-stabilizing. Constant adjustments are usually NOT needed.
Source Water: Test your top-up water source. Adjust its pH to ~6.4 before adding it to the fish tank. Use appropriate, safe acids (like phosphoric) or bases (like potassium bicarbonate/hydroxide) cautiously if needed. Avoid sodium-based products.
Monitoring: Check pH occasionally (e.g., weekly/monthly) once stable. Monitor more frequently during startup (first ~3 months) or if fish/plants show signs of stress.
Focus: Prioritize plant health; select fish tolerant of the ~6.4 pH range (like Tilapia).

14. Water Pumps

Water pumps are essential in iAVs, circulating water from the fish tank to the biofilter to ensure nutrient delivery and maintain the health of both fish and plants. Pump failures can severely disrupt system functionality, making it crucial to choose reliable, high-quality pumps. Using multiple pumps enhances system reliability by reducing the risk of total failure and allows for better control over removal of the solids that settle on the bottom of the tank.

The two main types of water pumps used in iAVs are:

Submersible Pond Pumps: These pumps operate fully submerged in water. They are affordable, easy to install, and require minimal plumbing, making them ideal for smaller systems.
Externally Mounted Centrifugal Pumps: These pumps are placed outside the water and use centrifugal force to move it. They are more powerful and efficient than submersible pumps, making them better suited for larger systems.

Parts of a centrifugal pump. Fantagu, Public domain, via Wikimedia Commons.

Centrifugal pumps are preferred for iAVs due to their ability to move large volumes of water efficiently while overcoming head height limitations. They use an impeller to create centrifugal force, which propels water outward from the intake, generating a steady flow that can be adjusted as needed. The impeller also helps break down solid waste particles, which is critical for:

Enhanced Solids Distribution: Finer waste particles improve nutrient distribution across the biofilter’s sand beds.
Accelerated Mineralization: Smaller particles decompose faster, speeding up nutrient cycling.
Improved Filtration Efficiency: Finer waste particles reduce clogging and increase biofilter efficiency.

Externally mounted centrifugal pumps are advantageous for larger systems where water needs to be pumped over long distances or heights. However, they require more complex plumbing and considerations for noise and cooling.

Pump Selection Considerations

When selecting a pump for iAVs, consider:

Flow Rate: Ensure the pump can deliver sufficient water volume per hour.
Head Height: The pump must overcome the vertical distance between the fish tank and biofilter.
Energy Efficiency: Choose a pump that minimizes energy consumption while maintaining performance.
Reliability: A high-quality pump ensures long-term durability and reduces maintenance needs.

For future scalability, select a pump with extra capacity. Modern pumps often come with variable-speed controls or digital controllers that allow you to adjust flow rates based on system needs.

14.1. Pump Redundancy and System Reliability

Using multiple smaller pumps instead of one large pump improves system reliability by providing redundancy. This ensures continuous operation if one pump fails and allows better control over water distribution across different parts of the system.

14.1.1. Pump Placement

Position the pump intake slightly above the fish tank floor (0.5–1 cm) to avoid obstruction from solid waste buildup. For larger systems, distribute multiple smaller pumps along long tanks or canals to improve water distribution and reduce strain on individual units.

14.1.2. Controlling and Adjusting Flow Rate

Controlling flow rate is essential for balancing water circulation, nutrient delivery, and filtration efficiency. Many modern pumps offer variable-speed controls or app-based monitoring for real-time adjustments.

14.1.3. Impeller Action and Fish Waste Breakdown

The impeller in a pump plays a key role in breaking down fish waste into finer particles, which improves filtration efficiency, speeds up mineralization, and ensures even nutrient distribution throughout the biofilter.

14.1.4. Importance of Filtering Water Before Returning to the Fish Tank

If unfiltered water is recirculated, fine particles will continue to circulate through the system, becoming progressively harder to remove. These particles can degrade water quality, potentially causing stress or harm to the fish. Over time, this can lead to issues such as reduced water clarity, increased ammonia levels, and lower oxygen availability – all of which negatively impact fish health.

14.2. Head Height

Head height refers to the vertical distance between the fish tank’s water surface and the highest point water must reach. This determines how much pressure a pump must overcome to move water efficiently. Choose a pump that can deliver an appropriate volume at your system’s head height.

14.3. Pump Quality

High-quality pumps ensure long-term durability and energy efficiency. Reliable pumps maintain performance for 1–2 years with a lifespan of 3–5 years. Inferior products lose efficiency quickly, leading to reduced flow rates or failure.

14.4. iAVs Research & Recommendations

Dr. Mark McMurtry used Little Giant submersible pumps, known for their affordability and durability, during his original iAVs research. Modern alternatives like Jebao pumps offer similar reliability at lower costs. For hobbyist applications, Eheim pumps are recommended due to their durability and efficiency.

15. Aeration

Aeration is the process of adding oxygen to water to increase its dissolved oxygen concentration (Djaelani et al., 2022). It functions to expand the contact area between air and water, allowing oxygen from the air to enter the water’s surface (Mohan et al., 2022). The function of an aerator can be likened to that of ‘lungs,’ introducing oxygen into the water to absorb carbon dioxide (Petersen & Walker, 2002).

The fish, the plants, and the beneficial bacteria – needs plenty of oxygen to thrive. We measure this oxygen dissolved in the water, called Dissolved Oxygen or DO, usually in milligrams per liter (mg/L) (Somerville et al. 2014).

Gas exchange between a liquid and the surrounding air occurs at their interface. The amount of gas that can dissolve in water depends on factors such as pressure, temperature, salinity, and the concentration of the gas already present in the liquid. This exchange takes place at the surface where the liquid and gas come into contact. Aeration increases oxygen levels in water, while degassing removes dissolved gases, such as carbon dioxide (CO₂).

Water temperature plays a big role here: colder water can hold much more dissolved oxygen than warmer water. This is really important to keep in mind if you’re raising warm-water fish or if your system is in a place that gets hot, because you’ll need to make sure enough oxygen is getting into the warmer water.

Maintaining adequate dissolved oxygen (DO) levels is crucial for the health and productivity of recirculating aquaculture systems (RAS such as iAVs. Sufficient DO supports the respiration of fish and plants, as well as the biological processes of the nitrifying bacteria essential for water quality (Rakocy, et al., 2008). Inadequate DO levels can rapidly develop during emergencies, such as power outages or equipment failures, posing a significant threat to aquatic life and system stability. Therefore, proactive DO management is a key aspect of successful iAVs operation.

Several strategies can be employed to increase DO levels, each with its own advantages and applications:

Increasing Surface Area for Gas Exchange: Enhancing the contact between water and air is a primary method for increasing DO. This can be achieved through:
- Creating Turbulence: Methods like whirlpools or vigorous stirring increase the surface area exposed to the air.
- Utilizing Fine Bubbles: Diffusers that produce small bubbles maximize the surface area of air in contact with the water, promoting efficient oxygen transfer.
Extending Contact Time: Prolonging the duration of contact between air and water allows for greater oxygen absorption. This can be accomplished by:
- Optimizing Bubble Size: Smaller bubbles rise more slowly, increasing their contact time with the water.

Aeration Considerations for Tilapia iAVs

When raising tilapia at low to moderate stocking densities, supplemental aeration (e.g., using air pumps and diffusers) may not always be strictly necessary. However, even in these situations, aeration provides a reliable safeguard for maintaining elevated DO levels, particularly during periods of reduced photosynthetic activity (e.g., nighttime). Supplemental aeration serves as a valuable backup and helps maintain near-optimal conditions, supporting improved growth rates and overall fish health.

Benefits of Maintaining Optimal DO Levels

Maintaining adequate DO levels offers numerous benefits to fish health and productivity:

Improved Feed Conversion Ratio
Enhanced Disease Resistance
Increased Vitality and Activity
Greater Muscle Density
Higher Overall Yield

In commercial aquaculture operations, mechanical aeration is generally recommended throughout the entire production cycle, from the hatchery to the grow-out phase, to maximize these benefits.

Aeration Equipment Options

A variety of equipment options are available for aeration, each suited to different system sizes and needs:

Mechanical Air Pumps: These are a common and reliable method for introducing air into the water. Models with battery backups provide essential protection during power outages.
Regenerative Blowers: These are a more efficient and powerful option for larger systems (e.g., 10 cubic meters or more). While the initial investment is higher, they offer greater long-term cost-effectiveness and reliability. Using multiple smaller blowers instead of a single large one provides redundancy.
Diffused Air Systems: These systems consist of an air compressor connected to a diffuser placed in the water. The diffuser releases air in the form of small bubbles, maximizing oxygen transfer.
Water Pumps and Mechanical Aerators: These devices agitate the water surface, increasing gas exchange.

Ideally, you should aim to keep the DO level between 5 and 8 mg/L. Measuring DO accurately can be a challenge, as professional meters can be expensive and sometimes hard to find. If needed you can buy a dissolved oxygen measuring kit used for aquariums.

15.1. Cascade Aerators

Cascade aerators, one of the oldest and most common aeration methods, create turbulence as water flows over a series of steps or cascades, similar to natural streams. Aeration occurs in the splash zones formed by placing blocks along an inclined path. These systems are often used to oxidize iron and reduce dissolved gasses.

By increasing surface area and turbulence, cascade aerators enhance oxygen transfer. Studies have shown that shaded cascade systems can improve oxygen saturation by 30-43%, depending on factors such as step height and design. Importantly, cascade aerators do not require external energy input, making them a simple, low-cost, and low-maintenance solution. Key performance factors include step height, water flow rate, and the number of steps.

When no electrical power is available for blowers, compressors, or pumps, cascade aerators can effectively increase dissolved oxygen (DO) levels in fish tanks. These devices rely on gravity to break the water flow into numerous droplets, increasing the surface area exposed to the atmosphere (which contains 21% oxygen).

While cascade aerators provide less control over DO levels compared to mechanical aerators, they are suitable for applications where simplicity and energy efficiency are priorities. In iAVs, aeration primarily occurs during irrigation events as water moves through sand beds and returns to the fish tank. Introducing cascade aerators can extend this aeration by passively increasing oxygen levels using gravity.

Although supplementary aeration may not always be necessary, it serves as inexpensive insurance against low DO levels – especially at night when irrigation is not occurring. Water can be directed onto cascade aerators either after biofilter drainage or directly from the tank using a secondary pump if needed. Shading the cascade helps reduce evaporation and heat gain, improving oxygen saturation capacity.

Even when electrical energy is available for aeration, adding a cascade can increase DO saturation and potentially lower energy costs. There are various ways to construct a cascade aerator; some examples are provided below;

The effectiveness of cascade aerators can be further enhanced by optimizing the design parameters such as step height, water flow rate, and ensuring the system is operated within the design specifications for maximum oxygen transfer efficiency.

15.2. Air Pumps

Selecting an air pump depends on system size, budget, noise tolerance, and maintenance needs. The pump should meet the specific oxygen demands of the fish species and system design. The use of blower aerators, for example, has been shown to enhance the growth and production of tilapia and synchronize other water quality parameters in pond systems (Mohan et al., 2022).

Diaphragm Air Pumps: Reliable and low-cost but noisy; suitable for smaller systems.
Piston Air Pumps: Quieter with less maintenance but more expensive.
Rotary Vane Air Pumps: Efficient but costly; typically unnecessary for small systems.
Linear Piston Air Pumps: High efficiency with a longer lifespan but more expensive than diaphragm or piston pumps.
Blowers: Suitable for large systems; options include centrifugal, regenerative, and positive displacement blowers.
Positive Displacement Blowers: Efficient for large-scale systems requiring deep water aeration.
Centrifugal Blowers: Less expensive but less efficient.
Regenerative Blowers: Similar to centrifugal blowers but with slightly different mechanics.

In early iAVs research, centrifugal blowers were used but later replaced by quieter and more efficient positive displacement blowers.

In an iAVs, the use of an air pump is not strictly necessary but can be beneficial depending on the design and context of the system. iAVs can function effectively as a “low-tech” system without air pumps or air stones, especially in regions with limited resources or unreliable electricity. However, in “high-tech” setups, air pumps are often employed to enhance dissolved oxygen (DO) levels, promote fish health, and serve as a backup in case of water pump failure.

Research comparing different aeration technologies indicates that microbubble technologies like Micro-Nano Bubbles (MNB) and Fine Bubbles (FBs) can produce higher and more stable dissolved oxygen concentrations (>7 mg/L) compared to conventional blowers or Venturi aerators (Kosasih et al., 2025; Naomi et al., 2020; Putra et al., 2020,; Marcelino et al., 2023). This is attributed to the smaller diameter and larger surface area of the bubbles, which increases the solubility of dissolved oxygen in water (Tsuge, 2015Andinet et al., 2016).

Key Points

Oxygenation: While not essential for all iAVs designs, air pumps can help increase dissolved oxygen levels in the fish tank. Higher DO levels improve fish health, promote faster growth rates, and enhance overall system resilience.
Backup Aeration: In high-tech systems, air pumps with built-in battery backups are recommended as a fail-safe to maintain oxygenation during power outages or water pump failures.
Water Circulation: Proper placement of air stones can create water currents that assist in directing fish waste toward the pump intake, improving waste removal efficiency.

15.3. Air Stones

Air stones release small bubbles that increase water’s oxygen content by maximizing surface area contact. High-quality air stones producing fine bubbles are recommended for optimal oxygen dispersion.

Do not allow the air stones to rest on the tank bottom because they will stir up the fish wastes between irrigation events. Ideally, air stones should be placed along the tank sides to enhance oxygenation without agitating waste materials.

Set the airflow so that the water just ‘wells up’ – creating a slight bump on the water surface.

16. Timers

A timer controls the water pump in iAVs to regulate irrigation times and duration. Proper calibration is essential to ensure the correct water volume is delivered to the sand beds. Key factors influencing this include the pump’s flow rate, head pressure (the vertical distance the water must travel), and the hydraulic conductivity of the sand (which affects how quickly water percolates). These variables must be balanced to maintain optimal moisture levels for plant growth, avoiding over-saturation or under-irrigation.

When selecting a timer, quality and reliability are critical. Mechanical timers are less precise and can lead to inconsistent schedules due to timing variations. In contrast, digital timers and smart plugs offer more accurate control over on/off cycles. Smart plugs also provide additional features like remote monitoring and alerts for malfunctions, enhancing system reliability.

All electrical components, including timers, should be installed safely and kept away from dust, water, wind, and rain to prevent malfunctions or safety hazards.

16.1. Types of Timers

There are several types of timers that can be used in iAVs, each with its own benefits and drawbacks.

Dr. McMurtry and the iAVs research group utilized advanced digital timers in their research to precisely control irrigation cycles. These timers featured four channels, allowing them to manage different biofilter ratios simultaneously. The timers were programmable in minutes or seconds, offering practically unlimited on/off cycles per day. Each cycle could have a unique duration and interval spacing, with additional features like skip days.

16.1.1. Mechanical Timers

24 hour plug-in mechanical electric outlet timer. Zenhydro, CC BY-SA 4.0 via Wikimedia Commons

Mechanical timers are a budget-friendly option that uses a clock mechanism to control irrigation. However, they lack precision and may result in inconsistent irrigation cycles due to timing variances.

20.1.2. Digital Timers

Digital timers offer precise control over irrigation cycles by allowing users to program specific on/off times down to the second or minute. This ensures consistent water delivery and is ideal for systems requiring high precision.

16.1.2. Smart Plugs

Mini Smart Plug. Gregory Varnum, CC BY-SA 4.0, via Wikimedia Commons.

Smart plugs provide enhanced flexibility by allowing users to remotely control power supply through smartphone apps or web interfaces. They offer real-time adjustments based on environmental conditions or system performance data.

16.1.3. Water Pumps with Wi-Fi Access and Apps

Wi-Fi-enabled water pumps allow users to set detailed irrigation schedules via smartphone apps or web interfaces. These pumps eliminate the need for traditional timers by offering greater flexibility and control but may require stable internet access for optimal performance.

17. Sand

Selecting the right sand is crucial for iAVs, but it doesn’t need to be overly complex. While technical details follow, the primary goal is practical: find sand that is clean, chemically inert, and drains well. Ideally, 40% by volume consisting of particles 1-2mm, 40% 0.5-1mm, 20% 0.25-0.5mm, and a small amount of particles larger than 2mm.

Finding Suitable Sand:

Common Types: Suitable sand, often labeled as concrete sand or washed builder’s sand, is widely available, particularly where construction materials are sold. These types generally meet the basic requirements.
Key Functional Criteria:
- Cleanliness: Must be free of fine particles like silt and clay, which clog the system.
- Inertness: Should not react with water or alter pH (avoid sands with carbonates like limestone or shells).
- Good Drainage: Must allow water to pass through efficiently to prevent waterlogging, while still retaining adequate moisture for plants between irrigation cycles.

Before purchasing a large quantity, simple tests on a sample can quickly assess suitability.

Why Details Matter (Context for Following Sections):

While focusing on these functional criteria (clean, inert, drains well) is often sufficient, subsequent sections delve into ideal particle sizes (0.4mm – 1.2mm), standards like ASTM C-33, and potential issues like fine particle migration. This detailed information is valuable for a deeper understanding, troubleshooting, or ensuring consistent quality, especially in commercial-scale operations.

The Bottom Line:

For most users, ensuring the sand is clean, passes the basic tests, and drains effectively is the key to successful implementation.

17.1. The Role and Benefits of Sand in iAVs

Sand is the cornerstone of iAVs, serving multiple critical functions simultaneously. It acts as the growing medium for plants, a mechanical filter for solids, and a biological filter housing essential microbial communities.

Unlike inert media used in some hydroponic or aquaponic systems (like gravel or expanded clay pebbles), sand in iAVs becomes a dynamic, living substrate that drives the system’s efficiency and sustainability. Its selection is based on proven effectiveness, accessibility, and unique properties that create an optimal environment for both plants and fish.

Traditional aquaponic systems that use clayballs or gravel have long-run challenges, including plant abrasion caused by media, a high propensity for clogging from solids that can create anaerobic zones, and a high labor input required for cleaning and handling (Palm 2018: Somerville 2014). Compared to sand, which offers great plant support and does not require cleaning.

Here’s a breakdown of the key benefits sand provides in an iAVs:

1. Superior Filtration & Water Quality:

Dual-Action Filtration: Sand excels as both a mechanical and biological filter. The vast surface area of the sand provides sufficient surface area for the growth of nitrifying bacteria and physical filtration eliminating the need for a separate, dedicated biofilter (Maucieri et al., 2018).
Water Purification: As water percolates through the sand bed, it is effectively stripped of solids (including microscopic particles) and dissolved wastes by this combined mechanical and biological action, returning purified water to the fish tank. This eliminates the need for separate, often complex and costly, mechanical filters and dedicated biofilters found in traditional aquaponic systems.

2. Optimal Plant Growth Medium:

Physical Support & Root Environment: Sand provides excellent physical anchorage for plant roots, supporting even large, fruiting plants.
Aeration & Drainage (Hydraulic Properties): Properly selected sand offers an ideal balance between water retention and drainage. The intermittent flood-and-drain irrigation cycle unique to iAVs leverages this:
- During flooding, water and nutrients are delivered efficiently.
- During the crucial drainage phase, water drains rapidly and completely, pulling fresh, oxygen-rich air (approx. 21% O2) deep into the sand pores. This high level of aeration (far exceeding dissolved oxygen in water) is vital for healthy root respiration and prevents waterlogging and anaerobic conditions that harm roots and beneficial microbes.
- Enhanced Nutrient Availability & Uptake: The sand medium fosters a rich “soil ecology” in the root zone (rhizosphere). Beneficial microbes thrive, interacting directly with plant roots and their exudates.

3. System Efficiency & Practicality:

Complete Nutrient Cycling & Capture: By retaining and processing virtually all fish waste solids within the biofilter, iAVs achieves near 100% nutrient capture and recycling. This allows the system to operate efficiently on the nutrients provided solely by the fish feed, typically eliminating the need for supplemental fertilizers when using a balanced feed and appropriate stocking/planting rates.
Supports Higher Productivity: Efficient nutrient cycling and excellent water quality allow for higher fish stocking densities and corresponding feed rates compared to less efficient systems, leading to greater overall food production (both fish and plants) per unit area and water used.
Accessibility & Cost-Effectiveness: Suitable sand (like washed construction or concrete sand) is widely available, relatively inexpensive, durable, and requires minimal maintenance. It can be reused indefinitely, and even if overloaded, can often be cleaned or repurposed as a soil amendment, contributing to the system’s low cost and sustainability.
Proven & Reliable: The use of sand filtration for water purification has a long history, and its effectiveness in iAVs has been rigorously validated through scientific research and long-term practical application (some systems running over 20 years without sand replacement). Plants grown in the sand also contribute to system maintenance by actively absorbing nutrients, acting as natural “filter cleaners.”

In summary, sand is not just a passive component in iAVs; it is an active, integrated bio-reactor. Its unique physical and chemical properties, combined with the iAVs operational method (intermittent irrigation), create a highly efficient, self-sustaining ecosystem that optimizes water quality, nutrient cycling, and plant growth.

Sand grains of yellow building sand. Microscope Lumam R-8. EPI lighting. The photo of each grain of sand is the result of multifocal stacking. This microscopic view illustrates how angular sand grains enhance filtration properties by increasing surface area for microbial colonization. Alexander Klepnev, CC BY 4.0, via Wikimedia Commons

17.2. Preventing Clogging and Anaerobic Conditions

A common concern is whether sand biofilters clog or become anaerobic (lacking oxygen) over time. In a properly designed iAVs using the correct type of sand, neither clogging nor anaerobic zones occur. This reliability stems from both the sand’s properties and the system’s design.

Why Properly Selected Sand Works:

Optimal Particle Size: Using medium to coarse sand (0.4 mm to 1.2 mm) ensures good porosity. This allows water to drain efficiently while leaving ample air-filled pore space for oxygen.
Absence of Fines: Crucially, the sand must be free of fine particles like silt and clay. These fines are the primary cause of clogging in unsuitable sand.
Surface Solids Management: In a correctly operated iAVs, solid fish waste accumulates on the surface of the furrows. It does not penetrate into the lower layers of the sand bed.
System Design for Drainage: The biofilter’s sloped bottom (2 cm per meter) and efficient drainage system (like the slit drain) ensure that water drains completely and rapidly after each irrigation cycle. This prevents waterlogging and actively pulls fresh, oxygen-rich air into the sand bed, eliminating the risk of anaerobic conditions. Systems have run successfully for over 20 years without clogging issues using this approach.

The Problem with Fine Particles (Silt, Clay, Very Fine Sand):

Using sand contaminated with fine particles leads to significant problems:

Particle Migration: During the reciprocating (flood and drain) cycles, these small, mobile particles (especially clay and silt) are washed downwards.
Pore Space Clogging: Fines accumulate in the voids between larger sand grains, effectively clogging the pore spaces, particularly in the lower layers.
Reduced Drainage: This clogging drastically reduces the sand’s hydraulic conductivity, slowing or preventing proper drainage.
Waterlogging & Anaerobic Zones: Impeded drainage leads to permanently saturated zones within the bed, creating anaerobic conditions detrimental to plant roots and essential aerobic microbes.
Reduced Oxygen: The filling of pore spaces limits the volume available for air, starving the system of the oxygen needed for healthy root respiration and efficient nutrient cycling.

Therefore, selecting clean sand within the recommended particle size range, free from silt and clay, is essential for the long-term, trouble-free operation of an iAVs biofilter, ensuring efficient filtration, optimal aeration, and healthy plant growth.

17.3. iAVs-Suitable Sand

Choosing the right sand is vital for a successful iAVs. The goal is to find sand that is clean, chemically inert (doesn’t change water pH), and drains well while still holding some moisture for plant roots.

Key Requirements:

Cleanliness: The sand must be free of fine particles like silt and clay, as these will clog the system, impede drainage, and harm root health. It should also be free of salts, organic debris, and potential chemical contaminants. Visually inspect sand for dustiness or muddiness when wet. A simple jar test (see Section 18.12.1) can confirm the absence of silt and clay.
Chemically Inert: The sand should not react with the water or significantly alter its pH. Avoid sands containing carbonates (like crushed limestone, shells, or coral found in some beach sands) as they will raise the pH, negatively impacting nutrient availability. A simple vinegar test can check for carbonates: if the sand fizzes or bubbles when vinegar is added, it contains carbonates and is unsuitable.
Particle Size and Drainage: The ideal sand is medium to coarse (roughly 0.4 mm to 1.2 mm particle size). This ensures good drainage, allowing water to flow through efficiently and preventing waterlogging, while also providing sufficient pore space for air (oxygen) to reach roots and microbes. It should still retain enough moisture between irrigation cycles. Angular sand grains are generally preferred over rounded ones as they provide better stability and porosity. For comparison, common table salt is 0.1 to 0.3 mm.

Focus on Function: While quartz/silica sand is often considered optimal due to its inertness and angular shape, the most critical factors are ensuring the sand is clean, chemically neutral (passes the vinegar test), and drains properly. If a readily available sand meets these functional criteria, it will likely work well in your iAVs.

17.3.1. The Effects of Using Sand Coarser Than the Ideal Range

While iAVs performs best with medium-coarse sand (ideally within the 0.4mm to 1.2mm particle size range), using sand with particles larger than the 1.2mm upper limit introduces several drawbacks that can compromise system efficiency:

Reduced Surface Area for Microbial Colonization:
Decreased Filtration Efficiency: The larger gaps between these coarser sand particles reduce the bed’s ability to effectively trap fine solid waste. This can lead to poorer water quality, as uneaten feed and fish feces may pass through to the lower layers the bed without adequate filtration.
Potential for Nutrient Loss & Poor Water Retention: While good drainage is essential, sand that is too coarse allows water (and dissolved nutrients) to pass through too quickly. This reduces the contact time between plant roots and nutrient-rich water, potentially leading to nutrient deficiencies. Furthermore, the reduced water retention capacity makes plant roots more prone to drying out between irrigation cycles, especially in hot or arid climates.

Conclusion:

Therefore, while adequate drainage is crucial, using sand that is predominantly coarser than the recommended 1.2mm upper limit compromises the system’s filtration capacity, microbial support, and moisture balance. The ideal medium-coarse range (0.4mm – 1.2mm) provides the necessary balance of good drainage, sufficient surface area for microbes, effective filtration, and adequate water retention for optimal iAVs performance.

This is an example of sand that is very coarse, with particles up to 2mm.

This is a example of coarse sand, it has a look and feel similar to granulated table salt

17.4. Sourcing and Selecting Suitable Sand

Finding the right sand is crucial for the success of your iAVs. While technical specifications exist, the practical goal is to source sand that is clean (free of silt, clay, and contaminants), chemically inert (won’t alter water pH), and drains well while retaining adequate moisture. Fortunately, suitable sand is abundant and often readily available.

Ideal Sand Characteristics:

Particle Size: Aim for medium-coarse sand, typically ranging from 0.4 mm to 1.2 mm. This size range provides the best balance of drainage, aeration, water retention, and surface area for microbial activity.
Shape: Angular grains (like quartz or silica sand) are preferred over rounded grains. Angular particles interlock better, providing stable root support, enhancing mechanical filtration, and creating more pore space for air and water movement.
Composition: The sand must be chemically inert. Quartz (silica) sand is ideal due to its stability and pH neutrality.
Cleanliness: Sand must be free from silt, clay, salts, organic debris, and potential pollutants (heavy metals, chemicals). Silt and clay clog pore spaces, impede drainage, and can lead to anaerobic conditions. Salts harm plants and fish.

What to Avoid:

Carbonate-Containing Sand: Sand with calcium carbonate (CaCO₃), found in limestone, crushed shells, or coral, is unsuitable. Carbonates dissolve in water, raising the pH significantly above the optimal iAVs range (6.0-6.8). This high pH hinders nutrient availability for plants (especially phosphorus and iron) and increases ammonia toxicity risk for fish.
- Simple Test: Add vinegar to a sand sample. If it fizzes or bubbles vigorously, it contains carbonates and should not be used.
Beach Sand: Generally unsuitable due to high salt content and likely presence of shell fragments (carbonates). Rounded grains also offer less effective filtration and aeration.
Play Sand: Often too fine and rounded, leading to poor drainage and compaction.
Potentially Contaminated River Sand: River sand, especially near urban or industrial areas, can contain pollutants (chemicals, heavy metals, sewage, agricultural runoff). Verify the source and test if unsure.
Fine or Dusty Sand: Indicates the presence of silt or clay, which will cause clogging.

Reliable Sources for Suitable Sand:

Concrete/Construction Suppliers & Quarries: Often the best source. Sand used for concrete (meeting standards like ASTM C33) typically has the required particle size distribution and is washed free of excessive fines and contaminants. Look for “washed concrete sand,” “construction sand,” or “sharp sand.” Landscape Suppliers: Offer various sands in bulk. Obtain samples for testing.
Cement/Cinder Block Manufacturers: Require quality sand for their products, which may be suitable.
Horticultural Suppliers: May offer “horticultural sand” or certified filter-grade sand, though potentially at a higher cost.
Hardware Stores: In countries like the United States and Australia, suitable sand can often be found at large hardware stores although convenient it is more expensive than buying in bulk.

Practical Steps for Selection:

Identify Potential Suppliers: Look for quarries, concrete suppliers, or landscape depots in your area.
Request Samples: Always obtain small samples from potential sources before ordering in bulk. Quality can vary even within the same quarry.
Perform Simple Tests:
1. Vinegar Test: Check for carbonates (fizzing = bad).
2. Jar Test: Check for silt/clay (cloudy water or distinct fine layers after settling = bad).
3. Visual Check: Ensure sand looks clean (not dusty/muddy) and allows water to drain reasonably well when wet.
Consider ASTM C33: This is a specification used for sand that is suitable for use in concrete. This specification is internationally recognized in countries such as the United States, Australia, China, and Egypt. While not the only option, asking suppliers if their sand meets ASTM C33 specifications can be a useful indicator of quality. ASTM C33 sand often contains a range of particle sizes, some of which may be outside the optimal iAVs range but the majority of particles fall within 0.4–1.2 mm.
Professional Testing (Optional): For commercial operations or if contamination is suspected, send a sample to a certified lab for analysis.

Quikrete All Purpose Sand is suitable for iAVs, although it is much more expensive to buy pre-bagged. The product is widely available across the US through major hardware and home improvement retailers.

Identifying suitable sand is generally straightforward and involves a quick internet search or a few phone calls to local suppliers, followed by a site visit to inspect the material before ordering in bulk.

By carefully selecting clean, inert, medium-coarse sand using these guidelines and simple tests, you provide the optimal foundation for an efficient and productive iAVs. The quality of the sand directly impacts the effectiveness of iAVs, making it important to invest in the right materials from the outset.

“The ATSM C-33 specification (US) ‘worked’ spectacularly for me. This specification is used throughout the world (by different terms in various countries) to make structural quality concrete, whether in the US, Oz, China, Egypt or anywhere else. It is not expensive or at all difficult to source – IMO. It has clearly defined criteria such as NO carbonate or salts or silt and defined particle size distribution limits. If you get material that meets this specification (not all vendors are competent, honest or knowledgeable but most who quarry for commercial contract work are) then it should work just fine – it always did for me. I’m not claiming that it is the ideal – no one actually knows what the “ideal” is. No one also knows what the limits are – how far one can deviate from what I tested/used and still achieve an adequate result – however defined. I know that I had absolutely NO problem whatever in sourcing or using sand that performed – more than adequately. “ – Dr. McMurtry

17.5. Sand Tests

Testing sand for use in an iAVs is to ensure the system’s efficiency and longevity. By conducting sand tests, you can confirm that the sand meets the necessary criteria and avoid potential issues related to system performance and safety.

Importance of Sand Testing

Ensuring Safety: Testing helps identify contaminants that could compromise the safety of produce grown in the iAVs, ensuring it is safe for human consumption.
Optimizing System Performance: By verifying that the sand is free from contaminants that could disrupt microbial communities or harm plants and fish, you can enhance the system’s productivity.
Preventing System Failure: Early detection of unsuitable sand can prevent costly and time-consuming failures, safeguarding your investment in the iAVs.

17.5.1. Testing Sand for Carbonates

Performing simple field tests can help determine if a sand sample is suitable for iAVs:

Carbonate Test: Apply a few drops of dilute acid (such as vinegar or hydrochloric acid) to the sand. If it fizzes or bubbles, this indicates the presence of carbonates like CaCO₃ and it means it is not inert. Sand that reacts with vinegar should not be used in iAVs due to its potential to disrupt pH balance
Turbidity Test: Assess the clarity of water after mixing it with sand to detect fine particles like silt and clay.
pH Test: Use a pH test kit to ensure that the sand does not alter the pH of water beyond acceptable levels (6.4 ± 0.4).
Professional Analysis: For more accurate results, consider sending a sample to a professional lab for elemental analysis to confirm whether the sand contains harmful contaminants or carbonate compounds that could affect your system’s pH.

17.5.2. Sedimentation and Turbidity Tests

The sedimentation test is a simple method to determine if a sand sample contains silt or clay, which are unsuitable for iAVs. This test leverages differential settling, where larger, heavier particles settle faster than smaller, lighter ones in water.

Materials Needed

A clear jar with a lid (e.g., mason jar)
Water
A ruler or measuring tape
Sand sample

Procedure:

Fill the Jar: Fill the jar about halfway with your sand sample.
Add Water: Add water to the jar, leaving a few inches of space at the top.
Secure the Lid: Screw the lid on tightly.
Shake Vigorously: Shake the jar vigorously for at least 30 seconds to ensure the sand, silt, and clay are thoroughly mixed with the water.
Let it Settle: Place the jar on a flat surface and allow the contents to settle undisturbed. This may take several hours, or even overnight, for a clear separation of layers.

Interpreting the Results:

After the water has cleared, you should see distinct layers in the jar.

Sand: The heaviest particles, sand, will settle at the bottom within 30 seconds to 1 minute.
Silt: Silt particles are finer than sand and will form a layer above the sand after 30 minutes to 1 hour.
Clay: The finest particles, clay, will settle above the silt after 24 hours or more. The water may still appear cloudy due to suspended clay particles.

If you observe any visible layers of silt or clay, the sand sample is unsuitable for iAVs. Ideal sand should have no silt or clay to ensure optimal drainage and performance.
Silt appears as a darker line above the sand, while clay forms a pale, fine layer on top of the silt.

Ideally, you want to see only a layer of sand at the bottom, with clear water above it, indicating a sample free from significant silt or clay contamination.

This sample suggests the presence of clay. This would be confirmed if the water remained cloudy for longer than a few minutes.

This sample is free of silt and clay. Note the small amount of powdered sand on the surface. The black lines in this photo are refracted light – not silt.

18. Furrows & Ridges

Furrows are shallow trenches or channels dug into the soil and direct the flow of nutrient-rich water to the plant roots within the biofilter. Water pumped from the fish tank is channeled directly into these furrows, ensuring a concentrated flow of nutrients where they are most accessible to plant roots. This targeted irrigation maximizes nutrient availability for the plants.

In the IAVS research there was a nutrient gradient in the sand beds, with higher concentrations of phosphorus, potassium, and manganese found closer to the furrows and at the surface (McMurtry 1987).

Furrows allow for even distribution of water and nutrients, and help to conserve water by allowing it to soak into the sand quickly (through the sloped sides on the furrow/ridges), rather than evaporating. They are similar to the furrows made in traditional agriculture for irrigation purposes.

Furrow Irrigated sugar cane in Northern Queensland, Australia. HoraceG, CC BY-SA 3.0, via Wikimedia Commons

18.1. The Role of Furrows

Furrows are essential for the efficient distribution of water and nutrients throughout the sand biofilter and allow the flooding of the sand media while keeping plant crowns dry.

The unique design of the furrow and ridge profile enhances the structure of the surface, leading to improved water absorption and retention.

Furrow irrigation is particularly beneficial for crops that would be damaged by inundation, such as tomatoes and vegetables, and is a farming technique that draws on established agricultural science.

During the drainage interval, the open pore status of the ridges allows for the complete recharge of the soil atmosphere (21% O2) by suction (nature abhors a vacuum).

The furrows are home to beneficial bacteria and other microorganisms that help to break down the fish ‘waste’ and other organic matter in the system. This process thrives due to: 1) High exposure to atmospheric oxygen, 2) Moist conditions, 3) Regular flushing of microbial byproducts (solutes) into the rhizosphere, and 4) Intermittent addition of organic solids and solutes for microbial metabolism.

Gigi_my_girl / Getty Images

18.2. The Furrow and Ridge Profile (Surface Structure) in an iAVs

The distinctive furrow and ridge profile sculpted onto the surface of the iAVs sand biofilter is far more than just a planting structure; it is a critical design element engineered to optimize the system’s core biological and physical processes.

The incorporation of a furrow and ridge surface structure in an iAVs filter bed significantly enhances its performance compared to a flat surface. This design creates varied topography, which improves water distribution, root interaction, and overall system efficiency.

The ridges facilitate the intake of atmospheric oxygen deep into the sand bed during drainage cycles and keep plant crowns dry while providing stable root support.

The furrows concentrate fish waste at the surface for efficient aerobic decomposition (mineralization) and ensure an even delivery of the nutrient-rich water across the biofilter.

In a flatbed, water spreads uniformly, which may not optimize root growth or water infiltration. In contrast, the furrow and ridge profile introduces micro-environments: ridges retain water in localized areas, while furrows promote deeper infiltration. This variation encourages more extensive root growth as plants adapt to different moisture zones.

The edge effect, created by the boundaries between ridges and furrows, further influences water dynamics and nutrient availability. These edges foster diverse conditions that can enhance plant growth by increasing exposure to both moisture-rich zones (in furrows) and aerated zones (on ridges). This added complexity helps optimize resource use within the system.

Plant roots also enhance infiltration by creating channels that improve water penetration and distribution throughout the bed. This process increases filtration efficiency, reduces dry spots or stagnation, and extends the functional lifespan of the filter bed by improving water management. Additionally, increased oxygenation – supported by both the ridge structure and root activity – promotes better plant health and system sustainability.

18.3. Furrows:

Furrows are the shallow trenches formed between, and around, the ridges. They serve several vital functions:

Targeted Irrigation: Water pumped from the fish tank flows directly into the furrows in close vicinity of the root zones located along the ridge slopes.
Waste Accumulation Zone: Fish waste solids on the surface of the furrows. This concentrates the organic matter on the surface, directly exposing it to atmospheric oxygen during drainage periods, which is essential for rapid aerobic decomposition and mineralization. (See Chapter 24 for more on detritus).
Maintaining Hydraulic Conductivity: Maintaining hydraulic conductivity (the rate at which water percolates through sand) by allowing the ridges to stay free of fish waste.
Allow flooding of the sand media while keeping the plant crown dry.
Facilitate rapid and even distribution of the nutrient-rich water across the bed.

18.3.1. Furrow Dimensions:

Depth: 10–15 cm (4–6 inches) for effective irrigation and root development. The furrows should be sufficiently deep to ensure proper irrigation throughout the bed and to prevent water from reaching the plant crowns. It is recommended to keep them within 3 to 5 cm below flood level, with at least an equal amount of dry sand above.The furrows should be designed in a narrow ‘V’ configuration, as this shape expedites the accumulation of detritus and aids in maintaining the stability of the furrow structure.
Width: 7–13 cm (3–5 inches), depending on crop spacing and plant type.
Layout: The layout of furrows can be adapted to accommodate different crops with unique spacing requirements within the same bed. For instance, a 1×2 meter sand filter could be divided into two sections, with one section designed for tomatoes and the other for leaf or herb crops.

Furrows are most stable when their cross-sectional profile approximates a parabola. Rounding the top edges prevents sand from collapsing into the trough.

Intermediate channels, as pictured above, can also be placed between adjacent longitudinal furrows and between plants within a row, if desired.

The design, size, and spacing of furrows in an iAVs are primarily determined by the crops being cultivated. For example, single-stem indeterminate tomatoes typically require a planting density of approximately four plants per square meter, while leaf or herb crops can be planted more densely, often at 12 to 16 plants (or more) per square meter.

General Guidelines for Furrow Spacing

Furrows should be spaced 30–60 cm (12–24 inches) apart and positioned between all rows of plants as well as around the entire perimeter of the sand biofilter bed. This layout ensures even distribution of water and nutrients across the entire biofilter surface, providing uniform access for all plants. The perimeter furrows play an additional role by ensuring water distribution remains consistent even if one or more intermediate furrows become temporarily blocked.

Customization of Furrow Design

Furrow dimensions (width and depth) and spacing can be adjusted to suit the specific crop requirements. For instance, crops with closer row spacing may require narrower or additional furrows, while crops with wider spacing may need fewer but larger furrows. It is also possible to have multiple furrow configurations within the same sand bed to accommodate different crop types simultaneously. For example, in a 1×2 meter sand biofilter, one section could be configured for tomatoes at a density of four plants per square meter, while another section could support leaf or herb crops at a density of 12–16 plants per square meter.

Key Considerations for Furrow Design

The primary objective of furrow design is to ensure that nutrient-laden water is distributed as uniformly as possible across the sand bed. This ensures that all plants receive equal access to water and nutrients. Adjustments to furrow arrangements can be made as needed to suit changing crop requirements. It is recommended that all furrows within the system be interconnected. This interconnection allows water to flow throughout the system even if temporary blockages occur in specific sections, thereby maintaining consistent irrigation and nutrient delivery.

By tailoring furrow spacing and layout to the needs of specific crops and ensuring system-wide connectivity, iAVs operators can maximize efficiency and productivity while maintaining optimal growing conditions for all plants.

18.4. Creating Furrows

The top surface (both before forming furrows and in the bottom of the finished furrows) should be level from side to side and also from end to end (and thereby from corner to diagonal corner). Since water ALWAYS seeks its own level, the easiest way to accomplish this is to block the drainage outlet, flood the beds to saturation and slightly more, and then adjust the sand (and furrow) surfaces to be consistent with the water level.

Alternatively, temporarily block the drainage outlet and flood the beds until saturation and slightly beyond. This method allows you to adjust the sand surfaces to align with the water level. all sand will settle somewhat during the first one to three saturation/drainage cycles. Some sand more so than others and not necessarily uniformly along the length and/or width. Therefore, it is suggested that one allow the bulk of this settling to occur before finalizing the surface preparations.

Once you have ensured that the sand surface is level and has settled adequately, proceed with forming multiple furrows across the top surface. Ensure that all furrow bottoms are also level and interconnected to facilitate uniform water distribution.

To create the first furrow, you can use your hands or a hoe to drag the sand up onto the ridge that separates the furrows.

Repeat this process for the second furrow, ensuring appropriate spacing. This process should be repeated on the other side of the sand bed.

Another way to create furrows is to use a former/screed (pictured below) – effectively a mirror image of the furrow, shaped from plywood or rigid plastic. Dragging the former through the sand will produce evenly spaced furrows very quickly.

The furrows must be perfectly level, meaning the surface should be completely flat without any incline.

Operators commonly create a downward slope on the top surface to facilitate water flow, but it is not recommended due to the risk of uneven distribution of nutrients along the bed length, ultimately resulting in nutrient deficiencies in the initial section of the biofilter.

Furrows should be placed between all plant rows and around the perimeter to ensure even water distribution and prevent clogging by keeping solids on the surface for decomposition. Ensuring the furrows are level provides every plant with an equal access to nutrients and so reduces competition amongst plants.

Ensure all furrows are connected at both ends to allow even water distribution during irrigation events.

18.5. Ridges: Plant Support and Aeration

Ridges are raised sections of sand between furrows where plants are grown. Ridges facilitate the flow of water through the furrows, preventing waterlogging and ensuring that excess water drains away from the plant roots. This is crucial in a sand-based system where drainage is essential to maintain proper aeration for plant roots. They keep plant bases dry, reducing risks of root rot and moisture-related diseases.

The raised structure of ridges promotes better air circulation within the growing medium which helps to prevent root rot, caused by Pythium (Cherif et al., 1997)

Ridges, combined with furrow irrigation, enable targeted nutrient application. The nutrients from the fish effluent are delivered directly to the root zone, maximizing uptake efficiency and minimizing nutrient loss.

Plants are grown directly on the ridges, which provide a stable base for the plants, supporting their growth and development and creating distinct areas where each plant has access to its own resources.

The ridges serve a dual-purpose in iAVs: they keep the plant crowns high and dry. Maintaining dry plant crowns is essential for their healthy growth. The crown, located where the stem and root meet, often sits at or just below the soil’s surface. It serves as the plant’s foundation. When crowns remain wet, it increases the risk of disease and can hinder the plant’s ability to absorb nutrients efficiently. Thus, ensuring that the crowns stay dry by using ridges significantly enhances plant health and productivity.

Ridges can be built from excavated sand or additional material to elevate them above the original surface level. Ridges can also be easily shaped by hand, or using basic materials like wood or PVC pipe.

18.6. Ridges as Ventilation Stacks

Ridges also provide an algae-free section of the bed that facilitates drainage and aeration. The ridges act as ventilation channels, significantly enhancing the system’s air exchange capabilities.

It’s important for these ridges to be constructed at a height that keeps them above the water level throughout the irrigation process. This design ensures that air can freely move out and back into the system during the watering and draining stages, respectively.

During the irrigation phase, water is pumped from the fish tank into the furrows in the biofilter. When the sand is saturated the water levels in the furrows rise, and air trapped within the sand’s pore spaces is displaced and forced upwards. The ridges, being the highest points in the sand bed, allow this displaced air to escape.

Following the irrigation phase, the drainage phase begins. As the water level drops, air is forcefully pulled back into the sand’s pore spaces. This provides the necessary oxygen for the microbes.

The ridges facilitate the re-entry of air into the biofilter, ensuring that the pore spaces are adequately aerated and promotes the aerobic decomposition of organic matter and the release of nutrients for plant uptake.

18.6.1. Gaseous Exchange

The process of gaseous exchange involves the intake of fresh air, which is rich in oxygen, and the expulsion of carbon dioxide and other undesirable gases. This process is similar to the operation of a car engine, where fresh air is drawn in and stale air is expelled.

This gaseous exchange is facilitated by the intermittent flooding and draining of the biofilter. The ridges on the sand filter enhance this effect, functioning like chimneys or ventilation tubes, further promoting the exchange of gases.

Unwanted gases, such as carbon dioxide, methane, nitrous oxide, and other compounds, can be generated through various processes. These processes include the decomposition of organic matter and the respiration of plant roots and soil microorganisms. At high levels, these gases can be toxic to both plants and fish.

19. Microbial Inoculation and Cycling

Cycling refers to the process of establishing the sand biofilter. Microbial inoculation introduces beneficial microorganisms into the system, which are essential for breaking down fish waste and converting it into plant-available nutrients.

While these microbes can naturally colonize the system from environmental sources like wind and water, the process can be accelerated by adding organic matter, such as compost or humus-rich soil. This jumpstarts microbial populations, which are critical for nutrient cycling and maintaining system health. The growth of these microorganisms is influenced by factors such as temperature, moisture levels, and the availability of organic matter.

Compost. Bernard Dejean, CC BY-SA 4.0, via Wikimedia Commons

19.1. Introduction to Microbial Communities in iAVs

In iAVs, a robust microbial population is crucial for converting fish waste into plant-available nutrients. While inoculating the system with compost or humus-rich soil can speed up this process, it is not strictly necessary. Microorganisms will naturally colonize the system if conditions such as temperature, moisture, and organic matter are favorable.

19.2. Optional Inoculation Techniques

To accelerate microbial colonization, inoculating with organic matter can be beneficial. A small amount of mature compost (e.g., one tablespoon) can be added near the water inlet to allow irrigation to distribute microbes throughout the filter bed. This may introduce beneficial organisms like amoeba, mycorrhiza, nematodes, and protozoa. Similarly, humus-rich soil – due to its high organic content and microbial diversity – can be used at a rate of about two tablespoons per furrow to stimulate microbial activity.

Natural colonization has the advantage of introducing microbes that are already adapted to local environmental conditions, such as temperature and water quality. This makes them potentially more effective and resilient than non-native species introduced through commercial inoculants.

Moreover, relying on natural processes eliminates concerns about the viability of commercial inoculants, which may lose effectiveness if improperly stored or transported. Natural colonization ensures that only viable microbes establish themselves in the system.

While inoculation can speed up microbial establishment, natural colonization will occur over time even without intervention. For those without access to compost or humus-rich soil, patience during the early stages will still lead to a functional microbial community.

19.3. Cycling

Cycling in iAVs refers to establishing a biological balance between fish, plants, and microorganisms. This process involves gradually introducing fish and plants while allowing beneficial bacteria to proliferate.

Unlike traditional aquaponic systems, cycling in iAVs is more natural and requires less intervention. The sand filter bed in iAVs acts as biologically active soil, supporting not only nitrifying bacteria but also a wider variety of soil microbes. This microbial diversity enhances organic matter mineralization, nutrient availability, and system resilience.

While studies on traditional aquaponic systems highlight the role of bacteria, fungi, archaea, and protozoa in nutrient cycling, these systems lack the microbial diversity found in soil-based environments. iAVs addresses this limitation by utilizing sand-based filtration, which supports a more diverse microbial community, including fungi and mycorrhizae. For example, mycorrhizal fungi improve phosphorus uptake – a nutrient often limited in traditional aquaponic systems.

This broader microbial diversity gives iAVs an advantage over systems that rely primarily on nitrifying bacteria in mechanical filters. Processes like nitrogen fixation and organic matter decomposition further enhance nutrient availability and system stability.

To start cycling an iAVs, introduce young fingerlings and a small selection of plants. Initially, feed the fish at a reduced rate, gradually increasing it as plant growth and water quality improve. As the system stabilizes, plant populations can be expanded based on feed input. Fast-growing plants like leafy greens or herbs are ideal for early stages due to their high nutrient uptake rates.

19.4. System Start-Up and Balancing

The start-up phase is the most delicate period in iAVs operation. During this time, there may be few or no plants while fingerlings require careful management. Balance is achieved by feeding fingerlings at a reduced rate, gradually increasing as plants grow and water quality stabilizes.

When nutrient-rich fish wastewater is first introduced into the filter bed, naturally occurring bacteria and algae begin to colonize the system. These organisms fully establish themselves within two months. Until then, feed inputs should be minimized to reduce waste production, and regular monitoring of water quality parameters (ammonia, nitrite, pH) is recommended to ensure safe conditions for both fish and plants.

To expedite nitrifying bacteria establishment, inoculating the system with Nitrosomonas and Nitrobacter (e.g., products like Fritz-Zyme #7) can significantly shorten cycling time – sometimes to just a few days – if ammonia is available to sustain the bacteria.

19.5. System Maturation and Long-Term Stability

As an iAVs operates continuously without excessive feed inputs or interruptions, their biological and chemical stability improves over time. Typically, these systems reach functional maturity within three months, with full maturation occurring after one year of continuous operation.

The diverse microbial communities in iAVs play a crucial role in enhancing the system’s resilience to environmental stressors. Research shows that microbial diversity strengthens resistance to temperature fluctuations, salinity changes, and pathogen outbreaks.

For instance, certain microbial populations adapt to shifts in water temperature or salinity, ensuring efficient nutrient cycling under suboptimal conditions. Additionally, a diverse microbial community can outcompete harmful pathogens, reducing the risk of disease outbreaks in both plants and fish.

As operators gain experience managing inputs like fish feed and outputs such as plant yields, they improve their ability to maintain optimal system balance. This expertise leads to increased productivity, resource efficiency, and long-term sustainability.

19.6. Conclusion

Inoculating an iAVs with compost or humus-rich soil can accelerate microbial development but is not essential for success. Unlike traditional aquaponic systems that require lengthy cycling periods and frequent water testing to establish stable microbial populations, iAVs naturally facilitates this process and promotes a gradual establishment of biological equilibrium without the need for chemical additives or synthetic nitrification agents and becomes a resilient and productive ecosystem that requires minimal intervention once fully matured.

The simplified cycling process in iAVs offers several advantages: it lowers the barrier to entry for beginners by reducing complexity and minimizing the risk of errors during startup. The system’s reliance on natural ecological processes allows users to focus more on managing plant and fish growth rather than technical water chemistry details.

20. Fish Selection, Care, and Management

Balzende Tilapias (Oreochromis mossambicus). Destinationkho, CC BY-SA 3.0.

In iAVs, while fish play a vital role in the process, the primary goal is the sustainable cultivation of high-quality, organic fruits and vegetables..

One of the standout features of iAVs is its simplicity. The system requires only basic aquaculture knowledge, making it more accessible to a wide range of users. This ease of operation sets it apart from more complex systems, allowing both novices and experienced practitioners to manage it effectively with minimal technical expertise.

Because fish are cold-blooded, water temperature directly impacts their health and growth (Azevedo et al., 1998).. The temperature of your system’s water is a key factor in deciding which fish species you can successfully raise (Hagar 2021).

20.1. Species

Selecting fish species for an iAVs involves evaluation of several key factors. It is essential to consider the fish’s ability to tolerate a slightly acidic pH (6.4), their growth rate, and how well they align with the local climate.

Although many fish species can survive in an iAVs, the most effective choices are those that are hardy, grow quickly, and efficiently convert feed into body mass. These traits are crucial because they promote the production of sufficient waste, which is then transformed into nutrients readily available to support robust plant growth.

Nile Tilapia is ideal for iAVs due to its hardiness, fast growth, and adaptability, but check local laws as it’s restricted in some areas.

20.1.1. Tilapia

Nile Tilapia (Oreochromis niloticus) is a widely favored species for use in iAVs and is one of the most widely farmed fish species globally (Biswas et al., 2018).

Worldwide production of tilapia (Oreochromis sp.) exceeded 2.2 million metric tons in 2002, with 68% of that total coming from farmed aquaculture (Lim and Webster, 2006).

Tilapia’s value stems from its adaptability to diverse aquaculture systems, rapid growth, efficient food conversion, disease resistance, ease of production, and high nutritional quality, particularly its protein content (Biswas et al., 2018; Huang, 2024; Romanzini, 2023). Its tolerance for a wide range of water quality conditions (Chapman, 2000; Lim and Webster, 2006; Popma and Masser, 1999; Watanabe et al., 1997) and relatively low-oxygen environments allows for high stocking densities (Graber, 2009; Tyson, 2008). These qualities have made it the second most cultivated aquaculture species globally (Huang, 2024; Romanzini, 2023), and its robustness and simple production capacity make it especially favored in developing nations.

This species thrives in warm climates and demonstrates remarkable physiological robustness, making it a successful choice for various aquaculture systems worldwide (Graber, 2009; Tyson, 2008). Red tilapia, a related variety, is noted for its high protein (17.8%) and low-fat (2.7%) content per 100 grams (Nurlaeny 2014).

The optimal temperature range for tilapia development, reproduction, and growth is generally 24-32 °C, influenced by factors such as species (Chervinski, 1982), size (Hofer and Watts, 2002), and genetic variations (Cnaani et al., 2000). Specifically for Nile tilapia (Oreochromis niloticus), optimal conditions for feeding, growth, and reproduction are reported between 22-30°C (Caulton, 1982), with optimal growth temperatures in controlled environments noted as approximately 27–30°C (Azaza, 2008).

Tilapia played a significant role in the original iAVs research due to these advantageous qualities. However, it is essential to confirm local regulations before selecting this species, as its use is restricted or even prohibited in certain regions (e.g., Australia). For areas where tilapia is permitted, all-male hybrid tilapia are particularly advantageous. These hybrids often exhibit faster growth rates, greater hardiness, and an insatiable appetite, making them exceptionally well-suited for integration into iAVs.

Advantages of Monosex Male Tilapia Culture

In aquaculture, the production of all-male tilapia populations is often preferred due to their faster growth rate and low management requirements (Dagne et al., 2013; Chakraborty et al., 2011; Mair and Little, 1991).

The advantages of using monosex male tilapia are:

Growth performance: Male tilapia exhibit higher growth rates and achieve more uniform sizes compared to mixed-sex populations [Dagne et al., 2013; Chakraborty et al., 2011]. Male mono-sex tilapia can grow approximately twice as large as mixed-sex tilapia [Dagne et al., 2013].
Reproductive control: Tilapia’s prolific breeding can lead to overpopulation and stunted growth in pond culture systems, which is prevented by using monosex male populations [Phelps & Popma, 2000].
Energy utilization: Female tilapia invest energy in egg production, diverting resources from growth [Tadesse, 1997]. Additionally, mouth-brooding females may fast, which affects their body condition and growth [Tadesse, 1988; Demeke, 1994]. Male tilapia do not have these reproductive constraints, allowing them to allocate more energy towards growth [Green et al., 1997].
Reduced competition: Mixed-sex populations can experience competition between the originally stocked fish and subsequent generations, stunting the initial stock, an issue negated in monosex culture [Green et al., 1997].
Economic returns: Male mono-sex tilapia can reach their optimum net return faster than mixed-sex groups [Dagne et al., 2013]. The mono-sex group attained its optimum net return after 6 months of culture, while the mixed-sex group took 8 months; culturing the mixed-sex group for the additional two months resulted in a 32% decline from the optimum net return [Dagne et al., 2013].

However, achieving 100% all-male tilapia using manual sexing is difficult [Mair & Little, 1991; Dagne et al., 2013]. You can buy all-male tilapia fingerlings. These are widely available due to their advantages in aquaculture.

Some hatcheries use hormonal treatments or genetic techniques like YY-technology to produce all-male tilapia fingerlings and others create predominantly male hybrids by crossing specific tilapia strains, such as Wami hybrids, which naturally develop as mostly males due to their genetic makeup.

20.1.2. Jade Perch

Jade perch (Scortum barcoo) is a recommended fish due to several beneficial attributes [Emerenciano et al., 2025].

These include:

Robust health
Rapid growth rates
High feed conversion efficiency
Adaptability to diverse environmental conditions
Excellent palatability

These characteristics make Jade perch an appealing choice for iAVs. Additionally, Jade perch is suitable for earthen pond production [Business Queensland, Accessed 2025]. References

20.1.3. Carp and Catfish

Common carp and Koi are actually the same species (Cyprinus carpio). Koi are simply a domesticated, ornamental variety bred for their coloration, while common carp are typically raised for food. Their big advantage is toughness: carp are very hardy, handle a wide range of temperatures, and tolerate crowding and poor water quality well. Finding young carp (fingerlings) is usually easy.

Channel catfish (Ictalurus punctatus) are a major fish farmed in the southern US. However, despite being good for pond farming, they aren’t as hardy as people often assume, especially when raised in tanks. In tanks, they can be aggressive, and their head barbs can cause injuries during feeding. Catfish are also susceptible to a bacterial disease (ESC – Enteric Septicemia of Catfish) when water temperatures are between 20-28°C (68-82°F).

In places like India and Southeast Asia, both native carp and catfish species are popular choices for aquaculture because they suit local conditions and people want to buy them.

20.1.4. Other Species

Barramundi, often marketed as Asian Sea Bass, is native to Southeast Asia and Australia. Similar to tilapia, it adapts well to various production systems. It’s a popular choice because it grows quickly and produces a fish that people enjoy eating.

Other fish commonly used in specific regions include Anabas testudinus, native to India, and various Gourami species found throughout Southeast Asia.

Cold Water Fish

Trout, especially Rainbow and Brown varieties, are often suggested as good cold-water fish for iAVs. They are relatively easy to find in temperate areas and can grow quickly on a high-protein diet.

However, be aware that trout are quite demanding. They evolved in cold, clean, oxygen-rich streams (preferring water around 14-16°C or 57-61°F). This means they need consistently high levels of dissolved oxygen in their water and don’t handle poor water quality well. Successfully raising trout in an iAVs system requires careful management and a good amount of fish-keeping experience.

20.1.5. Fish Selection based on Goals

The choice of fish species depends on the operator’s objectives:

For Consumption:

Tilapia: Known for its mild flavor and high protein content.
Catfish: Valued for its firm texture and versatility in cooking.
Trout: Prized for its delicate flavor and high omega-3 fatty acids.
Carp: Appreciated for its adaptability to various conditions.

For Non-Consumption:

Goldfish: Hardy species that tolerate a wide range of water conditions while producing nutrient-rich waste ideal for plant fertilization.

When selecting fish species for commercial purposes, it is crucial to consider local market preferences regarding size and form. Aligning with local demand ensures the economic viability of the iAVs operation.

20.1.6. Determining Stocking Density:

A general guideline is to start with 80–100 fingerlings, each weighing around 15 grams (0.53 ounces), per 1000 liters (264 gallons) of water. As fish grow, larger individuals should be removed to maintain optimal density and ensure overall well-being.

20.2. Sourcing Fish

You can source fingerlings from the following suppliers:

Fish Hatcheries: Cheapest option but may have minimum order requirements (e.g., 100 fingerlings).
Aquarium Supply Stores: Suitable for smaller orders but often more expensive and may carry disease risks.
Fish Restocking Programs: May be available depending on species requirements.
Specialist Breeders: For specific or rare species.

20.3. Acclimation Process for Fingerlings

Introducing fingerlings into a new environment requires careful acclimatization to ensure their survival. This involves gradually equalizing water temperature and pH between the original source and the new tank to avoid shocking the fish.

When receiving fingerlings from a hatchery, they are typically shipped in oxygen-filled bags. Follow these steps for acclimation:

Make a small cut in the bag and float it on the tank’s surface to allow temperature and pH levels to equalize.
Let the bag float for 30–60 minutes.
Once balanced, carefully open the bag and allow the fingerlings to swim out gradually.
Monitor them closely for 24–48 hours after acclimation.

This gradual process minimizes stress and improves their chances of adapting successfully.

20.4. Maturation

As the iAVs ecosystem stabilizes over time (typically 6–8 weeks), nutrient supplementation becomes less critical as natural processes self-regulate. The focus shifts to balancing nutrient generation from fish waste with plant uptake, ensuring optimal conditions for both without excess accumulation that could harm fish.

Fish should be fed just enough to meet plant nutrient demands without excess or deficiency.

20.5. Harvesting

As fish grow, maintaining healthy stocking density requires culling – selectively removing individuals from the tank either for harvest or relocation to another tank. Without culling, biomass density increases, leading to stress, disease, and reduced growth rates.

20.5.1. Optimal Harvesting Size

Fish harvesting is a flexible process and can be done at any stage of their growth. The decision largely depends on your intended use for the fish. Below are key considerations for harvesting based on fish size and purpose.

Small-sized fish (100 g / 3.5 oz): Suitable for certain dishes but often grown further. Fish can be incorporated into menus or consumed at smaller sizes starting from 100 grams. This is ideal for scenarios where smaller portions are acceptable or preferred.
Plate-sized fish (250 g / 8.8 oz to 400 g / 14 oz): For most practical purposes, plate-sized fish are a popular choice. These sizes are well-suited for direct serving on plates without additional processing.
Fillets: Marketable fillets typically require growing fish for at least 12 months.

For consumption, harvesting at around 250 grams (0.55 lbs) is ideal for filleting and meal preparation.

iAVs was originally designed for resource-limited regions like rural arid areas to combat malnutrition; in such contexts, portion size may be less important than nutritional value.

In some regions like sub-Saharan Africa, whole fish weighing between 200–250 grams are commonly added to porridge dishes with vegetables, providing protein without waste.

20.6. Fish Health Monitoring & Disease Management

Consistent monitoring of fish behavior and water quality is essential for early detection of health issues and maintaining system balance.

20.6.1. Behavior and Appearance

Healthy fish exhibit extended fins, straight tails, normal swimming, strong appetite, clear eyes, and no signs of stress or disease such as lesions or irregular breathing.

Regular observation during feeding helps detect early signs of health issues, such as appetite loss or lethargy.

The vigor of fish feeding activity is a reflection of the general health and stress level of the fish (Lim and Webster, 2006).

21. Fish Feed: Principles and Practices

21.1. Understanding the Central Role of Fish Feed in iAVs

Fish feed is what powers your iAVs. It provides the essential nutrients that your plants need to grow.

Fish Feed as the Primary Nutrient Source for Plants

In iAVs, fish feeding is not solely about maximizing fish growth; it’s fundamentally about providing a consistent and balanced source of nutrients for the plants. The ‘waste’ produced by the fish, directly linked to the quality of their feed, becomes the primary fertilizer for the plants in the system.

Proper fish feed formulation and feeding strategies are essential to minimize waste and maintain water quality. The effects of specific feeds on water quality through diet digestibility, faeces particle size, and settling ratio are also important aspects (Yildiz 2017).

Since fish feed composition varies across brands and types, it is important to review product labels or consult manufacturers for specific nutrient details..

21.2. Selecting the Right Fish Feed

21.2.1. Choosing High-Quality Feed

Opt for natural, high-quality feed specifically formulated for your fish species to ensure their nutritional needs are met and promote optimal growth.

Select food without unnecessary additives. Ensure the feed’s ingredient composition is verified for quality; avoid “bargain” feeds that may contain harmful chemicals or preservatives.

Floating Pellets

Floating pellets allow for easy monitoring of fish consumption, as they remain on the surface and can be removed if uneaten within 15 minutes. This helps prevent overfeeding and ensures no excess food remains in the water.

Tilapia can utilize the floating pellets and sinking pellets very efficiently (Santiago 1987).

Kawser (2016) summarized findings on fish feed preferences:

Floating pellets are usually more palatable and uniform than sinking pellets (Craig and Helfrich 2002). Except some bottom dwelling fish most fish species prefer floating pellets than sinking pellets (Craig and Helfrich 2002). Cruz and Ridha (2001) have conducted an experiment on growth and survival rates of Nile tilapia (Oreochromis niloticus) juveniles reared in a recirculating system fed with floating and sinking pellets and found that the survival rate was 100% in both cases. The overall performance of O. niloticus fed with floating pellet was better than sinking pellet in terms of growth response, feed utilization and nutrient retention (Kawser 2016).

When choosing pellet size for fish, the pellet should be small enough to fit easily into the fish’s mouth and be swallowed whole-ideally, slightly smaller than the fish’s maximum mouth opening (oral gape). As fish grow, their mouths get larger, so the size of the pellet should be gradually increased to match their growth. This practice ensures efficient feeding, minimizes feed wastage, and reduces the risk of choking or stress. Feed manufacturers are able to give directions on the right type of feed for each production stage.

21.2.2. Avoiding Additives

When selecting fish feed, choose products free from harmful additives such as antibiotics, hormones, or artificial colors. Overuse of antibiotics can lead to resistance, while hormones may harm fish health and potentially affect human consumers. Artificial colors can reduce nutritional value and hinder fish growth.

Supplementary vitamins in fish feeds can degrade quickly, especially when stored at room temperature, so it is best to avoid them unless properly stored.

Fish feed binders are crucial for preventing pellets from disintegrating in water and reducing dust during handling (Hardy 2002). However, many binders have no nutritional value (Lovell 1989) and are poorly digested, emphasizing the need to select feeds where such non-nutritive components are minimized. By selecting high-quality feed, you can ensure that your fish receive optimal nutrition while maintaining system cleanliness and efficiency.

21.3. Implementing Effective Feeding Strategies

21.3.1. Feed Rate Principles

Determining the correct amount of fish feed is crucial in iAVs, but the approach differs significantly from traditional aquaculture. In systems focused solely on fish growth, feeding is typically based on a percentage of the fish’s total body weight (% biomass/day). However, in iAVs, the primary goal is sustainable plant production, with fish serving as the in-situ nutrient generators. Therefore, the feeding strategy must prioritize providing the right amount of nutrients for the plants via the fish waste.

Why Feed Based on Biofilter Area (g/m²/day)?

The core principle is that the sand biofilter (the plant growing area) acts as the system’s biological processing unit. Its capacity to break down fish waste (mineralization) and make nutrients available is directly related to its size (surface area for microbial activity) and the nutrient uptake demand of the plants growing within it.

Biofilter Capacity: The biofilter has a finite capacity to process the ammonia and organic solids produced from fish waste. Overloading it leads to poor water quality (toxic ammonia/nitrite buildup) that harms fish.
Plant Demand: The total amount of nutrients needed depends on the type of plants being grown (leafy greens vs. demanding fruiting crops) and the total area dedicated to them.
Linking Input to Capacity: Feeding based on the biofilter’s surface area (grams of feed per square meter per day) directly links the nutrient input (feed) to the system’s processing and uptake capacity (biofilter area + plant type). This ensures you don’t provide more waste than the biofilter and plants can handle, nor too little to meet plant needs.

How Does This Relate to Fish Population Management?

While the target daily feed amount is determined by the biofilter area and plant type, the fish are the essential mechanism for converting that feed into the waste nutrients the system needs. This is where fish population management becomes critical:

Target Feed Intake: First, determine the target daily feed ration based on your biofilter area and the primary crops (see guidelines below).
Matching Fish Biomass to Intake: You must have enough fish (in total weight/biomass) in your tank to eagerly consume this target amount of feed within the recommended feeding times (e.g., twice daily, consumed within ~15 minutes).
Dynamic Management:
1. Startup: When starting with small fingerlings and young plants, feed what the fish consume readily. The initial feed rate will be low.
2. Growth Phase: As fish grow, their individual appetite increases. As plants grow, their nutrient demand increases, allowing you to gradually raise the target daily feed rate (g/m²/day) towards the optimum for your crops.
3. Balancing Act: Your task is to manage the fish population (number and size) so that their total daily consumption matches the target feed rate determined by the biofilter area.
  1. If your fish grow large and their combined appetite exceeds the target feed rate for your plants/biofilter, you need to harvest some of the larger fish (culling) to reduce the total biomass and bring consumption back in line.
The Role of Standard Ratios: The standard iAVs tank-to-biofilter ratios (e.g., 1:2 V:V, 1:6 V:A) are designed such that a reasonably stocked fish tank (e.g., starting with 80-100 fingerlings/1000L and growing them to harvest size) generally has the capacity to consume the feed required by the corresponding biofilter area when managed correctly.

General Guidelines (Grams of Feed per Square Meter of Biofilter per Day):

Fruiting Crops (Tomatoes, Peppers, Cucumbers): Aim for 20-30 grams/m²/day. These plants have high nutrient demands.
Root Crops (Carrots, Beets): Require less, around 15-25 grams/m²/day.
Leafy Greens & Herbs (Lettuce, Basil): Need the least, roughly 10-20 grams/m²/day.
Mixed Crops: If growing a mix (recommended), use the rate for the most demanding crop occupying a significant portion (e.g., if 50% tomatoes, use the 20-30 g/m²/day range as a starting point).

Always observe your plants and fish. Stunted or yellowing plants may indicate insufficient nutrients (slowly increase feed, ensuring fish consume it). Lethargic fish or cloudy/smelly water suggests potential overfeeding or water quality issues. Careful record-keeping of feed amounts, fish harvesting, and plant health will help you fine-tune the balance for your specific system.

A uniform feeding strategy can improve Nutrient utilization efficiency (Yang 2019).

21.3.2. Feeding Schedule

For optimal fish growth, feed them twice daily at 6:30 am and 1:45 pm, providing only what they can consume within 15 minutes. This schedule ensures the entire tank volume is fully irrigated into the biofilter between feedings. Avoid feeding the fish after 2pm to allow complete tank water exchange before the overnight pause.

Morning Feeding

Morning feeding aligns with peak plant photosynthesis, enhancing nutrient uptake from fish waste. Many fish species are naturally more active in the morning, improving feed utilization and digestion. This timing also supports better water quality, as uneaten food and fish waste are processed by the sand biofilter during daylight hours.

Afternoon Feeding

Feeding in the afternoon provides an additional nutrient boost for plants, sustaining growth through the remaining daylight. It allows sufficient time for digestion and waste processing before nightfall, maintaining water quality. Avoiding late afternoon or evening feeding helps keep ammonia levels low overnight, reducing stress on fish when plant nutrient uptake is minimal due to the absence of photosynthesis.

Research shows that each irrigation event reduces ammonia levels by 50%, helping maintain optimal water quality for fish. This is critical, as high ammonia levels can cause stress or toxicity, especially at night when plant uptake decreases.

Feed Rate

The feed rate varies with fish size, ranging from 15% to less than 0.5% of their biomass daily. As fish grow, reduce the feed percentage relative to their body weight. During system startup with small fish and young plants, feed as much as they will eat twice a day, gradually increasing the amount as both grow. For example, an initial rate of 40 g/m³/day (0.32 lb/35 ft³/day) can increase to 120 g/m³/day (0.96 lb/35 ft³/day) within a few weeks.

Promptly remove uneaten food to maintain water quality and prevent decomposition.

21.3.3. Feeding Times

6:00 am: Start first pump cycle.
6:30 am: Complete drainage; feed fish for 15 minutes.
8:00 am: Begin second pump cycle (1/4 tank volume).
10:00 am: Start the third pump cycle.
12:00 pm: Initiate fourth pump cycle.
1:45 pm: Feed fish for 15 minutes.
2:00 pm: Begin fifth pump cycle.
4:00 pm: Start sixth pump cycle.
6:00 pm: Initiate seventh pump cycle.
8:00 pm: Begin final pump cycle.

Note: Adjust feeding times based on factors such as fish species, growth stage, water temperature, and local conditions. Manually distribute feed across the tank surface and monitor fish behavior to avoid overfeeding.

21.3.4. Monitoring Consumption

Monitoring of feeding behavior is recommended to prevent excess feed from degrading water quality.

Food-anticipatory behavior exhibited by fish can serve as a valuable indicator of their welfare status (Kristiansen 2007). Uniform feeding regimes can increase nitrogen use efficiency (Yang & Kim, 2020).

Factors affecting consumption include feed quality, water temperature, and fish health or stress levels. Regular monitoring helps adjust feed rates accordingly to maintain system balance.

Keeping records of feed amounts provided, uneaten feed quantities, and observations of feeding behavior allows for informed adjustments to feeding strategies over time.

21.3.5. Overfeeding

Avoid overfeeding by providing 1–2% of fish body weight per day (10–20 grams per kilogram or 0.16–0.32 oz per pound). Feed only what they can consume in 15 minutes; remove uneaten food afterward. If all food is consumed within 10 minutes, offer a supplementary portion (~10% more) and observe consumption for another 15 minutes.

Signs of overfeeding include poor water quality (elevated ammonia levels, cloudiness, foul odors), organic matter buildup in biofilters, and potential algal blooms. Overfeeding can clog sand media and reduce filtration efficiency over time.

21.3.6. Automatic feeders

Hand-feeding fish can be time-consuming and labor-intensive. Automating this process requires an understanding of species-specific feeding behaviors. For example, carnivorous fish may need smaller, more frequent feedings, while herbivorous species tend to graze continuously. Additionally, it is essential to account for the number and size of fish in each tank. Although hand-feeding offers the benefit of close observation, automation can streamline the process.

Various automatic feeders are available, particularly for larger operations. In recirculating aquaculture systems (RAS), most feeders dispense dry pellets that float before sinking. Fish typically consume the pellets while they are still floating or descending.

Feeding behavior can be aggressive in many farmed fish species, which presents challenges. Modern automatic feeders are designed to mitigate these issues by ensuring even food distribution, preventing dominant fish from monopolizing feed while others go hungry.

21.4. Feed Management and Long-Term Considerations

21.4.1. Feed Storage

Proper fish feed storage is crucial for maintaining nutrition and preventing mold. Always keep feed in airtight containers stored in a cool, dark, dry place, away from sunlight. Moisture is the main concern, as it causes mold growth, potentially producing toxins dangerous to fish. Discard any moldy feed – never feed it to your fish.

Since feed quality degrades after production, storing it cold can help preserve nutrients longer, but ensure it stays completely dry and sealed to avoid mold from condensation. As a guideline, purchase only the amount of feed you anticipate using within roughly six months to maximize freshness.

22. Irrigation

Example of furrow layout showing how water flows through the sand substrate during irrigation cycles in an iAVs. This ‘flood and drain’ process enhances aeration and supports both plant roots and microbial activity. Photo courtesy of USDA NRCS.

Irrigation in iAVs involves timed cycles of flooding and draining, often referred to as “reciprocating biofilter”. This process ensures optimal conditions for plant roots and microbial communities by balancing water delivery with aeration. The goal is to move approximately 25% of the fish tank water per cycle, ensuring nutrient-rich water circulates through the biofilter while maintaining oxygen levels for both fish and plants.

The irrigation method resembles surface irrigation techniques used in traditional agriculture. During each cycle, a water pump floods the sand biofilter to saturation, after which it drains completely. Well-draining sand allows for full pore volume recharge with air (20% oxygen) during each cycle, supporting aerobic microbial activity that drives nutrient cycling. Fish waste serves as the primary nutrient source for these microbes.

The sand retains enough moisture to prevent over-saturation or drying out, providing ideal conditions for plant growth. The drain cycle is crucial as it facilitates gas exchange, ensuring oxygen-rich air reaches plant roots and microbes. Irrigation occurs only during daylight hours, aligning with peak photosynthesis periods when plants actively absorb water and nutrients. This also makes iAVs well-suited for solar-powered pumping in sunny climates.

This image shows an irrigation event at 100% saturation, water wicks up into the ridges.

22.1. Night-time Irrigation Considerations

In iAVs, irrigation is limited to daylight hours to coincide with photosynthesis when plants open their stomata to absorb water and nutrients efficiently. At night, plants reduce transpiration as photosynthesis halts, shifting their metabolic focus to respiration. Nighttime watering can disrupt this balance and increase the risk of fungal and bacterial diseases due to excess moisture and cooler temperatures. These conditions promote pathogen growth, which can harm plant health and reduce crop yield.

By avoiding nighttime irrigation, the system supports optimal microbial activity and plant health, creating a balanced environment where aerobic microbes can metabolize nutrients without interruption.

22.1.1. Daytime Irrigation and Photosynthesis

Daytime irrigation coincides with peak photosynthetic activity, ensuring that nutrient uptake aligns with plant metabolic demands. During daylight, stomata remain open, allowing efficient absorption of water and nutrients. This timing also maintains high oxygen levels in the root zone, supporting aerobic microbial activity essential for nutrient cycling.

At night, plants reduce transpiration due to the absence of light, which halts photosynthesis and shifts the focus to respiration. Root and rhizosphere processes benefit from the abundant oxygen available during non-flooded periods, which also supports aerobic soil organisms.

The avoidance of nighttime irrigation allows microbes to proliferate and metabolize the substrate without interruption, enhancing nutrient cycling and overall plant health.

22.1.2. Microbial Activity and Nighttime Irrigation

Watering at night can increase the risk of fungal and bacterial diseases due to excess moisture in cooler temperatures. Without sunlight to evaporate water, humidity around plants rises, creating conditions favorable for pathogen growth.

By avoiding nighttime irrigation, the system reduces the total energy required for water pumping, and also fosters optimal conditions for plant growth and soil microbial health.

22.2. Drainage Importance in iAVs

Drainage between irrigation cycles is essential for oxygenating plant roots and soil microbes. While moisture is necessary for microbial survival, free water, particularly at night, can be harmful. The thin film of water adhering to sand particles is sufficient to sustain microbial activity while maximizing oxygen exchange.

Proper drainage promotes slight drying of the root zone, encouraging root hair formation and branching. This drying also improves soil aeration, which enhances oxygen diffusion and supports aerobic microorganisms crucial for nutrient cycling. Oxygen reintroduction during drainage prevents anaerobic conditions that could lead to root rot or reduced microbial diversity.

Frequent irrigation without adequate drainage limits oxygen availability, reducing microbial diversity and abundance. Therefore, allowing sufficient drainage between irrigation events optimizes moisture levels, oxygen availability, and microbial activity for healthy plant growth.

22.3. Irrigation Cycle Duration

The ON cycle typically lasts 15 minutes, depending on the sand’s drainage capacity. In well-drained systems, drainage should begin within one-third to one-half of the ON cycle.

Pump until the furrows are fully saturated but avoid flooding the elevated ridges between them to prevent contamination from fish waste and reduce the risk of crown rot, a fungal disease that can damage plants.

22.4. Water Retention between Irrigation Events

Water retention refers to the amount of water that remains in the sand after the biofilter has drained. A small quantity of water will remain in the sand following the drain cycle – and it remains there (available to the plants) until the next flood cycle. The water that remains is bound to the surface of the sand particles by hydrostatic tension.

The exact amount of water retained in the sand will vary according to the elapsed time from the last flood cycle. For example, about 5% of the water that was pumped may be retained after the first flood cycle in the morning, whereas only 1% will be retained after subsequent flood cycles through the day (approximately two hours apart). Note: These numbers are not prescriptive – they may vary from situation to situation,

22.5. Fish Tank Water Level During Irrigation

During irrigation, effluent should begin draining from the sand biofilter within minutes. This rapid drainage means that while approximately 25% of the fish tank’s water volume is used for irrigation, the actual water level typically drops by only 10-15%.

This quick return of water not only facilitates air intake into the biofilter but also enhances aeration. As the water level in the fish tank decreases, the returning effluent falls from a greater height, further increasing aeration.

The layout of iAVs, with the biofilter draining directly into the fish tank, allows the water to be directed against the side walls, gently channeling solid waste towards the central depression for efficient removal. These features are intentionally integrated to optimize water quality and system performance by ensuring efficient removal of solids from the fish tank.

22.6. Example Schedule

At 6:00 am, the pump activates, sending nutrient-rich water into the sand bed, where it flows along the furrows and percolates through the sand. Within 2 to 10 minutes, water begins to drain back into the tank.

After approximately 15 minutes, the water reaches the top of the furrows (but remains below the ridges), at which point the pump shuts off. Adjust the flow rate to prevent water from reaching the base of the plants.

For the next 1 hour and 45 minutes, the bed drains fully and remains dry. At 8:00 am, the pump starts again for another 15-minute cycle. This process repeats every two hours during daylight hours, with frequency adjusted based on latitude and season.

In tropical regions, irrigation can start before dawn and end after dusk. During each cycle, up to half of a fish tank’s volume can be pumped without reducing its volume by more than 10-15%, ensuring no harm to fish or plants.

22.7. Minimizing Water Velocity

High water velocity in pipes or hoses can disturb the sand surface in iAVs, displacing particles and potentially damaging plant roots, especially where water first enters the sand bed. To prevent this erosion, several methods can be used to reduce water velocity and dissipate its energy before it contacts the sand:

Pipe Size Adjustments: One effective way to manage water velocity is by adjusting pipe sizes. As water moves from smaller-diameter pipes to larger ones, its velocity decreases, following the principle of conservation of mass. By using a larger pipe at the point where water enters the sand bed, water velocity is reduced, minimizing the risk of scouring.

If the cross section gets smaller the velocity of the fluid rises due to a constant volumetric flow rate. MikeRun, CC BY-SA 4.0, via Wikimedia Commons.

Energy Dissipation Methods: Directing water flow onto a pad, plastic sheet, or rocks before it contacts the sand can also dissipate energy and reduce the impact on the sand bed. These materials slow down the incoming water and prevent disturbances.

Distribution Headers: A more effective method for reducing water velocity is using a distribution header or manifold at the end of the sand filter. Perforated pipes with small holes or slits can spread the flow over a larger area, reducing disturbance to the sand. Dr. Mark McMurtry found that using a 20 mm (¾”) hose pipe from the pump, inserted into a 40–50 mm (1.5″–2″) diameter header pipe with 8–10 mm (3/8″) holes drilled at 10 cm (4″) intervals along its length (facing downward), effectively prevents scouring and ensures even water distribution across the bed.

A simple distribution header made from a larger diameter PVC pipe than the intake hose reduces water velocity and evenly distributes water across the sand bed, minimizing scouring and ensuring uniform irrigation.

By employing these strategies, water velocity is minimized, preserving the integrity of the sand biofilter and ensuring optimal conditions for plant growth and microbial activity.

22.8. Ball Valves

While ball valves can be incorporated, they are not strictly necessary, but can be useful to adjust the flow rate, especially if you are using more than one sand biofilter and need to ensure the water is delivered evenly to each one.

22.9. Plumbing

When designing the plumbing for the pump, it is important to account for power loss at each pipe fitting, as up to 5 percent of the total flow rate can be lost at every connection. Minimizing the number of connections between the pump and fish tanks is recommended to reduce flow loss.

Dr. McMurtry opted for no fittings or rigid PVC (except for a 2” PVC distribution header) and instead utilized a ¾” flexible garden hose rated for potable water.

Daderot, CC0, via Wikimedia Commons

Flexible hoses offer several advantages over traditional rigid PVC pipes. They are easier to install and adjust, reducing setup and maintenance time. Unlike rigid pipes, flexible hoses can bend and adapt to different layouts without requiring multiple fittings, which are prone to leaks or flow losses. This adaptability also helps reduce water velocity at key points, minimizing erosion in the sand biofilter and promoting consistent water distribution.

It is essential to use hoses certified for potable water to ensure the safety of both plants and fish in iAVs. Non-potable hoses may leach harmful chemicals into the water, negatively affecting plant health and fish well-being. Potable water hoses are food-safe, preventing contamination and ensuring system productivity.

22.9.1. PVC

PVC (polyvinyl chloride) pipes, commonly used in traditional aquaponic systems, degrade when exposed to sunlight over time due to UV radiation. This degradation leads to brittleness and microcracks, potentially releasing harmful chemicals that can affect fish, plants, and microbial communities.

To mitigate these risks, protect PVC pipes from direct sunlight using insulation or shade covers or opt for UV-resistant materials. Alternatively, flexible hoses designed for potable water are often more resistant to UV damage and could improve system longevity.

22.9.2. Float Switch

Maintaining safe water levels in the fish tank is crucial in aquaculture and iAVs. A significant risk arises if the pump runs continuously due to equipment failure (like a stuck timer), incorrect settings, or other system faults, leading to dangerously low water in the fish tank. This threatens fish survival and can damage the pump itself.

To prevent this, installing a low-water cut-out (float switch) is highly recommended. This device monitors the water level using a float. When the level falls below a safe minimum, the switch automatically cuts power to the pump. Normal operation resumes once the water level is restored.

Implementing a float switch is a vital safeguard for protecting fish, preserving pump integrity, and ensuring the overall health and efficiency of the system. It’s an essential component for robust and reliable aquaculture or iAVs setups.

Illustration of a water pump installed within a fish tank, equipped with a float switch as an emergency safeguard to prevent accidental drainage of the tank.

23. Surface Area and Biofilms

The Power of Surface

At the microscopic level, the efficiency of an iAVs biofilter hinges on two interconnected concepts: Specific Surface Area (SSA) and the biofilms that colonize it. SSA refers to the total surface area available within a given volume of material. In iAVs, the chosen medium – sand – provides an exceptionally high SSA. This vast surface area is not just inert space; it serves as the essential real estate for biofilms – complex communities of microorganisms – to establish and thrive. Understanding how this immense surface area enables the formation and function of biofilms is key to grasping the biological power of the iAVs biofilter.

Specific Surface Area (SSA): Maximizing Microbial Habitat

The choice of sand as the biofilter medium in iAVs is deliberate and critical, primarily due to its incredibly high Specific Surface Area (SSA).

What is SSA? SSA is a measure of the total exposed surface of a material per unit of volume or mass. Imagine unfolding every tiny grain in a cubic meter of sand – the total area would be enormous.
Sand vs. Other Media: Medium-coarse sand (ideally 0.4 mm to 1.2 mm particle size) boasts an estimated SSA of 7,000–10,000 square meters per cubic meter (m²/m³). This dwarfs the SSA offered by common alternatives like gravel or expanded clay pellets.
Why High SSA Matters: This vast surface area provides an expansive habitat for microorganisms. More surface means more space for bacteria, fungi, and other beneficial microbes to attach, grow, and form the dense communities known as biofilms. A larger microbial population translates directly to a greater capacity for biological filtration and nutrient processing.
Particle Size is Key: The recommended particle size range (0.4 mm – 1.2 mm) is crucial. While smaller particles offer even higher SSA, they can impede drainage and aeration. Conversely, sand particles significantly larger than 1.2 mm offer considerably less total surface area, limiting the potential density of the biofilm and hindering the system’s biological efficiency. The 0.4-1.2mm range strikes the optimal balance between maximizing functional surface area and maintaining good water/air flow.

Media like LECA (clay balls, e.g., 16 mm diameter with an SSA around 6.03 cm²/g and gravel (e.g., 24 mm diameter with an SSA around 3.18 cm²/g) offer some surface area (Goddek 2015; Lennard 2006).

However, the sand utilized in the iAVs research possessed a mean particle size of 750 microns, yielding a volumetric surface area greater than 6900 m²/m³. Consequently, its surface area is over 19 times larger than that of 9.5 mm (3/8″) pea gravel and more than 7 times larger than that of 16mm LECA.

Biofilms: The Living Communities on the Surface

Biofilms are the functional microbial communities that develop on the high SSA provided by the sand.

What are Biofilms? A biofilm is composed of densely packed microbial communities – including bacteria, fungi, and protozoa – encased within a protective, self-produced matrix of proteins and carbohydrates (Yep and Zheng, 2019). They coat the sand grains, particularly within the detritus layer in the furrows.
Key Roles Enabled by High SSA: The extensive biofilm development made possible by the sand’s high SSA performs multiple vital roles:
- Enhanced Mechanical Filtration: The sticky matrix traps fine particles, improving water clarity.
- Intensive Nutrient Cycling: The large microbial population efficiently carries out mineralization and nitrification, converting waste into plant food.
- Water/Nutrient Retention: The film helps retain moisture and nutrients between irrigation cycles.
- Pathogen Suppression: Dense beneficial communities outcompete harmful pathogens.
- Synergy: Biofilms interact beneficially with surface algae and the detritus layer.

Formation and Development of Biofilms

Biofilm development is a natural process occurring in stages:

Initial Adhesion: Microbes attach to the sand grain surfaces.
Matrix Production: Colonizers secrete the sticky matrix (EPS).
Colonization and Maturation: Diverse microbes join, forming complex, robust communities over time.

The iAVs Advantage: Synergy of Sand and Process

The iAVs design optimizes biofilm formation and function on the high-SSA sand:

Ideal Habitat: The combination of massive surface area, stable physical structure, and nutrient delivery creates an ideal microbial habitat.
Optimal Conditions: The intermittent irrigation cycle provides both moisture/nutrients (flood phase) and crucial access to highly concentrated atmospheric oxygen (drain phase), fueling the aerobic microbes within the biofilm.
Resilience and Diversity: This environment fosters a more stable and biologically diverse microbial ecosystem compared to constantly submerged hydroponic systems, contributing to system resilience.

Conclusion

The effectiveness of the iAVs biofilter stems directly from the synergy between the high Specific Surface Area provided by the carefully selected sand medium and the extensive, highly active biofilms that colonize this surface. The vast area maximizes the potential for microbial growth, while the iAVs operational process (intermittent irrigation) provides the ideal conditions for these biofilms to efficiently filter water, cycle nutrients, and maintain a healthy ecosystem. Understanding this relationship between physical surface area and biological function is fundamental to appreciating the design and performance of iAVs.

24. Mineralization and Oxidation

The Challenge: Nutrient Gaps in Other Systems

A common hurdle in many traditional aquaponic systems is providing complete plant nutrition solely from fish waste. These systems often show nutrient deficiencies, requiring operators to add supplements to support plant growth and achieve good yields. This adds complexity and increases operational costs (Delaide et al., 2016; Nicoletto et al., 2018). iAVs was specifically designed to overcome this by efficiently processing the entire spectrum of fish waste, including the nutrient-rich solids, directly within the system.

What are Mineralization and Oxidation?

This system targets the breakdown of the solid fish waste (sludge), which is rich in essential plant nutrients initially present as complex organic molecules (Yogev 2016). The core mechanism is mineralization, nature’s recycling process where microorganisms convert this organic matter into simple, plant-available inorganic forms like nitrates and phosphates (Delaide et al., 2018; Zhang et al., 2021). This conversion is chemically driven by oxidation (reactions involving oxygen). iAVs specifically employs aerobic mineralization, harnessing abundant oxygen to make this breakdown highly efficient and effective for nutrient release.

Why It Matters in iAVs

Efficient mineralization and oxidation are fundamental to iAVs’ success. This process converts fish waste into essential plant nutrients (McMurtry 1997a; Palada et al., 1995), typically eliminating the need for external fertilizers. It also cleans the water by breaking down organic load, preventing harmful sludge buildup deep in the sand (McMurtry 1997b; Delaide et al., 2021). This rapid, natural cycling creates a stable and highly productive system. Research confirms aerobic mineralization is faster than anaerobic methods (Chen et al., 1997).

How iAVs Design Enables Efficient Oxidation

The iAVs design maximizes aerobic mineralization:

The Sand Biofilter’s Dual Role: The sand bed is more than just a growing medium. It acts as a mechanical filter, trapping solids on the furrow surfaces, and as a biological filter, hosting the microbes that perform mineralization.
Direct Waste Application: Nutrient-rich water and solids are applied directly onto the furrow surfaces (McMurtry 1997a; Section 9.4). Frequent irrigation ensures a steady supply of fresh organic matter for microbes.
Oxygen Supercharging via Intermittent Irrigation: The flood-and-drain cycle is critical. As water drains, fresh atmospheric air (~21% oxygen) is pulled deep into the sand. This exposes the waste layer in the furrows to oxygen levels thousands of times higher than dissolved oxygen in water.

The Furrow: The Engine of Mineralization

The furrows are the primary site for this oxygen-fueled breakdown. Aerobic microbes (bacteria, fungi) in the detritus layer use the abundant atmospheric oxygen to efficiently decompose the waste (McMurtry 1997b). The reaction (Organic Matter + Oxygen → CO₂ + Water + Inorganic Nutrients + Energy) releases plant-ready nutrients like nitrates and phosphates directly where roots can access them. Diverse microbes, including bacteria, fungi, cyanobacteria, and actinomycetes, are crucial, especially for making elements like phosphorus available from otherwise unusable forms (Doilom et al., 2020; Rawat et al., 2021). This high-oxygen environment ensures faster decomposition, minimizes harmful anaerobic byproducts (like methane and hydrogen sulfide), and provides enhanced nutrient availability right at the root zone, allowing plants to focus energy on growth.

Aerobic vs. Anaerobic: The iAVs Advantage

Research shows aerobic digestion yields higher nutrient recovery and less nutrient loss (Zhang et al., 2021; Monsees et al., 2017), with significantly higher nutrient concentrations compared to anaerobic methods (Monsees et al., 2017; Delaide et al., 2018). Aerobic systems are also generally simpler, safer, produce fewer undesirable byproducts, maintain better water quality, reduce odors, and have lower greenhouse gas emissions (Delaide et al., 2018; Zhang et al., 2021; Delaide et al., 2021).

The Critical Role of Retaining Solids

Unlike systems that remove solids, iAVs retains and mineralizes this nutrient-rich fraction. Fish sludge is packed with phosphorus and micronutrients (Khiari et al., 2019; Timmons and Ebeling, 2007; Schneider et al., 2005). Discarding it means losing significant fertility (Yogev et al., 2016; Eck et al., 2019). Studies confirm plants grow better with the solids included (Palada et al., 1995). By processing these solids aerobically, iAVs provides a complete plant diet from the fish feed alone.

25. Nitrification

Nitrification is a critical subset of mineralization, specifically dealing with nitrogen.

The Role of Nitrifying Bacteria

Within the complex microbial community thriving in an iAVs sand biofilter, a specific group of bacteria plays a crucial role in the nitrogen cycle: the nitrifiers. Nitrification is the biological process where these specialized bacteria convert ammonia (NH₃), primarily excreted by fish, first into nitrite (NO₂⁻) and then into nitrate (NO₃⁻). Key players in this two-step process include bacteria like Nitrosomonas (converting ammonia to nitrite) and Nitrobacter (converting nitrite to nitrate), along with other important nitrifiers such as Nitrospira (Prosser, 1986). These microorganisms establish themselves within the biofilm coating the vast surface area provided by the sand grains, forming an essential part of the system’s living filter.

Nitrification and pH: The iAVs Difference

The efficiency of nitrification is known to be influenced by water pH. Much traditional aquaponics research suggests that nitrification operates optimally at a higher pH, typically between 7.5 and 9.0 (Hochheimer and Wheaton, 1998). This has led many conventional systems to aim for a pH around 7.0 as a compromise between the needs of fish, plants, and nitrifying bacteria.

However, iAVs operates differently. The system is intentionally managed at a slightly acidic pH of approximately 6.4 (± 0.4). This range is chosen primarily to optimize nutrient availability for the plants, which are the main focus of production in iAVs. While this pH is lower than the reported optimum for nitrification, extensive iAVs research and long-term operation have demonstrated that nitrification is not a limiting factor at this pH level within a well-functioning iAVs.

Several factors contribute to this:

Bacterial Adaptability: Nitrifying bacteria exhibit remarkable adaptability. Studies have shown they can function, albeit potentially at slower rates, at pH levels well below their optimum. Research by Haug and McCarty (1972) indicated that while nitrification slows below pH 6.0 and may cease below 5.5, these bacteria can adapt to function effectively even at pH 5.5 within a relatively short period (Collins 1975; Haug and McCarty, 1972).
Massive Surface Area: The sand biofilter provides an enormous surface area for microbial colonization compared to other filter media. This allows for a very large population of nitrifying bacteria to establish, potentially compensating for any reduction in individual bacterial efficiency at the lower pH.
Oxygen Availability: The intermittent irrigation cycle ensures high levels of oxygen throughout the biofilter, which is essential for the energy-intensive nitrification process.

Direct Plant Uptake and Reduced Nitrification Load

Perhaps the most significant reason why the lower pH doesn’t hinder iAVs performance relates to how plants utilize nitrogen in this system. Unlike systems where nitrate is the primary nitrogen form available, plants in iAVs have direct access to ammonium (NH₄⁺) in the nutrient-rich water within the sand bed. Ammonium is the less toxic form of ammonia present at the system’s pH of ~6.4.

Plants can readily absorb and assimilate ammonium directly into amino acids, a process that is metabolically less energy-intensive than converting nitrate back to ammonium first (Wongkiew et al., 2017; Andrews 2013). Because the plants efficiently take up a significant portion of the available ammonium, there is simply less ammonium remaining as substrate for the nitrifying bacteria. This effectively reduces the overall “load” on the nitrification process compared to systems where plants rely almost exclusively on nitrate.

Consequences for pH Stability

This reduced reliance on nitrification has a profound impact on the system’s natural pH stability. Nitrification is an acid-producing process; each molecule of ammonia converted releases hydrogen ions (H⁺), gradually lowering the pH of the water over time. This is why many traditional aquaponic systems experience a continuous downward drift in pH, requiring regular buffering with alkaline substances.

In iAVs, however:

Less Nitrification = Less Acid: Because the overall rate of nitrification is lower (due to direct plant uptake of ammonium), less acid is produced.
Balanced Ion Exchange: Plant nutrient uptake involves complex ion exchanges. While ammonium uptake releases some H⁺ (acidifying), nitrate uptake (which still occurs) releases bicarbonate or hydroxide ions (alkalizing) (Haynes and Goh, 1978; Noggle and Fritz, 1983). In a balanced iAVs, where plants utilize both ammonium and nitrate, these processes tend to counteract each other, resulting in a much more stable pH compared to systems dominated by nitrification.

This inherent stability means that once an iAVs system matures and achieves a balance between fish waste production and plant nutrient uptake, the pH naturally settles around the optimal 6.4 range and requires minimal, if any, adjustment. This was clearly demonstrated in iAVs research where removing the plants caused nitrification to become dominant, leading to a rapid drop in pH (McMurtry, 1990).

Conclusion

Nitrification remains an important process in iAVs, converting potentially harmful ammonia into valuable nitrate. However, unlike traditional systems, iAVs does not rely solely on nitrification for nitrogen processing or pH management. By operating at a plant-optimized pH of ~6.4 and facilitating direct plant uptake of ammonium, iAVs reduces the overall nitrification load. This, combined with the adaptability of nitrifying bacteria and the balanced ion exchange during nutrient uptake, results in remarkable natural pH stability. This inherent balance simplifies management, reduces the need for chemical buffers, and contributes to the overall robustness and efficiency of the iAVs approach.

26. Detritus & Algae

The Living Surface of the Furrows

The surface of the furrows within an iAVs sand biofilter is far from static; it’s a dynamic, biologically rich environment crucial to the system’s function. Two primary components define this zone: detritus, and algae, which often colonize the surface of the furrows when they are exposed to sunlight. Together, they form an interactive layer that drives nutrient cycling, stabilizes the physical structure, and influences water quality. Understanding the formation, function, and interplay of detritus and algae is key to managing a healthy and productive iAVs.

Image (above) shows the detritus layer forming along the furrows in an iAVs.

The Detritus Layer: Formation, Function, and Management

What is Detritus? Within iAVs, detritus is the layer of organic material that forms on the sand surface in the furrows. This layer originates from the insoluble components of fish waste (feces and uneaten feed) deposited by intermittent irrigation cycles. Importantly, this accumulated detritus retains a substantial amount (up to 40%) of the initial nutrients from the fish feed (Yogev et al., 2016).
Formation and Initial Effects: When an iAVs system begins operation, this detritus layer starts forming within days or weeks on the initially clean sand. As it builds, it slightly alters water flow, encouraging more lateral spread across the furrow bottom. This initial adjustment is beneficial, promoting colonization by microorganisms and ensuring a more uniform distribution of nutrients across the biofilter.
A Critical Microbial Hub: The detritus layer is the primary habitat and food source for the vast community of microorganisms responsible for mineralization – the breakdown of complex organic waste into plant-available nutrients (See Chapter on Mineralization). This process enriches the rhizosphere, the zone directly around the plant roots where crucial nutrient exchange occurs.
The Importance of Surface Confinement: A fundamental principle of iAVs is that the detritus layer, and its associated microbial activity, remains confined to the surface (typically the top inch or less) of the sand in the furrows. If organic matter penetrates too deeply, it can clog the pore spaces between sand grains, severely reducing drainage efficiency and compromising the biofilter’s ability to function effectively. Proper system design and management prevent this deep infiltration. Long-term observations (over 20 years) of functioning iAVs systems confirm that the sand beneath this active surface layer remains remarkably clean, eliminating the need for periodic deep cleaning or sand replacement.
Structural Stabilization: As the detritus layer matures, it contributes to the physical stability of the furrow channels. Microorganisms within and below the layer, including beneficial mycorrhizal fungi that form symbiotic relationships with plant roots, help bind sand grains together, creating a firmer structure. This, along with the cementing action of algae (discussed below), reduces the erosion of the ridges during irrigation events.
Indicator of System Health: A well-established, biologically active detritus layer signifies a healthy, mature iAVs with efficient nutrient cycling. Conversely, its absence might suggest insufficient waste production (indicating potential underfeeding or low fish stock) or other system imbalances.
Early Stage Management: During the initial startup phase, especially in longer biofilters, the detritus may not form evenly along the entire furrow length, potentially causing uneven water distribution. To assist establishment, a temporary strip of perforated plastic film (e.g., 4-6″ wide 5-mil clear polyethylene with closely spaced slits/holes) can be laid in the furrows. This channels water and waste more evenly until the natural detritus layer develops sufficiently to ensure consistent lateral flow. Once established, the film should be carefully removed.

The Multifaceted Role of Algae in iAVs

Algae, including various microalgae and cyanobacteria (blue-green algae), frequently colonize the sun-exposed surfaces of the furrows, particularly before a dense plant canopy develops. While sometimes perceived as problematic, algae perform several crucial functions in a balanced iAVs:

Nutrient Management and Phycoremediation: Algae are highly effective at absorbing nutrients directly from the water. This process, termed “phycoremediation” (Emparan et al., 2019), is particularly important in the early stages of plant growth when young plants have lower nutrient demands. Algae act as a temporary nutrient sink, efficiently taking up excess nutrients like nitrogen (especially ammonia) and phosphorus, effectively cleaning the water before it returns to the fish tank (Bhattacharjee, 2025; Shi et al., 2000; Xin et al., 2010; Leng et al., 2018; Wang et al., 2015). This helps maintain good water quality for the fish.
Water Quality Enhancement: By directly assimilating ammonia (NH₃) and through their potential to improve nitrification, algae help reduce levels of this compound, which is toxic to fish (Mohamed et al., 2017; Raven et al., 1992; Syrett and Morris, 1963; Bankston et al., 2020; Wang et al., 2023). This dual action is critical for both fish and plant health (Rezaei 2025). Furthermore, through photosynthesis, algae consume carbon dioxide (often as bicarbonate) and release oxygen, which slightly increases the water’s pH (Bhattacharjee, 2025; Li et al., 2019). This pH buffering effect helps counteract the natural acidification caused by nitrification, contributing to overall system stability. The oxygen produced also benefits the aerobic bacteria crucial for waste decomposition (Lu et al., 2019; Liu et al., 2017; Wang et al., 2015).
Synergy with Bacteria: Algae and bacteria work in a close partnership. Bacteria decompose organic matter, releasing CO₂ that algae use for photosynthesis. In turn, algae release oxygen needed by aerobic bacteria and exude organic compounds (like glycolic acid and extracellular polymers) that bacteria can use as food sources (Lau and Armbrust, 2006; Mishra et al., 2011; Cho et al., 2015; Su et al., 2012). Bacteria also produce substances like vitamins (e.g., B12) and iron-chelating siderophores that benefit algal growth (Croft et al., 2005; Amin et al., 2009). This symbiotic relationship enhances overall nutrient removal efficiency and pollutant mitigation (Hernandez et al., 2013; Liu et al., 2017; Yang et al., 2019; Nie et al., 2020).
Nutrient Cycling and Release: As the plant canopy develops and shades the furrows, the algae population naturally declines. When these algae die and decompose, they release the nutrients they had stored (like phosphorus and iron) back into the system. This release often coincides beneficially with the increased nutrient demands of maturing plants, especially fruiting varieties needing more phosphorus. Algal decomposition plays a role in phosphorus cycling, converting organic phosphorus back into inorganic phosphate that plants can use (Brembu et al., 2017).
Iron Availability and Chelation: Algae absorb iron from the water and, upon decomposition, can release it in more bioavailable forms. Importantly, algae also produce amino acids (like glutamic acid and glycine) that act as natural chelators. These bind with iron and other micronutrients, keeping them dissolved and accessible for plant uptake, preventing the precipitation issues common in other systems.
Bioactive Compounds and Plant Growth Promotion: Algae are a source of valuable compounds beyond basic nutrients. They produce proteins, lipids, carbohydrates, and specialized molecules like PUFAs (Chen et al., 2021). Critically, they also synthesize biostimulants that promote plant growth and enhance resistance to abiotic stress, including plant hormones (auxins, cytokinins, gibberellins), ethylene precursors, and potentially allelopathic chemicals that can enhance plant defenses (Bhattacharjee 2025; Banerjee and Modi, 2010; Banerjee and Srivastava, 2009; Banerjee et al., 2006; El Arroussi et al., 2018). Furthermore, by releasing beneficial hormones and amino acids, algae contribute to improved crop growth and yield (Renuka et al., 2018). Associated bacteria also contribute essential B-vitamins. These compounds collectively boost overall plant health, stress tolerance, and productivity.
Structural Stabilization: Similar to the detritus layer, algal growth helps to bind or “cement” sand grains together within the furrows, contributing to the physical stability of the channels and reducing erosion.

Conclusion

The detritus layer and the associated algal communities are not waste products but active, integral components of the iAVs biofilter surface. Detritus provides the substrate and location for essential microbial mineralization, while algae play vital roles in nutrient buffering, water purification, producing beneficial compounds, and contributing to nutrient cycling through their life cycle. Managing the system to maintain a healthy, surface-confined detritus layer allows these components to function synergistically, contributing significantly to the overall efficiency, stability, and productivity of the iAVs.

Image (above) shows visual progression of the detritus layer’s evolution over time.

Nitrogen-fixing cyanobacteria. Ahmed A. Issa, Mohamed Hemida Abd-Alla and Takuji Ohyama, CC BY-SA 3.0, via Wikimedia Commons

27. Plant Varieties

This chapter explores the range of plants that can be cultivated in an iAVs and their specific requirements. Selecting appropriate plant species, understanding their nutrient needs, and optimizing growing conditions are key to maximizing the system’s efficiency. Proper plant selection and nutrient management ensure resource efficiency and system health, which are critical for achieving high yields and contributing to food security and sustainability.

Jina Lee, CC BY-SA 3.0, via Wikimedia Commons.

We recommend maintaining a high plant density across the entire biofilter surface, with plants at varying stages of growth. This strategy maximizes nutrient uptake, optimizes space utilization, and promotes continuous nutrient cycling. Staggering plant development ensures that nutrient demands are met consistently, as young plants typically require fewer nutrients, while nutrient needs increase during the vegetative stage and decline around reproductive development.

During the logarithmic growth phase, plants experience rapid growth due to optimal resource availability and minimal competition. This phase is critical for maximizing nutrient uptake and biomass accumulation. Nitrogen, essential for photosynthesis, cell division, and protein synthesis, is heavily consumed during the vegetative and early bloom phases. Phosphorus, which supports cell division, root development, and flowering, becomes more critical as plants enter their bloom phase.

To optimize nutrient utilization, plant species with varying nutrient requirements should be grown in proportion to the feed input composition. A diverse mix of crops helps prevent imbalances in nutrient uptake. A recommended 50/50 mix of fruiting plants (e.g., tomatoes or peppers) and leafy greens (e.g., lettuce or spinach) ensures a balanced spectrum of nutrient removal. Fruiting crops generally require higher levels of phosphorus and potassium, while leafy greens demand more nitrogen.

Tomatoes are better at turning the nutrients from the fish waste into actual tomato plant growth compared to basil or lettuce (Yang 2020).

The risk of nutrient toxicity in plants stems from their limited ability to selectively absorb only essential elements, often leading to the uptake of unnecessary or harmful substances (Marschner 2012). Failure to diversify crops can exacerbate this issue, causing toxic accumulations manifested by symptoms such as leaf discoloration, stunted growth, or death, underscoring the need for growers to monitor for both nutrient deficiencies and toxicities to ensure optimal yields.

If there is not enough waste generated for the amount, and type, of plants in the system, nutrient concentration can decrease to levels that may be too low to sustain plant growth (Tyson 2008).

Research supports the benefits of plant diversity in agricultural systems. For example, crop rotation has been shown to improve nutrient utilization (Adler et al., 2003). Additionally, increasing plant diversity enhances nutrient recycling and promotes yield stability (Vermeulen & Kamstra, 2012).

27.1. Recommended Species

iAVs can support a wide variety of plants, including vegetable crops, fruits, herbs, root crops, and even tree seedlings for reforestation. Some examples include:

Leafy Greens & Herbs: Amaranthus, Arugula, Basil, Beet greens, Bok Choy, Chives, Collards, Coriander, Dill, Endive, Kale, Lettuce (all varieties), Mustard greens, Oregano, Palak (Spinach), Parsley, Rosemary, Swiss Chard, Thyme.
Legumes: Beans (bush, heirloom, pole, wax), Broad Bean (Fava), Cowpea, Groundnuts (peanut), Winged Bean.
Fruits & Berries: Banana, Blackberry, Cantaloupe, Figs, Grapes, Honeydew, Papaya, Raspberry, Strawberry, Tomato (all types), Watermelon.
Root Vegetables: Beetroot, Carrot, Horseradish, Leeks, Onions, Parsnip, Radish, Shallots, Turnip.
Other Vegetables: Bell Peppers, Bitter Gourd, Broccoli, Cabbage, Cauliflower, Cayenne Pepper, Chinese Potato (country potato), Cucumber, Eggplant (Aubergine), Garlic. Jalapeño Pepper, Okra, Pumpkin, Rhubarb, Snake Gourd, Snow Pea (sugar pea), Squash (acorn, butternut), Zucchini.
Melons: Ash Gourd, Cantaloupe, Casaba Melon.
Grains: Maize (sweet corn), Rice (upland).
Other Plants: Cannabis spp., Chrysanthemum spp., Marigold spp., Sugar Cane.

27.2. Companion Planting

Companion planting involves growing crops together that benefit each other by improving nutrient availability or repelling pests. This method can reduce the need for chemical inputs and improve plant health. However, its effectiveness depends on factors like pest pressure and plant density.

For example:

Beans & Corn: Beans fix nitrogen in the soil and improve corn growth.
French Marigolds & Tomatoes: Marigolds emit limonene that repels whiteflies from tomatoes.
Basil & Tomatoes: Basil increases tomato shoot dry weight by 10–20% and enhances secondary metabolites like shikimic acid and apigenin.

Additionally:

Borage & Pollination: Borage attracts pollinators like bees to crops such as tomatoes and squash.

27.3. Nutrient Requirements

iAVs uses sand as a filtration medium to fully process fish waste into nutrients for plants. This efficient nutrient cycling reduces the need for additional supplementation. Feed input is optimized based on plant type:

Leafy Greens: 10–20 grams per cubic meter per day.
Root Crops: 15–25 grams per cubic meter per day.
Fruiting Crops: 25–30 grams per square meter per day.

Fruiting crops require more nutrients – especially phosphorus and potassium – while leafy greens primarily need nitrogen. Micronutrients like iron and magnesium are also critical for plant health; regular water testing ensures optimal levels.

27.4. Plant Spacing

Plant spacing affects growth and yield. In warmer climates or dense plantings where air circulation is limited and disease risk is higher, spacing may need to be increased.

For single stem (indeterminate) varieties of tomato, cucumber, eggplant, and sweet pepper, it is generally recommended to plant at a density of 4 plants per square meter, as illustrated. Determinate or multi-stem cultivars should be spaced more widely, typically at 2 to 3 plants per square meter, and for particularly bushy tomato varieties, a spacing of 1 plant per square meter may be appropriate.

In general, following spacing guidelines similar to the square-foot gardening technique or high-density organic gardening practices is advisable, as it applies to any type of soil media. It is important to note that recommended spacing may vary based on cultivar, climate, and the size (duration) of the plants intended for harvest or market. Overcrowding should be avoided, as it can lead to several negative consequences. Adhering to species-specific recommendations is considered best practice for several reasons.

27.4.1. Furrow Layout

Adjust furrow size and spacing based on crop requirements to ensure even distribution of nutrient-rich water across all plants. For example:

In a 1×2 m sand filter bed: allocate one half for tomatoes at 4 plants/m² and the other half for herbs at 12–16 plants/m².

27.5. Direct Seeding

Direct seeding involves sowing seeds directly into the ridges of the biofilter, eliminating the need for transplanting, which can stress young plants. This method allows plants to establish their root systems in place, enabling better adaptation to their environment and potentially leading to stronger natural defenses and earlier harvests.

This approach is cost-effective and reduces labor, particularly for crops with delicate root systems that are sensitive to transplanting. Crops like carrots, radishes, and beans, which do not transplant well, often thrive when directly sown.

However, direct seeding may not be ideal for all crops or conditions. For small-seeded crops or those requiring precise spacing – such as carrots or lettuce – uneven germination can occur. In these cases, using seed tapes or pelleted seeds can improve germination uniformity and reduce thinning labor. The decision to direct seed should consider the specific crop requirements, local climate, and soil conditions.

For crops with longer growing seasons or slow initial growth rates, starting indoors and transplanting later may be more beneficial.

Transplanting

To transplant seedlings from typical starter tray cells, simply place the plug directly into the sand. Position the plug as deeply as possible, ensuring that 1/4 to 1/2 inch of the distal stem remains above the surface, with the cotyledons exposed. Gently firm the sand around the plug to ensure good contact, allowing water to wick easily into it. With proper placement and care, the plug will quickly integrate into its new environment, becoming virtually unnoticeable in no time.

27.6. Harvesting

Efficient harvesting techniques are essential for optimizing yields and minimizing waste in an iAVs. Follow these key practices for successful harvesting:

Monitor Plant Growth: Regularly assess plant development to determine the optimal harvest time, ensuring crops are neither over-ripened nor under-ripened. This maximizes both quality and yield.
Harvest at Peak Ripeness: Harvest crops when they reach peak ripeness to enhance flavor and nutritional value. Timing will vary by plant species and cultivar.
Remove Entire Plant: When harvesting, remove the entire plant, including roots and stems, from the biofilter. This prevents rotting and disease spread within the system. Prompt removal of plant residues also helps prevent pathogen buildup in the biofilter medium, which can affect future crops.
Replace Harvested Plants: After harvesting, replace removed plants with new seedlings or transplants to maintain a healthy and productive system. Keeping plants at different growth stages ensures continuous productivity.
Climate Considerations: In hotter climates, such as Australia’s, harvest early in the morning when temperatures are cooler to preserve freshness. Store harvested produce in shaded or refrigerated areas immediately after picking.

Also consider staggering planting times, such as 3 snake gourd initially, then the other 3 in a month or 6 weeks later, The initial ‘blank’ area could grow something quick such as leaf lettuce or radish in the meantime, That way, the harvest from fruiting/larger plants doesn’t happen all at once but more significantly when it comes time to remove them and plant something else, all the large plants aren’t removed at the same time and so there would always be some actively growing plants in the bed. (which helps buffer against pH swings (which will drop quickly in the absence of active plant growth) and generally provides for overall improved system stability than if pulling all plants and starting over again with all as seedlings).

27.6.1. Maintain Plant Balance:

It is advisable to avoid harvesting all plants simultaneously to prevent rapid pH fluctuations. Research on iAVs has shown that plants play a critical role in maintaining stable pH levels, and removing all plants at once can disrupt this balance causing the pH to drop rapidly.

27.7. Plant selection

A wide range of plants can be grown successfully in iAVs, including vegetable crops, fruits, herbs, leafy greens, root crops, and grains. To ensure balanced nutrient removal from the system, it is recommended that 50% of the crop selection consists of fruiting plants.

Varieties: Both field and greenhouse varieties can be grown in a greenhouse environment; however, greenhouse-specific varieties generally perform better under controlled conditions due to selective breeding for high yields.

27.7.1. High Value Crops

For commercial cultivation, prioritize high-value crops such as herbs or specialty vegetables that offer a higher return on investment compared to lower-value crops.

Market Trends: Research current market trends and consumer preferences to identify crops in high demand that command premium prices. For example, herbs like basil and cilantro are highly sought after in urban markets due to their culinary uses.

27.7.2. Seasonality

Planting crops during their optimal growing seasons improves yields by 20% to 30% (Smith et al., 2019; Nguyen et al., 2021). Align planting schedules with seasonal conditions to enhance crop growth and natural resistance to diseases and pests.

Warm Season Crops: Tropical species such as tomatoes, peppers, melons, and summer squash thrive in warm climates (25°C–35°C). However, temperatures above 35°C can cause flower drop in some species like tomatoes and peppers. In regions with extreme heat, shade nets or evaporative cooling may be necessary.
Cool Season Crops: Spring and fall crops like beans, greens, herbs, okra, and winter squash prefer milder temperatures (15°C–25°C). These crops are well-suited for cooler conditions with shorter daylight hours (10–12 hours).
Winter Crops: Species such as snow peas, sugar peas, Brassica varieties (e.g., broccoli), and some greens can be grown during colder months when temperatures drop below 10°C (50°F) with daylight hours reduced to 8–10 hours.

27.7.3. Disease-Resistant Varieties

Incorporating disease-resistant plant varieties into iAVs minimizes crop losses without relying on synthetic pesticides or harmful chemicals. These plants are bred or genetically engineered to resist specific diseases.

Natural Controls: iAVs emphasize natural biological controls over chemical interventions. Disease-resistant varieties help maintain plant health while ensuring food safety for consumers and protecting fish health within the system.

27.7.4. Leafy greens

27.7.4.1. Lettuce

Lettuce (Lactuca sativa) is a space-efficient, fast-growing plant that takes 5-6 weeks to mature from transplant or 9-11 weeks from seed under optimal conditions. It can be cultivated with a typical density of 20-25 heads per square meter.

Growing Conditions: Lettuce grows best in temperatures between 15-22°C with a pH range of 5.8-7.0. Seeds typically germinate within 3 to 7 days at temperatures of 13-21°C. Phosphorus supplementation during the second and third weeks of growth promotes root development and reduces transplant stress. Gradually hardening seedlings by exposing them to cooler temperatures and sunlight for 3-5 days before transplanting improves survival rates. Seedlings are usually ready for transplanting after about 3 weeks, once they have developed 2-3 true leaves.

Temperature Management: For optimal head growth, aim for nighttime temperatures of 3-12°C and daytime temperatures of 17-28°C. Long days and warm nights can cause bolting, while water temperatures above 26°C may lead to bitterness in the leaves. Some varieties are more heat-tolerant, so selecting bolt-resistant types is advisable in warmer climates. Providing shade for newly transplanted lettuce during hot weather can prevent water stress.

Nutrient Requirements: Lettuce is a heavy nitrogen feeder but requires relatively few other nutrients. Maintaining high nitrate levels ensures rapid growth, while higher calcium levels help prevent tip burn in hot conditions.

Harvesting and Post-Harvest Handling: Lettuce can be harvested once the heads or leaves are large enough to eat. It’s best to harvest early in the morning when the leaves are crisp and full of moisture, then chill them quickly. Handle lettuce gently during harvesting to avoid bruising, which can accelerate spoilage or lead to disease. Whole heads can be cut at the base with a knife, or the entire plant (including roots) can be harvested for longer shelf life.

Lettuce loses moisture quickly and should be stored just above freezing to extend freshness up to three weeks. However, freezing will cause the leaves to separate and spoil rapidly. Lettuce requires humidity to stay fresh, but excess moisture or condensation on the leaves should be avoided by maintaining consistent temperatures.

Processing: Minimal processing is recommended; only remove damaged or unhealthy leaves before delivery. Washing before delivery is generally discouraged, although some growers dip lettuce in cold water to close stomata and extend freshness.

Considerations for Growing Lettuce in iAVs

Lettuce is frequently used in traditional aquaponic systems due to its relatively fast growth cycle and adaptability to soilless systems (Frassine et al., 2024; Villarroel et al., 2016). In iAVs, lettuce can also be integrated; its rapid growth cycle and ease of cultivation make it a practical choice, especially for beginners and smaller systems, and it is well-suited as an initial crop in newly established biofilters, effectively utilizing readily available nitrogen during system cycling.

However, while lettuce offers these advantages, its high nitrogen demand must be managed carefully to avoid nutrient imbalances. Lettuce absorbs large amounts of nitrogen but relatively few other nutrients. Consequently, growing it exclusively or repeatedly in the same location may deplete essential nutrients from the system. Indeed, its high nitrogen demand and lower uptake of other nutrients make it less ideal as the sole or primary crop in a balanced iAVs focused on comprehensive nutrient cycling and diverse food production. To address this, rotating lettuce with flowering or fruiting plants helps maintain soil health and nutrient balance while reducing pest and disease risks.

It’s important to further note that lettuce is a heavy nitrogen feeder, primarily assimilating nitrates, and has a relatively low uptake of other essential elements. This characteristic can limit its effectiveness in balancing overall nutrient removal from the system. Furthermore, while lettuce provides essential vitamins, its overall caloric and nutritional density is low compared to fruiting crops. Therefore, while lettuce is a valuable and easily grown component, iAVs designs should prioritize a diverse crop selection, including nutritionally richer and more economically valuable species, to maximize system benefits.

Lettuce is also often promoted due to its quick harvest and rapid turnover rate. Some also note its low nutrient requirements and relative tolerance of root submergence, though its significant nitrogen uptake is a key consideration. Despite lettuce ‘giving’ more crop cycles per year and a typically higher planting density, fruit has a much greater economic value (in addition to food value) produced over time. From an economic standpoint, growing lettuce should only be considered if it offers a competitive return compared to other cool-season crops. Additionally, lettuce has specific post-harvest requirements – such as chilling and hydration – to maintain its quality for market sale. While relatively easy to grow, lettuce is more challenging to store and ship without compromising freshness and visual appeal.

While we appreciate salads as much as anyone else, it’s important to acknowledge that cultivating lettuce differs significantly from growing fruiting plants. iAVs was specifically designed to support the production of fruiting plants. Lettuce does contain some nutrients, including pro-vitamins A, C, and K, but its overall nutritional value is relatively low compared to other vegetables and fruits.

27.7.4.2. Chard

mercedesfromtheeighties, CC BY-SA 2.0 , via Wikimedia Commons

Chard (Beta vulgaris subsp. vulgaris) is a versatile crop that grows well in various iAVs. It is resilient but can occasionally be affected by aphids and powdery mildew. While extreme temperatures may impact its flavor, chard generally tolerates a wide range of conditions, including frost. The optimal temperature for growth is 16-24°C.

Chard requires moderate levels of nitrates and lower amounts of potassium and phosphorus compared to fruiting vegetables. Its high market value, fast growth rate, and nutritional benefits make it a popular choice for growers. Although typically grown as a late winter/spring crop, it can also thrive in full sun during mild summers. However, shading is recommended if temperatures exceed 26°C.

Chard is easily propagated from seeds, which germinate in 4-5 days at temperatures between 25-30°C. Each seed can produce multiple seedlings, so thinning is necessary as they grow. Transplanting density should be around 15-20 plants per square meter. As the plant matures, older leaves can be removed to encourage new growth.

Harvesting can begin approximately 4-5 weeks after transplanting. To promote continued growth, harvest only part of the leaves, leaving about 30% of the foliage intact for photosynthesis. Cut the largest leaves near the base of the plant. Harvesting during cooler parts of the day (morning or evening) helps maintain freshness. Chard can stay fresh for over a week if stored unwashed in sealed containers or bags in a cool environment to slow spoilage.

27.7.4.3. Kale

Rasbak, CC BY-SA 3.0 , via Wikimedia Commons

Growing kale is a straightforward and rewarding option for gardeners. This leafy vegetable matures in about six weeks and can be harvested incrementally, leaving around 30% of the plant in the ground to promote continued growth. Kale thrives in temperatures between 8-29°C, with cooler conditions (down to 5°C) often enhancing its flavor. When cultivated indoors, kale faces minimal pest pressure, though occasional issues with aphids and powdery mildew may occur.

27.7.4.4. Pak choi

Forest & Kim Starr, CC BY 3.0 , via Wikimedia Commons

Pak choi, also known as bok choy or Chinese cabbage, comes in various sizes, with larger varieties like Joi Choi and smaller ones like Shanghai Green Pak Choy, which have compact, tender heads and a mild flavor. Another similar vegetable is tatsoi, which has thick leaves and light veins and can be grown under the same conditions as pak choi. Napa cabbage, while different in appearance from pak choi and tatsoi, thrives in the same temperature range and develops a better flavor when grown in cooler weather.

The ideal temperature range for pak choi is 13-23°C. While it grows best in cooler conditions, it can tolerate a range of temperatures, making it suitable for iAVs. Unlike other crops, pak choi rarely shows common deficiency signs like yellowing or burning; instead, you may observe stunted growth, curling leaves, or some yellowing.

To cultivate pak choi, start from seeds and transplant them once they develop true leaves, typically after about four weeks. The optimal harvest time is around six weeks after transplanting, though shorter cycles of about four weeks are also possible.

27.7.4.5. Cabbage

I, KENPEI, CC BY-SA 3.0 , via Wikimedia Commons

Cabbage (Brassica oleracea) is a relatively easy crop to grow, with proper pest management. Integrated Pest Management (IPM) can effectively control most pests, and cabbage requires minimal pruning or special care. The heads can grow quite large, sometimes reaching 3.5 kg, allowing for high yields in small areas.

The ideal temperature range for cabbage is 15-20°C, though it can tolerate frost. However, cabbage is susceptible to pests like aphids and bacterial diseases. A common issue is head splitting, which occurs when the head cracks open, making it more vulnerable to dirt and disease. To prevent splitting, timely harvesting is essential. Cabbage prefers full sun and cooler temperatures, so it should be harvested before daytime temperatures exceed 23-25°C.

For optimal seed germination, maintain a slightly warmer environment for seedlings (18-29°C) than for mature plants. Lightly scratching seeds before planting can accelerate germination, which typically occurs within 4-7 days. Seedlings are ready for transplanting after 4-6 weeks when they have 4-6 leaves and are about 15 cm tall. Ensure adequate spacing to allow each head room to grow.

If temperatures exceed 25°C, consider using light shading nets to prevent bolting. Depending on the variety and desired head size, cabbage is usually ready for harvest 45-70 days after transplanting. Harvest when heads are firm and large enough for sale by cutting them from the stem with a sharp knife and removing outer leaves.

27.7.4.6. Mustard greens

Mustard greens, closely related to kale and cabbage, thrive in temperatures between 10-23°C. They can be cultivated similarly to kale. Seeds typically germinate within 4-7 days, and after 2-3 weeks, the seedlings are ready for transplanting. Harvesting can begin after 4-6 weeks of growth, but it’s advisable to remove only about 30% of the leaves at a time to allow continued plant development.

Green mustard is a low-calorie vegetable but rich in nutrients, beneficial for health, and widely cultivated throughout the world. Green mustard is often used for salads, soups, and as a garnish. With only about 13 calories per 100 grams, green mustard is an ideal food for those on a diet because it only contributes a few calories, and reduces fat, thus helping with weight loss. Green mustard also contains sulfur compounds, which can reduce the risk of cancer (breast, prostate, and lung cancer) by helping the body eliminate toxins and prevent cancer cells. The essential minerals (iron, magnesium, and calcium) it contain support bone growth and prevent osteoporosis. Vitamin A (beta and alpha carotene) in green mustard can improve eye health and prevent oxidative stress on the retina (Sahubawa 2025).

Other important nutrients include folate and vitamin B6, which are beneficial for heart health by lowering homocysteine levels (a risk marker for cardiovascular disease). Each cup of collard greens provides about 20% of the recommended daily intake of potassium, which is essential for heart health because it acts as a vasodilator, reducing blood vessel tension and lowering cardiovascular stress. Additionally, the vitamin C in collard greens boosts immune function, reduces stress, and stimulates the production of white blood cells to ward off chronic disease. Vitamin C also plays a key role in collagen synthesis, helping to maintain healthy and rejuvenating skin (Sahubawa 2025).

27.7.4.7. Nasturtium

Acabashi, CC BY-SA 4.0 , via Wikimedia Commons

Nasturtium, native to South America, is an edible plant with both leaves and flowers offering a spicy flavor similar to mustard or watercress. It is susceptible to pests like aphids and spider mites. There are two primary growth forms: vining and bush types.

Nasturtiums thrive in temperatures between 13°C and 23°C, preferring light but not excessive heat. Seeds germinate best at 13°C to 18°C, and established plants grow well around 21°C. They perform well in low-nutrient systems, similar to those used for leafy greens or strawberries. Seeds typically sprout within 7 to 10 days under optimal conditions, and can be transplanted once true leaves develop, usually after 2 to 3 weeks. Flowers appear in approximately 5 to 6 weeks, though leaves can be harvested earlier if desired. Some gardeners plant nasturtiums densely and harvest the young leaves.

27.7.5. Herbs

Herbs can be more profitable than leafy greens, but each herb has specific post-harvest requirements to maintain freshness and prevent spoilage. Proper temperature and moisture control are essential. For example, while most herbs benefit from cooler temperatures, basil should not be stored below 13°C and can last up to 12 days at 15°C. Harvesting during the cooler parts of the day also helps preserve freshness.

Maintaining stable temperature and humidity levels is crucial, as fluctuations can lead to disease and rot. Minimizing handling and ensuring consistent conditions during storage and transport can prevent these issues. Careful harvesting techniques, such as using clippers instead of tearing, reduce plant damage and limit ethylene production, which accelerates spoilage.

Packaging should be tailored to the specific needs of each herb. For instance, delicate herbs like basil or chives retain moisture better in plastic bags but excessive moisture can cause decay. Additionally, light exposure management is important since some herbs spoil faster when exposed to light, while others may tolerate or even benefit from it.

27.7.5.1. Coriander

Photo by David J. Stang, CC BY-SA 4.0 , via Wikimedia Commons

Growing coriander can be challenging due to its tendency to bolt (go to seed) quickly, particularly in hot conditions. It thrives in cooler temperatures, ideally between 5°C and 23°C, and prefers low soil salinity. Optimal germination occurs at temperatures between 15°C and 20°C. Bolting can result in more bitter-tasting leaves, so it’s advisable to trim the flower stalks and adjust growing conditions accordingly. To mitigate bolting, slow-bolting seed varieties are available, which can improve crop success.

Coriander is also prone to diseases like bacterial leaf spot and powdery mildew. Seeds typically germinate within 7-10 days, and the leaves can be harvested approximately 40-48 days after planting. The full growing cycle from planting to harvest generally takes 50-55 days. Coriander can be harvested either fully or partially. For partial harvesting, the first batch is usually ready around five weeks after transplanting, with a second, smaller harvest around eight weeks later. Packaging preferences vary based on farmer and market requirements.

27.7.5.2. Mint

Mint is a versatile herb, with the most common varieties being spearmint, peppermint, and pennyroyal. While some plants, like lemon mint, contain “mint” in their name, they are not part of the true mint family. Mint is easy to cultivate, growing quickly and requiring minimal effort to harvest. It thrives in temperatures between 19-21°C but struggles in heat above 26°C.

Mint is generally resistant to pests compared to other herbs but can occasionally be affected by diseases such as verticillium wilt and powdery mildew. While it can be grown from seeds, propagation through cuttings is faster and more efficient for larger-scale cultivation. To propagate, simply cut healthy green stems and place them in water until they develop roots, which typically takes a few weeks. For harvesting, cut the plant about 5 cm above the ground. With proper care, a second harvest can be obtained within 2-3 weeks when the plant reaches approximately 20 cm in height.

27.7.5.3. Basil

Basil requires moderate watering, regular pruning, and warm temperatures to thrive, which can be challenging when grown alongside other crops. To begin growing basil, seeds should be kept at a consistent temperature of 20-25°C for optimal germination, which takes about 6-7 days. Once seedlings have developed 4-5 true leaves, they can be transplanted. Basil grows best in warm conditions with ample sunlight, though partial shade can improve leaf quality. If temperatures exceed 27°C, additional ventilation or shading may be necessary to prevent leaf tip burn.

Basil is susceptible to fungal diseases, particularly in high humidity or suboptimal temperatures. Ensuring good air circulation and maintaining water temperatures above 21°C can reduce plant stress and disease risk. Since basil leaves tend to trap moisture, managing humidity levels between 40-60% is crucial to prevent fungal issues. Proper air circulation without strong drafts is recommended, and basil benefits from 10-12 hours of light daily; supplemental lighting can further boost yields.

Dying leaves should be removed promptly to prevent fungal growth or damage to healthy leaves. For top-heavy plants, pruning with sharp shears is preferred over pinching to avoid stem damage. Harvesting before flowering and removing tough or damaged growth helps maintain leaf quality and prevents bitterness.

Basil is often grown as a single-stemmed plant, but many growers prefer bushier varieties. Pruning above the side buds of younger plants (12-25 cm tall) encourages fuller growth by promoting the development of lateral buds rather than just the main stem. Cutting above the second pair of buds ensures proper air and light penetration, leading to higher yields during the first three harvests.

Harvesting begins when plants reach approximately 15 cm in height and can continue for 30-50 days. Basil should be handled gently to avoid bruising, which accelerates spoilage. It should not be stored in chillers (5-7°C), as low temperatures cause rapid decay in this warm-weather crop. For optimal freshness, basil should be stored at temperatures above 13°C, ideally around 16°C, where it can last up to 12 days. Packaging that minimizes moisture loss is beneficial, but temperature consistency must be maintained to avoid condensation.

27.7.5.4. Chives

Chives (Allium schoenoprasum) are hardy plants that tolerate a wide range of temperatures and can survive short periods without water without compromising their quality. They are resistant to most pests and diseases, though viruses and fungus gnats may occasionally pose problems.

The optimal temperature range for chives is 18-26°C. Chives propagate quickly through their roots, making division of mature plants the most common method of planting. Seeds are typically only used when mature plants are unavailable. If grown from seed, seedlings are ready for transplanting after about 4 weeks, with harvesting possible 3-4 weeks later. When planted from divisions, chives establish in 2-3 weeks and grow thicker with each harvest. Regular trimming every 2-3 weeks is recommended, leaving 2.5-5 cm above the ground.

27.7.5.5. Parsley

Parsley (Petroselinum crispum) is a popular, easy-to-grow herb with high market value, especially in commercial gardens. Large-leaf varieties, such as Italian flat-leaf parsley, are particularly well-suited for cultivation. While parsley is generally pest-resistant, occasional infestations of aphids or thrips may occur.

The optimal temperature range for parsley growth is 15-25°C, though it can tolerate colder conditions. Parsley is a biennial plant, typically grown as an annual. In its first year, it produces leaves; in the second year, it develops flower stalks and seeds. Parsley thrives with up to eight hours of sunlight per day but benefits from partial shade when temperatures exceed 25°C.

Parsley seeds are inexpensive and germinate within 8-10 days if kept moist at 20-25°C. Older seeds may take up to five weeks to sprout. Soaking seeds in warm water (20-23°C) for 24-48 hours can accelerate germination by softening the seed coat. Seedlings initially resemble grass with two narrow leaves and can be transplanted after 5-6 weeks once true leaves have formed. Planting density should be around 10-15 plants per square meter.

Harvesting can begin 20-30 days after transplanting when stalks reach at least 15 cm in length. It’s recommended to pick the outer stems first to encourage further growth. Alternatively, parsley can be cut down to about 5 cm above the ground, allowing for a second harvest in approximately three weeks. After the second harvest, a new planting cycle should be initiated.

27.7.5.6. Fennel

Fennel (Foeniculum vulgare) is generally resilient and faces few pest issues, though aphids may occasionally appear. It thrives in temperatures between 16°C and 21°C but is sensitive to frost. Fennel seeds have a variable germination rate, typically between 60% and 90%, and they sprout within 1 to 2 weeks. Seedlings are ready for transplanting after 3 to 5 weeks. Post-transplant, fennel takes about 6 to 8 weeks to reach harvest maturity.

Bulbs can be harvested when they reach market-preferred weights of 250 to 500 grams. Fennel can also be harvested twice: first for the greens, and later for both greens and bulbs if there is demand. When harvesting greens, it is advisable to remove no more than 70% during the initial cut.

27.8. Fruiting crops

The use of sand in iAVs provides superior root support and allows for a broader variety of crops to be cultivated. This sand-based medium promotes the development of stronger root systems, as roots can spread naturally in search of nutrients. As a result, plants in iAVs can better support heavier fruit loads due to improved anchorage, overcoming the common limitation in traditional aquaponic systems where roots often lack sufficient support.

Pruning is essential for fruiting plants, particularly in greenhouse production where space is limited and costly. Regular pruning helps manage plant growth, allowing for closer planting and improving fruit quality by directing energy toward fruit development.

27.8.1. Tomatoes

Tomatoes are a staple crop globally, recognized for their high economic value and as a rich source of essential nutrients and antioxidants like lycopene, factors contributing to their widespread demand (Beckles, 2012). They grow in two primary forms: bush (determinate) and vining (indeterminate) varieties. Bush types, often found in heirloom breeds, tend to sprawl, making them harder to manage in controlled environments like greenhouses due to difficulties in setting up supports and accessing fruit. Vining varieties are generally preferred by growers because they can be pruned to a single stem and supported easily, simplifying harvesting and pruning tasks.

Tomatoes are susceptible to various pests and diseases, including Verticillium wilt, Fusarium wilt, nematodes, spider mites, aphids, damping off, and mosaic virus. When purchasing seeds or plants, look for labels indicating resistance (e.g., ‘VFN’ signifies resistance to Verticillium, Fusarium, and Nematodes) to mitigate some of these common issues.

Optimal growing conditions for tomatoes include temperatures between 13°C and 26°C and a soil or substrate pH of 5.5 to 6.5. They are heavy feeders with high nutrient requirements and thrive in warm environments, often benefiting from companion plants like basil. Seeds typically germinate within 4-6 days when kept at 20-30°C. It’s advisable to establish stakes or supports before transplanting to avoid subsequent root damage. Tomatoes can also be propagated from cuttings or seeds planted directly in sand media.

Tomatoes require plenty of sunlight, with ideal daytime temperatures between 22°C and 26°C and nighttime temperatures between 13°C and 16°C for optimal fruit set and development. Pruning is essential for directing the plant’s energy efficiently towards fruit production. When plants reach about 60 cm tall, growers can choose to maintain bush types by allowing 3-4 main branches or train vining types by removing side shoots (suckers) weekly. For bush tomatoes, trimming the growing tip after 7-8 flower clusters form can encourage more concentrated fruiting. Vining tomatoes can reach significant heights (up to 4 meters) but are typically pruned to a manageable height (around 2 meters) in controlled environments. Removing the bottom 30 cm of leaves improves air circulation and reduces fungal risks. Leaves that heavily shade developing fruit clusters should also be removed just before ripening to enhance light exposure and potentially direct more resources toward the fruit.

In outdoor settings, tomatoes are primarily pollinated by wind or bees. However, in enclosed environments like greenhouses, manual pollination or introducing pollinators like bumblebees may be necessary due to reduced air movement. Manual pollination can be achieved by gently tapping or vibrating flower clusters (e.g., with a stick or an electric toothbrush) to release pollen. This is most effective between 11:00 AM and 3:00 PM on sunny days when humidity is moderate (around 70%) and flower petals curl back, indicating pollen receptivity.

Tomatoes typically take about 50-70 days from planting to the first harvest, depending on the variety and conditions. Bush varieties generally produce fruit over a shorter period (90-120 days), while vining types can bear fruit continuously for up to 8-10 months under ideal conditions. For the best flavor, harvest tomatoes when they are firm and fully colored. However, they will continue ripening indoors if picked partially ripe. Tomatoes can be stored for 2-4 weeks at cool temperatures (around 5-7°C) with high humidity.

27.8.2. Bell peppers

Bell peppers thrive in warm weather with plenty of sunlight. Optimal growth occurs at temperatures between 19-23°C, and they prefer a soil pH of 5.5 to 6.5.

Seeds typically germinate within 8-12 days when kept at temperatures between 22-30°C. Once nighttime temperatures consistently exceed 10°C and seedlings have developed 6-8 healthy leaves, they can be transplanted into larger pots or directly into the garden. For bushy or fruit-heavy varieties, staking or using strings tied to overhead wires provides necessary support. Removing the first few flowers encourages stronger plant growth, and limiting flower numbers can help remaining fruits grow larger.

Pruning is essential for optimizing pepper production, reducing disease susceptibility, and increasing yield. Unlike tomatoes, peppers do not produce side shoots, so pruning sweet peppers focuses on developing a strong plant structure to support fruit weight. After the plant reaches about 40 cm in height, pinch off the top to encourage branching. Alternate between removing inner and outer shoots on each stem, trimming side shoots when they reach approximately 5 cm. Additionally, thinning flower clusters ensures better fruit quality and helps prevent issues like blossom end rot. Regularly remove yellow leaves to maintain plant health.

Peppers take around 60-95 days to mature. Like tomatoes, they require pollination, which can be done manually or by introducing bumblebees in greenhouse settings. For sweet red peppers, allow green fruits to ripen on the plant until they turn red. Harvesting should begin when fruits are market-ready, with continuous picking throughout the season to promote further flowering and fruiting. Freshly harvested peppers can be stored for up to 10 days at 10°C with high humidity (90-95%).

Pepper (Capsicum annum L.) is an important source of nutrients such as vitamins C, proteins, and carbohydrates for human consumption. Also, capsaicin, dihydrocapsaicin and related compounds, namely capsaicinoids, are the secondary metabolites available in pepper fruits (Maksimova 2016). Thus, peppers are used as an important spice in various foods. Additionally, peppers have high medical value, as capsaicinoids are utilized for curing biological ailments and improving overall human health (Robbins 2000).

27.8.3. Cucumbers

Cucumbers (Cucumis sativus) are categorized into three types based on their flower structure:

Monoecious: Contains both male and female flowers.
Gynoecious: Predominantly female flowers (approximately 70% female, 30% male).
Parthenocarpic: Produces only female flowers and does not require pollination for fruit production. However, parthenocarpic varieties can be affected by pollen from bees and other pollinators, so it’s advisable to grow them in a controlled environment, such as a greenhouse, to prevent pollination.

Cucumbers thrive in warm climates with optimal daytime temperatures between 24-27°C (75-81°F) and nighttime temperatures around 18-20°C (64-68°F). They prefer a soil pH of 5.5-6.5 and high humidity levels (70-90%). Full sunlight and a soil temperature of approximately 21°C (70°F) are ideal for growth. The plants are sensitive to frost, so they should be protected from cold weather. Adequate potassium levels in the soil can enhance fruit set and overall yield.

Seeds typically germinate within 3 to 7 days at temperatures between 20-30°C (68-86°F). Transplanting can occur once seedlings have developed 4-5 leaves, usually after 2-3 weeks. Under optimal conditions, cucumbers begin producing fruit within 2-3 weeks post-transplantation and can be harvested up to 10-15 times during the growing season. Regular harvesting prevents overgrowth and promotes continuous fruit production.

To manage rapid growth, trim the stems when they reach about 2 meters in length and remove side branches to improve air circulation. Retaining only the two buds farthest from the main stem encourages vertical growth. Providing structural support helps maintain plant health by improving airflow, which reduces the risk of diseases like powdery mildew and gray mold. Effective pest management is essential due to the plant’s susceptibility to pests, and companion planting with resistant varieties can help mitigate treatment impacts.

27.8.4. Eggplant

Aubergine (eggplant) is a warm-weather crop that requires ample space, sunlight, and nutrients, particularly nitrogen and potassium. Ideal growing temperatures range from 22°C to 26°C during the day and 15°C to 18°C at night. The plant thrives in humidity levels of 60-70% but is highly sensitive to frost.

Seeds typically germinate within 8-10 days when temperatures are between 26°C and 30°C. Once seedlings develop 4-5 leaves, they can be transplanted outdoors in spring. As summer wanes, it’s advisable to remove new flowers to encourage the maturation of existing fruits. At the end of the season, pruning the plant back to 20-30 cm with three main branches can help it overwinter and produce again in spring. Alternatively, you can opt for staking or stringing the branches without pruning. The growth cycle lasts about 90-120 days.

Aubergines require pollination, which can be done manually or with the help of bumblebees. Harvest the fruits when they reach 10-15 cm in length, using a sharp knife to leave at least 3 cm of stem attached. The skin should be shiny; dull or yellow skin indicates overripeness. Delayed harvesting can result in seedy, unmarketable fruits. Each plant typically yields 10-15 fruits, producing a total of 3-7 kg per plant.

27.8.5. Strawberries

The garden strawberry (Fragaria spp.) is a widely cultivated hybrid plant known for its fruit and perennial lifespan, though it is susceptible to diseases. One common issue is crown rot, a fungal disease that affects the area where the roots meet the stem. To prevent this, it’s crucial to keep this region dry. Mites are another common pest concern for strawberry plants.

Strawberry varieties differ in their fruiting timelines. Some produce fruit within a month of planting, while others may take several months. Certain varieties only fruit seasonally, even when grown indoors, but ever-bearing or day-neutral types are ideal for indoor cultivation due to their extended fruiting periods.

Strawberries thrive in temperatures between 18-20°C and prefer soil with a pH of 5.5 to 6.0. It’s generally more efficient to start with rootstock rather than seeds, as this accelerates fruit production by months or even years. In optimal conditions, new growth appears within a week, and flowers may emerge in two weeks. However, it’s recommended to pinch back flowers during the first 4-6 weeks to promote stronger plant development and higher future yields. Once flowers form, fruits typically ripen in about two weeks, depending on the variety and growing conditions.

Outdoors, pollination is aided by natural pollinators like bees and flies. Indoors, pollination may require manual assistance, either by introducing bees or hand-pollinating with a paintbrush to transfer pollen between flowers.

Pruning is essential for healthy strawberry plants. Removing older leaves improves airflow and reduces disease risk. Runners – offshoots that divert energy from fruit production – should also be trimmed to focus growth on flowers and fruit. Early flower removal encourages stronger crowns and larger fruit later in the season.

The size of strawberries is inversely related to the number of flowers; fewer flowers generally result in larger fruit. Crown pruning helps maintain an appropriate plant density, particularly during winter greenhouse production.

27.9. Crop selection

It is recommended to grow a mix of 50% leafy greens and herbs alongside 50% fruiting vegetables. This polyculture approach aids in pest and disease management while optimizing space. For instance, shade-tolerant shorter plants can thrive beneath taller ones.

Vining crops are also recommended for maximizing space. These plants can be trained to grow vertically on structures, making them easier to care for and observe.

27.10. Planting schedule

Planting all crops simultaneously can lead to production surges rather than a steady supply, which is problematic for meeting consistent weekly or bi-weekly demand. A staggered planting and harvesting schedule that accounts for each crop’s growth time is essential for maintaining a continuous output.

Examples:

Leafy greens like chard, lettuce, and cabbage take 4-6 weeks from planting to harvest.
Fast-growing herbs like chives and mint are ready in 3-4 weeks.
Coriander, parsley, and basil typically take around 5 weeks under optimal conditions.
Fruit-bearing plants like strawberries and tomatoes produce continuously over time.

Harvesting all plants at once can disrupt the system’s balance, leading to water quality issues due to reduced plant filtration. Some farmers harvest everything simultaneously, often coinciding with a large fish harvest or reduced fish feeding. However, a staggered harvesting and replanting schedule is preferable to avoid nutrient shortages and maintain stable water quality.

Indoor growers benefit from year-round harvests but must minimize downtime between crops by having seedlings ready when the previous crop is harvested. This requires careful planning by tracking germination and propagation times.

Steps for Minimizing Downtime:

Mark your harvest day on the calendar.
Calculate germination and propagation times.
Count back from the harvest date to determine when to start germinating the next batch.
Ensure transplanting occurs immediately after the previous harvest.
Overlapping planting schedules enable smaller weekly harvests, which is beneficial for fulfilling consistent supply contracts.

Steps for Creating an Effective Schedule:

Harvest Plan: Allocate sufficient time for preparation and sales.
Crop Knowledge: Understand growth rates and specific needs of each crop.
Harvest Method: Choose between full harvesting or cut-and-come-again methods based on crop type.
Farm Size Consideration: Larger farms require more time for harvesting; plan accordingly.
Market Demand: Grow only what your market demands, ensuring you allocate resources efficiently to meet customer needs.

27.11. Example Planting Schedule

This planting schedule is designed to ensure a continuous supply of fresh, nutritious food throughout the year using iAVs in a subtropical climate. Adjust the timing based on your specific location and weather conditions.

January: Start warm-season crops (e.g., tomatoes, peppers, eggplants) indoors. Directly plant cool-season crops (e.g., lettuce, spinach, radishes) in the sand bed.
February: Continue planting cool-season crops. Transplant warm-season crops started indoors.
March: Plant herbs (e.g., basil, parsley, cilantro). Start root vegetables (e.g., carrots, beets).
April: Continue planting herbs and root vegetables. Begin planting warm-season crops (e.g., cucumbers, zucchini, squash).
May: Introduce tropical fruits (e.g., melons, pineapples). Continue planting warm-season crops.
June: Continue planting tropical fruits. Start beans and corn.
July: Begin planting fall crops (e.g., broccoli, cabbage, kale). Continue planting beans and corn.
August: Continue planting fall crops. Start winter crops (e.g., garlic, onions).
September: Continue planting winter crops. Plant cool-season crops for a second fall harvest.
October: Continue planting cool-season crops. Start herbs for a second fall harvest.
November: Continue planting cool-season crops and herbs. Begin root vegetables for a winter harvest.
December: Continue planting root vegetables. Prepare for the next growing season by cleaning and maintaining your iAVs.

27.11.1. Staggered Planting

Staggered planting helps maintain balanced nutrient levels in iAVs and ensures a continuous supply of fresh produce. For example, sow lettuce seeds every 14 days to maintain a steady harvest. Some plants, like salad greens, basil, coriander, and tomatoes, can be harvested continuously throughout the growing season, while others, such as kohlrabi, lettuce, and carrots, are harvested once they mature.

27.12. Intercropping

Intercropping involves planting complementary species between rows of main crops like tomatoes or cucumbers. This technique optimizes space and sunlight while improving system performance. Fast-growing crops like radishes, soft herbs, and salad greens can be planted between slower-growing crops like tomatoes. For instance, you can harvest three radish crops and one lettuce crop before broccoli matures and shades smaller plants.

Research supports the benefits of intercropping for resource efficiency: “Complementary patterns of resource use and facilitative interactions between intercrop components can lead to greater capture of light, water, and nutrients” (Liebman & Staver 2001).

27.12.1. Multi-story cropping

Multi-story cropping maximizes vertical space by growing vining plants such as grapes, melons, pole beans, or squash on overhead trellises. These plants create a canopy that provides partial shade for crops like lettuce or spinach that thrive in cooler conditions. This method creates a beneficial microclimate and increases crop yield per square meter.

Construct trellises approximately 2 meters high to ensure adequate space for both vining plants and the crops below. Research shows that intercropping and vertical gardening improve plant growth and resource use efficiency.

27.13. Supplemental Fertilizers

When using a properly formulated feed and planting at the correct rate, additional supplements are generally unnecessary. However, if required, supplemental fertilizers can provide extra nutrients to complement fish waste.

Foliar application, where nutrients are sprayed directly onto leaves, can deliver specific nutrients without altering a system’s water chemistry, thus avoiding impacts on fish or biofilter bacteria in integrated agri-aquaculture systems (iAVs) (Frassine et al., 2024). It can also serve as an emergency measure for rapidly correcting specific, diagnosed nutrient deficiencies (Mariano et al. 2021). However, foliar uptake is generally less efficient than root uptake, with only a small percentage of nutrients absorbed through leaves. Its effectiveness is also conditional, being more pronounced under mild temperatures, high humidity, and for crops with thinner leaf cuticles. Therefore, while foliar feeding can be a valuable supplemental tool, it is not a replacement for primary fertilization (e.g., soil or root-zone) and should be considered a targeted intervention used cautiously rather than a primary strategy (Frassine et al., 2024; Mariano et al. 2021).

Tomatoes may benefit from aspirin as a foliar feed, while boric acid applied to the soil can address boron deficiencies if needed. In Dr. McMurtry’s research, a boron deficiency in one tomato variety was easily corrected with a trace amount of boric acid.

Staggering plant production helps maintain consistent nutrient uptake, preventing nutrient accumulation to toxic levels.

28. NUTRIENTS

Plant nutrition as a subject is closely related to other disciplines such as soil science, plant physiology and biochemistry (Marschner 2012).

Understanding plant nutrition can seem complex, but iAVs simplifies it significantly. The core principle is that in a properly managed iAVs, the fish feed provides virtually all the essential nutrients your plants need. Fish waste, processed by the microbes in the sand biofilter, acts as a complete, balanced, natural fertilizer.

For most users, focusing on using a quality fish feed and applying the correct feeding rate (based on your biofilter size and plant types) is sufficient. You generally do not need to add supplemental fertilizers or micronutrients. Observing your plants for obvious signs of health (good color, steady growth) is your primary guide.

This chapter delves into the details of plant nutrition, the specific forms of nitrogen available, the role of biostimulants, and the history of nutrient tracking in iAVs research . This information is useful for troubleshooting, advanced optimization, or deeper scientific understanding. However, for successful day-to-day operation, trust the system’s design: feed the fish appropriately, and the plants will typically get what they need.

28.1. Fish ‘Waste’

Aquaculture effluents, often termed fish ‘waste’, represent the organic byproducts generated within aquaculture systems, primarily comprising uneaten fish feed, fish excreta, and other accumulated organic matter. These effluents are a potential nutrient resource and can be broadly categorized into two main fractions: the liquid fraction (fish water) and the solid fraction (fish sludge).

Similar in chemical composition to some livestock manures, aquaculture effluents contain key nutrients required for plant growth, including nitrogen (N) and phosphorus (P) (Naylor et al., 1999). The solid fraction, fish sludge, is particularly recognized as a nutritious animal waste, containing essential plant macronutrients and micronutrients such as N, P, iron (Fe), and copper (Cu) (Khiari et al., 2019; Strauch et al., 2018). Overall, fish excretion is considered among the most nutritious animal wastes compared to many other livestock sources (Khiari, 2020).

The liquid fraction typically contains lower concentrations of essential nutrients like phosphorus, potassium, and calcium (Delaide et al., 2019; Harika et al., 2024).

Conversely, the solid fraction, fish sludge, is significantly more nutrient-dense. It concentrates a substantial portion of the nutrients from the aquaculture system (Cripps & Bergheim, 2000). This solid fraction holds the majority of many essential plant nutrients, including iron (Schneider et al., 2005; Neto & Ostrensky, 2013; Khiari et al., 2019; Strauch et al., 2018) and particularly rich in phosphorus (Timmons and Ebeling, 2007). This nutrient richness makes fish sludge a valuable resource.

The precise chemical composition of aquaculture effluents, like other animal manures, is highly variable. Factors such as fish species, size, age, and particularly feed composition significantly influence nutrient profiles (Naylor et al., 1999). For specific nutrients like iron, the average Fe content in fresh fish manure has been reported to be higher than that in beef and poultry manure, although lower than in dairy cattle and swine manure (Naylor et al., 1999, citing Fulhage 1992; Olson 1992; Smith 1992; Westerman et al. 1993; Mudrak 1981; Muir 1982).

Reusing fish waste as a natural fertiliser in crop production offers significant benefits. It provides an eco-friendly alternative to artificial fertilisers, which require large amounts of energy for production (Rahimi et al., 2020) and depend heavily on finite natural resources (Vaccari, 2009; Scholz et al., 2013). Additionally, repurposing fish effluents decreases the energy and resources needed to process and treat aquaculture waste (Tom et al., 2021), creating a more sustainable and efficient system for nutrient recycling.

28.2. Plant nutrition

28.2.1. Essential nutrient elements

Plants require 14 mineral nutrients which they primarily absorb from the soil, as well as Carbon (C), Hydrogen (H), and Oxygen (O) (which plants primarily get from air and water) (Marschner 2012). These nutrients are vital for normal functioning.

Figure 8: Classification of essential elements (nutrients) that are needed for the plant growth

Nutrients are classified into macronutrients (needed in larger quantities) and micronutrients (required in smaller amounts), both of which are crucial for plant health.

Macronutrients are divided into three categories: primary macronutrients (Nitrogen, Phosphorus, Potassium), secondary macronutrients (Calcium, Magnesium, Sulfur), and micronutrients (Iron, Manganese, Zinc, Copper, etc.). The terms “primary” and “secondary” refer to the quantity needed by plants, not their importance. A deficiency in any nutrient – whether primary, secondary, or micronutrient – can equally impair plant growth. Understanding the role of each nutrient is critical for optimizing plant health. Identifying nutrient deficiencies allows for targeted adjustments, such as modifying fish feed or feeding rates.

Since most micronutrients primarily function as constituents of enzyme molecules, plants require them in only small amounts overall (Marschner 2012).

Figure 9: Representation of nutrient amounts in dried plant material

Essential elements are critical for plant growth and development, each playing specific roles in physiological processes.

Carbon (C) forms the backbone of biomolecules like proteins, starches, and cellulose. It is central to photosynthesis, where CO₂ is converted into carbohydrates for energy storage and transport within the plant.
Hydrogen (H), primarily obtained from water, is a component of all organic compounds involving carbon. It plays a key role in cation exchange in plant-soil interactions and is necessary for the electron transport chain in photosynthesis and respiration.
Oxygen (O) is a component of many organic and inorganic compounds in plants. It can be sourced from O₂, CO₂, H₂O, NO₃⁻, H₂PO₄⁻, and SO₄²⁻. Oxygen is essential for aerobic respiration to produce ATP and is involved in anion exchange between roots and the external medium.
Nitrogen (N) is a fundamental element in amino acids, proteins, coenzymes, nucleic acids, and chlorophyll. It supports photosynthesis, cell growth, and metabolic processes. Plants typically absorb nitrogen as nitrate (NO₃⁻) but can also utilize ammonia (NH₃) and free amino acids.
Phosphorus (P) forms part of nucleic acids like DNA and ATP. It is crucial for photosynthesis, sugar formation, germination, and root development in seedlings.
Potassium (K) acts as a coenzyme or activator for many enzymes involved in protein synthesis and cell signaling. It regulates stomatal function and plays a significant role in flower and fruit development, sugar transport, water uptake, disease resistance, and fruit ripening.
Calcium (Ca) strengthens cell walls through calcium pectate formation and aids stem strengthening and root development. It also maintains membrane integrity and is part of the enzyme α-amylase.
Magnesium (Mg) is essential for chlorophyll formation and enzyme activation needed for growth. It also helps maintain ribosome structure for protein synthesis.
Sulfur (S) is incorporated into amino acids like methionine and cysteine as well as proteins such as photosynthetic enzymes. It also forms part of coenzyme A, thiamine, and biotin.
Boron (B) is involved in cell wall synthesis with calcium and is essential for cell division. It enhances sugar transport from mature leaves to growing regions and developing fruits.
Chlorine (Cl) is absorbed by plants in relatively significant quantities despite being a micronutrient. It aids stomatal function, enzyme activation during photosynthesis, cation balance, disease resistance, nitrate uptake reduction, and may help suppress diseases associated with high nitrate levels. However, excessive chlorine can cause toxicity symptoms like leaf burn and reduced growth. Chlorine poses a significant threat to fish health. Chlorine reacts with fish tissues – especially gills – causing acute necrosis (cell death), respiratory distress, or even death at concentrations as low as 0.02-0.05 ppm. Levels above 0.1 ppm are lethal over time. Therefore, chlorine must be removed from source water before introducing it to fish tanks. Municipal tap water often contains chlorine or chloramine (a compound of chlorine and ammonia), which are harmful to aquatic life but safe for human consumption.
Copper (Cu) activates enzymes involved in lignin synthesis and supports photosynthesis and respiration.
Iron (Fe) is crucial for chlorophyll synthesis and ferredoxins that act as electron carriers in photosynthesis and respiration.
Manganese (Mn) activates enzymes involved in fatty acid synthesis, DNA/RNA formation, respiration, chloroplast formation, nitrogen assimilation, pollen germination/tube growth, root cell elongation, and resistance to root pathogens.
Molybdenum (Mo) acts as an electron carrier in nitrate conversion to ammonium for amino acid synthesis within plants.
Nickel (Ni) functions as a metal cofactor for urease enzymes responsible for detoxifying urea.
Zinc (Zn) activates enzymes responsible for protein synthesis and aids chlorophyll formation. It also supports carbohydrate conversion to starches/sugars, cold temperature tolerance, auxin hormone formation for growth regulation.

These elements are vital to various physiological processes that contribute to plant growth, development, reproduction, disease resistance, and overall health.

28.2.2. Nutritional disorders in plants

Nutritional disorders in plants occur when there is an imbalance – either a deficiency or excess – of essential nutrients. Early detection is crucial to prevent symptoms from worsening and damaging the plant. However, diagnosing these disorders can be challenging as many deficiencies exhibit similar symptoms, which can also resemble those caused by diseases. Identifying these issues requires careful observation, experience, and comparison of symptoms with water quality tests. For beginners, consulting an expert can be helpful.

A key aspect of diagnosis is understanding the difference between mobile and immobile nutrients. Mobile nutrients – such as nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), and zinc (Zn) – can move from older to younger leaves when deficient, meaning symptoms appear first on older leaves. In contrast, immobile nutrients – like calcium (Ca), iron (Fe), sulfur (S), boron (B), copper (Cu), and manganese (Mn) – cannot be redistributed once used, so deficiencies show up on younger leaves.

Specific terms are used to describe the symptoms of nutrient imbalances:

Necrosis: Dead tissue that gives a scorched, dry appearance.
Chlorosis: Yellowing of leaves due to reduced chlorophyll.
Interveinal chlorosis: Yellowing between leaf veins, often signaling nutrient deficiencies.
Mottling: Irregular blotchy patterns of light and dark areas.
Cupping: Leaf margins curling upward or downward.
Dieback: Death of growing points or leaves.
Stunting: Reduced plant height or growth.

Understanding these terms is essential for diagnosing plant nutritional disorders. Below is an overview of common nutrient deficiencies and toxicities:

Nitrogen (N): Deficiency causes stunted growth, pale yellow older leaves, and reduced flowering/fruiting. Toxicity results in dark green foliage but poor root development.
Phosphorus (P): Deficiency leads to poor root growth and delayed maturity, with older leaves turning dark green or reddish. Excess phosphorus can induce copper and zinc deficiencies.
Potassium (K): Deficiency affects water uptake and disease resistance, causing leaf curling and necrotic spots. Excess potassium may lead to magnesium deficiency.
Calcium (Ca): Deficiency causes tip burn in leafy plants and blossom end rot in fruiting plants. Calcium toxicity is rare.
Magnesium (Mg): Deficiency leads to interveinal chlorosis on older leaves. Toxicity information is limited.
Sulfur (S): Deficiency resembles nitrogen deficiency but affects younger leaves first. Toxicity causes reduced growth and leaf size.
Boron (B): Deficiency affects new growth, causing brittle leaves and dieback. Toxicity results in yellowing leaf tips followed by necrosis.
Chlorine (Cl): Deficiency causes wilting and stunted roots; toxicity leads to salinity stress with scorched leaf margins.
Copper (Cu): Deficiency causes cupping of young leaves; toxicity reduces growth and induces iron chlorosis.
Iron (Fe): Deficiency results in interveinal chlorosis starting at younger leaves; toxicity is rare but can cause necrotic spots after foliar sprays.
Manganese (Mn): Deficiency causes interveinal chlorosis on young leaves; toxicity may lead to uneven chlorophyll distribution.
Molybdenum (Mo): Deficiency resembles nitrogen deficiency; toxicity is rare but can cause yellowing in some crops.
Nickel (Ni): Deficiency may impair urea detoxification, causing leaf burn; toxicity inhibits plant growth by affecting photosynthesis and respiration.
Zinc (Zn): Deficiency leads to stunted growth with shortened internodes; excess zinc induces iron chlorosis.

This summary provides a foundational understanding of how nutrient imbalances affect plant health across various crops.

28.3. Nutrient supply in iAVs

In iAVs, the water contains a complex mix of chemicals, including dissolved ions, organic materials from fish metabolism and feed breakdown, and substances released by plants. Many of these interactions are not fully understood, but they influence water chemistry, acidity, nutrient absorption by plants, fish health, and microbial activity.

Nutrients enter iAVs primarily through water and fish feed. Fish feed typically contains 7.5% nitrogen (N), 1.3% phosphorus (P), and 46% carbon (C), along with proteins, fats, and carbohydrates. Herbivorous fish like Tilapia require about 25% protein in their diet, while carnivorous species need around 55%. Excess protein increases nitrogen waste in the system. However, both fishmeal and soybean-based feeds are unsustainable, prompting research into alternative feed sources.

28.3.1. Iron

iAVs maintains a lower pH (~6.4), enhancing iron solubility and accessibility for plants (Wang 2023). Beneficial microbes in the sand filter also produce siderophores, further improving iron absorption, contrasting with traditional aquaponics systems that often experience iron deficiencies at neutral pH (~7).

While iron in fish waste isn’t directly available, bacterial activity in mature sand biofilters releases and chelates it. Research indicates that fish feed provides sufficient iron for thriving plants in iAVs, emphasizing that the system’s method of handling fish waste is key to iron availability.

This capability distinguishes iAVs from traditional aquaponics, where iron deficiency frequently necessitates supplementation through fortified fish feed or direct addition of iron chelates, potentially risking fish or beneficial bacteria (Frassine et al., 2024; Kasozi et al., 2019). By maintaining an optimal pH and efficiently mineralizing nutrient-rich fish solids in the sand biofilter, iAVs typically eliminates the need for external iron supplements when a balanced fish feed is used.

28.4. Understanding Nitrogen Forms

Nitrogen is arguably the most critical nutrient for plant growth, forming the building blocks of proteins, nucleic acids (like DNA), and chlorophyll, which is essential for photosynthesis. Nitrogen is a mineral nutrient required in the largest amounts by plants after carbon, and its availability is a decisive factor for plant growth (Marschner 2012).

In an Integrated Aqua-Vegeculture System (iAVs), the primary source of nitrogen comes from the fish feed, which is processed by the fish and released as waste. Understanding how this nitrogen transforms within the system and becomes available to plants is key to appreciating the efficiency of iAVs.

Diverse Nitrogen Forms in iAVs

Unlike many hydroponic or traditional aquaponic systems that primarily focus on delivering nitrogen as nitrate (NO₃⁻), iAVs provides plants with access to a richer, more diverse range of nitrogen sources:

Ammonium (NH₄⁺): Fish primarily excrete nitrogenous waste as ammonia (NH₃). However, at the typical operating pH of iAVs (around 6.4), most of this ammonia rapidly converts into the less toxic ammonium ion (NH₄⁺) in the water.
Nitrate (NO₃⁻): Through the process of nitrification, beneficial bacteria in the sand biofilter convert ammonium first into nitrite (NO₂⁻) and then into nitrate (NO₃⁻).
Organic Nitrogen: As fish waste and any uneaten feed decompose within the biologically active sand biofilter, complex organic nitrogen compounds are broken down. This releases simpler organic forms like amino acids, peptides, ureides, and even proteins, which some plants can also absorb directly (Marschener 2012; Andrews 2013).

Why Plants Benefit from Mixed Nitrogen Nutrition

While plants primarily take up nitrogen as ammonium (NH₄⁺), nitrate (NO₃⁻), and amino acids (Rentsch et al. 2007, Sanchez and Doerge 1999) and can grow using only one ionic form, the availability of ammonium alongside nitrate confers an advantage, leading to the best growth outcomes for most plants (Wongkiew et al., 2017). There are several reasons for this:

Energy Efficiency: Absorbing ammonium (NH₄⁺) is metabolically cheaper for plants. It can be directly incorporated into amino acids via pathways like the GS/GOGAT system (Li et al., 2013), bypassing energy-intensive steps. In contrast, nitrate (NO₃⁻) must first be converted back into ammonium inside the plant cells before it can be used, a process that consumes significant metabolic energy (Andrews 2013). Having readily available ammonium allows plants to conserve energy for growth and other functions. This is because ammonium assimilation is significantly less energy-intensive than the combined reduction and assimilation process required for nitrate (Marschener 2012).
Physiological Balance: Different nitrogen forms can influence the uptake of other nutrients and affect the internal pH balance of plant cells. Accessing both forms allows plants to better regulate these processes under varying conditions. Specific growth stages might also favor one form over the other (Wongkiew et al., 2017). Highest growth rates and plant yields are obtained by combined supply of both ammonium and nitrate (Marschener 2012).

The Ammonia-Ammonium Equilibrium: Protecting Fish, Feeding Plants

The conversion between toxic ammonia (NH₃) and less toxic ammonium (NH₄⁺) is a crucial chemical equilibrium governed by water pH:

NH₃ + H⁺ ⇌ NH₄⁺

The Role of pH: In more alkaline water (higher pH), the equilibrium shifts towards ammonia (NH₃), which is highly toxic to fish even at low concentrations. In the slightly acidic conditions of a well-managed iAVs (pH ~6.4 ± 0.4), the equilibrium strongly favors the formation of ammonium (NH₄⁺).
Fish Safety: Maintaining the pH near 6.4 is therefore critical for fish health, ensuring that the primary nitrogen waste product exists predominantly in its much safer ammonium form.
Plant Nutrition: This conversion simultaneously benefits plants by providing nitrogen in the readily usable ammonium form.

Ammonia exists in two forms: un-ionized ammonia (NH3) and ionized ammonium (NH4+), which are collectively referred to as total ammonia nitrogen (TAN) (Wongkiew 2017). Monitoring Total Ammonia Nitrogen (TAN) – which measures both NH₃ and NH₄⁺ – along with pH is important, especially during system startup or if issues arise. If TAN levels climb or pH drifts too high, reducing feed input is a primary corrective action to prevent potential ammonia toxicity.

Ammonia/Ammonium and pH Buffering

The ammonia/ammonium balance also plays a role in stabilizing the system’s pH. When ammonia dissolves in water, it can react as follows:

NH₃ + H₂O ⇌ NH₄⁺ + OH⁻

In the slightly acidic environment of iAVs, ammonia effectively acts as a weak base, reacting with excess hydrogen ions (H⁺) to form ammonium. This “soaks up” acidity, providing a natural buffering effect that contributes to the remarkable pH stability observed in mature iAVs systems.

Conclusion: The Balanced Nitrogen Cycle in iAVs

The iAVs naturally facilitates a balanced and efficient nitrogen cycle. It provides plants with nitrogen in multiple forms (ammonium, nitrate, and organic compounds), allowing for optimal uptake and energy efficiency. Critically, the system’s operating pH ensures that potentially toxic ammonia is primarily converted to safer ammonium, protecting fish while simultaneously providing a readily available nutrient for plants. This inherent chemical balance, coupled with biological processes like nitrification and direct plant uptake, contributes significantly to the overall stability, productivity, and sustainability of iAVs.

28.4.1. pH and Nitrogen

Ammonium uptake acidifies the rhizosphere as plants release protons (H+). Nitrate uptake alkalizes the rhizosphere by releasing bicarbonate or hydroxide ions. This dual uptake helps plants regulate their local pH environment, optimizing nutrient availability (Marschener 2012).

Plants have evolved mechanisms to modulate their nitrogen acquisition efficiency in response to the availability and form of external nitrogen. This overall adaptability is based on factors like soil properties including temperature and moisture, as well as microbial activity (Marschener 2012).

28.5. Benefits of This Nitrogen Balance

Improved Plant Growth: Access to both ammonium and nitrate act synergistically to promote plant growth in most plant families (Andrews 2013).
Energy Efficiency for Plants: Ammonium assimilation is less energy-intensive than nitrate assimilation, allowing plants to conserve energy for other metabolic processes when ammonium is available (Andrews 2013).
System Balance (Fish Health): While nitrate is an essential plant nutrient, maintaining excessively high nitrate levels can adversely affect fish health, potentially increasing disease risk and causing physiological damage (Banerjee et al., 2023). Therefore, the ideal nitrogen balance in iAVs considers both optimal plant nutrition and fish well-being.
Iron Availability: High NO3− supply, however, can increase pH at the root surface, potentially leading to interveinal chlorosis (Fe deficiency). A mixed N source could mitigate these adverse pH-related effects by balancing H+ and OH− generation (Andrews 2013). In simpler terms, if a plant gets too much nitrate, it makes the soil right around its roots too alkaline which makes it much harder for the plant to pick up essential iron (Fe) from the soil. Even if some iron gets into the plant, the high pH can make that iron unusable inside the leaves.

Nitrate nutrition results in Fe deficiency chlorosis exclusively by inhibited Fe acquisition by roots due to high pH at the root surface (Nikolic 2003). A balance of ammonium and nitrate ensures the plant can utilize the iron.

Nitrate uptake usually causes alkalinisation of the rhizosphere due to the concomitant excretion of OH~ or HCO^~ (Bienfait, 1989; Marschner, 1995; Romheld et al., 1984). When iron availability is low, nitrate uptake may lead to iron deficiency in so-called iron inefficient plants. These plants continue to excrete OH” or HCO^~ when iron stress develops, instead of initiating the excretion of H+ ions as do iron efficient plants under the same conditions (Aktas and van Egmond, 1979; Romheld et al., 1984).

Root Growth: The combined application of NH4+ and NO3− has been shown to synergistically induce both the number and length of lateral roots in plants like Arabidopsis (Thale Cress). This results in a more branched and potentially more efficient root system compared to when either form is supplied alone (Andrews 2013)
pH Stability: .The assimilation of N forms affects the internal and external pH of the plant. Assimilating one molecule of NH4+ generates 1.33 H+, which must be excreted or neutralized to maintain cytoplasmic pH, with much of this H+ extruded into the soil from the root. In contrast, the assimilation of one NO3− molecule results in the generation of 0.67 hydroxyl ions (OH−), which are largely extruded into the soil from the root or neutralized by organic acid synthesis in the shoot. A balance between NH4+ and NO3− supply can help maintain a more stable pH in the rhizosphere and within plant tissues (Andrews 2013).

In simpler terms, if a plant gets too much of one type of nitrogen, it can throw off its internal pH and the pH of the soil. But by providing a balance of both ammonium and nitrate, plants can more easily maintain a stable, healthy pH both inside themselves and in the soil where their roots grow.

28.6. Biostimulants and Plant Growth-Promoting Bacteria

Beyond providing essential nutrients, the biologically active sand biofilter in iAVs fosters conditions that actively promote plant health and growth through natural biostimulants and beneficial microorganisms.

Natural Biostimulants: Fish waste itself contains biostimulant molecules (Korbee 2025). Dissolved organic matter (DOM) derived from fish effluent, particularly humic-like and protein-like substances, has been shown to act as a biostimulant, improving nutrient uptake and plant metabolism (Hambly et al., 2015; Delaide et al., 2016; Nicoletto et al., 2018). These interactions can also stimulate the production of beneficial secondary metabolites (e.g., phenolics, flavonoids) in plants, enhancing their natural defenses and antioxidant capacity.
Plant Growth-Promoting Bacteria (PGPB): These beneficial bacteria interact with plant roots, enhancing nutrient extraction and growth (Ferreira et al. 2024, 2025). PGPB can influence plant metabolism (Pang et al. 2021; Ferreira et al. 2023, 2024), often redirecting resources towards stress resistance pathways (Mhlongo et al. 2020) and potentially increasing the economic value of crops through enhanced beneficial compounds (Bakaeva et al. 2024; Puccinelli et al. 2024).
Mechanisms of Action: These beneficial effects are linked to various microbial activities, including:
- Enhanced amino acid biosynthesis, which supports protein production and drives further nutrient uptake (Lopez and Mohiuddin Shamin 2024; Elshamly et al. 2024; Gupta et al. 2024).
- Production of siderophores, which improve iron acquisition (Ferreira et al. 2021; Shojima et al. 1990; Kuzmicheva et al. 2017) and subsequently stimulate pathways linked to growth and stress resilience (Araki et al. 2015; Hasanuzzaman et al. 2017; Saltveit 2018; Schefer et al. 2021).
- Improved sulfur metabolism, leading to the production of protective compounds like glutathione (Li et al. 2020; Mandal et al. 2022).
- Potential reduction of anti-nutritional compounds like oxalic acid, improving food quality (Sc Noonan 1999; Wang et al. 2024; Fougère et al. 1991; Mokrani et al. 2020).

In essence, the iAVs sand biofilter creates a synergistic environment where natural compounds and beneficial microbes work together to boost plant health, nutrient use efficiency, and resilience, contributing significantly to the system’s overall productivity and sustainability.

28.7. Elemental Tracking and Nutrient Management in Early iAVs Research

Dr. McMurtry and his team meticulously tracked the movement and transformation of essential elements in iAVs, starting with their earliest studies in 1984-1985. These initial experiments used hydroponics (based on Hoagland’s solution) as a control and involved six plant species. In 1986, subsequent research expanded to twelve plant species across 4,000 square feet, using an organic soil-based system as the control. This tracking continued through various randomized complete block design (RCBD) volumetric ratio studies.

No elemental toxicities or deficiencies were observed in any plant species, except those documented in published research. Recommendations regarding plant nutrition were outlined in a study published in HortScience. It was suggested that sulfur and copper levels may have been elevated due to the use of Purina fish chow, which could raise concerns for long-term use. However, fish feed formulations can be adjusted for larger-scale operations as needed. Importantly, no toxicities were observed during these studies.

Key Takeaway: Nutrients in iAVs

Source: Fish feed is the primary (and usually only) source of plant nutrients.
Process: Fish waste is broken down by microbes in the sand biofilter, making nutrients available to plants.
Completeness: A balanced fish feed provides the full spectrum of macro- and micronutrients needed by plants in iAVs.
Supplementation: Generally not required if using quality feed and correct feeding rates.
Management: Focus on appropriate fish feeding rates (grams of feed per square meter of biofilter per day, see Chapter 22) and maintaining a diverse mix of plants (Section 25.7). Observe plant health as the main indicator.

29. Alternative Tank Designs

29.1. Alternative Tank Shapes: Rectangular and Circular

While tank shape can vary, with round or oval tanks sometimes demonstrating efficiency (Knaus et al. 2015), the sloped bottom remains a key feature for effective solids removal. The recommended shape for a fish tank in an iAVs is rectangular when viewed from above, with rounded corners. This design minimizes dead zones where water flow might stagnate, promoting efficient movement of solids and reducing the risk of anaerobic conditions that could harm fish health or water quality.

The tank’s rectangular shape further optimizes space usage and allows for straightforward plumbing and aeration setups. If an in-ground catenary-shaped tank is not feasible, consider a circular tank with a gentle slope leading to a central low point at the bottom which concentrates solids for easier removal.

29.2. IBC Tanks

The iAVs in this picture were built by Gary Donaldson.

Intermediate Bulk Containers (IBCs) are large, reusable containers commonly used for storing and transporting bulk liquids or granular materials. While not ideal for fish tanks due to their shape, they are often repurposed in aquaculture systems as a cost-effective option.

A significant concern when reusing IBCs is the potential for chemical contamination. Plastics like LDPE can absorb and slowly release substances previously stored in them, including toxic chemicals. This poses risks to fish, plants, and humans if harmful substances leach into the water. To mitigate this risk, only IBCs that have stored non-toxic, food-safe materials should be used. Containers that have housed pesticides, herbicides, or industrial chemicals should be strictly avoided. Although some IBCs are made from HDPE (High-Density Polyethylene), which is less prone to chemical leaching than LDPE, the safest option is to use new or food-grade IBCs whenever possible.

Aside from potential contamination, IBC tanks have design limitations. Their flat-bottom structure is not optimal for removing fish waste efficiently. The ideal fish tank shape is a catenary curve, which directs waste toward a central drain point for easier removal. To improve an IBC tank’s functionality, sand can be placed beneath a liner to create a catenary curve at the bottom. The liner also prevents potential contaminants from contacting the fish and reduces light penetration into the tank.

An IBC container filled with sand strategically placed in the corners to form a catenary shape.

An IBC container prepared for use as a fish tank, shaped into a catenary form by strategically placing sand in the corners and lined with a food-safe liner.

30. Pathogens and Food Safety

It is the responsibility of each iAVs operator to familiarize themselves with the specific food safety regulations and guidelines applicable to their location and intended use. This chapter serves as a starting point, highlighting key areas to consider and encouraging further investigation into local requirements.

It is important for commercial iAVs operators to stay updated on the regulations specific to their location by consulting local authorities or food safety agencies. This ensures they remain compliant with applicable laws and standards, which can change over time.

A commercial-scale farm is often defined as one that meets food safety certification standards (Tokunaga et al., 2015). However, most small-scale or personal farms are not subject to strict food safety regulation. That said, it’s still important to take basic precautions when growing your own food. These include washing your hands regularly, rinsing vegetables thoroughly before eating, keeping rodents and other animals away from your system, and wearing gloves to protect against cuts or scratches that could lead to infection (Hollyer et al., 2009).

Consumers are increasingly concerned about food safety and quality, driven by frequent media coverage of food-related issues. Ensuring food safety involves proper handling, storage, and preparation to prevent illness and maintain nutritional value. Ignoring food safety can lead to spoilage, health risks, and even life-threatening conditions.

Anyone selling food has an ethical and legal responsibility to ensure its safety. This applies to all stages of production, from harvesting crops to processing fish. Fresh produce must be protected from biological, chemical, and physical hazards. In aquaculture, biological hazards like bacteria are a primary concern, making it essential to identify risks and take preventive measures.

Hazard Types:

Microbiological Hazards: Harmful bacteria, viruses, and parasites. Sand filtration in iAVs helps reduce these risks.
Chemical Hazards: Residues from plant protection products, veterinary medicines, sanitizers, and cleaning agents.
Physical Hazards: Foreign objects like metal, glass, plastic fragments, or stones.
Allergens: Common allergens include gluten-containing cereals, crustaceans, eggs, fish products, peanuts, soybeans, milk (including lactose), nuts, celery, mustard, sesame seeds, sulfur dioxide/sulphites, lupin, and mollusks.

30.1. Fish Waste Classification

Since fish are not warm-blooded, they are unlikely to emit common human pathogens in their waste (Sobsey et al., 2006), contributing to the generally lower pathogen load and greater safety of fish waste compared to manure from warm-blooded animals (Somerville 2014).

While fears about pathogen transfer from fish sludge to plants are often raised, they lack substantiation in the literature (Goddek 2019); in contrast, poor hygiene during food handling and processing represents a significant source of food contamination (Admasu 2023).

Under U.S. Department of Agriculture (USDA) guidelines, fish waste is not classified as “manure,” which simplifies its use in integrated aquaculture systems like iAVs by imposing fewer restrictions. While the USDA’s decision is specific to the United States, it can serve as a useful guideline internationally, as many regions recognize the distinction between fish waste and traditional manure in terms of food safety risks. Fish waste breaks down quickly into essential nutrients for plants without posing the same contamination risks associated with livestock manure.

30.2. Food safety risks

Bacterial contamination presents risks, primarily originating from fish waste and plant debris within the water. Potential pathogens, such as E. coli or Salmonella, can be introduced via the water itself or contaminated tools. However, research indicates that significant contamination is not typically observed unless specific conditions prevail, like high bacterial loads or compromised plant roots (e.g., Moriarty et al.). Furthermore, fish sourced unreliably can introduce diseases impacting water quality, even if not directly plant-related. Poor-quality water might also harbor parasites like Cryptosporidium and Giardia.

Even hydroponic systems, while distinct, face their own set of microbial challenges. Research highlights that pathogen absorption varies by plant type, pathogen species, and growing conditions (Hirneisen et al. 2012). In hydroponic cultivation specifically, the continuous exposure of plant roots to the nutrient solution creates a direct interface with potentially contaminated water. This constant immersion, unlike soil-based agriculture where soil matrices provide barriers, significantly increases opportunities for pathogens like E. coli and Salmonella to adhere to and penetrate root tissues, potentially reaching edible portions (Flett 2017). Studies demonstrate rapid attachment; pathogens like E. coli O157:H7 or Salmonella introduced into hydroponic solutions can attach to root surfaces within hours (Sela 2023). Experiments confirmed this pathway, showing E. coli O157:H7 inoculated into hydroponic medium was later detected in both spinach roots and shoots, with shoot concentrations increasing over 14 to 21 days (Sela 2023). This direct and prolonged root-water contact is a fundamental risk factor in hydroponics.

Without the natural filtering effect of soil, microbial contaminants in the water can enter the plant vascular system more directly. Research using murine norovirus in hydroponic microgreens showed the virus in edible tissues and roots just two hours post-inoculation, with levels remaining relatively stable for the first 12 hours (Wang 2016). This rapid translocation underscores how the hydroponic environment can accelerate pathogen movement compared to soil systems. Furthermore, unlike in soil-based systems such as iAVs, with its rich, suppressive microbial communities, hydroponic systems often start with minimal microbial diversity. This lack of competitive and antagonistic microorganisms removes a natural barrier against pathogen proliferation and colonization, missing the protective functions inherent to complex soil microbiomes. While recent research explores using beneficial bacteria like Plant Growth-Promoting Bacteria (PGPB) (e.g., Azospirillum brasilense, Pseudomonas fluorescens) to enhance nutrient uptake and potentially compete with pathogens on root surfaces, this represents an active intervention rather than an inherent characteristic of the system. The fundamental lack of a complex, established microbiome remains a key distinction and vulnerability of hydroponics compared to soil cultivation.

Traditional aquaponic systems also face significant pathogen risks. A comprehensive Purdue University study detected Shiga toxin-producing E. coli (STEC) throughout such systems, finding it “in fish feces, the recirculating water and on the plant root surfaces in both aquaponic and hydroponic systems” (Wang 2020). This demonstrates how recirculation can distribute pathogens widely once introduced.

The iAVs approach differs fundamentally from traditional aquaponic systems by employing sand as both the growing medium and a filtration barrier. Irrigation water from fish tanks percolates through the sand before reaching plant roots, creating physical separation and filtration to mitigate any risks. This process resembles slow sand filtration, a known water treatment method effective at removing microbial contaminants. Research on related sand filtration techniques supports this protective potential; studies on zero-valent iron-sand filtration showed antimicrobial efficacy, and standard sand filtration also demonstrated some effectiveness against pathogens (Baker 2017). The sand medium directly addresses the vulnerability of pathogen-root contact seen in water-based systems, and the schmutzedeck (detritus layer) forming on the sand surface likely enhances filtration through physical and biological action.

The intermittent irrigation schedule in iAVs may also reduce pathogens by creating aerobic conditions unfavorable to many harmful bacteria. As noted in research on related systems, “the use of organic fertilizers in aquaponics has been observed to have a positive impact on the resident microbiota, which in turn could control several plant diseases”. The sand in iAVs likely fosters similar beneficial aerobic microbial communities. Perhaps the most significant advantage is the potential for robust microbial community development.

The sand medium provides vastly more surface area for colonization compared to water-based systems. Research suggests “pathogen suppression is likewise, linked to the use of organic amendments in aquaponics,” and show suppressive effects. This extensive habitat in iAVs can support diverse microbial communities capable of competitive exclusion. Specific soil bacteria demonstrate potent pathogen suppression; for instance, Paenibacillus alvei was found to reduce E. coli O157:H7 by over 3 log CFU/ml (a thousand-fold reduction) in lab conditions (Baker 2021). The sand environment in iAVs is conducive to establishing such beneficial, suppressive microbial populations, offering a distinct advantage over hydroponic and traditional aquaponic systems.

31. Scalability

A key strength of iAVs is its inherent scalability, allowing it to be adapted for a wide range of applications, from small home systems to large commercial farms. This scalability is directly enabled by the scientifically validated system size ratios discussed in the previous chapter. By maintaining the core ratios, iAVs can be expanded while preserving its efficiency and biological balance. This chapter explores the principles of scaling iAVs and considerations for commercial viability.

31.1. Introduction: Scaling iAVs – From Small to Large

The scientifically validated ratios discussed in Chapter 7 are not only crucial for individual iAVs units but also form the foundation for scaling the system to meet diverse needs, from small-scale home setups to large commercial operations. This chapter explores how these ratios facilitate scalability and the key considerations for commercial viability.

31.2. Modular Design and Scalability

The scalability of iAVs is fundamentally driven by its modular design. Each iAVs unit, adhering to the established tank-to-biofilter ratios, functions as a module. These modules can be replicated and interconnected to create larger systems, allowing for both physical expansion and operational flexibility.

31.2.1. Modular Design Principles

Replicability: Each iAVs module, whether a small backyard setup or a larger greenhouse bay, can be easily replicated. This means that expansion is not about redesigning the system but about building more units based on the same proven principles.
Interconnectivity: Modules can be connected in series or parallel to form larger, integrated systems. This allows for efficient use of space and resources, as water and nutrients can be shared across multiple modules.
Independent Operation: While interconnected, each module can also function independently. This provides operational flexibility and redundancy. If one module requires maintenance or experiences an issue, the rest of the system can continue to operate.
Example of Modular Expansion: A greenhouse bay measuring 4 x 12 meters, designed as a single iAVs module, can be connected in strings to form longer rows. Groups of these bays can then be arranged side-by-side, utilizing gutter-connected designs like Venlo-type greenhouses, to create very large-scale systems. This modular approach allows for expansion from small units to areas spanning several acres, while maintaining the core iAVs principles.

31.2.2. Managing Biological Factors in Scaled Systems

While the modular design simplifies physical scaling, maintaining biological balance is crucial at any scale. The tank-to-biofilter ratios are not just about physical dimensions; they represent a biological balance point. Therefore, scaling iAVs successfully requires attention to these biological factors:

Minimum Functional Size: There is a practical minimum size for a functional iAVs module. Fish tanks smaller than 500L may not produce sufficient nutrients to support a meaningful number of plants, even if the ratios are technically correct.
Balancing Inputs and Outputs: The core principle of matching nutrient production (from fish feed) to plant uptake remains paramount as you scale. Scaling up requires proportionally increasing fish biomass, feed rates, and the corresponding biofilter capacity (plant growing area) to maintain this balance. Simply increasing fish density without scaling the biofilter will overwhelm the system’s biological processing capacity.
Dynamic Adjustments: Regardless of system size, feed input rates, fish stocking density, and plant selection must be managed dynamically based on factors like fish growth stage, plant nutrient demands, water temperature, and overall system maturity.
Biological Limits: Even with correct ratios, biological limits exist. For example, exceeding optimal fish stocking densities can lead to stress and reduced growth, impacting nutrient production, irrespective of the overall system size.

In essence, while the ratios provide a blueprint for scaling, successful operation at any size requires continuous attention to the biological interactions within each module and the system as a whole. The ratios simplify the design process, but the operator must still manage the living components to ensure stability and productivity at any scale.

32. Fish Growth and Stocking Density

32.1. Understanding Stocking Density

Stocking density refers to the total biomass of fish within a given volume of water, typically expressed in kilograms per cubic meter ( kg/m ³) or pounds per cubic foot (lb/ft³). Fish biomass changes daily as they grow, making weight a more reliable metric than count. Due to its daily fluctuations and the primary focus on nutrient generation for plants, stocking density itself is not typically used as the primary operational management metric in iAVs. However, it remains a critical factor influencing fish growth, plant growth, and overall water quality within the system (Ani et al., 2021).

It is important to point out that the appropriate fish biomass (and thus stocking density) should ultimately be determined by the daily feed amount required to meet the nutritional requirements of the plants (Rocha 2025).

Dr. Mark McMurtry defines stocking density as the initial biomass of fish per cubic meter of water at the time of stocking, calculated using the formula:

Stocking Density = (N × Pmi) / m³
N: Number of fish
Pmi: Initial average weight of each fish (in kilograms or pounds)

As the fish grow, the standing density (the prevailing biomass per unit volume) increases daily. By harvest time, the harvest density can be calculated as:

Harvest Density = (N × Pmf) / m³
Pmf: Final average weight of each fish

Optimal Stocking Densities and Consequences

Optimal stocking densities depend on species-specific requirements and environmental conditions. For example, Dr. McMurtry’s research suggests that a harvest density of 30 kg/m ³ is practical for most Cichlid species under well-managed conditions. Exceeding optimal densities – such as attempting 50 kg/m ³ – can lead to slower growth rates due to overcrowding stress.

Furthermore, high stocking densities significantly impact water quality. Parameters like dissolved oxygen (DO), pH, and nitrogenous toxicants (TAN, NO₂-N, NO₃-N) are directly influenced by the fish biomass (Ani et al., 2021). Higher densities increase oxygen demand due to greater fish respiration and organic waste accumulation. This can lead to reduced DO, lower pH, and elevated levels of toxic nitrogen compounds if nutrient budgeting and system filtration capacity are insufficient (Ani et al., 2021; Nuwansi et al., 2021). Low DO and potentially high free CO₂ levels cause stress in fish, impairing their oxygen uptake and overall health (Hargreaves and Brunson, 1996). This degraded water quality, particularly the accumulation of nitrogenous waste, further inhibits fish growth (Trang et al., 2010). Increased crowding associated with high densities can also reduce fish growth rates and feed conversion efficiency, negatively impacting weight gain, specific growth rate, and feed conversion ratio (Ani et al., 2021; Nuwansi et al., 2021). In mixed-sex populations, higher densities may also result in increased aggression, particularly from males toward females.

Conversely, adequate plant mass plays a crucial role in filtering the water by absorbing nutrients, thereby improving conditions for fish growth and overall system health (Verma et al., 2020). Therefore, determining the optimal stocking density in aquaponics requires careful balancing of fish requirements, water quality maintenance, nutrient cycling dynamics, and the productivity of both fish and plants (Nuwansi et al., 2021).

Monitoring Fish Growth and Feeding Efficiency

Since fish biomass changes over time, monitoring food consumption provides a practical way to assess growth and health. Overfeeding should be avoided as it can degrade water quality by increasing ammonia levels and reducing dissolved oxygen availability.

Two key metrics used to evaluate feeding efficiency and growth are:

Feed Conversion Ratio (FCR)

This measures the efficiency with which feed is converted into fish biomass.

FCR = Weight of feed given / Increase in biomass (Pmf – Pmi)

Specific Growth Rate (SGR)

This calculates the percentage increase in individual fish weight over time.

SGR = [(ln Pmf – ln Pmi) / (t2 – t1)] × 100
Pmf: Final average individual weight
Pmi: Initial average individual weight
(t2 – t1): Elapsed time in days
ln: Natural logarithm (base e)

Ethical and Practical Limits

While it is technically possible to achieve higher stocking densities than those recommended, doing so poses significant risks to both productivity and animal welfare. Overcrowding increases stress on the fish, raises the likelihood of water quality failures, and heightens vulnerability to disease outbreaks. These issues can lead to catastrophic system failures.

High fish stocking densities directly impact water quality as well as other welfare issues such as fin damage, disease transmission and social behaviour (e.g., competition) (Yavauzcan 2017).

For ethical and practical reasons, it is advisable to prioritize metrics such as FCR and SGR over simply maximizing stocking density. These metrics provide a more comprehensive understanding of system efficiency and fish health.

Related Metrics for Plant Growth

In iAVs, plant growth is another critical component tied to nutrient availability from fish waste. A related metric for plants is the Relative Growth Rate (RGR):

RGR = (ln W2 – ln W1) / (t2 – t1)
W2: Tissue dry weight at time 2
W1: Tissue dry weight at time 1
(t2 – t1): Elapsed time in days

This metric helps evaluate plant growth efficiency relative to nutrient inputs from aquaculture.

By carefully monitoring fish biomass, feeding practices, and growth rates while adhering to ethical limits, practitioners can optimize system performance while safeguarding both animal welfare and environmental sustainability.

32.2. Yield

In a system with a 1:2 fish-to-biofilter volume ratio and a stocking density of 80 fish per cubic meter (2.27 fish per cubic foot), annual production can reach approximately 60 kg/m³ (3.74 lb/ft³). A setup with a 1:3 ratio and a stocking density of 120 fish per cubic meter (3.40 fish per cubic foot) can yield up to 90 kg/m³ annually (5.62 lb/ft³).

During research in the 1980s, yields ranged from 50–70 kg/m³/year (3.12–4.37 lb/ft³/year), depending on tank-to-biofilter ratios, demonstrating iAVs’ scalability for commercial applications. In one USDA-funded facility, novice operators achieved yields of 133 kg/m³/year (8.31 lb/ft³/year) under suboptimal conditions.

32.2.1. Managing Fungal Infections and Related Health Concerns

32.2.1.1. Understanding the Role of Salt

In iAVs, plant production takes precedence over aquaculture management. While salt is sometimes recommended in traditional aquaponic systems to combat fungal infections, this practice can harm plants in iAVs by increasing Total Dissolved Solids (TDS), leading to osmotic stress and nutrient absorption issues. Leafy greens and sensitive crops are particularly vulnerable to salt damage.

Sodium competes with essential nutrients like potassium and iron, potentially causing nutrient lockout, which impairs plant growth and health. Since commercial fish feed already contains sodium, adding more can exacerbate these problems.

If treatment is necessary, use a separate quarantine system to avoid compromising the beneficial microorganisms in the sand filter or affecting plant health.

32.2.1.2. Quarantine Procedures for New Fish

Quarantining new fish before introducing them into an iAVs is crucial to prevent disease introduction:

Quarantine Tank Setup: Use a tank proportional to the size and number of fish, equipped with air stones for oxygenation and proper filtration.

Salt Treatment:

General health: 1-2 grams per liter (g/L).
“Ich” treatment: Up to 5 ppt over several days.
Severe fungal infections: Short-term dips at up to 10 ppt for 2-6 hours (monitor closely).
Duration: Quarantine lasts from a few hours to two weeks, depending on the source and health status of the fish.

Observe fish for signs of illness like lesions or abnormal behavior during quarantine and ensure water quality remains stable.

32.2.1.3. Preventing Fungal Issues in iAVs

Fungal issues are rare in well-managed iAVs but may indicate design or management flaws:

Stocking Density: Avoid overcrowding to reduce stress.
Plant Area: Ensure sufficient plant area to handle nutrient loads.
Feed Quality: Use high-quality feed and remove uneaten food promptly.
System Maintenance: Regularly clean air stones and pumps.
Liner Installation: Ensure proper liner installation to prevent debris buildup.
Contamination Prevention: Protect tanks from external contaminants like bird or rodent droppings.
Water Quality: Regularly test parameters such as pH, ammonia, nitrite, and nitrate levels to ensure they are within acceptable ranges.

By following these guidelines, you can maintain a healthy environment for both fish and plants in your iAVs.

32.3. Growth Rate

In iAVs research, the average weight of Tilapia after 103 days ranged between 205 and 230 grams (0.45 – 0.51 lbs). By the end of four months, some fish reached 250 grams (0.55 lbs). Over the next 85 days, with culling, the remaining fish were expected to weigh between 405 and 455 grams (0.89 – 1 lb). In the subsequent 102 days, continued culling led to weights of 650 to 715 grams (1.43 – 1.58 lbs).

It’s important to note that maximizing growth was not the primary goal of the study. The fish experienced mild stress once a month when they were caught, sedated, weighed, and then allowed to recuperate in a separate tank before being returned to their original environment. This likely slowed their growth rate.

Without such disturbances, and with aggressive feeding and a bioactive filter, Tilapia could potentially reach 250 grams (0.55 lbs) in just three months.

Note: The growth rate of Tilapia can vary significantly due to factors such as water temperature, feed quality, and genetics, so these figures are estimates.

32.4. Energy Needs & Efficiency in Fish Growth

Fish derive energy for daily activities and bodily functions from the oxidation of organic components in their feed. This energy supports basic activities like breathing and swimming, as well as tissue growth and repair. The energy requirements vary based on physiological state and environmental conditions, with additional energy needed for immune responses when fish face suboptimal conditions or pathogens.

Fish convert feed into biomass more efficiently than terrestrial mammals for several reasons:

Poikilothermy: Their body temperature matches the surrounding water, eliminating the need for energy expenditure on thermoregulation.
Aquatic environment: Water buoyancy reduces the need for a strong skeletal structure to support body weight against gravity.
Nitrogenous waste elimination: Fish excrete ammonia directly through their gills, a process that is less energy-intensive than urea or uric acid production in mammals or birds.

The distribution of ingested energy among physiological processes varies based on living conditions. Under stress (e.g., poor lighting or low water quality), fish may use up to 40% of their feed energy just to cope with stress, leaving only about 30% for growth. In optimal conditions, up to 40% of energy intake can be allocated toward growth. This underscores the importance of providing optimal living conditions for economic viability.

Overfeeding should be avoided as it degrades water quality and leads to nutrient imbalances from uneaten food.

In well-managed iAVs, Feed Conversion Ratios (FCR) typically range from 1.2:1 to 1.5:1, meaning that 1.2-1.5 kg of feed produces 1 kg of fish biomass – significantly more efficient than traditional aquaculture systems. For comparison, FCRs in traditional aquaponic systems like those at the University of the Virgin Islands (UVI) are reported between 1.6:1 and 2:1 for Tilapia.

This improved efficiency in iAVs is attributed to its unique sand-based biofilter, which enhances nutrient recycling and water quality, promoting better fish growth with less feed input.

32.5. Welfare

Fluctuating water levels in the fish tank during iAVs irrigation cycles serve as a form of environmental enrichment by mimicking natural tidal conditions, offering fish a dynamic habitat that promotes adaptability, natural behaviors, and reduced stress.

Environmental Enrichment

Environmental enrichment refers to modifications in the habitat that stimulate natural behaviors, improve physiological health, and reduce stress in fish.

In iAVs, the fluctuating water levels in the fish tank during irrigation cycles can serve as a form of enrichment by mimicking natural conditions such as tidal changes or seasonal water variations in the wild.

Environmental enrichment (EE) enhances the welfare of captive fish by incorporating physical stimuli, thereby improving their health, behavior, and adaptability while reducing stress and aggression.

Behavioral Stimulation

Studies have shown that fish exposed to variable environmental conditions are less prone to stress and exhibit more natural behaviors compared to those kept in static environments. Periodic reductions in water levels during irrigation cycles create a dynamic habitat that encourages fish to explore different water depths, adjust their swimming patterns, and engage in social interactions. This can reduce boredom and stereotypic behaviors often observed in aquaculture systems with constant water levels.

Welfare Benefits

Fluctuating water levels during irrigation also align with growing concerns about animal welfare in aquaculture. Welfare legislation in some regions, such as the European Union, emphasizes the importance of providing conditions that allow farmed fish to exhibit natural behaviors. By integrating controlled water level changes into iAVs operations, practitioners can meet these welfare standards while maintaining system functionality.

Environmental enrichment (EE) – a practice that enhances the complexity of captive environments by integrating physical, cognitive, social, or sensory stimuli – has been increasingly recognized as essential to improving fish welfare in aquaculture and research systems. Studies consistently demonstrate that enrichment positively influences fish physiology, behavior, and overall health, resulting in reduced stress and aggression, increased disease resistance, and improved survival rates (Näslund and Johnsson, 2016; Zhang et al., 2022; Arechavala-Lopez et al., 2019). These benefits extend to increased welfare indices such as growth performance, better adaptation to stressors, and enhanced mental states, meeting not only basic survival needs but also facilitating behaviors typical of wild fish (Brydges and Braithwaite, 2009; Fife-Cook and Franks, 2019).

Growing evidence highlights the cognitive and emotional capacities of fish, including the ability to experience pain, stress, and emotions like fear and frustration (Kittilsen, 2013; Sneddon and Brown, 2020), making EE a crucial management tool to meet their ethological and psychological needs. Research also reveals fish possess memory systems enabling learning and behavioral adaptation, which environmental enrichment can effectively stimulate (Gerlai, 2017; Salwiczek and Bshary, 2011). Despite these findings, a significant knowledge gap exists regarding the application of EE on commercial fish farms, where practical trade-offs like maintenance costs and labor remain concerns (Gerber et al., 2015).

Legislation and public demand for humane farming practices are driving the adoption of strategies like EE, as enhanced fish welfare aligns with improved economic outcomes, such as higher-quality products, reduced mortality rates, and positive consumer perception (Ashley, 2007; Martins et al., 2012; Yildiz et al., 2017). Research specifically calls for routine implementation of EE in management practices, particularly for high-value or long-term captive species, to mitigate unavoidable stressors such as husbandry procedures (Cabrera-Álvarez et al., 2024; Zhang et al., 2023).

In aquaponics, integrating EE alongside strategies like using soil in hydroponic sections further supports fish welfare and sustainability (Fruscella et al., 2021). Optimal aquaponic systems not only promote fish growth but also ensure health and welfare, which are critical to maintaining product quality and consumer trust (Yildiz et al., 2017). Therefore, EE is increasingly recognized as a foundational element for advancing fish welfare across research, aquaculture, and aquaponics sectors, bridging ethical considerations with ecological and economic benefits.

33. Fish Feed Science:

33.1. The Benefits of Fish-Processed Nutrients

While fish typically assimilate only 30-40% of their feed into biomass, the remaining 60-70% is expelled as nutrient-rich waste that presents significant advantages over synthetic fertilizers.

This effluent possesses a distinct nutrient profile optimized for plant growth. The gut microbiome of fish plays a vital role in this process, mediating the biotransformation of feed components into a complex suite of organic compounds. This includes essential amino acids, lipids, vitamins, enzymes (such as amylase, protease, and lipase), and phytohormones (like auxins and gibberellins), all of which contribute to enhanced plant physiology and development. iAVs is specifically designed to capture and utilize both the dissolved and solid waste fractions of fish effluent, maximizing nutrient recovery and minimizing waste.

A primary benefit of fish-mediated nutrient processing is the generation of amino acids in a directly absorbable form for plants. This facilitates more efficient nitrogen utilization compared to inorganic nitrogen sources, minimizing plant energy expenditure on nutrient conversion and promoting accelerated growth and increased productivity. When plants uptake amino acids directly, they are accessing a source of nitrogen that is independent of the nitrification process.

Furthermore, the enzymatic activity within fish waste aids in the breakdown of complex organic molecules into simpler, more readily available forms, enhancing overall nutrient uptake efficiency. This efficient nutrient delivery contributes to the high yields achieved in iAVs without supplementary fertilizers.

Phytohormones present in fish waste, including auxins and gibberellins, act as natural plant growth regulators. They stimulate cellular division and elongation, potentially leading to improved crop yields and enhanced plant vigor. Moreover, the organic matrix of fish waste, including the solid components, more closely emulates the complex environment of natural soil compared to the sterile conditions of hydroponic systems. The diverse microbial community within the system contributes to a more resilient and biologically active rhizosphere, fostering a robust growing environment. The effective management and utilization of solid waste in iAVs contribute significantly to this robust and balanced ecosystem.

33.2. Understanding Fish Feed Composition

33.2.1. Proximate composition of fish feeds and essential nutrients

Over 50 years ago, researchers began studying fish diets by analyzing what fish naturally consume. For example, trout, being carnivorous, typically eat a diet containing approximately 50% protein, 15% fat, 8% fiber, and 10% minerals (ash). This protein content is notably higher than that of land mammals. Since then, efforts have focused on determining the optimal balance of protein, carbohydrates, fats, fiber, vitamins, and minerals for farmed fish.

Protein is a key component of fish feed, composed of amino acids essential for growth. Critical amino acids such as lysine and methionine are necessary for protein synthesis. Even if overall protein levels are sufficient, a deficiency in these amino acids can hinder growth. In iAVs, the protein in fish feed is particularly important because it contributes to nitrogen waste that plants can later utilize. Recent research has shown that optimizing the amino acid profile in fish feed can improve nitrogen uptake by plants and reduce nitrogen losses through volatilization or leaching.

Carbohydrates, primarily in the form of glucose, provide energy for fish. Starch, the most common carbohydrate in fish feed, serves as both an energy source and a binder for feed pellets. Recent innovations in feed formulations include alternative protein sources such as insect meal and microalgae. These alternatives reduce reliance on traditional fishmeal, offering more sustainable options, even for carnivorous species. However, this shift can introduce higher levels of plant-based carbohydrates into the diets of carnivorous fish, potentially altering their feeding behavior. While some studies suggest this change can positively impact growth and health, fishmeal remains a key protein ingredient in aquafeeds. Its desirable attributes, including a balanced profile of essential amino acids, high digestibility, palatability, and enhanced nutrient digestion and absorption, continue to make it a valuable component (Guedes et al., 2015; Jannathulla et al., 2019; Abdel-Tawwab et al., 2020). Alternative protein sources include rendered animal proteins (poultry by-product meal, meat and bone meal, blood meal, and krill meal), as well as plant-based options like soybean meal, groundnut oil cake, rapeseed meal, sunflower oil cake, cottonseed meal, and single-cell protein (Langeland et al., 2016; Hamidoghli et al., 2019; Hodar et al., 2020).

Initially, fish were fed direct by-products of fisheries and slaughterhouses, but various ingredients have replaced fish meal in aquaculture, provided they offer consistent quality, wide availability, lower prices, low fiber and nonstarch polysaccharide content, and minimal antinutritional elements (Jannathulla et al., 2019). Black soldier fly larvae (BSFL) meal has gained significant attention as a potential sustainable and high quality protein source in various industries, including aquaponics (Spranghers et al., 2017; Oteri et al., 2021).

Since black soldier fly larvae meal can be made on organic waste substrates, requires little energy and water inputs, and has high amounts of amino acids, it is a potential substitute for fishmeal and plant proteins in the diets of farmed fish (Huyben et al., 2019). Meal made from black soldier fly larvae is valued for its significant lipid content, balanced amino acid and high protein content. The larvae also contain essential vitamins, minerals, and bioactive compounds that contribute to their nutritional value as feed for both fish and plants (Surendra et al., 2016).

Incorporating black soldier fly larvae meal into the fish diet results in increased nutrient uptake by plants, leading to improved growth and yield (Lalander et al., 2013). Other insect based ingredients used to replace fish meal in aquaculture include common housefly, silkworm, house cricket termites and grasshoppers (Hodar et al., 2020; Tilami et al., 2020).

Fats are another essential nutrient in fish diets, providing energy and aiding in the storage of nutrients within organs. Cold-water species often require higher fat content (up to 15%), including essential omega-3 and omega-6 fatty acids. These fats also assist in the absorption of fat-soluble vitamins. To prevent spoilage during processing and storage, antioxidants are commonly added to high-fat diets. Incorporating polyunsaturated fatty acids (PUFAs) into feeds has been shown to improve both fish health and the nutritional quality of fillets for human consumption.

Crude fiber, though indigestible by fish, aids in gut movement. Ash, representing mineral content such as potassium, phosphorus, copper, and zinc, is also important. Excess minerals not absorbed by fish dissolve into the water – an advantage in iAVs where these minerals can be made available to plants.

A critical concept in fish nutrition is the digestible protein to digestible energy ratio (DP/DE). A balanced DP/DE ensures that fish stop eating once they have consumed enough energy from fats, carbohydrates, or proteins. Carbohydrates are typically the most accessible energy source, followed by fats and proteins. If the DP/DE is too high (excess protein relative to energy), fish may consume more protein than needed for growth; this excess is either metabolized for other functions or wasted. Conversely, if the DP/DE is too low, fish may not eat enough to support proper growth.

33.2.2. Fish Feed Used in iAVs Research

In the iAVs research, fish feed was intentionally formulated without vitamin and mineral supplementation to mimic the nutritional deficiencies often found in locally produced feeds used in regions like the African Sahel. These domestically sourced feeds frequently fall short of the quality standards observed in more developed markets, such as the United States and Europe. Kenya’s aquaculture sector, for example, grapples with significant hurdles related to fish feed quality, availability, and affordability (Munguti et al., 2021), hindering its overall development.

Additionally, many vitamins degrade quickly at room temperature, a typical storage condition for bulk feed. As a result, commercial growers purchasing fish feed in bulk might consider requesting a custom blend without these supplements.

The feed composition used in the iAVs research was verified by both the North Carolina Department of Agriculture and North Carolina State University’s Horticultural Science laboratories. The goal of this research was to analyze mineral nutrient concentration, balance, and accumulation in tomatoes grown in sand biofilters irrigated with aquaculture effluent.

Based on nutrient assimilation rates by tomatoes, adjusting the mineral content of fish feed could better meet plant requirements while still satisfying fish nutritional needs. For instance, the iAVs study titled “Effects of Biofilter/Rearing Tank Volume Ratios on Productivity of a Recirculating Fish/Vegetable Co-Culture System” found that while good plant growth occurred with low nutrient levels, potassium was notably low compared to nitrogen, calcium, and magnesium. Sea kelp could be added as a supplement to rectify this imbalance since it is rich in potassium and contains a wide range of micronutrients, trace elements, growth hormones (auxins, cytokinins, gibberellins), amino acids, and bioactive carbohydrates.

Zinc levels were higher than other trace nutrients; however, no signs of nutrient imbalance were observed in plant growth. It is important to note that the primary focus of this study was water quality related to biofilter culture tank ratios rather than nutrient management.

In another iAVs paper titled “Mineral Nutrient Concentration and Uptake of Tomato Irrigated with Recirculating Aquaculture Water as Influenced by Quantity of Fish Waste Products Supplied,” it was demonstrated that tomato growth could be sustained with low levels of nitrogen (N), phosphorus (P), and potassium (K), due to the continuous replenishment from recirculated aquaculture water. However, it was recommended that calcium content in fish feed be increased from 1.3% to approximately 3% dry weight to address observed deficiencies in tomatoes.

The same study showed that sulfur levels were high relative to N, P, and K in the fish effluent, suggesting that sulfur concentration in fish feed could be reduced from 1600 ppm to less than 800 ppm without negatively affecting either fish or tomato production.

Concentrations of iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) were high across all plant tissues but did not reach toxic levels. Zinc concentrations were particularly high across two experiments, indicating excess zinc in the fish feed. Reducing zinc content from 65 ppm to about 10 ppm would likely not harm either fish or plants.

Based on these findings, adjustments to fish feed composition are recommended as follows:

Increase nitrogen (N) by 5–10%
Decrease phosphorus (P) by 50%
Reduce potassium (K) by 30–50%
Increase calcium (Ca) by 200–300%
Maintain magnesium (Mg) and boron (B) at current levels
Reduce sulfur (S) by 50%
Cut iron (Fe), manganese (Mn), and copper (Cu) by 75%
Lower zinc (Zn) to 15% of current levels

33.2.3. Types of Commercial Fish Feeds

Intensive fish farming began in the late 1800s when governments bred fish to produce fingerlings for restocking lakes and rivers, addressing protein shortages and hunger. Initially, the focus was on species like salmon. As aquaculture expanded, farmers developed specialized feeds for fish raised in controlled environments. Early feeds included small organisms and slaughterhouse scraps, which were seasonally available. To overcome this limitation, leftover fish from ports were processed into fish meal, often mixed with plant proteins to create pellets. However, these feeds were prone to spoilage.

By the mid-20th century, dry granulated feeds became common. These feeds were nutritionally balanced and easier to store. Advances in extrusion technology improved feed buoyancy and durability in water.

Recently, there has been a shift towards sustainable and organic feeds, focusing on reducing the use of fish meal and oil by incorporating plant proteins like soybean meal. Alternative protein sources such as algae and insect meal are also being explored.

Fish waste provides essential nutrients for plants, including nitrogen, phosphorus, potassium, calcium, and trace elements like iron, zinc, and manganese. For optimal plant growth, it is advisable to test feed for nutrient content at a certified lab to ensure it meets plant requirements without compromising fish health.

33.2.4. Custom Fish Feed

33.2.4.1. DIY Fish Feed Preparation

It is generally recommended to use commercially available fish feeds specifically formulated for your fish species and life stages. These feeds are widely used in commercial aquaculture because they are designed to meet the precise nutritional requirements of fish and are often more cost-effective than preparing feed from scratch. Because fish waste quality is directly linked to diet quality and digestibility, using high-quality, easily digestible feeds is essential.

While creating your own fish feed can offer a more sustainable approach by reducing reliance on ocean-derived oils and proteins, it requires a strong understanding of fish nutrition and must be tailored to the specific fish species.

DIY feed can be rewarding, but it may not be practical or efficient in terms of time and resources for all iAVs operators. Commercial feeds offer a more convenient and reliable solution, allowing operators to focus on other aspects of iAVs management.

33.2.5. Custom Fish Feed Nutrient Composition

By adjusting feed formulations, it is possible to fine-tune the balance between nutrients excreted by fish and those absorbed by plants, enhancing the symbiotic relationship between the two. Incorporating bioavailable micronutrients into feed can improve plant nutrient uptake.

Manipulating the mineral content of fish diets influences nutrient accumulation (Seawright, 1993) and by adjusting the nutrient content of the feed, the proportions of nutrients excreted by fish can be made more similar to the proportions of nutrients needed by the plants (Seawright 1998) to help prevent nutrient deficiencies or toxicities.

Developing tailored fish feed compositions to meet specific needs can improve both sustainability and productivity. For instance, specialized feeds can be formulated to support the nutrient requirements during different stages of plant development. One type of feed might be designed to optimize plant growth during the vegetative stage, while another could be crafted to enhance nutrient availability during the fruiting stage.

Multiple feed types could address specific needs, such as micronutrient supplementation or different stages of fish growth. For example, a feed containing copper and zinc could be used when deficiencies are visible or as part of a monthly regime to enhance growth while reducing the risks of toxic levels which would harm the fish.

33.2.6. Toxicity from Metal Supplements

Fish feeds high in copper and zinc should be avoided due to the risk of these metals accumulating in the system, potentially harming both fish and plants. If not absorbed by the fish, these metals persist in the ecosystem, with plants being the only removal mechanism. Other heavy metals, such as cadmium, may also accumulate in fish tissues, posing health risks. Excessive copper can impair fish gill function, while high zinc levels may interfere with plant nutrient uptake

Animal feed and feed materials can be contaminated with undesirable substances, which may originate from the environment and/or the production process. In the European Union (and most of the rest of the world) legislation is in place to manage the feed and feed material contamination (Adamse 2017).

One group of relevant contaminants in feed materials and animals feeds are certain heavy metals and elements. The heavy metals mercury, cadmium and lead and the metalloid arsenic are of concern because they are readily transferred through food chains, have toxic properties and are not known to serve any essential biological function (NRC Citation2005; Lopez-Alonso, Citation2012). Industrial and agricultural development has been largely responsible for pollution of the environment, although some contamination is also derived from natural geological sources (Rajaganapathy et al. Citation2011; Lopez-Alonso, Citation2012).

33.2.7. Testing

For those focused on commercial plant production, consider having your fish feed analyzed by a certified lab to ensure it contains essential plant nutrients in appropriate proportions. Nutrients should be in organic forms without salts or acids to safeguard fish health.

Regular monitoring of metal levels in fish feed is recommended in commercial operations to maintain ecosystem balance.. Although toxicity was not observed in iAVs research, it is important to monitor for potential accumulation from unbalanced inputs over time.

Carefully select feed ingredients to balance elemental inputs with outputs on an annual or biannual basis, as these elements remain in the ecosystem until harvested.

33.2.8. Nutrients

Copper (Cu) is a vital metal that plays a key role in various enzymes, especially those that help protect against oxidation. One important enzyme is the Cu/Zn superoxide dismutase (CuZnSOD). Additionally, copper is involved in energy production in cells, communication between nerve cells, the creation of collagen, and the production of melanin. Low levels of copper can lead to decreased feed efficiency and growth in animals, while too much copper can cause damage to the gills and harm the liver and kidneys (Watanabe 1997; Halver 2002; Tang 2023) .
Iron (Fe) plays a key role in transporting electrons, transferring oxygen, and supporting cellular respiration, especially in haemoglobin. While some iron can be absorbed through the gills, most is taken in through the intestine. A lack of iron can lead to anaemia, lower blood cell levels, and reduced iron in the bloodstream. On the other hand, getting too much iron can result in poor growth, inefficient use of food, increased mortality, and diarrhea (Watanabe 1997; Halver 2002; Bury 2003).
Manganese (Mn) is another important metal necessary for life, serving as a cofactor for essential enzymes that help develop the organic structure of bone. The enzyme Mn superoxide dismutase (MnSOD) helps prevent harmful reactions during oxidation processes. If there’s not enough manganese, the activity of MnSOD in fish tissues decreases, along with the levels of manganese, calcium, and sodium in their vertebrae. Too much manganese might harm the gut’s immune function, which is particularly important for marine fish to keep their ion levels balanced (Knox 1981; McDowell 1992; Jiang 2015).
Zinc (Zn) is a vital cofactor for many metabolic processes in fish and is a part of up to 20 different enzymes involved in breaking down fats, carbohydrates, and proteins. It is crucial for building structures like bones, skin, and scales, and it helps manage oxidative stress and immune responses, as well as playing a role in reproduction. Zinc also supports bone formation and mineralization by promoting bone-building cells and limiting bone breakdown. Therefore, a zinc deficiency can slow growth, cause cataracts, lead to damage of skin and fins, and result in dwarfism. Fish can absorb zinc through both their gills and their digestive system, but certain substances, like calcium, high salt levels, and acidic water, can interfere with zinc absorption. A zinc deficiency can negatively impact growth and production throughout a fish’s life cycle. However, the effects of excess zinc are not well-studied, with most research focusing on the survival of freshwater fish exposed to high levels of zinc in water. One major toxic effect of zinc is its interference with calcium absorption since calcium and zinc use the same pathways for absorption. When zinc levels are high, calcium intake can drop significantly (Hogstrand 1996; Watanabe 1997; Yamaguchi 1998; Alsop 1999; Hansen 2002; Halver 2002; Bury 2003; Zhang 2007; Prabhu 2014; Domínguez 2016).

33.3. Probiotics

Incorporating probiotics into fish feed can be a beneficial practice in iAVs management. Probiotics are essentially beneficial live microorganisms that, when administered adequately, can improve the health of the host – in this case, the fish. Their primary roles include enhancing gut health, improving nutrient absorption from feed, and modulating the gut microbiota, which can help protect fish from various pathogens (Abid et al., 2013; Merrifield and Carnevali, 2014; Vargas-Albores et al., 2021).

One common probiotic used effectively in aquaculture is the yeast Saccharomyces cerevisiae. Yeast is naturally rich in protein and contains components like β-glucans, which are known to act as immunostimulants, helping to boost the fish’s natural defenses (Mahdy et al., 2022). Studies have shown that supplementing fish diets (like Nile tilapia) with S. cerevisiae can lead to improved growth and overall health (Owatari et al., 2022; Mashhadizadeh et al., 2024; del Valle et al., 2023).

Furthermore, even non-viable (inanimate) yeast cells and their components, sometimes referred to as ‘postbiotics’, can provide benefits such as antioxidant and immunomodulatory effects (Salminen et al., 2021; Lynch et al., 2018).

While the primary target is fish health, some research suggests potential secondary benefits within the broader aquaponic system. Yeast products might act as biofertilizers, releasing nutrients beneficial for plants (Hernández-Fernández et al., 2021; El Ghit, 2020), and potentially aid in water quality management by assisting in ammonia decomposition (Khastini et al., 2019). Adding probiotic supplements, particularly during morning feeds, can thus contribute positively to both fish well-being and potentially the overall balance of the iAVs ecosystem.

33.3.1. Sustainability

Fish feed remains a contentious aspect of aquaculture. Commercially available pellets are the most practical and efficient option because they are easy to source, store, and use. However, these feeds often rely on fish protein derived from wild-caught fish, with fishmeal and oil content varying from 20-30% in shrimp feed to 50% in rainbow trout feed, and even up to 90% for black sea bass (Rust et al., 2011). For small-scale or artisanal aquaponics farmers aiming for organic or non-GMO certification (Wilson, 2006), reducing dependence on wild-fish-based or GMO-containing feeds is a key priority.

Alternative protein sources are being explored, including soy, barley concentrates, high-protein bacterial products from food and brewery waste, and insect protein (Nelson, 2010; Makkar et al., 2014). Notably, commercial production of insect protein is gaining traction, with successful projects in England (Fleming, 2016), South Africa (Byrne, 2017), and Europe, where insect protein is now legally permitted in animal feeds under EU regulations (Fernandez, 2016; PROteINSECT, 2016). A significant challenge, highlighted by companies like Matorka, is ensuring that alternative feeds maintain the nutritional quality of the aquaculture products. Omega oils in fatty fish, in particular, depend on their diet, and different species have distinct nutritional needs. To address this, feed manufacturers are creating the International Aquaculture Feed Formulation Database, a collaborative tool to compile species-specific requirements and explore sustainable feed alternatives (Orlowski, 2017). It is urgently needed to search for an alternative source for FM because the current production of FM is not sufficient to satisfy its increased demand for aquaculture production (Wu, Yu, et al., 2022b; Yu et al., 2022). Chicken by-product meal (CBM) mainly composed of chicken heads, bones, feathers, and feet is predominantly produced from chicken processing plants and considered as waste. CBM is inexpensive but contains an appreciable amount of crude protein and lipid. CBM containing relatively high crude protein, especially in essential amino acids including arginine, leucine, phenylalanine, and threonine (Ha et al., 2021) was tested as Abalone feed and can be highly regarded as a good substitute for FM. Similarly, Ha et al. (2021) reported that diets substituting FM up to 50% with CBM, which is the same CBM used in this study achieved comparable growth performance and feed utilization of olive flounder to fish fed a 65% FM-based diet when fish were fed with a 65% FM-based diet or one of the diets replacing 10%, 20%, 30%, 40%, and 50% FM with CBM for 8 weeks (DAI 2023).

34. Advanced Topics

34.1. Understanding Potential Yields

Yield estimates are based on optimal conditions and specific crop choices. Actual yields can vary depending on factors such as crop type, local climate, and farmer expertise. An optimized iAVs can achieve higher yields than those reported in the original research.

Operating an iAVs requires managerial skills that develop with experience. The system is user-friendly and resistant to rapid changes in water chemistry, which helps prevent long-term issues. Prior gardening or husbandry experience is highly recommended for operators.

First-time operators should receive basic training in aquaculture management, pest control, and water quality monitoring. As the system matures biologically and chemically over time – typically within three months of operation – it becomes more stable. After one year of continuous operation, the system is considered fully mature.

34.2. Understanding Ratio

In iAVs, the volume-to-volume (v:v) ratio of biofilters is crucial for maintaining water quality, particularly as aquaculture intensity increases. As fish density and feed rates double, the recommended biofilter volume, area, and the number of plants should also double to maintain effective filtration and nutrient absorption. This adjustment ensures that the biofilter can handle the increased nitrogenous waste produced by the higher fish biomass.

At high-density aquaculture levels, targeting production rates greater than 100 kg per cubic meter per year, v:v ratios could reach or exceed 1:4. This ratio depends on several factors, including the type of plant crops used and the management and scheduling techniques employed in the system.

34.3. Optimization

The iAVs research focused on maximizing production in a simple and efficient manner, particularly for use in arid regions of the developing world where such systems are most needed.

There are many opportunities for further research to optimize iAVs. In more advanced settings, technology could be used to monitor and regulate variables within Controlled Environment Agriculture (CEA) systems. This would include precise control of environmental factors, strategic crop rotations, custom feed formulations, high stocking densities, and enhanced disease and pest management strategies.

Sand substrate remains recommended for its proven effectiveness, with solid waste removal limited to the surface of the sand biofilter.

In any system, optimizing a single dependent variable at a time is crucial because each variable is influenced by various independent factors. When attempting to enhance a specific aspect of a system, such as fish growth rate, plant yield, total plant biomass, or energy consumption, the focus should be on one dependent variable at a time. This approach allows for more precise adjustments and improvements.

Optimization involves modifying independent variables to achieve the best possible outcome for the chosen dependent variable. In systems like aquaponics, overall optimization aims to balance fish growth rate and plant growth rate rather than focusing on biomass or the number of plants. It’s important to note that plant growth follows a sigmoidal pattern: it starts slowly, accelerates during mid-growth, and slows down as maturity approaches. This growth pattern varies significantly across different species.

By focusing on one dependent variable at a time and understanding the underlying growth patterns and constraints, systems can be optimized effectively to achieve desired outcomes.

34.4. Fish Tank: Advanced Design Principles and Dynamics

34.4.1. Creation of Elliptical Currents

The catenary shape, when paired with strategically placed air stones along the long axis of the tank, helps generate elliptical water currents. These currents promote vertical water turnover, evenly distribute oxygen throughout the tank, and also aid in directing ‘waste’ toward the pump or uptake manifold. Elliptical currents help sustain high oxygen levels in water, and also reduce stress on structural components by distributing weight more evenly.

By leveraging the natural physics of water flow and carefully designing the tank’s shape, this system ensures an optimized environment for fish health and plant growth while minimizing labor and maintenance efforts.

34.4.2. Influence of Tank Geometry on Waste Management and Water Quality

Fish tank geometry significantly affects solid ‘waste’ removal efficiency, dissolved oxygen (DO) distribution, and overall water circulation – all of which impact water quality, stocking density, and system yields. Traditional rectangular tanks are less effective due to their sharp corners and flat bottoms, leading to stagnant areas where ‘waste’ accumulates.

In contrast, tanks with a parabolic cross-section or an ovoid/rounded rectangle shape promote smoother water flow and more efficient ‘waste’ collection by minimizing dead zones. Intermediate designs featuring sloped (approximately 45-degree) or ‘V’-shaped bottoms with rounded-rectilinear plans also improve ‘waste’ extraction compared to rectangular tanks.

A recommended depth-to-width ratio for effective water turnover is approximately 1:1 but should not exceed 1:1.5. Proper placement of aeration devices like air stones or bubblers can further enhance DO distribution and water movement. To prevent ‘waste’ buildup, sharp corners should be minimized or eliminated from the tank design. Installing a grate or net above the ‘waste’ collection area can prevent fish from disturbing settled ‘waste’, improving water clarity.

Liners should be carefully installed to avoid folds or creases that could trap ‘waste’. In summary, optimizing tank geometry, ‘waste’ extraction mechanisms, and water flow dynamics is essential for maximizing fish tank performance in iAVs and ensuring a healthy aquatic environment.

34.4.3. Walkways and Accessibility

In-ground tanks can be installed beneath a walkway with removable sections, such as wooden decking or slatted panels (as pictured below). This design optimizes space utilization, reduces the need for extensive piping, and allows for convenient monitoring and access to the fish. The removable sections should be lightweight and easy to handle, but also strong enough to support the weight of people walking on it and that the removable sections fit securely to prevent accidents. The gaps between the slats or planks should be narrow enough to avoid tripping hazards but wide enough to allow sufficient light penetration for the fish. This setup is ideal for locations where space is limited, and efficient use of the available area is essential.

An example of tanks located beneath a walkway composed of operable sectional grates, which are panels of slats that open.

34.4.4. Management of Solids in iAVs

The term “solids”, or “waste” refers to fish excreta and uneaten feed, encompassing both settleable and suspended particulate matter.

The wastewater from the fish tank is characterized by the presence of diverse pollutants, primarily solid waste (such as feces and uneaten feed) and excess nutrients (including nitrogen and phosphorus). These pollutants, if not effectively managed, can result in production losses. The sources of these pollutants include overfeeding, fish feces, and metabolic waste products, notably ammonia (Maillard et al., 2005; Sharrer et al., 2007).

The nutrients in fish waste significantly boost plant yields, often making the plant component more economically valuable than the fish.

The presence of waste in the water where fish are reared is stressful for the fish, reducing their growth performance and exposing them to pathological risks (Rosenthal 1982; Klontz, 1985).

Suspended solids can directly harm fish by damaging or smothering gills and indirectly by providing habitats for pathogenic organisms (Braaten 1988; Liltved 1999). The decay of waste in water consumes oxygen, decreasing the oxygen available for fish (Welch 1992).

The primary sources of solid waste in aquaculture are uneaten feed and fish feces. This waste essentially consists of the feed components that fish cannot digest, and its quantity can be estimated based on the feed’s proximate composition and the fish’s digestive capabilities (Yavuzcan 2017). Fish metabolism releases significant soluble substances into the water, while the undigested, insoluble materials (feces and leftover feed) form fish sludge within the system’s effluent (Turcios and Papenbrock, 2014). The original feed composition and its digestibility therefore dictate the nutrient levels and types found in both the aquaculture water and the sludge. These nutrients are potentially available for plant absorption in aquaponic systems (Goddek et al., 2018), with the sludge being particularly rich, retaining most required plant macronutrients and micronutrients (Strauch et al., 2018).

A key difference between iAVs and traditional aquaponics lies in the handling of solid fish waste (sludge). While iAVs is designed to fully utilize this nutrient-rich waste, traditional systems often remove the fish solids (Gao 2021), recovering nutrients primarily from the liquid effluent (Khiari et al., 2019). This removal of nutrient-rich solids can lead to significant nutrient loss, potentially discarding up to 40% of the nutrients originally present in the fish feed (Yogev et al., 2016; Eck et al., 2019).

Consequently, the dissolved nutrients remaining in the aquaculture effluent after solids removal are often insufficient on their own to meet the full nutrient requirements of the plants, particularly for demanding fruiting crops (Anjana et al., 2007; Madady 2025; Nicoletto et al., 2018; Yep and Zheng, 2021; Tsoumalakou et al., 2022). Achieving commercially acceptable yields in such systems often necessitates adding supplemental fertilizers (Lewis et al., 1978, 1981; Rakocy, 1989; Goddek et al., 2019; Ezziddine, 2020; Panana, 2021).

Maintaining optimal water quality is paramount, and efficient solids management plays a critical role in achieving this goal. The accumulation of solid waste, including uneaten feed and fish feces, can trigger negative effects, compromising both water quality and fish welfare (Yildiz et al., 2017).

Effective solids removal improves water quality by reducing the decomposition of organic matter, which consumes dissolved oxygen and releases ammonia – a toxic compound that can stress or kill fish if not properly managed (Masser et al., 1999; Yildiz et al., 2017). Solids removal also enhances water clarity, important for fish visibility and feed uptake, and limits bacterial growth due to reduced organic material (Yildiz et al., 2017).

Proper solids management directly benefits fish health and welfare. Suspended solids can damage fish gills, leading to respiratory stress (Hughes & Morgan, 1973; Newcombe & MacDonald, 1991; Yildiz et al., 2017). Accumulation of solids can also damage sensitive tissues and facilitate pathogenic growth (Yildiz et al., 2017).

By minimizing suspended solids, the risk of these issues is significantly reduced, promoting healthier fish populations. Clear water allows for better observation of fish, facilitating early detection of health problems and timely intervention (Yildiz et al., 2017). Efficient solids management is fundamental for maintaining water quality, ensuring fish welfare, and maximizing system productivity (Yildiz et al., 2017).

A significant factor contributing to the failure of traditional aquaponic systems is inadequate solid waste removal. A 2015 study indicated that over 85% of system failures could be attributed to this issue (Thorarinsdottir, 2015).

Solid waste accumulation negatively impacts fish health, plant growth, and the substrate environment. Plant roots can become clogged, hindering nutrient uptake, while organic matter decomposition increases oxygen demand and creates harmful compounds like hydrogen sulfide and methane (Thorarinsdottir, 2015).

In iAVs, waste is deposited on the sand surface, keeping plant roots and lower sand layers clear of organic matter, preventing clogging. The catenary-shaped tank design in iAVs plays a key role in waste management. Its curved bottom concentrates solids at the lowest point, where the pump intake efficiently removes them. The irrigation schedule is synchronized with the feeding schedule for maximum efficiency so that after the last feed of the day (no later than 2pm) the entire volume of the tank will be irrigated through the sand biofilter.

34.4.5. Water Use: Transpiration and Biomass Incorporation

In iAVs, most water loss occurs through transpiration, which plays a critical role in:

Plant growth
Maintaining turgor pressure
Nutrient transport
Temperature regulation

Transpiration refers to the movement of water through plants and its evaporation from leaves and other aerial parts. Additionally, water is incorporated into plant tissues, contributing to biomass production. These processes are essential to the system’s operation and should not be viewed as wasteful losses.

Transpiration rates vary based on plant species, growth stage, and environmental conditions. By managing factors such as temperature, humidity, and air circulation within the iAVs environment, transpiration efficiency can be optimized, improving overall water-use efficiency.

This table compares the average daily water additions across various volume ratios in iAVs. The data highlights the system’s efficiency, with daily water losses ranging from 1.54% to 3.26% of total system capacity, depending on the volume ratio. These results demonstrate the minimal water input required to maintain optimal plant and fish production.

For fruiting species like tomatoes in arid to temperate climates, a given volume of water can be reused between 120 to 300 times in iAVs, compared to just 1 to 3 times in other recirculating systems. This enhanced water reuse results in a 100-fold increase in fish yield per unit of water consumed.

In addition to fish production, iAVs also produce vegetable crops, which consist of 85% to 95% water by weight. The water incorporated into the plant biomass contributes directly to food production and income generation, rather than being considered a loss.

The table below compares iAVs performance with the best available data from the University of the Virgin Islands (UVI). The Boone Mora 1992 (USDA) data was collected using a 1:1 volume ratio (or 1:3 v:a), while subsequent Mora data reflects a 1:2.4 ratio, corresponding to fish growth and feed rates.

This table compares the water reuse efficiency of iAVs with that of the University of the Virgin Islands (UVI) deep-water culture (DWC) system. iAVs is shown to be at least 13 times more water-efficient than UVI’s system, with a significantly lower daily water requirement and higher reuse potential. This efficiency translates into a greater yield of both fish and vegetables per unit of water used.

iAVs is at least 13 times more water-efficient than the University of the Virgin Islands (UVI) deep water culture (DWC) system. This estimate is based on UVI’s reported water usage data, though their study did not account for rainwater added to their unsheltered, outdoor system in a tropical climate. Given this environment, the actual water input for the UVI system was likely 3 to 4 times higher than reported.

For example, if UVI’s reported daily water usage was 100 liters (26.4 gallons), the actual amount, including unreported rainwater, could be as high as 300 to 400 liters (79.3 to 105.7 gallons). In comparison, an iAVs of the same size would require only 7.7 to 10.3 liters (2 to 2.7 gallons) per day, highlighting its superior water efficiency.

This table illustrates the relationship between water input and yield in an iAVs system. For every liter of water used, the system can produce approximately 6 grams of fresh-weight fish and up to 400 grams of fresh-weight vegetables, depending on species. These figures underscore the high productivity and sustainability of iAVs in terms of both aquaculture and horticulture.

Considering annual water losses due to evapotranspiration, biomass incorporation (food production), and seepage, the iAVs method can produce significant yields with minimal water consumption. For every liter (0.26 gallons) of water input, the system can yield approximately:

6 grams (0.21 ounces) of fresh weight (FW) fish
17 grams (0.60 ounces) of dry weight (DW) vegetables

The fresh weight of vegetables can vary between 150 and 400 grams (5.29 to 14.11 ounces) per liter, depending on the specific plant species and its water content.

In non-optimized experimental trials combining tilapia and tomato cultivation, iAVs achieved yields of 0.7 grams (0.025 ounces) of dry weight protein and 7,000 calories per liter (0.26 gallons) of water used.

34.5. Side Drainage in Longer Biofilters

For biofilters exceeding 5-6 meters in length, consider implementing the slit drain on the side walls. This allows drainage into a gutter sloped towards a tank, canal, pond, or sump, effectively reducing the need to increase sand depth along the slope.

Spreading out the drainage exit path reduces the force of water on the sand grains or any other materials within the bed. The water flow exiting the slit can be directed in several ways:

Directly into a tank or sump.
Into a cascade aerator for oxygenation.
Through a semi-circular gutter (e.g., a longitudinally sliced PVC pipe or a lined wooden V) for directed flow.

This setup allows for flexibility in water management and can be adapted to suit various needs and configurations.

34.6. Enhancing Drainage in Larger Biofilters

For optimal performance, complete drainage of the bed is required. When you have a large biofilter, it’s a good idea to use a type of pipe called an agriculture drainage pipe. This pipe contains slots to increase drainage and needs to have a permeable sleeve or sock to keep the sand out. Where you place this pipe depends on how big and wide your biofilter is.

Beds up to 3-4 meters (9.8-13.1 feet) long: May not require additional drainage assistance if the bottom plane is properly sloped towards the exit, though they may still benefit from it.
Beds 4-6 meters (13.1-19.7 feet) long: Will likely benefit from additional drainage assistance.
Beds 6 meters (19.7 feet) or longer: WILL require additional drainage assistance.

If your biofilter is 3 meters or more in length, and between 1 and 2 meters wide, you should place the drain pipe in the middle, running lengthwise, towards the drainage point.

For beds 1 to 1.5 meters in width, a single central drainage line is sufficient. If beds are wider than this, install two or more parallel drainage lines spaced approximately 2 meters apart (as many as needed). While we recommend adhering to the 1 to 1.5 meter width for optimal performance, this drainage configuration can accommodate wider beds if necessary.

If your biofilter is on the ground, you can also place the drainage pipe(s) into a half-round channel below the surface. You can also create a slight slope from the edges of the bed towards the central drain line. In all cases, you should place an impermeable liner material under the drainage line(s).

When using drainage lines, these need (do) not penetrate the end wall or cap of the bed. Merely terminate the lines into a small mound of pea gravel covering the drain line exit and also covering the bottom slit (exit) of the drain end wall. This pea gravel covers the slit that is cut into the liner at the bottom of the end wall (NOT cut into the bottom plane of the bed).

34.7. Effects on Plants

pH plays a critical role in nutrient absorption by plants. When the pH exceeds 7.0 (alkaline), nutrient availability decreases as essential elements transform into forms that plants cannot easily absorb. Conversely, slightly lower pH levels generally increase the availability of metals, often in more soluble or ionic forms, which can create an optimal environment for plant growth with increased iron absorption (Marschener 2012: Wang 2023).

Optimal nutrient uptake generally occurs within the slightly acidic range identified for iAVs (around pH 6.4 ± 0.4), allowing plants to efficiently absorb nutrients from both water and the biofilter, promoting healthy growth and maximizing productivity. Deviations from this range can lead to reduced nutrient availability or nutrient lockout, where nutrients are present but inaccessible to plants.

For example:

Iron (Fe): Becomes significantly less soluble above pH 7, leading to potential deficiencies such as chlorosis (yellowing between veins of young leaves). As noted, absorption is best between pH 5.5-6.0 (Lennard and Goddek, 2019; Maucieri et al., 2019b).
Manganese (Mn): Its availability decreases at high pH, leading to symptoms similar to iron deficiency.
Phosphorus (P): When the pH increases above 7.0, most of the dissolved phosphorus can react with calcium to form calcium phosphate (Sahubawa 2025), resulting in stunted growth and dark green or purplish leaves.

Since the primary product by weight, nutritional value (excluding lettuce), market availability, and economic value from an iAVs operation is the vegetable crop(s), it is recommended that the ‘system’ pH be maintained below 7.0, with pH 6.4 to 6.8 being a general range acceptable for adequate mineral nutrition of every essential element in virtually all vegetable crops. Therefore, it is suggested to grow (choose, select) a fish species that either prefers or is generally/largely tolerant of this pH range.

In an iAVs, when growing tilapia and tomato (or most other common vegetable garden species), a pH of between 6.4 and 6.6 (+/- 0.2) is ‘basically ideal’ in facilitating adequate nutrition of every plant essential element.

34.8. Effects on Fish

The best pH level for raising a specific fish species is often a topic of discussion. Most fish can tolerate a range of pH levels, although some are more adaptable than others. Fish can adjust their body chemistry to cope with pH fluctuations, but this adaptation consumes energy that would otherwise support growth. When fish are stressed by pH changes, they may become more vulnerable to diseases and parasites. While a less-than-ideal pH doesn’t usually harm fish neurologically, it can slow their growth as the pH moves closer to the extremes of their preferred range.

It’s important to remember that pH interacts with other water quality factors, like temperature and dissolved oxygen, all of which contribute to the health and growth of fish. Water temperature and pH significantly affect the form of ammonia present in the water (Lim and Webster, 2006). At higher pH levels (above 7.0), ammonia becomes more toxic due to its conversion into un-ionized ammonia (NH₃), which is highly harmful to fish (Collins 1975) and toxic at levels above 0.05 mg/L (Francis-Floyd and Watson, 1996). For example, at 22°C, the un-ionized ammonia fraction is 0.46% and 4.4% of Total Ammonia Nitrogen (TAN) for pH 7.0 and 8.0, respectively (Francis-Floyd and Watson, 1996). This represents nearly a 10-fold increase in un-ionized ammonia substrate for the nitrification reaction as pH increases one unit (Francis-Floyd and Watson, 1996). In contrast, at lower pH levels, such as around 6.4, ammonia primarily exists as ammonium (NH₄⁺), a far less toxic form, reducing the risk of ammonia poisoning.

pH Tolerance of Specific Fish Species:

Tilapia: When Tilapia is the cultivated fish species, pH is not a particular concern since these species have a wide tolerance range. They can thrive (if slowly acclimated) to as low as pH 5.0. Tilapia are not only extremely tolerant to a wide-range in pH, but also to every other water quality parameter as well. Tilapia’s ideal range is 6.5 to 8.0, allowing them to live comfortably at the lower end without compromising health or growth. The recommended pH range for tilapia is 6.0 to 9.0 (Popma and Masser,1999).
Jade Perch: Jade perch are adaptable to a wide pH range, specifically from 6 to 8.5, though the system’s pH is typically maintained at levels that support plant health. Fortunately, these species tolerate the slightly acidic conditions favored by plants.
Barramundi: Barramundi ‘prefer’ pH 7.0 to 8.5 but are known to acclimate to pH 6.6 (and perhaps lower).
Bluegill: Bluegill will grow well down to pH 6.5 and survive in as low as pH 4.0 (other prevailing factors being non-limiting).

Image Credit: Huang, Ju-Chang & Shang, Chii. (2007). Air Stripping. 10.1007/978-1-59745-029-4_2. This chemical equation illustrates the conversion of ammonia (NH₃) to ammonium (NH₄⁺) in water, a key process in iAVs. At a pH of 6.4, ammonia reacts with hydrogen ions to form ammonium, which is less toxic to fish and serves as an important nitrogen source for plants.

The Intermittent Irrigation Cycle

In iAVs, bacteria operate in a soil-based environment that undergoes periodic flooding and draining. This cycle mimics natural soil conditions, exposing bacteria to both water and air phases. The combination of the sand’s massive specific surface area for bacterial colonization and the “turbo-charged” forced recharge of oxygen creates highly favorable conditions for nitrification. As a result, nitrification has not been found to be a limiting factor in iAVs operations, and ammonia does not accumulate to levels toxic to fish.

Nitrogen Utilization by Plants

It’s worth noting that for many vegetable species, a combination of aqueous Total Ammonia Nitrogen (TAN) and nitrate (NO₃⁻) is actually the preferred nitrogen source, with the optimal ratio varying by plant species. This natural preference aligns well with the nitrogen transformation processes occurring within properly functioning iAVs systems.

The extensive surface area for biofilm development in iAVs allows for adequate nitrification even at pH levels as low as 5.0, at least over periods of several weeks, making these systems remarkably resilient to pH fluctuations while maintaining efficient nutrient cycling.

. Once plants are established (typically after about five weeks) and the rate of nutrient input (from fish feed) matches the rate of nutrient uptake by the plants, the pH naturally stabilizes around the optimal 6.4 range without needing external buffers (Rakocy 1989b). This inherent stability simplifies management and reduces operational costs.

34.9. Alternative Pumping Mechanisms

Several alternative pumping mechanisms can be used in iAVs:

Animal-Powered Pumps: Treadle or ox-driven pumps can provide sustainable power for larger systems but require initial investment.

A treadle pump being demonstrated in Malawi.. Babakathy, Public domain, via Wikimedia Commons

Manual Water Transfer (Shadoof): A simple bucket-and-rope method suitable for small systems but impractical on a larger scale.

Human-Powered Pumps: Mechanical hand-operated pumps work well for small-scale systems but require close monitoring.

Details of a Hand Pump. Manco Capac, CC BY-SA 3.0, via Wikimedia Commons.

Solar-PV Pumps: Solar-powered pumps are ideal for off-grid setups but may need battery storage in areas with limited sunlight.

Windmills: Wind-powered systems can be effective in areas with consistent wind patterns.

Rope Pumps: Manually operated rope pumps are cost-effective but limited in capacity.

Rope pump schematic. Xofc, CC BY-SA 3.0, via Wikimedia Commons.

34.10. Solids Lifting Outlet

A solids lifting outlet (SLO) is often used in traditional aquaponic systems to remove solid waste from fish tanks. It uses a pipe system to lift settled solids from the tank bottom.

In an iAVs, using a Solids Lifting Overflow (SLO) is not recommended. Instead, the water pump plays a crucial role in breaking down solid fish waste into smaller pieces, which accelerates their decomposition. A centrifugal pump, equipped with an impeller, is particularly effective because it grinds the waste into finer fragments. This process ensures the even distribution of suspended solids throughout the biofilter’s channels, enhancing both decomposition and mineralization.

A solids lifting outlet is mostly used in systems with flat-bottomed tanks which are unsuitable for iAVs and should be avoided.

34.11. Dissolved Oxygen

Dissolved oxygen (DO) is one of the most important parameters affecting aquaculture water quality. The dissolved oxygen concentration in the aquaculture environment directly impacts growth, survival rates, feed consumption, and digestion, with decreased concentrations causing stress for aquaculture species (Tanveer et al., 2018, as cited in Kosasih et al., 2025). Fish, like all aerobic organisms, absorb DO through their gills. Warmer water holds less DO than cooler water due to the inverse relationship between temperature and oxygen solubility. Insufficient DO levels can lead to reduced growth rates, feed efficiency, and even mass mortality (Mohan et al., 2022, as cited in Kosasih et al., 2025; Yildiz 2017).

Most fish species thrive with DO levels between 5–8 mg/L (ppm). Levels below 3 mg/L can cause stress and health issues. While Tilapia can tolerate lower DO levels (1–3 mg/L), optimal health and growth occur at 5 mg/L or higher. Goldfish and Jade Perch can survive short periods below 3 mg/L but should have DO levels above 5 mg/L for long-term health. The recommended DO levels for fish culture are 6 ppm for coldwater fish and 4 ppm for warmwater fish. Most fish species can tolerate a decrease below these thresholds for short periods, but mortality can occur if DO concentration falls below 2 mg/L (Mohan et al., 2022).

34.12. Fish Requirements

Different fish species have varying oxygen needs. Tilapia, used in early iAVs research, are hardy and can thrive in lower-oxygen environments without additional aeration. In contrast, species like Barramundi and Trout require higher oxygen levels, especially cold-water species like Trout, which need colder water to maintain oxygen saturation.

It’s important to distinguish between survival conditions (e.g., minimum DO or temperature) and optimal conditions for growth. Low dissolved oxygen can have side effects on fish growth (Sultana et al., 2017).

34.13. Degassing

Degassing removes excess dissolved gases like carbon dioxide (CO2), which can accumulate due to fish and bacterial respiration. Elevated CO2 levels can harm fish health. The function of an aerator is not only to introduce oxygen but also to help absorb carbon dioxide (Petersen & Walker, 2002). Degassing is achieved by increasing the contact surface area between water and air through aeration or cascading water through the air. Often, air stones or cascade aerators suffice for degassing without needing additional units.

34.13.1. Solenoids

Open solenoid valve diagram. Joey Corbett, CC BY-SA 4.0, via Wikimedia Commons.

Solenoid valves control water flow by opening or closing based on electrical signals from a programmable controller. While useful in large or complex systems with multiple irrigation zones, solenoids are generally unnecessary for most iAVs setups where a reliable timer can suffice.

34.14. What is Sand?

Sand is a naturally occurring granular material composed of particles ranging from 0.06 mm to 2 mm in size, formed from the breakdown of rocks and minerals. Silica quartz sand, one of the most abundant types on Earth, is particularly suited for iAVs due to its durability and resistance to weathering.

These properties make it an effective filtration medium while providing a stable environment for plant roots to grow. By using silica quartz sand, iAVs can efficiently support both plant growth and water filtration, making it a sustainable solution in areas with poor soil or limited water resources.

Sand dunes of Khongoryn Els, Gobi Desert, Mongolia. Bernard Gagnon, CC0, via Wikimedia Commons

34.14.1. Historical Significance and Proven Effectiveness

Sand has been used as a natural water filtration medium for thousands of years. Ancient civilizations, including the Babylonians, Egyptians, Chinese, and Native Americans, utilized sand to purify water, even if they did not fully understand the scientific principles behind it. This practice continues today in modern facilities like SeaWorld and Epcot Center, where sand filters remain the preferred choice for water purification.

The first large-scale public water filter using sand was constructed in London in 1829, leading to widespread adoption of sand filtration systems across Europe and the United States. These systems significantly reduced waterborne diseases in urban areas. By 1885, rapid sand filters became common for municipal water purification due to their efficiency and durability. Quartz sand, in particular, is highly effective because of its indestructibility and high specific gravity, allowing it to maintain its filtering capacity over time.

34.14.2. From Sand to Soil

While iAVs utilizes sand as its primary medium, it’s crucial to understand that this sand doesn’t remain inert. Over time, through the system’s operation, it transforms into a biologically active, functional equivalent of soil. This transformation is key to the system’s efficiency and sustainability, distinguishing it sharply from purely hydroponic setups.

Natural soil is a complex mixture of mineral particles, organic matter, water, air, and living organisms. Here’s how iAVs replicates and accelerates the formation of this vital ecosystem within the sand bed:

Mineral Foundation (The Sand): The carefully selected sand provides the stable mineral structure, physical support for plant roots, and a vast surface area. Its properties ensure proper drainage and aeration, essential for a healthy soil environment.
Organic Matter & Nutrients (Fish Waste): Nutrient-rich effluent from the fish tank continuously introduces organic matter (fish waste, uneaten feed) onto the sand surface. This serves as the crucial food source for microorganisms and the primary source of plant nutrients.
Water Delivery (Irrigation): Regular, intermittent irrigation cycles deliver water throughout the sand bed, transporting dissolved nutrients and sustaining both plant and microbial life.
Oxygen Supply (Aeration): The flood-and-drain cycles are critical for oxygenating the system. As water drains, it pulls atmospheric oxygen deep into the sand’s pore spaces. This abundant oxygen is vital for the aerobic respiration of plant roots and, crucially, for the beneficial microbes that drive decomposition.
Living Organisms (Microbial Community & Roots): The combination of minerals, organic matter, water, and abundant oxygen creates ideal conditions for a diverse and thriving microbial community (bacteria, fungi, protozoa, etc.) to colonize the sand grains. These microbes actively decompose the organic matter, mineralizing nutrients into forms plants can readily absorb. Plant roots further interact with this microbial community, absorbing nutrients and contributing to the physical structure of the developing soil-like medium.

In essence, the iAVs sand bed becomes a dynamic ecosystem where fish waste is rapidly decomposed and mineralized by a rich microbial community, fueled by consistent oxygen supply. This process mimics natural soil formation but occurs at an accelerated rate within the controlled iAVs environment. Therefore, the sand bed in a mature iAVs is far more than inert physical support; it functions as a true living soil, driving nutrient cycling and supporting robust plant growth.

Components of Soil – Minerals, Organic Material, Water, Air. JasonHS, CC BY-SA 4.0, via Wikimedia Commons

34.15. Soil Ecology

Sand is ideal for iAVs as it temporarily retains nutrients while allowing direct microbial interaction with plant root exudates. This interaction fosters a diverse soil ecology that supports plant growth and enhances system sustainability.

Associations in the rhizosphere between plant roots, microbes, and root exudates under biotic and abiotic influences. Kanchan Vishwakarma,Nitin Kumar, Chitrakshi Shandilya, Swati Mohapatra, Sahil Bhayana and Ajit Varma, CC BY-SA 4.0, via Wikimedia Commons

Root exudates – organic compounds secreted by plant roots – are essential in shaping the rhizosphere, the soil region surrounding roots. These exudates attract beneficial microbes that aid in nutrient solubilization and pathogen suppression.

Nutrient exchanges and communication between a mycorrhizal fungus and plants. Charlotte Roy, Salsero35, Nefronus, CC BY-SA 4.0, via Wikimedia Commons.

Sand acts like a temporary nutrient reservoir, holding onto nutrients until plants need them. Plant roots significantly affect the rhizosphere, the narrow soil region around them, by releasing substances like oxygen and exudates that influence local chemical conditions and microbial activity (Xu 2012). These natural root exudates play a key role by attracting beneficial microbes, which then help break down nutrients into forms the plants can absorb, functioning much like an external digestive system to process food for the plant.

34.16. Sustainability Considerations for Sand Use in iAVs

When sourcing any raw material, including sand for iAVs, considering the environmental impact of extraction, such as potential habitat destruction from irresponsible mining, is important. Opting for suppliers committed to responsible practices is advised whenever possible.

While concerns about a global “sand crisis” are often highlighted, recent analyses suggest the core issue isn’t an absolute physical shortage of sand particles geologically. Instead, the challenge often lies in the intensive extraction of specific types of sand (often angular river and coastal sands) driven primarily by the vast global demand for construction aggregates like concrete, and in managing this extraction sustainably and economically. The environmental pressure is often concentrated on these specific, easily accessible sources rather than reflecting a total lack of sand material worldwide.

In this context, iAVs offers a particularly sustainable application for sand. Unlike its typical single-use fate when locked into concrete structures, sand in an iAVs system is reused indefinitely. It can be cleaned and utilized across multiple crop cycles for decades, drastically reducing the ongoing demand for new material for that specific system. This inherent reusability contrasts sharply with the high-volume, consumptive use in construction.

Furthermore, this sustainable use of sand occurs within a system designed for overall resource conservation. iAVs dramatically reduces water consumption compared to traditional agriculture and requires less energy than many conventional aquaculture or hydroponic methods. The sand itself facilitates natural filtration, eliminating the need for energy-intensive purification processes.

Therefore, while responsible sourcing remains a key consideration for any material, the use of suitable sand within a closed-loop, highly efficient iAVs represents a sustainable practice. It leverages a durable resource for long-term food production, water conservation, and reduced energy input, aligning well with broader goals for environmental stewardship and food security.

34.16.1. Micro-Plastic Considerations

Beyond its filtration and biological functions, the use of sand as a natural biofilter medium in iAVs offers a potential advantage in mitigating contamination from micro- and nanoplastics (MNPs). Research in commercial recirculating aquaculture systems (RAS), which often rely heavily on plastic components (like PE beads for biofilters or PVC pipes), has shown that these systems can be sources of MNP pollution through the weathering and degradation of these materials (Blonç et al., 2023). The same study suggests exploring natural biofilters as a non-plastic alternative to minimize MNP presence, highlighting a key benefit of the sand-based iAVs design (Blonç et al., 2023).

34.16.2. Contaminant Testing for iAVs

While contaminant testing is generally unnecessary for most sand sources, it can provide peace of mind for individuals growing their own food and is particularly advisable for commercial operators. Most virgin sand from quarries is not contaminated, as it is typically excavated from natural deposits that have not been exposed to industrial, agricultural, or urban pollutants. In Australia, for instance, such sand is often classified as Virgin Excavated Natural Material (VENM) under the Protection of the Environment Operations Act 1997. This classification ensures that the material is free from manufactured chemicals, process residues, sulfidic ores, or other waste, making it suitable for use.

Harmful substances such as salts or heavy metals can negatively impact plant growth, fish health, and overall system performance. To check for salt contamination, a simple test involves dissolving a sample of sand in distilled water, stirring thoroughly, and measuring the electrical conductivity (EC) with an EC meter; high readings indicate excessive salt levels.

Government agencies and affiliated organizations often provide soil testing services for home vegetable growers, and these services can be relatively affordable. In Australia, for example, local agricultural extension services or programs like Veggie Safe (run by Macquarie University) offer soil testing for a small donation. These tests can analyze soil for contaminants such as heavy metals (e.g., lead).

For more comprehensive testing, professional laboratories can analyze sand for heavy metals, pesticides, or other pollutants. Certified environmental testing services or agricultural extension labs are reliable options.

Although most clean, washed sands are safe for iAVs use, testing ensures the highest standards of safety and system efficiency.

34.17. Edge Effect

The use of furrows and ridges in iAVs creates a 3D profile that contributes to increased growth and microbial activity, similar to the “edge effect” in ecology. The edge effect in iAVs refers to the dynamic interplay between the ridges and furrows, creating diverse conditions that benefit both plants and microbes.

In the context of iAVs with furrow irrigation and raised ridges, the ‘edge effect’ can be understood as the unique conditions created in the border areas where two different environments meet – such as where irrigated furrows meet the raised ridges where plants grow. These edge areas experience noticeable changes in environmental factors like light exposure, temperature, water availability, and interactions between plants and other organisms (Golubkina 2023).

The edges between ridges and furrows create a transition zone with varying moisture and oxygen levels. This variety encourages more extensive root growth as plants adapt to the different moisture zones. The furrows, being frequently irrigated with nutrient-rich water, become hotspots for microbial activity. This activity is further enhanced by the oxygen-rich environment created by the ridges.

The different conditions in the furrows and ridges create micro-environments that support diverse microbial communities. This diversity is analogous to the increased biodiversity observed at the boundaries of different ecosystems. The combination of effective irrigation and nutrient distribution in the furrows, along with the aeration provided by the ridges, leads to increased plant growth and microbial activity. This is similar to the higher productivity often seen at the edges of ecosystems where resources from both sides are available.

The “edge effect” refers to the phenomenon where plants growing at the edges of a field often exhibit better growth and higher yields compared to those located within the interior. This effect is primarily attributed to two key factors: increased light availability and higher carbon dioxide (CO2) concentrations at the field edges. Plants at the boundary of a field are less shaded by neighboring plants, allowing them to intercept more sunlight, which is vital for photosynthesis. Additionally, the open environment at the edges facilitates better air circulation, leading to a localized increase in CO2 concentration. This combination enhances photosynthetic efficiency, promoting robust growth and greater productivity. The edge effect is a manifestation of how environmental conditions vary spatially within agricultural systems, offering insights into optimizing plant growth and resource use (Yang 2006).

The paper titled “The ‘Edge Effect’ Phenomenon in Plants: Morphological, Biochemical and Mineral Characteristics of Border Tissues” explores the concept of the edge effect and its implications for individual plants. The edge effect is described as a fundamental ecological phenomenon crucial for maintaining ecosystem integrity. While traditionally applied to ecosystems, the study highlights how this concept can also be observed at the level of individual plants. Specifically, the properties of a plant’s outer tissues are shown to closely mimic the edge effect characteristics found in various ecosystems. This insight suggests that the edge effect may play a significant role in enhancing the resilience and functionality of both ecosystems and individual organisms. These benefits suggest that the edge effect could be advantageous by increasing plant resilience, nutrient content, and overall productivity (Golubkina 2023).

34.17.1. Considerations Regarding Worms in iAVs

Worms are a natural part of many ecosystems and may find their way into systems over time. However, their role in iAVs is speculative and not supported by any scientific research to date.

Are Worms Necessary in iAVs?

Worms are not necessary for the optimal performance of iAVs. The system is designed to function efficiently without their presence. All essential microbiological activity required for nutrient cycling and plant growth occurs naturally within the sand biofilter, provided the system is properly managed. Unlike other media-based systems, such as those using gravel, sand beds do not rely on worms to process organic material or maintain functionality.

Potential Advantages of Worms

While worms could provide some potential benefits, these remain speculative and lack formal investigation or scientific validation.

Disadvantages of Worms

There are several reasons why introducing worms into iAVs sand beds may be counterproductive:

Disruption of the Schmutzdecke Layer: The schmutzdecke is a critical microbial layer on the surface of the sand bed that facilitates biological filtration. Worm activity could disturb this layer, potentially harming the microbial processes essential for nutrient cycling.
Mixing of Organic Residues: In iAVs, it is preferable for organic matter to remain on the surface, where it can be more easily managed. Worms may integrate detritus and silty residues deeper into the sand bed, which could create the need for cleaning and maintenance. Over time, this could lead to the accumulation of solids and worm castings in the lower sand layers. If these materials are fine and compact, they could reduce the drainage efficiency of the sand bed, compromise filtration performance, and potentially create anaerobic conditions.
Uncertain Impact on Microbial Communities: Worms consume bacteria on decaying organic matter. This behavior may create competition with or disrupt the microbial communities responsible for breaking down fish waste into plant-available nutrients.
Lack of Evidence for Long-Term Benefits: There is no definitive research demonstrating that worms enhance iAVs performance. Any potential benefits are outweighed by the risk of unintended negative consequences.

Observations from Practitioners

Several practitioners have shared anecdotal experiences regarding worms in iAVs:

In one case, worms introduced to a sand bed disrupted the schmutzdecke layer, leading to potential harm to microbial processes.
Worms have been identified as a potential cause of mechanical issues in certain systems. For instance, there have been reports of worms infiltrating internal components of pumps, which could result in operational disruptions. Additionally, one user reported a malfunction of a float switch caused by a worm entering the mechanism. This interference led to a temporary failure of the system when the float switch failed to activate.

Scientific Perspective

Dr. Mark McMurtry has emphasized that worms are unnecessary for achieving excellent results in iAVs. He cautions against proactively adding them to sand beds due to the lack of empirical evidence supporting their benefits and the potential for negative impacts. While worms may appear naturally if conditions suit them, their presence should be monitored closely. If no adverse effects are observed, they can be left undisturbed; however, if problems arise, efforts should be made to remove them.

35. Understanding iAVs

35.1. What iAVs is NOT

Not Hydroponics, But Organic Symbiosis: iAVs is not hydroponics. Instead, it fosters a natural symbiosis between fish and plants, where fish ‘waste’ provides nutrients for the plants, and the plants, in turn, filter and clean the water for the fish. This cycle mimics natural ecosystems and operates organically.
Not a Miracle, But Proven Science: iAVs is not based on pseudoscience or unfounded claims. Instead, its effectiveness stems from scientific principles and rigorous research. Developed through experimentation and observation, iAVs represents innovative agricultural science.
Not a Singular Solution, But a Valuable Complement: iAVs is not a singular solution to global hunger. Instead, while efficient in producing diverse, nutrient-rich foods, it complements, rather than replaces, conventional agriculture. Grains, the primary source of global caloric intake, are not the focus of iAVs. However, iAVs can significantly enhance nutritional diversity and availability for those who adopt it.
Not California’s Water Savior Alone, But Highly Water-Efficient: iAVs cannot resolve systemic water mismanagement issues on its own. Instead, it should be part of a broader conservation strategy. However, its adoption can contribute significantly to water conservation efforts in agriculture, making it a valuable tool in water-scarce areas.
iAVs Minimizes the Use of Plastic, Unlike Many Modern Agricultural Systems: iAVs does not rely heavily on synthetic materials like plastic. Instead, its design can be simple and sustainable, minimizing the environmental footprint associated with its setup and operation.
Not Enriching Polluters, But Promoting Sustainability: iAVs does not contribute to the profits of companies known for environmental pollution, such as those producing large quantities of PVC pipe or Styrofoam. Instead, its reliance on natural processes and minimal use of synthetic materials sets it apart from systems that have a significant environmental impact. You won’t find Dow Chemical or similar corporate interests promoting iAVs since it does not require proprietary products or equipment.
Not Just Basic Flood and Drain, But a Refined Method: iAVs goes beyond the simple mechanics of flood and drain systems found in some aquaponics setups. Instead, it’s a refined method that has proven its effectiveness and reliability through years of application and research, as documented by Dr. Mark McMurtry.
Not a Newcomer, But a Foundational System: iAVs is not a recent invention. Instead, it has been a foundational system that has influenced the development of traditional aquaponic systems and other integrated agriculture-aquaculture systems (Wang 2022). Its principles have been guiding the evolution of sustainable food production methods for decades, with extensive documentation available at iavs.info.
Not a Replacement for Fertile Soil, But a Sustainable Alternative: While it offers a sustainable approach to agriculture, fertile soil should still be utilized if available. Instead, there is no “one right perspective” for everyone and/or everywhere. What anyone does with what they have where they are can only be assessed fully within their context by them.

By understanding what iAVs is not, we can better appreciate its value and potential as a sustainable food production system.

35.1.1. iAVs is not Sandponics

It is critical to distinguish iAVs from a separate, unrelated system known as “Sandponics.” Although both utilize sand, their functionality, underlying principles, and origins differ fundamentally.

“Sandponics” refers to hydroponic methods using sand as a medium without integrated aquaculture, and the term itself is trademarked by a specific corporation. In contrast, iAVs, developed earlier, integrates aquaculture with sand-based horticulture and was intentionally released as an open-source methodology.

The conflation of these terms, particularly the mislabeling of iAVs as “Sandponics,” has unfortunately led to inaccuracies in some research publications and broader discussions. This can obscure the unique, scientifically validated principles and documented performance of the iAVs methodology.

For clarity in research, practice, and communication, accurately identifying the Integrated Aqua-Vegeculture System as “iAVs” is essential. This ensures that research findings are correctly attributed and comparable, allowing practitioners to make informed decisions based on reliable, system-specific data and acknowledging the distinct developmental history of iAVs.

35.2. Illustrative Analogy: iAVs as a High-Performance Vehicle

iAVs can be likened to a high-performance engine, such as the Ariel Atom, due to its focus on simplicity, efficiency, and optimized performance.

The Ariel Atom is a lightweight, open-wheeled sports car renowned for its minimalist design and exceptional performance. It features a tubular spaceframe chassis, which is both lightweight and strong, prioritizing functionality over unnecessary aesthetics. The Atom eliminates non-essential features like roofs, doors, or cupholders to focus purely on performance and agility. Its engineering ethos follows the principle of “less is more.”

Despite its simplicity, the Atom delivers extraordinary speed and handling. For example, the Atom 4R boasts a power-to-weight ratio of 611 bhp per ton, enabling it to accelerate from 0-62 mph in just 2.7 seconds. This combination of minimalism and optimized performance makes the Atom an icon in automotive design.

The Ariel Atom and iAVs share a common ethos of simplicity and efficiency, delivering exceptional performance in their respective domains. The Ariel Atom, with its minimalist exoskeleton design and focus on essential components, achieves remarkable speed and handling. It does so at a lower cost than many high-performance vehicles. Similarly, iAVs offers a streamlined agricultural solution that maximizes productivity and sustainability. Both the car and the system prioritize functionality over complexity. This demonstrates how thoughtful design can yield superior results.

Fish = Engine: The fish act as the engine, converting feed into ‘waste’, which becomes the nutrient source for the plants.
Fish Feed = Fuel: The fish feed is akin to fuel. Its quality and quantity directly influence system performance, just as fuel impacts a car’s efficiency.
Plants = Tyres: The plants function like tyres, absorbing nutrients from the fish ‘waste’ and converting them into growth, similar to how tyres convert engine power into motion.
Sand = Carburetor: The sand serves as a carburetor by regulating air and water flow. Each dewatering cycle recharges the filter with oxygen, benefiting nitrifying bacteria and aiding nutrient assimilation by plants. This process mirrors the scavenge effect in an internal combustion engine, where stale exhaust gases are replaced with fresh air for optimal performance.
- The ridges act like chimneys or ventilation stacks, facilitating this gaseous exchange by venting stale air during flooding and drawing fresh oxygen deep into the sand bed during drainage.
- The slit drain, located at the base of the sand biofilter, ensures rapid and complete drainage of water. This swift drainage amplifies the suction effect that pulls fresh air into the biofilter, maintaining an oxygen-rich environment for beneficial microbes.
Ridges & Slit Drain = Air Intake System: Together, these components ensure efficient oxygenation within iAVs. The ridges facilitate airflow dynamics akin to intake manifolds in engines, while the slit drain acts like an exhaust valve ensuring rapid venting of stale air.
Water = Chassis & Suspension: Water provides structure and support within the system, transporting nutrients from the fish to the plants, much like a car’s chassis and suspension support its structure and absorb shocks.
Microbes = Drivetrain: Microbes convert fish ‘waste’ into plant-usable nutrients, analogous to how a drivetrain converts engine power into motion.
Feeding Rates = Accelerator: Feeding rates control the speed of nutrient cycling in the system, just as an accelerator controls a car’s speed.
Checking Water Level and pH = Checking Oil: Regular monitoring of water levels and pH ensures smooth operation, similar to checking oil levels in a car.

The “scavenge effect” refers to the process where the fresh, incoming fuel/air mixture entering the cylinder helps to push out, or “scavenge”, the remaining burnt exhaust gases from the previous combustion cycle. This analogy describes the highly efficient way the sand biofilter exchanges air during the flood-and-drain cycle, actively replacing old air with fresh air.

Here’s the breakdown in the iAVs context:

“Exhaust Gases” = Stale Air: After a drain cycle, the air trapped in the pore spaces between sand grains becomes depleted of oxygen (O₂) and enriched with carbon dioxide (CO₂) due to respiration by plant roots and aerobic microbes. This is the “stale air” analogous to exhaust gases.
“Incoming Fresh Charge” = Atmospheric Air: Fresh air from the atmosphere, rich in oxygen (approx. 21%), is the desired replacement.
The “Scavenging” Process in iAVs:

Flooding (Pushing Out): When the irrigation cycle starts and water floods the furrows and saturates the sand bed from the bottom up, it physically displaces the stale air, forcing it upwards and out, often through the dry ridges which act like vents. This is like the initial push of exhaust out of an engine cylinder.
Rapid Draining (Pulling In): This is the key part of the analogy. As water rapidly exits the bed through the efficient slit drain (see Section 12.3), it creates a significant negative pressure or suction effect within the sand pores. This suction actively pulls fresh atmospheric air down deep into the sand bed, replacing the stale air much more effectively than simple passive diffusion could. This active pulling-in mirrors how the incoming charge in an engine helps clear the remaining exhaust.

An iAVs is dynamic, requiring continuous monitoring and adjustments – much like driving a truck. When operating a truck, you begin by assessing key parameters such as fluid levels and tire pressure. As you drive, you constantly gather information from your surroundings, making numerous subconscious decisions based on road and traffic conditions. Similarly, managing an iAVs involves continuously gathering data – such as temperature, flow rates, air circulation, nutrient balance, pH levels, and feeding rates – and making real-time adjustments to optimize system performance.

Each time you enter the greenhouse, conditions will vary. The ability to make timely adjustments based on these changing circumstances is what distinguishes a skilled operator from an inexperienced one. For example, you might notice subtle signs that lettuce is about to bolt, prompting you to harvest the crop early and replant. This type of decision-making becomes more intuitive as your experience with the system grows.

The process of mastering iAVs can be understood through the four stages of competence:

Unconscious Incompetence: You are unaware of what you don’t know.
Conscious Incompetence: You recognize your lack of skill and seek to improve.
Conscious Competence: You can perform tasks but must focus on each step.
Unconscious Competence: The skill becomes second nature, allowing for efficient and effortless management.

As you progress through these stages, your ability to manage an iAVs improves, leading to a more productive and sustainable system. However, this level of expertise cannot be fully conveyed through written guidelines alone – it must be developed through hands-on experience.

Just as driving a truck requires constant adaptation to changing conditions, managing an iAVs demands continuous learning and adjustment. While protocols can provide guidance, true mastery comes from repeated practice and direct engagement with the system.

36. Commercial Market Considerations

For iAVs to be commercially viable, scalability must be coupled with a sound understanding of market demand and efficient business practices.

Market Demand: Before scaling up for commercial production, thorough market research is essential. The size of the operation should be carefully aligned with local and regional demand for the types of produce iAVs can efficiently produce. Overscaling without sufficient market demand can lead to financial losses, even with high productivity. Market research should consider both local demand and potential export opportunities.
Value-Added Products: Commercial iAVs operations can enhance profitability by focusing on value-added products. This includes seeking organic certification to command premium prices, specializing in niche or specialty crops that are in high demand, and processing produce into value-added goods (e.g., packaged salads, herb blends).
Skilled Management: Scaling an iAVs requires expertise in both aquaculture and horticulture practices. Continuous education and training in system monitoring, pest management, water chemistry, and marketing are critical for maintaining productivity and profitability. Effective management also includes adapting operational practices to local environmental conditions and available resources.

36.1. Challenges and Considerations

Market Demand Fluctuations: Market demand for fresh produce can fluctuate seasonally and be influenced by various factors. Commercial iAVs operations need to be adaptable and responsive to these changes.
Competition: Commercial iAVs will face competition from traditional agriculture, hydroponics, and traditional aquaponics systems. Differentiation through product quality, organic certification, or unique crop offerings can be key to success.
Initial Investment and Operating Costs: While iAVs can be cost-effective, commercial-scale operations require significant initial investment in infrastructure and ongoing operating costs for energy, labor, and inputs. A detailed business plan and financial projections are essential.
Regulatory Compliance: Commercial iAVs operations must comply with all relevant local, regional, and national regulations related to food safety, environmental standards, and business operations. Understanding and adhering to these regulations is crucial for legal and sustainable operation.

For commercial viability, thorough market research, efficient business practices, and skilled management are essential. While iAVs offers significant advantages in resource efficiency and sustainability, commercial success depends on a holistic approach that integrates production expertise with market awareness and sound business planning.

Dr. Mark McMurtry highlighted that while commercial-scale production is achievable with proper skills and capital, marketing perishable commodities is challenging and requires business acumen, marketing expertise, and adherence to regulations.

Biosecurity and Sanitation: In commercial operations, strict biosecurity is essential. Dr. McMurtry stresses the importance of maintaining a clean environment, which includes limiting visitor access or enforcing bio-decontamination procedures for anyone entering the facility. This applies to all operators and staff to prevent disease transmission. For instance, southern tomato wilt, common in deep soils, can be controlled by sterilizing sand before inoculating it with nitrifying bacteria and implementing sanitation protocols such as requiring showers, designated greenhouse clothing, boots, and foot baths before entering sand beds.

Sand Sizing and Irrigation: Proper sand sizing is critical but often overlooked or treated anecdotally. Dr. McMurtry recommends testing sand before use to ensure the correct particle size, as this directly affects irrigation frequency and the risk of wilt. In the Mora project, a 1:1 aspect ratio was used, which was suboptimal and may have contributed to challenges with fish stocking and production.

Fish Handling and Purging: Efficient fish handling is crucial to minimize stress on the fish and labor for operators. Instead of using hand dip nets, which can be labor-intensive and stressful for the fish, each cohort in a tank or canal should have its own net that can be moved along the tank with minimal disturbance to the fish. Additionally, purging fish for 2-3 days before sale is standard in Western markets to remove off-flavors from algae, though this practice is not universally required.

Marketing and Commercialization: While achieving commercial-scale production is feasible with adequate skills and capital, Dr. McMurtry highlights that marketing perishable commodities at scale presents distinct challenges. Successful commercialization requires not only production but also strong business management, marketing expertise, and compliance with regulatory standards. Many large-scale growers operate under contract agreements that guarantee pre-sold volumes at specific quality levels, timeframes, and prices. Staggered production schedules are also vital to ensure consistent daily or weekly harvests.

Skill Sets and Experience: Growing crops and marketing them are distinct activities requiring different skill sets, and Dr. McMurtry advises that neither should be undertaken by novices in a commercial context without proper experience or guidance. The profitability of an iAVs operation depends on multiple factors such as scale, climate/location, market prices/channels, local costs, capital expenses, and various other variables. The annual Internal Rate of Return (IRR) at full operational capacity can range from 150% to 400%, depending on how depreciation, opportunity costs, and taxes are accounted for.

37. The iAVs Research Group

37.1. Scientific Foundation of iAVs

A defining characteristic that distinguishes iAVs from many other integrated aquaculture-horticulture approaches, often broadly termed “aquaponics,” is its robust foundation in rigorous scientific research and validation. This commitment to the scientific method ensures reliability, predictability, and a clear understanding of the system’s operational principles.

37.2. Early Research and Development:

The development of iAVs was spearheaded by Dr. Mark McMurtry, a horticultural scientist at North Carolina State University (NCSU), beginning in the mid-1980s. This work, which predates the widespread adoption of the term “aquaponics,” was fundamentally rooted in scientific methodology.

From its inception, the research was characterized by controlled experiments, meticulous data collection, and rigorous analysis. These hallmarks ensure objectivity and allow for the establishment of cause-and-effect relationships, moving beyond simple observation to verifiable understanding.

37.3. Peer-Reviewed Publication and Scrutiny:

Crucially, Dr. McMurtry’s findings were disseminated through peer-reviewed scientific journals. This process involves subjecting research manuscripts to critical evaluation by independent experts within the relevant fields before publication.

Peer review serves as a vital quality control mechanism in science, helping to ensure the credibility, validity, and significance of the research. The successful navigation of this scrutiny established a solid, verifiable scientific basis for the iAVs methodology.

37.4. Controlled Experiments and Replicability:

Dr. McMurtry’s doctoral research exemplified the system’s rigorous development. It involved constructing a 16-tank iAVs facility specifically designed to systematically test different tank-to-biofilter volume ratios. These trials spanned multiple crop intervals and included a non-crop period, allowing for a comprehensive assessment of system performance under varied conditions.

The research focused on establishing quantifiable relationships and identifying critical operational parameters, such as the optimal biofilter volume required per unit of fish biomass (or feed input) and the expected plant yield per unit increase in fish weight.

This data-driven approach ensures replicability – meaning that others following the established protocols can reasonably expect to achieve similar, predictable results, a cornerstone of reliable technology transfer.

37.5. USDA Funding and Validation

The potential of iAVs was recognized early on by federal agencies. The foundational research conducted at North Carolina State University (NCSU) received partial funding from the United States Department of Agriculture (USDA) through Special Grant P.L. 89-106, titled “Agricultural Adjustment in Southeast Through Alternative Cropping Systems.” This initial support highlights the perceived relevance of iAVs even during its developmental stages as a promising alternative approach to conventional agriculture.

Building upon this foundational work and recognizing the system’s promise, the USDA subsequently sponsored a dedicated commercial-scale trial in 1991-92. This trial was specifically designed to test and demonstrate the system’s viability and productivity at a larger, commercially relevant scale. It successfully moved iAVs beyond controlled laboratory or small research settings into a practical, real-world production environment.

The success of this USDA-sponsored trial, following the earlier research grant, further solidified iAVs’ standing as a proven, scalable, and federally recognized technology.

37.6. The Importance of a Scientific Foundation:

A rigorous scientific foundation ensures that the system’s design – including specific component sizes, critical ratios (like tank-to-biofilter volume and area), and operational parameters – is not based on speculation, guesswork, or anecdotal evidence, but on empirical data and validated principles.

This provides practitioners, whether beginners or seasoned professionals, with confidence that the system, when implemented according to guidelines, will perform predictably and reliably.

This evidence-based approach offers a distinct advantage over many other aquaponic variations that may lack the same depth of scientific validation and documented performance.

37.7. A Call for Continued Research and Recognition:

Despite its proven track record and robust scientific underpinnings, iAVs remains relatively under-recognized within the broader aquaponics community. This is exemplified by its omission from significant publications, such as those by the Food and Agriculture Organization (FAO).

The iAVs community continues to advocate for greater awareness and recognition of the system’s scientifically validated potential and its significant contributions to sustainable food production.

Continued research, focused dissemination efforts, and clear communication are crucial to ensure that iAVs gains wider adoption and contributes effectively to addressing global food security and resource management challenges.

37.8. iAVs Research Group Members

From 1984 to 1994, the iAVs Research Group comprised a diverse team of researchers and consultants from various fields, including agriculture, horticulture, and engineering. This team worked in collaboration with numerous external institutions, earning widespread recognition for their contributions.

Notably, 10 team members received the honor of being named “Fellows” in their respective professional disciplines. Their pioneering research has not only been cited in numerous journal articles but has also undergone rigorous testing and validation.

iAVs is a reputable and scientifically supported system for sustainable agriculture, thanks to the thorough research and interdisciplinary collaboration led by Dr. Mark R. McMurtry and his team.

Active from 1984 to 1994, the iAVs research group comprised seven co-investigators across five disciplines, with additional support from nine principal consultants.

This team also benefited from collaboration with faculty from 16 departments across four colleges at North Carolina State University (NCSU) and other institutions.

The variety of expertise within the team, ranging from horticultural science to environmental engineering, underscores the system’s strong foundation in rigorous scientific research and interdisciplinary collaboration.

Furthermore, the iAVs research has been acknowledged and validated by the scientific community through publications in five refereed journals and citations in journal articles at least 114 times as of June 2016.

37.8.1. Fellows

Ten members of the iAVs Research Team were honored as “Fellows” of their respective professional disciplines. This is the highest professional honor conferred on a scientist, except for a Nobel Laureate.

The Fellows came from various professional organizations, including the American Academy for the Advancement of Science and the American Society of Agricultural and Biological Engineers, American Society of Horticultural Science, and of Crop Science, et al.

Fellows are recognized by their peers for their significant contributions to their respective fields.

The Fellows’ roles within the iAVs research team are significant, as their appointments attest to the credibility and depth of knowledge that underpin the research.

37.8.2. Principle Investigator:

Dr. Mark R. McMurtry: Dr. Mark R. McMurtry is the “Inventor of Record” of iAVs technology at North Carolina State University in Raleigh, North Carolina (1984-1994).

McMurtry’s expertise in Horticultural Science, Integrated Bio-production Systems, Environmental Design, and International Development, along with his Ph.D., positions him as the pioneering figure behind the creation and advancement of iAVs.

His academic and professional journey reflects a deep commitment to addressing global challenges such as hunger, environmental degradation, and water scarcity through innovative agricultural solutions.

37.8.3. Co-Investigators:

Douglas C. Sanders (deceased) was a distinguished scientist and expert in the field of olericulture and was a renowned authority in the field of plant physiology. He holds the title of Fellow of the American Society for Horticultural Science (FASHS).

Sanders’ work has helped shape the understanding and practices of horticulture, benefiting both the scientific community and the broader horticultural industry.

By understanding the physiological responses of plants to different environmental conditions, Sanders has contributed to the development of plant management strategies that maximize plant growth and yield.

Dr. Edward A. Estes holds a Ph.D. in Agricultural and Biological Engineering, specializing in sustainable agriculture and an expert in Aquacultural Economics.

He has dedicated his career to researching and promoting innovative solutions for sustainable food production. Dr. Estes has conducted extensive research on aquaponics and hydroponics systems, focusing on optimizing nutrient cycling, water management, and plant growth in controlled environments.

Paul V. Nelson is a renowned authority in the field of Botanical Mineral Nutrition and Greenhouse Management.

With a deep understanding of plant physiology, nutrient assimilation, and greenhouse technologies, Nelson has dedicated his career to researching and promoting sustainable agricultural practices.

Paul has been honored as a Fellow by the American Society of Horticultural Science (ASHS) for his contributions to the field of horticulture and sustainable agriculture.

Paul Nelson was a Professor Emeritus at North Carolina State University and a key figure in the development and promotion of iAVs.

Nelson’s involvement with the iAVs began in the 1980s when he provided greenhouse space for the initial formal research. He continued to support the system as a valued advisor, mentor, and co-author for the next ten years.

He was a prolific author and published numerous (100’s) articles and papers on topics related to horticulture, botanical nutrition, greenhouse management, and sustainable agriculture.

Not only that, but he was also a frequent speaker at conferences and workshops and was known for his ability to communicate complex scientific concepts in an accessible way.

Nelson is also well-known in the field of horticulture for his definitive text “Greenhouse Operation and Management”, which is currently in its 7th edition.

This text has been employed for over four decades in universities throughout the US and the world and is considered a valuable resource for students and professionals in the field of horticulture.

Robert P. Patterson holds a Ph.D. in Agronomy and has dedicated his career to researching and promoting sustainable agricultural practices.

With a specialization in soil fertility and plant physiology, Patterson has conducted extensive research on the interactions between plants, soil, and nutrients.

Ronald G. Hodson holds a Ph.D. in Aquatic Ecology and has dedicated his career to studying and managing aquatic ecosystems.

With a specialization in aquatic ecosystems, fisheries management and genetics, Hodson has conducted extensive research on the interactions between aquatic organisms, their environment, and the genetic factors influencing their growth and survival.

The skills required in this field include a deep understanding of the relationships among physical, chemical, and biological components of aquatic ecosystems, which are fundamental to ensuring the health and productivity of both the aquaculture and horticulture components of iAVs.

37.8.4. Principle Consultants:

Blanche C. Haning, Ph.D., is an expert in Integrated Pest Management and Plant Pathology.

IPM is a sustainable approach to managing pests by combining biological, cultural, mechanical, physical, and chemical tools in a way that minimizes economic, health, and environmental risks. Plant pathology involves the study of plant diseases and the pathogens that cause them.

Donald Huisingh, Ph.D., is a distinguished expert in the field of Ecology and Environmental Resource Recovery.

J. Lawrence Apple, Ph.D., is an expert in International Development and Plant Pathology and has dedicated his career to researching and implementing sustainable agricultural practices in the context of international development.

With a specialization in international development, Apple has conducted extensive research on the intersection of agriculture, food security, and sustainable development.

J Burkholder,Ph.D., FAAAS, is an expert in Aquatic Ecology with a specialization in Phycology, the study of algae.

Throughout her career, she has focused on the ecological dynamics of aquatic systems, particularly the interactions between algae and their environment. Burkholder is a researcher who has been honored as a Fellow of the American Association for the Advancement of Science (AAAS) for her contributions to the field of aquaponics and sustainable agriculture.

L. George Wilson, Ph.D., is a distinguished expert in the field of Horticultural Science. Dr. Wilson holds the title of Fellow of the Crop Science Society of America (FCSSA).

Marc A. Buchanan, Ph.D., is an expert in Agricultural Ecology and Soil Science with a specialization in agricultural ecology, Buchanan has conducted extensive research on the interactions between agriculture, ecosystems, and soil health.

Merle Jensen was a horticulturist who was instrumental in the development of hydroponic greenhouse culture.

He was a professor at the University of Arizona and was known for his work on the use of sand as a substrate for growing plants. Jensen’s research showed that sand was an effective substrate for growing plants and that it had several advantages over other substrates.

Merle Jensen was also involved in the development of the Land Pavilion at Epcot Center, Walt Disney World in Orlando, Florida. The Land Pavilion was a showcase for sustainable agriculture and featured several innovative agricultural systems, including hydroponics and aquaponics.

He was instrumental in the development of the fluidized-bed sand filters that were used to manage water quality in the large aquariums at the Center. These filters were a key component of the system and helped to maintain water quality and provide nutrients to the plants.

Stanley W. Buol, Ph.D., is an expert in Geomorphology, Mineralogy, and Soil Genesis and has dedicated his career to researching and understanding the formation and properties of soils. Buol has conducted extensive research on the processes that shape soils and the factors influencing their composition and fertility.

Thomas Losordo, Ph.D., is a renowned expert in the field of Recirculatory Aquaculture Systems (RAS) and has made substantial contributions to the development and advancement of sustainable aquaculture practices.

37.8.5. Ad Hoc Consultants:

BA Costa-Pierce is a researcher who has been honored as a Fellow of the American Association for the Advancement of Science (AAAS) for his contributions to the field of aquaponics and sustainable agriculture.

PA Sanchez is a researcher who has been honored as a Fellow of the American Association for the Advancement of Science (AAAS) for his contributions to the field of soil science and sustainable agriculture.

R Sneed is a researcher who has been honored as a Fellow of the American Society of Agricultural and Biological Engineers for his contributions to the field of controlled environmental agriculture.32.4.6. Technical Resources:

Boone. M. Mora, D.V.M. Commercial iAVs Demonstration project
Brandy Noon, M.A. Presentation and Graphics Design
Dale E. Ettel, Ph.D. Fish Feed Formulation (Purina Mills, Inc.)
Martin L. Price, Ph.D. Development Assistance and Networking (ECHO)
Nancy Mingus, M.S. Plant Tissue Analysis
Ray Campbell, Ph.D. Plant Nutrition and Tissue Analysis (NCDA)
Ray Tucker, Ph.D. Soil Fertility and Analysis (NCDA)
Reed Altman, M.S. Aquaculture Development (US Peace Corps)

Reed Altman is an aquaculture specialist who has dedicated his career to promoting sustainable aquaculture practices around the world. He holds a Master of Science degree in Aquaculture Development from the US Peace Corps and has worked with various organizations to develop aquaculture projects in Africa, Asia, and Latin America.

Stephen F. Pekkala, AIA Development Programming.
Vincent M. Foote, FIDSA (Fellow Industrial Design Society of America) Integrated Systems Design

38. iAVs and Urban Agriculture

Urban agriculture, broadly defined as the cultivation of crops and potentially livestock within urban areas (Kumar and Yadav, 2023), and the closely related concept of urban horticulture (growing plants within urban centers), have gained considerable attention in recent years (Khanpoor-Siahdarka, & Masnavi, 2025).

This growing interest stems from its accessibility and efficient utilization of limited space, effectively addressing challenges posed by rapid urban population growth and the need for local food production (Pradhan et al., 2023).

Urban horticulture offers various advantages, including enhancing air quality, mitigating urban heat island effects, contributing to food security, promoting psychological well-being (Khanpoor-Siahdarka, & Masnavi, 2025), fostering carbon sequestration, preserving biodiversity, and aiding climate change mitigation (Sia et al., 2023).

Compared to traditional rural farming, urban farming often exhibits distinct attributes such as potentially higher productivity per unit of space, reduced energy consumption, and lower capital requirements (Smit 1980; Jose 2025).

As cities increasingly face challenges like limited space, resource scarcity, and the need for resilient local food systems, innovative approaches like producing vegetables, herbs, medicinal, and ornamental plants in and around cities provide a promising strategy (Priya & Senthil, 2024). iAVs addresses many of these issues making it particularly suitable for urban agriculture.

Integrated systems like iAVs, are increasingly recognized for their potential in urban agriculture. They offer a sustainable and efficient farming technique that can help meet the growing food demands of urban populations by maximizing yields, conserving water, and supporting environmentally friendly practices (Basumatary et al., 2023; Pantanella, 2018; Frassine et al., 2024).

38.1. iAVs: A Solution for Sustainable Urban Farming

iAVs offers several advantages that make it well-suited to urban environments.

iAVs offer a promising approach for urban food production due to several key characteristics:

Scalable & Accessible: Systems can range from small family units to large commercial operations and require minimal technology, making them accessible even with limited resources.
Sustainable: iAVs minimize resource use and waste, aligning with urban sustainability goals.

Benefits in Urban Environments:

High Productivity in Small Spaces: iAVs efficiently produce significant food yields (e.g., ~200kg fish and 1400kg vegetables annually from 28 sq meters) in constrained urban areas like rooftops or backyards.
Resource Efficiency:
- Water Conservation: Highly water-efficient, reusing water hundreds of times (e.g., producing ~6g fish and 17g vegetables per liter). Ideal for water-scarce cities.
- Natural Fertilization: Fish waste naturally fertilizes plants, eliminating the need for synthetic fertilizers and reducing pollution.
- Minimal Waste: Recycles water and nutrients internally, avoiding the nutrient-rich runoff common in other systems.
Local Food Production: Enables fresh food production close to consumers, reducing transportation (“food miles”), costs, and emissions while enhancing food security.
Community Engagement: Can serve as educational tools, teaching sustainable practices and connecting communities to their food source.
Versatile Setup: Adaptable to various urban locations (rooftops, backyards, community spaces), provided the infrastructure supports the load.

Challenges in Urban Adoption:

Space & Cost: Finding suitable, affordable locations is difficult due to high urban land costs and density.
Energy Requirements: Supplemental energy for lighting or climate control may be needed in some climates, increasing costs.
Regulatory Hurdles: Zoning laws, building codes, and lack of public awareness often hinder adoption.

Enabling Urban iAVs Success:

To realize the full potential of iAVs in cities, the following are needed:

Supportive Policies: Updated zoning and regulations to accommodate urban farming.
Public Education: Increased awareness of iAVs benefits.
Innovative Business Models: Viable pathways for urban iAVs entrepreneurs.

As cities expand and face challenges like food insecurity and malnutrition (Priya & Senthil, 2024), finding sustainable ways to produce food locally becomes increasingly important. iAVs offers a promising solution for integrating food production into urban environments due to its scalability, accessibility, and sustainability.

38.2. Rooftop iAVs

Rooftop gardening and horticulture, which maximize unused urban rooftop areas to grow plants, represent an increasingly recognized eco-friendly solution contributing to food production, environmental uplift, and urban resilience (Hîrlav, 2024). Transforming these often-barren spaces into green areas offers numerous benefits, such as enhanced building insulation, improved stormwater management, urban beautification (Singh, 2024), mitigation of the urban heat island effect (cooling surfaces and reducing energy needs for air conditioning) (Awal, 2023), air purification, and the creation of habitats for beneficial insects and pollinators, thus enhancing urban biodiversity (Lin, et al., 2015). Furthermore, it provides local, fresh produce, reducing food miles and improving food security (Fei et al., 2025).

Within this context, flat rooftops present a particularly suitable opportunity for implementing iAVs systems due to their level surface, stability, and typically ample sunlight exposure. As a form of intensive rooftop agriculture, iAVs can contribute significantly to the benefits mentioned above. A key advantage of iAVs for rooftop applications is its inherently modular design. The system is constructed from distinct, interconnected components (fish tanks, sand biofilter/grow beds), which offers significant advantages for rooftop settings.

The primary challenge for any rooftop installation is the substantial weight load. The combined weight of sand media, water, plants, fish, and tanks requires careful structural consideration.

However, the modularity of iAVs helps mitigate this challenge:

Weight Distribution: Instead of a single massive structure, the weight is divided among separate modules (tanks and beds). This allows for more strategic placement to distribute the load across the roof’s structural supports, potentially reducing point stress. Modular systems are noted as an innovation enabling flexibility in rooftop farming (Abera, 2023).
Installation Logistics: Transporting and assembling smaller, individual modules onto a roof is generally easier than handling large, pre-fabricated units.
Scalability: The modular nature allows systems to be scaled up or down more easily based on available space and load capacity.

Despite the benefits of modularity, ensuring the roof possesses sufficient total load-bearing capacity remains critical. The cumulative weight of all components filled with water and sand is significant. Therefore, consultation with a structural engineer to perform a thorough load assessment is essential before proceeding.

Beyond structural capacity, other key practical considerations include effective waterproofing, adequate drainage, and convenient maintenance access. Lightweight materials (e.g., composite tanks instead of concrete) can be used for the modules to further reduce the overall weight. Integrating iAVs with other rooftop technologies, like solar panels (Han et al., 2010; Abera, 2023), could further optimize space efficiency and sustainability.

Additional considerations for rooftop iAVs installations include potentially higher wind exposure compared to ground level, logistical challenges for ongoing supply transport and harvests, and navigating specific building codes or permits governing rooftop structures and agricultural activities. When planned and implemented correctly, considering these factors, modular iAVs on rooftops offers a feasible and potent solution to enhance environmental sustainability, urban living standards, and local food systems, contributing meaningfully to sustainable urban development (Fei et al., 2025; Huang & Chang, 2021).

38.2.1. Rooftop iAVs for Urban Food Production

Dr. Mark McMurtry envisioned iAVs being implemented on the rooftops of large retail centers, such as Walmart Supercenters. In this model, fresh produce would be grown on-site using iAVs technology, harvested daily, and delivered directly to the store below. This approach highlights the potential of iAVs in urban environments by reducing transportation distances, minimizing supply chain inefficiencies, and providing locally grown, nutrient-rich food. It aligns with sustainable agriculture practices and offers a vision for enhancing food security in densely populated areas worldwide.

39. Case Study

39.1. Boone Mora’s iAVs Greenhouse

39.1.1. Introduction

Boone Mora’s project in Bath, North Carolina, serves as a key example of the feasibility and profitability of iAVs. This case study outlines the project’s key aspects, challenges, and successes, supported by the Mid-East Resource Conservation and Development Council and North Carolina State University.

Dr. McMurtry was not involved in the design or operational aspects of this project as he was in Africa during its implementation. Therefore, he remained unaware of the developments taking place in Bath

39.1.2. Background and Objectives

Conducted from 1992 to 1993, the project aimed to provide alternative income sources for farmers in the Southeastern Coastal Plains. Mora expanded upon Mark McMurtry’s research at North Carolina State University to develop a commercial-scale iAVs operation.

39.1.3. Facility Design and Operations

The greenhouse measured 100 x 100 feet and featured two 26,000-gallon fish tanks lined with plastic. Male hybrid tilapia were stocked for their efficient feed conversion, while vegetables were grown in adjacent sand beds using a recirculating water system. Water from the fish tanks irrigated the sand beds hourly during daylight, filtering waste before returning to the tanks.

This layout was used in the Mora/Garrett NC Commercial Scale Demonstration Project. ‘Industrial scales’ (hectares) can be approached similar to the above or in any entire different configuration ( where very long beds are drained laterally (to the side) with provision for proper return slope (et al) to the associated grow-out tanks situated in access aisles (doubling as drainage and mechanical distribution corridors).

39.1.4. Crop and Fish Production

High-value crops like tomatoes, cucumbers, and peppers were grown alongside experimental crops such as okra and passion fruit. The USDA-funded trial reported significant yields:

Fish Yield: 22,700 kg/year of tilapia.
Vegetable Yield: Over 45,400 kg/year of mixed produce.

39.1.5. Economic Viability

The project demonstrated strong economic potential, with an estimated wholesale value of $325,000 per year (2016).

Boone Mora et al (NCRDC) reported that from the 10,000 sq. ft facility… after paying all costs… and when selling ALL production (tilapia, tomato, pepper, etc) at $1/lb (this i was in a very rural NC in 1992-94), they determined that profitability was in the range of $30- to $40,000/yr.

Based on suggested baseline ratios (v:v 1:2+, v:a 1:6+, feed-fish:fruit 1:7+), the system could support:

Fish Production: 22.7 kg of tilapia valued at $75,000/year at $3.30/kg.
Vegetable Production: Up to 170,000 kg of organic tomatoes valued at $935,000/year at $5.5/kg, plus 40,000 kg of No. 2 tomatoes valued at $140,000/year at $3.5/kg.

39.1.6. Challenges and Solutions

Challenges included maintaining optimal pH levels due to sand containing mollusk shells and phosphate nodules, which initially caused high pH (8.3-8.5). This was resolved by replacing the sand.

Disease management was another issue – particularly southern tomato wilt – which could be mitigated through sand sterilization before inoculating with nitrifying bacteria and maintaining strict sanitation.

39.1.7. Fish Management

Fish fry or fingerlings were added monthly, with marketable fish (1.25-1.50 lbs.) harvested after six to seven months. The tanks were divided into seven compartments to separate fish by size for continuous harvesting without moving large numbers of fish.

39.1.8. Lessons Learned and Recommendations

Mora recommended starting with a smaller greenhouse (e.g., 30 x 50 feet) to troubleshoot system issues before expanding operations. He emphasized using coarse sand inoculated with nitrifying bacteria and maintaining a proper slope in the sand beds for effective drainage.

39.1.9. USDA Trial Outcomes

The USDA-funded Commercial Trial confirmed iAVs commercial potential:

Water Efficiency: iAVs used only 27% of system water capacity and 19% of annual water volume compared to the University of the Virgin Islands (UVI) system.
Revenue Generation: iAVs generated 7.5 times more gross revenue per square meter (minus direct fish costs) than UVI.
Equipment Costs: iAVs equipment costs were only 30% of UVI’s system, with annual revenue/equipment + material costs being 15.7 times higher.
Yield Comparison: Fish yield per cubic meter was 2.8 times UVI’s best result; plant yield was 9.3 times UVI’s mean best.

39.1.10. Conclusion

Boone Mora’s iAVs demonstration project proved that integrated aquaculture and vegetable culture can be both environmentally sustainable and economically viable when designed correctly and paired with effective marketing strategies.

39.2. Comparative Analysis of iAVs and UVI Systems

39.2.1. Introduction

Traditional aquaponics often suffers from a lack of verifiable data. However, iAVs stands out with a strong data foundation. This section compares iAVs with the University of the Virgin Islands (UVI) raft system, focusing on their respective efficiencies and productivity metrics.

39.2.2. Historical Context and Data Sources

iAVs was developed in 1984 and registered in September 1985, preceding the UVI raft system, which has reported start dates ranging from 1987 to 2001. Despite numerous demonstrations, comprehensive data on UVI remains limited. The following analysis uses the most successful UVI trial results over 25 years and compares them with iAVs data from experiments conducted in the late 1980s.

39.2.3. Comparison of Productivity Metrics

Key productivity metrics differentiate iAVs from UVI:

Lo-tech iAVs: Data were adjusted by a 40% reduction to account for low stocking densities, male tilapia use, and forced aeration. This suggests potential yield rates without electrical aeration, though yields could increase with higher stocking densities or aeration.
Hi-tech iAVs: Reflects a 10% reduction in yield from a USDA-sponsored commercial-scale demonstration project in 1992-93.

Notably, UVI’s data does not account for precipitation water volumes, which significantly impacts water usage comparisons. For example, St. Thomas’ mean annual rainfall exceeds the total water used by iAVs in a North Carolina greenhouse when scaled similarly.

39.2.4. Merit and Efficiency

iAVs is simpler to establish and operate than UVI/DWC systems while offering higher resource efficiency and productivity. It excels at producing high-value crops such as tomatoes, cucumbers, peppers, and various greens.

39.2.5. Commercial Applications

iAVs demonstrates strong economic viability in commercial contexts. For instance, a 1989 iAVs crop at North Carolina State University produced USDA Grade No. 1 tomatoes at a rate of 61 kg/m²/year. Modern projections suggest yields could reach or exceed 80 kg/m²/year with CO₂ supplementation in greenhouses.

The economic benefits extend beyond crop yields; iAVs can also generate revenue from fish sales and other value-added products, making it attractive for both small-holder operations aiming for food self-sufficiency and large-scale commercial enterprises near urban centers.

39.2.6. Conclusion

iAVs offers significant advantages over traditional aquaponic systems due to its simplicity, efficiency, and high productivity.

39.3. Gordon Watkins’ 22-Year iAVs System

39.3.1. Background

In October 1997, Gordon Watkins, an organic farmer and tropical fish enthusiast from Arkansas, established an iAVs inspired by Dr. Mark McMurtry’s research at North Carolina State University. His goal was to achieve year-round production and diversify his crops beyond organic blueberries.

System Design: Greenhouse Structure: A 22’ x 14’ greenhouse attached to Watkins’ home, built with a cement block foundation and framed with white oak and redwood. The roof was glazed with twin-wall polycarbonate, while the sides were made from recycled insulated glass panels. Ventilation was controlled using top-hinged Thermopane windows and a thermostatically-operated exhaust fan.
Fish Tank: A 22’ x 4’ concrete vat with a V-shaped bottom, divided into five sections to accommodate different fish species and sizes. The tank was shaded with slatted panels for accessibility.
Sand Biofilter: A 22’ x 8’ sand biofilter adjacent to the walkway, built with cement block walls and filled with sand and gravel. The biofilter drained water back into the fish tank, with an epoxy coating applied to prevent lime leaching.

39.3.2. Operational Features

Water Circulation: Danner submersible pumps fed water from each fish tank section to an 8′ x 4′ sand bed, operating on a timer for efficient water turnover.
Aeration: Air stones maintained dissolved oxygen levels at around 5 ppm.
Heating: A two-zone hydronic heating system powered by a natural gas water heater ensured optimal temperatures.

39.3.3. Challenges and Adaptations

Watkins found that constructing the iAVs was more complex than using prefabricated tanks, and viewing the fish was difficult due to the tank design. Over time, he switched from tilapia to hybrid bluegill to reduce heating costs.

39.3.4. Outcomes

The iAVs successfully supported crops such as tomatoes, cucumbers, and herbs. By maintaining a 1:1 ratio of biofilter volume to biological load, Watkins achieved a balance between fish production and plant growth.

39.3.5. Long-term Sustainability

After 22 years, the iAVs remains operational in maintenance mode, primarily growing ferns and perennials. The greenhouse now relies on passive solar heating, demonstrating the system’s resilience and disproving concerns about sand clogging.

39.4. Building an iAVs in Developing Nations

iAVs was developed as an agricultural solution specifically designed for arid and underdeveloped regions, such as the African Sahel. The images below illustrate the creation of a low-cost, low-tech iAVs, which can also be adapted to provide fresh fish and nutritious vegetables for a family of four in a space no larger than a typical supermarket parking spot.

Proportions depicted are approximate and the materials and configuration can be varied to suit the resources and skills of the user.

An iAVs consists of a biofilter filled with medium-coarse sand, which serves as both mechanical and biologocal filtration and plant substrate, connected to a fish tank.
The sand biofilter and fish tank can be made watertight using puddled clay, plastic liners, or fiberglass.
Furrows are formed in the sand, and seedlings are planted in the raised sections. Nutrient-rich water is periodically pumped from the fish tank into the furrows.

As the water percolates through the sand, fish waste solids are trapped and mineralized, providing nutrients for plant growth. The filtered water then drains back into the fish tank. This closed-loop system allows water to be recycled up to 300 times before being fully utilized by the plants.

The reddish tint in the image indicates the use of expansive clay (where available) as a natural alternative to synthetic membranes for water retention. The weir can be constructed from various locally available materials such as woven sticks and thatch, bricks or rocks, scrap tin, logs and mud, or wooden boards. Numerous configurations, both low-tech and high-tech, are feasible depending on the resources at hand.

The image above shows a pipe or hose to move water to the far end of the bio-filter This is not actually necessary. Return (drainage) with cascade aeration is not clearly depicted.

The example above demonstrates water transfer using a hand-operated mechanical pump. Alternative methods could include solar-powered pumps, shadoofs, animal-powered pumps, windmills, or even a simple bucket on a rope.

iAVs achieves up to 100 times greater water-use efficiency compared to traditional pond culture of tilapia. This system produces both fish and vegetables using the same amount of water that would otherwise be required solely for fish production. Annual water consumption can be as low as 5 cubic meters per year for each cubic meter of fish culture volume, with a significant portion of this water converted into edible biomass.

Credits: Pastel renderings by Brandy Noon, a Kenyan, circa 1992. Captions by Dr. McMurtry.

40. Guidelines & Monitoring

The success of an iAVs depends on balancing fish feed input with plant nutrient uptake.

40.1. General Operating Guidelines

To prolong the useful cycle life of a biofilter in an iAVs, the following practices are recommended:

Fish Stocking: Stock fish to meet the nutritional needs of the plants. iAVs is primarily a horticultural system, with fish production serving as a nutrient source. Start with 80-100 fish (15g each) per 1000 liters and grow them to 250-300g before harvesting larger fish.
Biofilter Ratio: Maintain a 1:2 ratio of fish tank volume to sand biofilter volume.
Water pH: Adjust water pH to 6.4 (± 0.4). Rainwater is often ideal.
Feeding Schedule: Feed the fish twice daily, with the last feed no later than 2:00 pm (adjust for tropical or winter climates). Avoid overfeeding; all feed should pass through the fish’s digestive system.
Lighting: Provide at least 12 hours of light daily, though this may vary depending on plant species.
Temperature Control:

Ambient air temperature: 15°C – 35°C (species/season-dependent).
Water temperature: 25°C – 30°C.

Irrigation: Design irrigation to exchange tank water volume twice daily, with two hours of pumping spread across eight cycles per day. Pump 25-30% of the tank volume (15-20 minutes ON) every two hours from dawn to dusk. Complete one full exchange after morning feeding and another after midday feeding, before dark.
Plant Density: Maintain high plant density across the biofilter surface, with most plants in their logarithmic growth phase. Avoid having all plants either too young or fully mature.
Feed Composition: Use a balanced feed that meets both fish and plant nutrient requirements. Avoid feeds high in sulfur or metals.
Crop Selection: Grow plant species with high nutrient demands relative to feed input composition. Avoid growing primarily lettuce or other low-demand crops; instead, maintain a mix of leafy greens and legumes, with at least 50% of the area dedicated to fruit-bearing crops.

By following these practices, you can optimize the performance and longevity of an iAVs.

40.1.1. Feed Input Rate and Plant Nutrient Requirements

Managing feed input relative to biofilter area is critical for long-term success:

Indeterminate Tomatoes: Feed input of 140–160 g/m³/day or 20–30 g/m²/day, with a planting density of 4 plants/m².
Root and Cole Crops: Require 80–100 g/m³/day or 10–20 g/m²/day.
Leaf Crops and Herbs: Generally need less feed due to lower nutrient requirements.
Mixed Cropping Systems: A feed rate of 120–160 g/m³/day is recommended under optimal conditions (pH ~6.4).

41. MONITORING

41.1. Monitoring and Management in iAVs

iAVs is designed to be low-maintenance and requires minimal intervention. Visual checks of plant and fish health are usually sufficient to ensure smooth operation.

41.2. Key Monitoring Tasks:

Water Flow: Ensure consistent water flow through the sand beds, checking for blockages or sediment buildup.
Fish and Plant Health: Regularly observe fish and plants. Healthy fish should be active, and plants should be green and growing well. Signs of stress (e.g., gasping fish or yellowing leaves) may indicate the need for intervention.
pH: iAVs naturally stabilizes around a pH of 6.4, ideal for both fish and plants. While frequent testing isn’t necessary, it is recommended as a precaution with extra monitoring,especially during the first few weeks of operation until the system stabilizes. If health issues arise in the fish or the plants you should check the pH regularly, and reduce feeding, until the system is back to normal.

41.2.1. System Monitoring .

41.2.2. Some advice for system design and safety

When designing an iAVs:

Position equipment for easy access.
Use low-voltage options (5 VDC, 12 VDC, or 24 VDC/AC) for safety.

41.2.2.1. System maintenance

Develop a clear maintenance schedule with daily visual checks of water flow, fish behavior, and plant health. For larger systems, use checklists for weekly and monthly tasks such as cleaning pumps or replacing air stones.

41.2.2.2. Automated monitoring and control systems

Automated systems can be useful but are less essential in iAVs compared to RAS or traditional aquaponic systems due to the self-regulating nature of iAVs.

Traditional methods of water quality monitoring, such as manual sampling and laboratory analysis, are described as laborious and costly processes that do not allow for immediate detection of changes. iAVs, with stabilized pH and effective filtration experience fewer fluctuations in key parameters, reducing the necessity for frequent manual interventions and the associated costs.

41.3. Important parameters

Water Quality

Maintaining optimal water quality is crucial for both fish and plant health in iAVs:

Dissolved Oxygen (DO): Ensure proper aeration through air pumps; low DO can stress fish.
pH: The system naturally stabilizes around a pH of 6.4.
Ammonia/Nitrite/Nitrate: Monitor these occasionally; at a pH of 6.4, most ammonia is converted into less toxic ammonium.
Water Temperature: Keep between 25°C to 30°C for optimal growth.

Equipment Performance

Regularly check pumps, timers, and backup systems (e.g., air pumps with battery backups) to ensure continuous operation during power outages.

Total nitrogen (ammonia, nitrite, nitrate)

In iAVs, nitrogen management is simplified due to the system’s target pH of approximately 6.4. At this pH, toxic ammonia (NH₃) is predominantly converted into its less harmful form, ammonium (NH₄⁺), reducing the risk of ammonia toxicity and minimizing the need for frequent monitoring. Most commercial test kits measure Total Ammonia Nitrogen (TAN), which includes both ammonia and ammonium but does not account for pH’s role in determining toxicity. Therefore, these kits may be less useful in iAVs compared to traditional aquaponics systems where pH fluctuations can increase ammonia toxicity.

To monitor nitrogen compounds (TAN, nitrite, and nitrate), it is recommended to test the water daily or at least weekly to detect any spikes in ammonia or nitrite. Affordable aquarium test kits are sufficient for basic monitoring, but spectrophotometric analysis can provide more precise measurements.

If high levels of nitrite or ammonia are detected, reduce fish feeding for a few days but avoid stopping entirely to maintain biofilter health. Nitrite (NO2−) has a target value of 0.0 mg/L with a threshold of 0.2 mg/L, as it can interfere with oxygen transport in fish, leading to “brown blood disease.” Nitrate (NO3−), while less immediately toxic, should not exceed 300 mg/L to prevent long-term health risks like eutrophication.

Maintaining a pH around 6.4 ensures ammonia remains in its safer ammonium form, safeguarding aquatic life.

Phosphorus and other nutrients

Plant health is closely linked to nutrient availability. Leaf color and growth patterns can indicate deficiencies that require prompt investigation. Below are key nutrient deficiencies and their symptoms:

Phosphorus (P): Stunted root growth, reddish leaves, delayed maturity.
Potassium (K): Burnt patches on older leaves, wilting, poor flower/fruit development.
Calcium (Ca): Burnt leaf tips, blossom end rot in fruits like tomatoes.
Magnesium (Mg): Yellowing between veins on older leaves.
Sulphur (S): Yellowing of new leaves; rare in iAVs due to typically high sulphur levels.
Iron (Fe): Yellowing of young leaves with brown patches.
Zinc (Zn): Stunted growth; zinc toxicity is more common than deficiency in aquaponics due to galvanized equipment.

Water hardness

Two types of water hardness are important in iAVs: general hardness (GH) and carbonate hardness (KH). GH measures calcium and magnesium levels, essential for plant and fish health. KH buffers pH fluctuations caused by biological processes like nitrification.

For optimal iAVs performance, water hardness should be between 60-120 mg/L. Regular testing ensures adequate calcium and magnesium levels for plant uptake and prevents osmotic stress in fish.

Algae

Excess algae growth in the fish tank can disrupt water chemistry and clog pumps. Algae produce oxygen during the day but consume it at night, potentially leading to oxygen depletion harmful to fish. Monitoring algae growth is straightforward – look for green water or algae buildup on tank walls.

To prevent algae growth, minimize light exposure to the fish tank using shading methods

41.3.1. Sand Quality Monitoring

Regular monitoring of the sand bed is essential for maintaining optimal system performance:

Drainage: Water should drain completely within 15-20 minutes after irrigation cycles.
Ridges: The ridges, where plants are grown, should be kept free of debris and organic matter to ensure healthy root development and prevent blockages.
Water Distribution: Ensure water distribution irrigation throughout the furrows.

41.3.2. Plant health

Regularly inspect plants for signs of nutrient deficiencies or disease.

Periodically reassess crops for optimal productivity.

Relative humidity

Relative humidity measures air moisture relative to its maximum capacity at a given temperature. Managing humidity is crucial for preventing diseases and pests like spider mites or mold. A hygrometer can easily measure humidity levels.

Adjust humidity by controlling temperature or improving ventilation. Dehumidifiers can also help maintain optimal humidity levels automatically.

Hygrometer. Rhetos, CC0, via Wikimedia Commons

Air temperature

Air temperature significantly affects plant growth and vulnerability to pests. Most vegetables thrive between 18-30°C, though some crops prefer cooler or warmer conditions. Choose plants suited to your local climate for optimal results.

41.3.3. Fish health

Maintaining fish health is critical for a successful iAVs. Regular observation of fish behavior and appearance is essential to recognize what is “normal” for the species you are raising. Good water quality is crucial, as it helps reduce stress and strengthens the fish’s immune system, enabling them to resist diseases and parasites.

Daily Monitoring: Check your fish daily for signs of stress, illness, or parasites. Observe their behavior during feeding and note any changes in activity or appearance. Healthy fish should be active, have clean and intact fins, and display normal swimming patterns.
Stocking Density: Avoid overcrowding to reduce stress and maintain water quality. Adjust stocking density as the fish grow by harvesting larger individuals when necessary.
Feeding Practices: Feed fish twice daily, with the last feeding completed by 2pm, especially in warmer climates or during winter months. Monitor how much the fish consume to prevent overfeeding, which can degrade water quality. Underfeeding can stunt growth, so adjust feeding rates based on growth patterns.
Feeding Rates: Weigh feed to monitor consumption or visually assess feeding behavior until the fish stop eating. Keep records of feeding amounts to track trends over time. Reduced appetite may indicate environmental issues, while increased appetite may suggest the need for more food.

Indicators for assessing fish stocks

Healthy fish exhibit normal behavior and physical condition:

Behavioral Signs: Normal swimming, clean fins, clear skin, and no gasping for air.
Physical Signs: Intact gills, no bleeding or lesions, clear eyes, and no swelling around the vent.

Watch for abnormal behaviors such as lethargy, erratic swimming, gathering near oxygen outlets, or jumping out of the water. Physical signs like pale gills, skin lesions, or bulging eyes may indicate illness.

Stress

Stress weakens immunity in fish, making them more susceptible to infections from bacteria, viruses, fungi, and parasites. Long-term stress can also reduce their ability to adapt to environmental changes. Prevent stress by maintaining optimal stocking density, providing proper nutrition, and ensuring ideal water conditions (temperature, pH, oxygen levels). Hormonal indicators like cortisol can be used to monitor stress but require professional handling.

Disease Management

Disease prevention is vital in any aquaculture system but especially in iAVs due to the closed-loop nature of the system. Poor water quality can exacerbate disease outbreaks. Regular monitoring helps detect early signs of illness so that treatments can be more effective. If disease is suspected or mortality rates increase significantly, consult a veterinarian.

41.4. System Inspection

Leaks and Damage: Regularly inspect the physical structure, including tanks, and irrigation lines, for any leaks or signs of wear and tear. Prompt repairs prevent system failure and maintain efficiency.

41.5. Long-Term System Evaluation:

Performance Review: At least once a year, evaluate the overall system performance. Review the health and productivity of both fish and plants, and assess the efficiency of water flow, and aeration. Make any necessary adjustments to improve the system’s long-term sustainability.
Equipment Upgrades: Inspect all equipment, including pumps, tubing, and sensors, and replace any worn-out components. Consider upgrading equipment if new technologies or more efficient solutions are available.

41.6. Record Keeping and Observation

Keep detailed records of:

Fish feeding rates and consumption patterns.
Plant growth rates, health, and production.
Environmental parameters (pH, temperature, light).

System Responses:

Monitor fish behavior (e.g., feeding habits) and plant health (e.g., yellowing leaves) to detect imbalances early. Over time, you’ll develop an intuitive understanding of how to adjust system parameters based on these observations.

By following these general monitoring and maintenance guidelines, your iAVs can operate efficiently with minimal intervention, allowing you to focus on maximizing plant and fish productivity.

42. History of iAVS and Aquaponics

42.1. Terminology: “Aquaponics”

iAVs predates the widespread use of the term “aquaponics,” which began appearing in academic literature in the late 1990s (Milicic et al., 2017). Dr. McMurtry’s work laid much of the foundational science behind modern aquaponics (Wang 2022).

The term “aquaponics”, blending the words “aquaculture” and “hydroponics, is thought to have originated in the late 1990s as a blend of “aquaculture” and “hydroponics.” It first appeared in literature when describing the functions of the new Disney EPCOT (Experimental Prototype Community of Tomorrow) theme park “The Land,” where sand culture featured prominently alongside other integrated systems . EPCOT had planned ‘The Land’, where ‘the organizers plan to grow everything from bananas to shrimps through aquaponics, hydroponics, multicropping, sand culture, aquacell modes and whatever else today’s farmer has never dreamed of’. However, the specific meaning and origin of the word ‘aquaponics’ remain unconfirmed (Palm 2024).

(Marth 1981)

The term, “aquaponics,” begins to appear in the titles for academic literature in the late 1990’s. Prior to this, the literature reveals that what would today be termed as aquaponics was referred to in the 1970’s and 1980’s by names such as “hydroponic aquaculture pond,” “hydroponic solar pond,” “integrated agriculture,” “integrated aquaculture,” “integrated fish culture hydroponic vegetable production system,” and “Integrated Aqua-Vegeculture System (iAVs) (Goodman 2011).

The historical connection between the term “aquaponics,” the Disney EPCOT project, and iAVs highlights the significant role of sand culture and the contributions of Dr. Merle Jensen in shaping modern aquaponics. As a known expert in sand culture, Merle Jensen’s involvement in designing “The Land” at EPCOT, where aquaponics and sand-based cultivation methods were prominently featured, underscores the importance of sand as a growing medium in integrated systems. This connection is further strengthened by Jensen’s association with the iAVs research group, which developed the first scientifically validated system using sand as both a biofilter and growing medium.

The use of sand in iAVs demonstrated its unparalleled efficiency in nutrient cycling, water filtration, and plant productivity compared to other mediums like gravel or mechanical filters. The validation of iAVs at North Carolina State University established it as a foundational system, emphasizing low-input, high-yield sustainable practices. Given Jensen’s expertise and credibility in sand culture, his involvement with both EPCOT and iAVs bridges the historical evolution of integrated aquaculture from experimental concepts to scientifically grounded systems.

The use of sand in iAVs is not merely a technical choice but a cornerstone of its development. It also positions iAVs as a critical milestone that influenced subsequent systems (Wang 2022), while maintaining scientific rigor and operational efficiency unmatched by many later adaptations. The integration of sand culture into both EPCOT’s vision and the practical application of iAVs highlights its enduring relevance in sustainable food production systems.

Terminology: iAVs

The terminology chosen by the NCSU team is significant, they named their invention the “Integrated Aqua-Vegeculture System” (iAVs). This was a deliberate choice that occurred before the term “aquaponics” gained widespread popularity. The name itself underscores the core design philosophy: it was a truly integrated system where the components were symbiotic and inseparable by design. The emphasis on “vegeculture” highlights the system’s capacity to cultivate a wide range of horticultural crops.

iAVs was the “first known closed-loop aquaponic system”. A closed-loop system is defined as one that is “entirely self-sustaining,” where water is continuously recirculated between the fish and plant components, and where no external nutrients or chemicals are required to maintain the ecosystem beyond the initial input of fish feed. This stands in contrast to earlier or parallel systems that may have integrated fish and plants but did not feature a fully recirculating design where the plant component served as the complete filtration system for the aquaculture component.

This development must be placed in its proper historical context. While ancient agricultural practices such as the Aztec chinampas and Asian rice-paddy farming represent early forms of integrated aquaculture, they are not analogous to the modern, scientifically engineered, and fully recirculating systems. The scientific literature consistently attributes the pioneering of the modern, documented closed-loop system to the work conducted at NCSU in the mid-1980s. While some sources acknowledge earlier work, such as that by Naegel in Germany in 1977, as the “first example of a modern coupled system,” the specific distinction of a closed-loop design, where the hydroponic component performs the complete biofiltration, is credited to McMurtry and his colleagues at NCSU.

42.2. Aztec Chinampas

There has been much dispute about the origin story of aquaponics; however, many records trace early forms back to ancient agricultural systems. Among these are the Aztec chinampas, developed between 1150-1350 AD (Shabeer, 2016; Konig 2018; Okomoda 2023) or approximately 1000 years ago (Roy 2025) in the shallow lakes of Central Mexico. The Aztecs, founders of a vast empire with their capital Tenochtitlán (modern-day Mexico City) established along the shores of Lake Texcoco, constructed these islands, termed “floating farms” or chinampas, due to the lack of fertile land in the wetlands (Roy 2025). They built these fertile plots by layering reeds, sediment, soil, mud, and plant debris (Roy 2025), cultivating crops such as maize, beans, squash, tomatoes, and flowers (Roy 2025). Some accounts suggest the roots of these plants extended into the lake water, absorbing nitrogenous wastes from the lake which was enriched by aquatic animal waste (Roy 2025). Today, chinampas remain a testament to the Aztecs’ agricultural innovation and are recognized as an important agricultural heritage system (Arumugam 2021), continuing to produce significant amounts of vegetables and flowers annually.

An artist’s conceptual illustration of chinampas, a wetland agriculture-aquaculture system that was common from the valley of Mexico City to the western Amazon regions of South America. Development of the systems stretch back as far as 6,000 years B.P. From Aghajanian (2007).

The chinampas system is often regarded as an early precursor to aquaponics due to its integration of plant cultivation and aquatic environments. However, it was likely not a true aquaponic system as defined today. While fish and other aquatic animals inhabited the surrounding canals and their waste may have enriched the water (Roy 2025), their role in nutrient cycling for the crops appears to have been largely incidental rather than intentionally integrated. Instead, chinampas likely relied primarily on the nutrient-rich lake sediments and layered organic matter to sustain plant fertility, focusing on soilless cultivation without actively managing fish for nutrient input (Palm 2024; Okomoda 2023; Jones 2002; Arumugam 2021). This distinction fuels the debate about whether chinampas qualify as aquaponics. Despite this, chinampas remain a remarkable example of sustainable agriculture and ecological ingenuity, serving as an inspiration for modern aquaponics (Palm 2024; Okomoda 2023; Jones 2002; Arumugam 2021).

42.3. Asian Rice-Fish Systems

Originating approximately 1,500 years ago in South China, Thailand, and Indonesia (Roy 2025; Colman and Edwards, 1987), rice-fish systems represent a more direct precursor to modern aquaponics compared to the Aztec chinampas. These systems integrated fish farming with rice cultivation in flooded paddy fields (Shabeer, 2016; Roy 2025). Farmers stocked fish in rice paddies, a practice likely originating from harvesting wild fish that entered the fields during planting (Pillay, 1990). In this symbiotic cycle, fish waste acted as a natural fertilizer, providing nutrients for the rice plants (Rakocy et al., 2004; Arumugam, 2021; Roy 2025). This integration has been shown to increase rice yields by up to 15% while producing significant amounts of fish per hectare (Lightfoot et al., 1990).

Unlike Aztec chinampas, where the role of fish waste was likely incidental, rice-fish systems represented a deliberate integration of aquaculture and agriculture. This purposeful synergy, combining terrestrial crops and aquatic organisms in a mutually beneficial system, aligns closely with modern aquaponic principles (Okomoda, 2023). Moreover, integrated fish culture has a long history across Asia, where fish ponds benefited from agricultural and livestock by-products as nutrient inputs (Schimittou et al., 1985; Tan and Khoo, 1980; Colman and Edwards, 1987). Such integrated systems underscore their significance as foundational models for modern aquaponic practices.

One entrepreneur expanded on this concept by raising ducks, finfish, and catfish in a single system. Ducks were kept above the finfish, whose waste then flowed downstream to feed the catfish. Any remaining nutrient runoff was used to fertilize rice crops. This stacked, multi-species design maximized resource use but was limited by seasonal freezing, rendering the system inactive for five months of the year (Jones, 2002; Rakocy et al., 2004; Okomoda, 2023).

42.4. Inca Agricultural Systems

Before the arrival of the Conquistadors, the Incas of Peru used a different system involving ponds near their mountain homes. Fish were added to the ponds which attracted geese that would eat from the water and relax on the islands. Goose droppings and fish scraps fertilized the islands. This system provided food and protection, as the pond acted as a moat. It also created a warmer microclimate, extending the harvest season. The Inca systems were very efficient and fed more people per square mile than any other type of farming in similar arid areas. While efficient and ecologically integrated, this system lacked direct nutrient cycling between fish waste and plant cultivation . Thus, it is better categorized as integrated farming rather than aquaponics (Jones 2002). While innovative, claims of their exceptional efficiency in feeding large populations per square mile are intriguing but require comparative data for validation.

Summary

While utilizing nutrient cycling principles, these traditional practices lacked the controlled, scientific approach characterizing modern aquaponics.

42.5. Early Experiments in the 1960s-1970s

Until the late 1960s, the importance of nitrifying bacteria was largely overlooked and rarely intentionally utilized for water reconditioning (Burrows 1968).

The research of the 1960s and early 1970s was not about aquaponics but about the development of Recirculating Aquaculture Systems (RAS). This era established the engineering principles of biofiltration. The first scientific efforts involved adapting technology from the field of municipal wastewater treatment, specifically the use of activated sludge.

Sengbusch et al. (1965) experimented with raising carp in recirculating water systems using activated sludge for water treatment.

Published in Germany’s Archiv für Fischereiwissenschaft, this work by R. von Sengbusch and his colleagues represents the first known scientifically documented attempt to raise fish in a completely closed, recirculating water system where the water was continuously purified using an activated sludge process. The focus was exclusively on fish survival and growth through water treatment; there was no consideration of integrating plants.

Building on the foundation laid by Sengbusch, the research of K. Scherb and F. Braun at the Bavarian Biological Research Institute provided a more detailed and quantitative analysis of RAS technology. Their 1971 paper, published in a German journal on wastewater and fisheries biology, described experiments with rainbow trout (Salmo gairdneri) in a similar activated sludge system.

The work of Sengbusch (1967) and Scherb (1971) was not framed as an effort to “grow fish and plants together.” Instead, it was driven by a singular problem: how to mitigate the toxic effects of fish waste in high-density aquaculture. The problem was waste accumulation, and the solution was adapted from existing wastewater treatment technology.

The 1970s marked the pivotal decade when the abstract idea of combining fish and plant culture transitioned into a subject of deliberate scientific inquiry and practical experimentation. Building on the successful development of Recirculating Aquaculture Systems (RAS), researchers began to intentionally link hydroponic plant cultivation with these closed-loop fish systems. This period saw the emergence of two distinct but parallel movements: one driven by an ecological, holistic philosophy at the New Alchemy Institute, and the other by a rigorous, quantitative approach within university laboratories.

One of the first documented experiments explicitly using aquaculture effluent for plant fertilization was by William McLarney (1974) in “Irrigation of Garden Vegetables with Fertile Fish Pond Water”. Published in the second volume of The Journal of the New Alchemists, this is one of the first documented accounts of an experiment explicitly using aquaculture effluent to fertilize terrestrial plants. The methodology was straightforward: water from ponds used to culture tilapia was used to irrigate garden vegetables. The NAI’s research was iterative, as evidenced by a follow-up article in 1975 titled “Further Experiments in the Irrigation of Garden Vegetables with Fertile Fish Pond Water,” which continued to explore this synergy.

While not published in a peer-reviewed journal, it was a practical, hands-on demonstration of the core principle of nutrient recycling. McLarney’s work framed the integration of fish and plants not as a mere technical solution but as an ecological imperative, a way to create more resilient and sustainable food systems.

Collins et al. (1975) explored hydroponic plant culture to treat effluent from catfish holding tanks. Theirs was a single-pass system and did not involve biofiltration (Lewis et al., 1978: Baker 2010). The catfish began dying on day 8 and the cumulative mortality reached 100% on day 15. Despite these initial setbacks in integrating hydroponics with RAS, the concept of nutrient recycling continued to evolve and eventually contributed to the development of more successful aquaponic systems in later years.

An early and influential publication in a trade journal that explicitly linked the two disciplines by name, signaling the recognized potential for their integration to the wider aquaculture community was by Sneed (1975) in “Fish farming and hydroponics” (Aquaculture & The Fish Farmer).

While less detailed than the academic papers that would soon follow, its importance lies in its role as a signal of emerging interest. It indicated that the concept of integration was moving from the philosophical realm of ecological design into the practical considerations of the commercial aquaculture industry. This paper helped to prime the scientific and agricultural communities for the more rigorous academic inquiries that would define the latter half of the decade.

In the late 1970s, significant advancements were made in the field of aquaculture, particularly with the development of recirculating aquaculture systems (RAS) in Europe and the integration of hydroponics with RAS water and nutrient cycles. Reducing the concentration of nitrogen compounds, toxic to fish, became a major challenge for recirculating aquaculture and the beginning of the aquaponic era, (Bohl M., 1977, Collins M, Gratzek J, Shotts Jr E, Dawe D, Campbell L, et al., 1975; Voicea 2024).

Bohl (1977) was instrumental in the early development of RAS technology, which aimed to minimize water consumption and improve sustainability in fish farming and also conducted some experiments with aquatic recirculating system for aquaculture and soilless plant systems as a means of treating fish wastes and removing nitrogen compounds (Sneed et al. 1975; Lewis et al. 1978; Naegel 1977; Sutton and Lewis 1982; Datta 2018).

Naegel’s work in 1977, titled “Combined Production of Fish and Plants in Recirculating Water,” represents an early example of coupled aquaponics research. Although stocked at a low density (20 kg/m ³) with tilapia (Tilapia mossambica) and carp (Cyprinus carpio), the system yielded harvests of tomatoes (Lycopersicon esculentum) and iceberg lettuce (Lactuca scariola).

Naegel’s system was remarkably advanced for its time. It included not only a nitrification tank (an activated sludge system) for converting ammonia to nitrate, but also a separate denitrification step to manage total nitrogen levels, demonstrating a deep understanding of aquatic chemistry. The paper provided quantitative data on fish weight gain, water quality parameters (pH, ammonia, nitrite, nitrate), and plant growth, concluding that the plants grew well in the wastewater without any supplemental fertilizers. Crucially, Naegel explicitly built upon previous research, citing both Sengbusch (1965) and Scherb (1971), thereby establishing a clear and traceable scientific lineage from RAS to integrated systems. This paper provided the international scientific community with the first robust, peer-reviewed evidence that combined fish and plant production in a recirculating system was not only feasible but also highly effective(Loyacano and Grosvenor, 1973; Palm 2019).

In 1978 a paper, published by William M. Lewis and his colleagues at Southern Illinois University in the Transactions of the American Fisheries Society, provided another piece of scientific validation from a different angle. The research team linked the production of channel catfish (Ictalurus punctatus) with three varieties of tomatoes (Lycopericon esculentum) grown in outdoor gravel hydroponic tanks.

While the primary source of nutrients for the plants was fish waste, the researchers still had to add supplemental plant food nutrients (Baker 2010). This work was continued with Sutton (1982).

Muir, Paller, and Lewis introduced reciprocating biofilters (RBFs) in the development of aquaponics during the late 1970s.

The first study from UVI on aquaponics was conducted in 1984 by Watten and Busch, marking a milestone in integrating vascular plants with recirculating aquaculture systems (RAS). The study detailed an integrated system designed specifically for operation in a tropical environment, using tilapia and tomatoes.

A 1986 publication by Zweig (New Alchemy Institute) was first widely cited publication detailing a system where plants were grown on floating rafts directly on the surface of a solar-algae pond, providing the direct technical blueprint for modern DWC.

In 1987 McMurtry published the first comprehensive scientific description of the Integrated Aqua-Vegeculture System (iAVs), establishing the “media-based” methodology where a sand bed acts as a combined mechanical, mineralization, and biological filter.

The Integrated Aqua-Vegeculture System (iAVs) developed at NCSU represents a truly integrated design philosophy. Rather than separating functions into multiple components, McMurtry’s system combined them into a single, robust unit: the sand biofilter. This media bed performs mechanical filtration, biological filtration (nitrification), and mineralization all in one place, while also providing the substrate for plant growth. This approach benefits growers because of its elegant simplicity (fewer moving parts and components), its biological stability, and its ability to support a wider variety of crops, including heavy-fruiting vegetables like tomatoes and cucumbers.

42.6. South Carolina

In the 1970s, at the South Carolina Agricultural Experiment Station, researchers Loyacano and Grosvenor conducted experiments to address nutrient buildup in channel catfish ponds by integrating hydroponics with water chestnut cultivation. Their goal was to utilize water chestnuts (Eleocharis dulcis) to absorb excess nutrients, such as nitrate nitrogen and ammonia nitrogen, from aquaculture systems. This approach aimed to improve water quality while simultaneously producing a secondary crop (Naegel 1977).

These early experiments laid the groundwork for nutrient recycling technologies and highlighted the potential of plants to act as biofilters in closed-loop systems but faced challenges related to nutrient balance and system stability.

42.7. Woods Hole Oceanographic Institution

In the 1970s, researchers at the Woods Hole Oceanographic Institution explored using wastewater effluent mixed with seawater to grow lobsters and flounders at the end of a food chain. This involved cultivating algae in high-rate oxidation ponds on wastes, a process that was reaching industrial levels and could contribute significantly to protein production. These efforts aligned with pioneering concepts by scientists like Oswald and Golueke (1968) and Soeder (1972), who emphasized the potential of such systems to address global protein needs through sustainable practices

The Woods Hole Oceanographic Institution (WHOI) is a prominent private, nonprofit research and higher education organization focused on marine science and engineering. It was established in 1930 in Woods Hole, Massachusetts, and is the largest independent oceanographic research institution in the United States. WHOI has a long history of advancing marine science, including significant contributions to aquaculture and marine ecosystem studies. This research was part of broader efforts to utilize high-rate oxidation ponds for algae cultivation, which could convert waste into usable resources for protein production. These efforts aligned with pioneering concepts by scientists like Oswald and Golueke (1968) and Soeder (1972), who emphasized the potential of such systems to address global protein needs through sustainable practices.

The work conducted by researchers at the Woods Hole Oceanographic Institution (WHOI) in the 1970s, involving the use of wastewater effluent mixed with seawater to grow lobsters and flounders, contributes indirectly to the history of aquaponics despite its focus on saltwater systems. This research aligns with the principles of integrated systems that recycle nutrients and support multiple trophic levels, which are foundational to aquaponics.

Dr. McMurtry and Dr. Ronald Zweig, FAAAS, co-presented a multi-day “integrated aquaculture” workshop at Wood’s Hole in 1989.

42.8. New Alchemy Institute

The conceptualization of modern aquaponics is credited to William McLarney, John Todd, and Nancy Jack Todd of The New Alchemy Institute (Fox 2010; Ruiz-Velazco 2024; Ansaba 2024). Although it closed in 1991, this institute pioneered research on integrated aquaculture systems through the 1970s and 80s (Carrasco 2020).

The New Alchemists were a group of scientists and environmentalists who founded the New Alchemy Institute (NAI) in 1969. Their mission was to develop sustainable, self-sufficient systems for living that integrated ecological principles into food production, energy use, water purification, and shelter. The institute was established by John Todd, Nancy Jack Todd, and William McLarney, with contributions from others like Ronal Zweig, and operated until 1991.

The New Alchemy Institute was a pioneering research center located in Cape Cod, Massachusetts. It aimed to create ecologically derived human support systems that minimized reliance on fossil fuels and emphasized small-scale, decentralized technologies.

Key Figures

John Todd is a marine biologist and ecological designer known for developing “Eco Machines,” systems for water purification using natural processes. He co-founded the New Alchemy Institute and later established Ocean Arks International and John Todd Ecological Design. His innovative work earned him numerous awards, including the Buckminster Fuller Challenge Award.
Nancy Jack Todd co-founded the New Alchemy Institute alongside her husband John Todd. She played a significant role in the institute’s operations and later co-founded Ocean Arks International. Nancy has contributed extensively to ecological design literature.
William McLarney, a marine biologist, co-founded the New Alchemy Institute with John and Nancy Todd. He focused on integrating aquaculture with sustainable ecosystems. Later, he founded ANAI (Association de los Nuevos Alquimistas) in Costa Rica to continue similar ecological work.
Ronald Zweig was involved with the New Alchemy Institute during its active years and contributed to its aquaculture research. He co-developed the “raft” system for aquaponics alongside William McLarney, which laid the foundation for modern deep-water culture systems used in aquaponics today37. Zweig also collaborated with Dr. Mark McMurtry on integrated aquaculture workshops in 1989.

The foundations of contemporary aquaponics were laid by researchers at the New Alchemy Institute in the United States who played a pivotal role in advancing aquaponics and scientists at NAI are considered pioneers of modern aquaponics. They first used hydroponic plant culture as a way to improve water conditions for fish, not as an innovative technology for food production. The water quality in fish ponds deteriorates rapidly and requires regular replacement. Starting from the finding that aquatic plants clean water in natural sites, they first added aquatic plants and later terrestrial plants to clean water in fishponds.

In 1969, William McLarney, Nancy, and John Todd constructed a prototype system inspired by the Aztec model, aiming to provide a year-round source of shelter, fish, and vegetables and also experimented with integrated ecological systems, including a natural wastewater treatment system called the “living machine”.

In 1986, Ronald Zweig promoted the idea of integrating plants into a simple aquaculture system by matching the feeding rate and biomass of fish to the estimated nitrogen needs of plants. The only electrical component used was an air pump to maintain dissolved oxygen levels suitable for fish culture.

Nutrient deficiencies in magnesium and iron were observed. These were addressed by adding dolomite weekly for magnesium, and replacing 20% of the fish feed with rabbit feed for iron. This work demonstrated the efficacy of a nutrient based approach, but no research was conducted to commercialize the system (Baker 2010). The New Alchemy Institute, through its early experiments, laid the foundation for what would later become known as raft and Deep Water Culture (DWC) systems (Okomoda 2023; Voicea 2024). Although financial difficulties eventually led to the discontinuation of many of their programs, their work had a lasting impact on aquaponics development.

In parallel to the work of Zweig, Nair et al. (1985) developed a recirculating aquaponic system at the University of the Virgin Islands (UVI). The system used numerous mechanical components which kept operating costs high, at $3.18/kg of tilapia produced in 1985 prices. Tomato plants grew poorly despite an estimate that nitrogen production by fish exceeded plant requirements by tenfold. Salts (including plant nutrients) accumulated to 2.75 millisiemens in the system. Levels above 2.0 millisiemens 3 inhibit the growth of some plant species (Jones 2005). Iron averaged 0.1 mg/L in the system, which is less than the minimum of 1–2 mg/L suggested for hydroponic plant culture (Jones 2005). In a later experiment, plant growth was improved by adding nutrients suspected of being deficient (iron, potassium, calcium, and phosphorus) but salt accumulation remained an issue (Rakocy 1989) (Baker 2010).

42.9. University of the Virgin Islands (UVI)

At the Agricultural Experiment Station of the University of the Virgin Islands (UVI), St. Croix, the first experiments were carried out by Barnaby Watten and Robert Busch in 1984. Further results were obtained under the leadership of Dr. James Rakocy (Voicea 2024).

In an interview, James Rakocy said, “There was no research facility. We had some inexpensive vinyl-lined steel-walled swimming pools and were told to make the aquaculture research facility a showpiece. The first aquaponic system consisted of 3 metal oil barrels. One was used to raise fish. One was cut in half to create two hydroponic beds. One was used as a clarifier with a cone welded into the bottom. And half of the final barrel was used as a sump.”

The plant roots, in gravel, were regularly clogged with ‘waste,’ and, according to an interview with James Rakocy, gravel is “difficult to work with and not feasible for large commercial operations.” Around 1986, they started to test the use of floating rafts of Styrofoam, commonly referred to today as deep water culture (DWC).

This method, known as the “raft” system, was initially conceived in 1986 by Dr. Ronald Zweig, FAAAS, while at The New Alchemy Institute. Dr. Zweig and Dr. McMurtry co-presented a week-long seminar on integrated aquaculture at Wood’s Hole Oceanographic Institute in May 1989.

Dr. James Rakocy subsequently adopted and modified the DWC technique at the University of the Virgin Islands. These efforts, beginning as demonstrations (not formal research) in late 1986 or early 1987 and continuing through 2010, were influential in popularizing the approach.

Notably, in June 1986, while Rakocy was beginning site construction, Dr. McMurtry offered him his data and findings to date (gratis, as a professional courtesy), which was summarily and indelicately refused. The DWC method has since been serially and variously adapted over the decades.

42.10. History of the Integrated Aqua-Vegeculture System (iAVs)

While ancient agricultural practices such as the Aztec chinampas and Asian rice-paddy farming represent early forms of integrated aquaculture, they are not analogous to the modern, scientifically engineered, and fully recirculating systems. 1 The scientific literature consistently attributes the pioneering of the modern, documented closed-loop system to the work conducted at NCSU in the mid-1980s. 2 While some sources acknowledge earlier work, such as that by Naegel in Germany in 1977, as the “first example of a modern coupled system,” the specific distinction of a closed-loop design, where the hydroponic component performs the complete biofiltration, is credited to McMurtry and his colleagues at NCSU.

While early attempts to merge plant cultivation with aquaculture faced significant challenges, North Carolina State University (NCSU) is widely recognized as a birthplace of modern aquaponics, where researchers developed efficient integrated systems driven by a desire to reduce dependence on finite resources like land and water (Okomoda et al., 2022).

A key breakthrough occurred at NCSU in the 1980s when Dr. Mark McMurtry and Professor Doug Sanders engineered what is now recognized as the first genuinely “closed-loop” system integrating fish and plants (McMurtry, 1997b; Goodman, 2011; Datta, 2018; Ruiz-Velazco 2024; Ghosal 2025). In this pioneering design, effluent from fish tanks provided nutrients for tomatoes and cucumbers grown in sand beds, which simultaneously functioned as biofilters (Paul et al., 2022). This integrated system (iAVs) is notable for its high water-use efficiency and technological simplicity (McMurtry et al., 1997; Yang et al., 2025).

Konig (2018) acknowledges McMurtry as “the originator of aquaponics” and describes this system as the foundational model for subsequent flood and drain systems. Further reinforcing this, Ansaba (2025) states that researchers at the New Alchemy Institute at North Carolina State University laid the foundation for modern aquaponics. The early innovations from NCSU researchers established the groundwork for what would become a global movement in sustainable food production, cementing the institution’s legacy as a foundational force behind modern aquaponics (Goddek et al., 2015; Love et al., 2014).

Their foundational research provided critical evidence that iAVs held the potential to operate as a highly productive food system requiring minimal external inputs, pointing towards a more sustainable model.

A common operational strategy in earlier integrated fish and vegetable production systems involved the deliberate removal of suspended solids originating from the fish component. Techniques such as mechanical filtration were employed to clarify the water before it reached the plant roots (Rakocy et al., 2006; Nelson and Pade, 2007; Danaher et al., 2013; Senthilkumaran, 2024). While functional, a significant operational consequence of removing these solids was that the remaining dissolved nutrient levels in the water were often insufficient for optimal plant growth. Achieving commercially acceptable crop yields, particularly for fruiting vegetables, therefore typically demanded substantial additions of supplemental fertilizers (Lewis et al., 1978, 1981; Rakocy, 1989; Goddek et al., 2019; Ezziddine, 2020; Panana, 2021).

The introduction of the reciprocating biofilter represented a key refinement in managing the system’s biofiltration component. Operationally, this design achieves its periodic draining and re-saturation of the filter bed through an intermittent irrigation cycle. This controlled cycling proved highly effective. It significantly reduced operational problems such as filter media clogging, uneven water flow (channelization), and the development of anaerobic, low-oxygen zones detrimental to beneficial microbial activity (Lewis et al., 1978; Paller and Lewis, 1982).

Crucially, this improved biofilter management opened the door to retaining the fish solids within the system. Instead of being viewed solely as waste for removal, the solids could now be managed effectively within the filter bed itself, allowing them to decompose and serve as a valuable, slow-release source of essential nutrients for the plants (McMurtry et al., 1997).

From a plant nutrition standpoint, it’s crucial to recognize that the byproducts generated by fish culture represent a significant reservoir of essential mineral elements (Jung and Lovitt, 2011; Goddek et al., 2016; Gilbert, 2009; Seawright et al., 1998; Schneider et al., 2005; Neto and Ostrensky, 2013; Delaide et al., 2019). Discarding these solids, as was common practice, essentially meant discarding valuable fertilizer resources. Dr. McMurtry’s work was partly driven by the understanding that a truly efficient integrated system should ideally harness these inherent nutrients, thereby reducing or eliminating the dependence on costly external fertilizer inputs (Ogah et al., 2020). The goal was to move towards a system where the nutrient cycles were more completely closed.

42.11. Development and Early Experiments

In the early 1980s, Dr. Mark R. McMurtry began researching alternative approaches to agricultural production. He recognized that traditional farming methods faced major environmental and resource challenges on a large scale. Key problems motivating his research included the degradation of farmland through desertification, salinization, and soil erosion; the pollution of surface water and groundwater by nitrates; the overuse and depletion of essential aquifer resources; an increase in drought conditions; and the growing threat of climate change.

Faced with these issues, Dr. McMurtry set a clear objective: to establish and prove that sustainable methods for producing food were technically possible. His aim was to create agricultural systems capable of providing long-term food security for populations while significantly reducing negative impacts on the natural environment.

Dr. Mark McMurtry brought a unique perspective to sustainable agriculture research, transitioning in the 1980s from a professional background in architectural woodworking. His subsequent investigations into water treatment methodologies yielded a critical insight. Through systematic experimentation, Dr. McMurtry identified the exceptional efficacy of sand as a substrate for biological and physical filtration. This fundamental discovery regarding the properties and performance of sand filtration proved pivotal, forming the foundational principle upon which iAVs was subsequently developed.

In 1983, Dr. Mark McMurtry established a professional association with Merle Jensen, an individual recognized for his expertise in the disciplines of sand culture, horticulture, and greenhouse design. Mr. Jensen’s practical contributions included significant projects such as the design oversight for the Land Pavilion at EPCOT Center, Walt Disney World, Orlando, Florida.

Subsequently, in the autumn of 1984, Dr. McMurtry commenced graduate studies at North Carolina State University (NCSU). His academic advisor during this period was Paul V. Nelson, Professor Emeritus, whose areas of specialization encompass greenhouse operations management and the principles of plant nutrition.

Through his interactions with Dr. Jensen, Mark discovered that the water quality in the large aquarium, which holds 57 million gallons at EPCOT Center, is maintained using fluidized-bed sand filters. These biological filters utilize sand as a growth medium for beneficial bacteria, along with substantial daily water replacement. This prompted him to consider the potential of adapting sand filter technology, successfully utilized in major fish tanks like those at the EPCOT Center and other commercial aquariums, for his own smaller, home-based aquariums. This concept inspired him to devise a comparable filtration system for his aquaculture endeavors..

Mark, a passionate angler and aquarist, was frustrated with the significant time and effort required to maintain the approximately twelve three-stage external canister filtration systems for his home aquariums. As an avid gardener, Mark knew that nitrates – typically managed in aquariums through water changes – were valuable plant food. This led him to wonder if he could use plants to help purify his aquarium water and reduce maintenance.

In 1984, Mark began experimenting with sand as a potential filtration medium. His initial setup was simple: he filled a small ‘Tupperware’ dishpan (approx. 12″x16″x8″ deep) with sharp quartz sand acquired from a glass-maker friend. Small holes (~1/16th”) were drilled near the bottom edges of the dishpan’s side walls (not the bottom itself). He placed this container of sand on a shelf overlooking an 80-gallon tank of fathead minnows (kept to feed African Knifefish).

Mark quickly discovered two key benefits. First, the sand acted as a highly effective mechanical filter, trapping particulate and suspended solids. Initially, before plants were added, the surface would eventually clog, requiring him to simply scrape away the accumulated detritus layer. Second, the sand proved to be an excellent bio-filter medium, offering significantly more surface area for beneficial bacteria colonization than his previous canister filters. The results were so promising that Mark found he could eliminate the two Eheim canister filters on that tank while achieving even better water quality.

After about a month, Mark integrated his gardening interest by planting leaf lettuce directly into the sand filter. He observed that once the plants were established, the need for manually scraping the sand surface decreased significantly. Encouraged, he expanded his trials to include other crops like dill, chives, spinach, and bush beans, all of which demonstrated remarkable growth and health.

To optimize the system for plant roots and further enhance biological activity, Mark introduced a timer to the circulation pump. This allowed him to employ a technique known as reciprocating biofiltration (RBF), or ‘flood and drain’. This method prevented root drowning by periodically draining the sand bed, which also recharged the filter with oxygen during each dewatering cycle. This ‘supercharging’ benefited both the nitrifying bacteria and facilitated nutrient assimilation by the plants.

Ultimately, Mark’s innovative sand-based system dramatically reduced his maintenance time from several hours per week to just a few minutes per month. He successfully replaced his expensive, high-maintenance canister filters with a low-cost, highly effective system that simultaneously purified water and grew healthy plants. These early findings and the effectiveness of the experiments led to his decision to continue further.

42.12. Collaboration and Advancements

In the Autumn of 1984, Mark began to study greenhouse operations and management with Dr. Paul V. Nelson (Professor Emeritus), a renowned expert in botanical mineral nutrition and greenhouse management, based at NCSU.

Dr. Nelson’s contributions to the field of horticulture have been significant and far-reaching. His book, Greenhouse Operation and Management, is widely regarded as an industry standard and is extensively used in university-level courses worldwide.

Dr. Nelson played a crucial role in the development of the iAVs. He generously provided the greenhouse space for the initial, formal iAVs research and offered his technical expertise, without which the iAVs project may not have come to fruition.

In the winter of 1984-85, Mark’s studies led him to establish two 375-liter tanks, each equipped with biofilters filled with sand. One tank contained Hoagland solution (a standard nutrient mix well known to hydroponicists and horticultural researchers), and the other contained fish – mixed-sex Tilapia niloticus.

Each bed had five furrows, and along each furrow, a different plant species was grown: lettuce, spinach, carrots, beets, and bush beans. Irrigation frequency and volume, pH, temperatures, relative humidity, insolation, etc., were held constant (identical) across treatments.

The principal outcome of Mark’s trial was that plant growth in the integrated aquaculture system utilizing sand filters with furrows significantly outperformed that from the inorganic hydroponics system by a margin of 200% to 300%.

Dr. Nelson remained a key advisor, mentor, and co-author throughout the following decade, contributing to several papers and helping refine iAVs’ application.

42.13. Research and Expansion

In the summer of 1986, Dr. Mark McMurtry developed a much larger (approx. 500m²) iAVs demonstration system off campus with personal funds – effectively serving as a proof of concept at the ‘village scale.’ This project was specifically designed to simulate environmental conditions typical of the Middle East, Northern Africa, and the Sahel region.

Funded entirely by McMurtry, the study aimed to validate the iAVs method while fulfilling part of the requirements for his Master’s Degree in Environmental Design. It also supported his concurrent pursuit of a Master’s Degree in Technology for International Development, which served as a precursor to his admission to the College of Agriculture and Life Sciences. During this time, he was also a single parent raising a high-school-aged daughter.

During the winter of 1986-87, Dr. McMurtry spent many months tracking all nutrient inputs from fish feed to meticulously assess their distribution and impact. He conducted detailed elemental analysis of plant tissues and monitored changes within the filter volume’s composition in a laboratory setting.

The first study was entirely self-funded by Dr. McMurtry, while the second study, comparing iAVs to Hoagland’s solution, was also primarily funded by McMurtry, with greenhouse space provided by Paul V. Nelson.

The third study, comparing iAVs to organic soil systems, was fully funded by McMurtry, including tissue and media assays. For the fourth study on ratio analysis, McMurtry covered 66-75% of the costs, with additional support for greenhouse space from Doug C. Sanders and funds for tissue analysis from N. Mingus, Paul V. Nelson, and R.P. Patterson.

42.14. Academic Pursuits and Challenges

In May 1987, Dr. Douglas C. Sanders from North Carolina State University (NCSU) encouraged Dr. McMurtry to pursue a PhD in Horticultural Science. This program featured a unique interdisciplinary committee comprising six senior faculty members representing four life-science disciplines. At that time, the idea of integrating aquaculture into the field of Horticultural Science was not widely accepted within academic circles by many academics and administrators at NCSU, a conservative Land Grant Institution.

Dr. McMurtry acknowledges and expresses gratitude for the support he received from several numerous esteemed scientists who supported and facilitated his research in iAVs. His dissertation involved constructing another 16 tanks to test four different tank-to-filter volume ratios across three crop intervals, including one non-crop period. The objective was to establish biometric relationships, constraints, and limits, such as determining the appropriate biofilter volume per fish (feed) and the yield of plants per increase in fish weight.

Despite these milestones, McMurtry could not secure funding to study elemental accumulation and microbial development in the biofilter – a critical aspect of iAVs – by depth and ratio. This research predated what is now known as “aquaponics,” a concept not widely understood at the time. Granting agencies dismissed iAVs as a novelty with limited practical value.

Dr. Sanders explained that aqua-vegeculture research at NCSU has been discontinued because the technology had evolved to the point where it is ready for grower application (Diver 2000).

42.15. iAVs Research Group

From 1984 to 1994, the iAVs Research Group at North Carolina State University (NCSU) consisted of seven co-investigators from five disciplines, along with nine principal consultants, nine co-authors published in five refereed journals, and over four dozen other consultants and technicians. Ten members of the iAVs research group were recognized by their peers as ‘Fellows’ in their respective disciplines, a prestigious professional honor, which is the highest professional honor conferred on a scientist, aside from a Nobel Laureate.

42.15.1. Fellows

American Academy for the Advancement of Science: J. Burkholder, B.A. Costa-Pierce, PA Sanchez
American Society of Agricultural and Biological Engineers: J.C. Sager, R. Sneed
American Society of Horticultural Science: P.V. Nelson, D.C. Sanders, L.G. Wilson
Crop Science Society of America: R.P. Patterson
Industrial Design Society of America: V.M. Foote

Several other contributors (non-Fellows) were exceptionally well-known and highly respected within their fields, including J.L. Apple, R.J. Downs, H.D. Gross, R.G. Hodson, D. Huisingh, M.H. Jensen, G.A. Marlowe, among others.

iAVs participants included faculty from 16 departments within the College of Agriculture and Life Sciences at NCSU, four other colleges at NCSU, as well as contributors from:

Over 20 external institutions,
Three UN Agencies (UNDP, UNEP, FAO),
Five US Government Departments (DOS, NASA, OECD, USAID, USDA),
Two USDA Commercial Demonstration Project participants,
Over ten foreign governments’ agriculture/development ministries,
More than 30 development assistance and humanitarian relief NGOs.

42.16. International Outreach and Impact

Dr. Mark McMurtry completed his dissertation at North Carolina State University (NCSU) and subsequently submitted several articles that were published in peer-reviewed journals focused on aquaculture and horticulture. Progress was slow due to the interdisciplinary nature of iAVs, which combined multiple scientific fields.

He then extended his work to sub-Saharan Africa and the Middle East, initially serving as a Research Associate with NCSU International Programs in collaboration with several U.S. universities and various international aid organizations. Between 1989 and 1994, Dr. McMurtry traveled extensively, visiting over a dozen countries to promote the practical applications of iAVs in regions facing food security challenges.

Notably, Dr. McMurtry self-funded the majority of his travel expenses, associated medical costs, and most of the iAVs research expenditures. His international outreach laid the groundwork for broader experimentation and validation of iAVs, demonstrating its potential as a scientifically sound, scalable solution for sustainable agriculture in areas confronting food insecurity and water scarcity.

Meanwhile, a graduate student continued working on an iAVs greenhouse project using a slightly modified system with mixed cropping for about a year. However, these results were never reported as the student left before completing their work.

42.17. Speraneos and Bioponics

42.17.1. The Meadowcreek Project: A Foundation for Sustainable Innovation

In 1979, brothers David and Wilson Orr established The Meadowcreek Project in Arkansas as a community centered around sustainable living, environmental protection, renewable energy, and cooperative principles. Throughout the 1980s, the organization experienced significant growth, securing funding to support various educational programs and innovative projects.

By 1990, the property had developed substantially, featuring an 18,000 square foot conference center, two dormitories, seven houses, workshop facilities, and a renovated historic barn. The organization maintained a professional staff of over 20 people who managed educational programs, operated the farm and associated projects, and maintained the facilities.

42.17.2. Dr. McMurtry’s Work and Early Demonstrations

Following the completion of his PhD dissertation at North Carolina State University, Dr. Mark R. McMurtry embarked on a series of presentations to demonstrate iAVs principles and benefits to academic faculty, students, and aquaculture industry professionals across multiple locations. His system represented a scientifically validated approach to integrated aquaculture and plant production, with sand-based media serving as a critical component of the design.

42.17.3. The Pivotal Meeting with the Speraneos

In December 1989, a presentation in Arkansas connected Dr. McMurtry with Tom and Paula Speraneo, owners of S&S Aqua Farm in Missouri, who were attending an event at the University of Arkansas in Little Rock. A week later, McMurtry facilitated a comprehensive three-day workshop at the Meadowcreek Project in Fox, Arkansas, for faculty, staff, students, and interested parties – including the Speraneos.

42.17.4. The Critical Divergence in Methodology

Following the workshop, Tom and Paula Speraneo modified the concepts presented by Dr. McMurtry to construct their own system (Diver 2000). Reportedly facing cost constraints for acquiring the specified sand medium central to iAVs, they opted to use gravel from their driveway as the biofilter substrate. This substitution marked a significant departure from the core iAVs principles related to filtration and nutrient cycling. Dr. McMurtry, upon learning of this modification during his subsequent travels promoting iAVs in sub-Saharan Africa and Middle Eastern countries, advised against the use of gravel based on the established iAVs research findings regarding particle size, surface area, and filtration efficiency. However, the Speraneos continued with their gravel-based adaptation.

42.17.5. Commercialization and Popularization

The Speraneos played a pivotal role in popularizing what became known as flood-and-drain aquaponics. They marketed their gravel-based system as “bioponics” or the “Speraneo system,” which gained traction among hobbyists due to its simplicity and accessibility.

Leveraging the early internet, they sold instructional kits for $200 (Diver 2000), making the system widely available to small-scale practitioners. This approach contributed significantly to the global spread of aquaponics, despite the system’s reduced efficiency compared to iAVs.

Interestingly, when their information package first became available, purchasers were required to sign legal agreements prohibiting them from marketing their own versions of the materials. This restriction suggests that the Speraneos sought to prevent others from replicating their actions – modifying an open-source concept and commercializing it for profit. Despite these efforts, their gravel-based system gained widespread adoption globally, overshadowing the more efficient and scientifically validated iAVs design.

They also developed a blend of microbes which they sell as an inoculant to start new fish tanks (Diver 2000).

42.17.6. Technical Implications of Media Substitution

The substitution of gravel for sand created significant technical challenges. Plants would dry out more quickly in gravel media, necessitating continuous pumping and the installation of bell siphons, which increased system complexity and operational costs.

By using gravel instead of sand, it removed the filtration capacity and so the Speraneo system only works well if the system is fitted with dedicated mechanical and biological filtration. Without these additions, the system risks eventual failure due to organic matter accumulation, media clogging, and oxygen depletion needed for fish, beneficial bacteria, and plant root zones (Kledal 2018; Okomoda 2023; Knaus and Palm 2017a; Palm et al. 2018; Rakocy 2006).

This adaptation has drawn scrutiny. Critics argue that the “bioponics” approach lacks the rigorous scientific underpinning and optimized performance characteristic of the original iAVs design, raising questions about its overall efficacy (Datta, 2018; Diver, 2000; Konig, 2018; Milliken, 2021; Purkait, 2018; Rharrhour, 2022).

42.17.7. The Sand Biofilter: Heart of the iAVs “living machine”

The sand biofilter represents a critical component of the iAVs “living machine.” The substitution of gravel for sand impacts the efficacy of the iAVs in several ways including:

Substantial reduction in mechanical filtration capability
Decreased soil organism populations and biological activity
Reduced aeration of media bacteria and plant root zones
Lower nutrient utilization and system stability
Decreased fish survival rates, feed conversion, and growth
Increased capital costs with reduced fish and plant yields
Higher operating cost per unit of production

42.17.8. Commercial Viability Challenges

A notable consequence of this change in media was the reduced commercial viability of the adapted system. The basic flood-and-drain system has struggled to gain commercial traction because gravel does not facilitate the mechanization and automation that characterizes modern controlled environment agriculture. In contrast, sand has been successfully employed in hydroponic greenhouse culture for decades. Additionally, the flood-and-drain system requires greater expertise due to the increased operational risks.

Solids capture is a critical component, as the clogging of media such as gravel has far-reaching implications and requires a large amount of labour to clean up. In severe cases where the gravel media is clogged, the hydroponic component actually produces ammonia as opposed to removing it, as a result of organic matter decaying (Lapere 2010).

42.17.9. Global Proliferation Despite Limitations

The Speraneos promoted their system through an internet mailing list. Interestingly, early purchasers of this information were required to sign a legal agreement not to market their own information packages, suggesting the Speraneos sought to prevent others from adapting their work as they had done with McMurtry’s design.

This restriction appears to have eventually lapsed, as in 2005, Joel Malcolm purchased the Speraneos’ information kit and adapted it for an Australian context. When Australia’s ABC Gardening TV program featured Malcolm’s home-based system, the flood-and-drain approach experienced renewed popularity. However, this adaptation maintained the fundamental limitation of inappropriate media particle size.

The Speraneo model was subsequently adopted by various other kit manufacturers, including Murray Hallam and Sylvia Bernstein. While these developers made their own modifications, none addressed the fundamental issue of using gravel or expanded clay pebbles instead of sand as the growing medium.

While this gravel-based approach became the most widely implemented aquaponics system globally, research consistently indicates it is fundamentally less effective than iAVs for sustainable food production.

McMurtry has consistently emphasized that gravel does not provide the same mechanical filtration or biological activity as sand, which research documents as delivering superior water filtration and nutrient cycling.

42.18. The Freshwater Institute

The Freshwater Institute in Shepherdstown, West Virginia also copied their work from the original design created by Dr. McMurtry at NCSU. They named it the Tallmansville system. In 1998, the Freshwater Institute produced several manuals focused on how to design and operate their system (Goodman 2011; Bogash 1997).

The story of the Speraneos and the Freshwater Institute and their impact on IAVS is a tale of unintended consequences and the challenges of maintaining the integrity of an open-source innovation.

42.19. USDA Examination

During Dr. McMurtry’s time overseas, Boone Mora and Tim Garrett established and managed a USDA-funded iAVs Commercial Demonstration Project in Eastern North Carolina. From 1992 to 1993, this project received a $100,000 USDA grant, which funded greenhouse construction and operating expenses for one year.

Despite being novices in both aquaculture and horticulture, with only minimal training and a three-day workshop conducted by Dr. McMurtry, they achieved an impressive yield of 115 kg/cu m/yr of hybrid Tilapia, alongside significant production of cucumber, pepper, and tomato. Produce from the project was sold locally at discounted prices, covering labor and distribution costs.

The project faced challenges, including suboptimal management practices and pathogen introduction due to frequent visitors. Additionally, there was uncertainty about the fate of approximately 22,700 kg of tilapia produced, as the fish was relatively unknown in rural North Carolina at the time.

Ultimately, the greenhouse was sold to another farmer for tobacco production, per the grant’s terms, with proceeds returned to the USDA. Interestingly, Dr. McMurtry was entirely unaware of the trial until its publication in Furrow magazine, and his subsequent efforts to verify details with the USDA have remained inconclusive.

42.20. Unanswered Communications with FAO

On July 17, 1989, the NCSU iAVs Research Group contacted Dr. Khadi of the FAO Irrigation Program in Rome to share detailed information about the iAVs methodology, research findings, and their intention to implement iAVs in areas where food and water are most lacking and demand is most urgent. This outreach was encouraged by both USAID and USDA/OICD, which advised the group to approach and inform FAO of the iAVs technology and solicit FAO’s advice and input. However, despite these efforts, no response was ever received.

Dr. Douglas C. Sanders, FASHS Chair of the iAVs Research Group, visited the FAO headquarters in Rome on September 2-3, 1990, where he reported that he felt his presentation was well received. However, after this visit, a significant amount of time passed without any communication from FAO officials. Despite multiple follow-up attempts – including reaching out repeatedly – no response was ever received from anyone connected with the FAO.

42.21. iAVs Implementation in Namibia

In early 1990, as Namibia transitioned into a newly established republic, Dr. Mark McMurtry successfully advocated for support from U.S. Senator George Mitchell, then Senate Majority Leader, and Robert C. Byrd, Chair of the Senate Foreign Appropriations Committee. Collaborating with Sir David Godfrey and the Rössing Foundation, their collective goal was to implement iAVs across Namibia. This initiative aimed to address food security challenges and promote sustainable agriculture in the region.

Namibia’s first President, Dr. Sam Nujoma, personally expressed gratitude to North Carolina State University (NCSU) for Dr. McMurtry’s contributions to improving food security in the country. By March 1991, a comprehensive five-year development plan was formulated, and preparations were in place to advance this initiative. A special appropriation of US$7.5 million (equivalent to approximately $18 million today) was secured through Senator Mitchell’s efforts to fund integrated agricultural projects throughout Namibia.

“Having examined the iAVs food production technology, I believe that the methodology is ideally suited to the requirements of Namibia…Following consultation with the leadership of the indigenous NGO’s, I believe that the iAVs technology would provide significant opportunities and benefits for the people of Namibia…I actively support the proposed approach outlined/developed by DR McMurtry, et al., and suggest that his direction and guidance be applied to the continued evolution of the programmatic details (comprehensive planning) as well as in the implementation/execution of the iAVs and supporting technologies for Namibia.” – His Excellency, Dr. Sam Nujoma, 18 April 1991.

However, in April 1991, these funds were allegedly misappropriated by the incoming USAID Mission Director, who claimed they would be used to acquire housing to attract his anticipated staff to Windhoek. Despite objections from the U.S. State Department, Congress, and the Administration regarding this diversion of resources, the funds had already been expended and could not be recovered.

This misallocation represented a significant setback for iAVs implementation in Namibia and dealt a blow to iAVS’s momentum and undermined NCSU’s efforts to showcase its real-world applicability. The initiative had garnered widespread support from both Namibian and U.S. stakeholders, including government officials, NGOs, and local communities. The potential benefits of iAVs – enhancing food production and addressing critical issues such as malnutrition – were widely recognized.

Nevertheless, this bureaucratic decision effectively halted progress on a project that could have significantly improved food security in Namibia. Today, with the population having doubled since that time and severe malnutrition affecting hundreds of thousands of children, the failure to realize this initiative underscores the long-term consequences of missed opportunities in addressing hunger and poverty sustainably.

42.22. Challenges and Controversies

NCSU stated that the iAVs technology had been sufficiently proven, and the Horticultural Science department (Hort Sci) and the College of Agriculture and Life Sciences (CALS) at NCSU deemed iAVs as “ready for commercialization.”

Upon returning to the United States in 1996 after his work in Africa, Dr. McMurtry discovered that his tenure at NCSU had been terminated due to his opposition to the university’s plans to license iAVs technology to large food production conglomerates.

The iAVs method was purposefully thrust into the public domain (made open-source in 1985), and Dr. McMurtry thwarted several attempts by NCSU and TULCO (Triangle University Licensing Consortium) in the late 1980s to monetize the technology through the transfer of proprietary rights to any one of several multinational agricultural conglomerates. This included efforts to sell research results and intellectual property for which he was the original inventor, developer, and primary funder.

This was partially accomplished through legal argument, and also by popular press releases, as well as through nationwide presentations Dr. McMurtry gave to many universities and institutes across the United States, Africa, and the Middle East – with the assistance of NCSU’s Office of International Programs and the USDA’s Office of International Cooperation in Development (OICD).

In December 1989, TULCO returned all intellectual property rights related to iAVs to Dr. McMurtry.

42.23. Challenges in Israel and Palestine

On September 13, 1993, Yitzhak Rabin and Yassir Arafat concluded a peace agreement between Israel and the PLO with a historic handshake on the White House lawn. That same day, North Carolina State University’s (NCSU) Office of International Programs (OIP) received a call from the White House attempting to locate Dr. Mark McMurtry.

As it happened, Dr. McMurtry was on vacation, fishing in Yellowstone National Park, and the OIP staff only knew he was “somewhere out West.” The National Security Agency (NSA) was tasked with finding him, tracking his recent credit card activity to the lodge where he was staying. By the next day, he had been “spirited away” to Little Rock, Arkansas, where he presented at a significant conference.

The conference was attended by key stakeholders, including the PLO Delegation to the UN, the U.S. Department of State, USAID, senior staff from Vice President Al Gore’s office, the International Bank for Reconstruction and Development (IBRD, also known as the World Bank), and approximately 30 member institutions of the Joint Center for NGO/PVO and University Collaboration in Development.

Dr. McMurtry delivered a presentation entirely from memory, still wearing the fishing attire he had been wearing in Yellowstone. The reception was enthusiastic, particularly from the Palestinian delegation.

Dr. McMurtry was then escorted to New York City and Washington, D.C., for multiple substantive discussions on scaling iAVs technology to feed one million people using 128 hectares of land in Jericho.

The plan hinged on accessing fossil groundwater located approximately 1,000 meters beneath the Dead Sea. Returning to NCSU, the university’s leadership – including the Chancellor, the Dean of CALS, and the Director of OIP – expressed great optimism, with “dollar signs replacing the pupils of their eyes,” as the IBRD had pledged development funds totaling several billion U.S. dollars to support this ambitious project.

The initiative received the declared backing of Vice President Al Gore and Senate Majority Leader George Mitchell, along with funding assurances from IBRD and USAID. Dr. McMurtry and his collaborators began detailed planning, including location research, scheduling, and brainstorming.

However, once Israel learned of the project, significant political opposition surfaced. The entire U.S.-Israeli lobby on C-Street, along with a broad coalition of Congressional representatives, reacted strongly, culminating in what was described as “the gates of hell opening” against the proposed development.

It quickly became clear that Israel would not permit Palestine to access fossil water beneath recently ceded Palestinian territories or any fresh water sources in the West Bank. Furthermore, Israel showed no interest in allowing Palestine to achieve even marginal food self-sufficiency.

At this point, Jesse Helms, North Carolina’s Senior U.S. Senator and Chairman of the Senate Committee on Foreign Relations, became a vocal opponent. He expressed his strong objections, viewing the project as anti-Israeli policy, and made his ire known to the NCSU administration, faculty, and Dr. McMurtry directly. Despite extensive efforts by the Clinton Administration to appease Senator Helms and other opponents, these efforts ultimately failed. Dr. McMurtry was warned that continuing to pursue the project could lead to heads “rolling from the bottom (McMurtry) all the way to the top.”

Several years later, the Israeli government and its U.S.-based lobby effectively blocked plans by the World Bank (IBRD) and the UN/FAO to implement integrated agricultural systems across 100 hectares in Jericho. These systems could have provided food security for one million Palestinians by utilizing deep fossil water reserves beneath the Dead Sea.

42.24. Adversity and Setbacks

Dr. Mark McMurtry encountered significant challenges during a difficult period in his life. Struggling with poor health, he subsisted on a modest service-connected Vietnam veteran disability pension. In 2018, a forest fire destroyed his home, causing him injury and the loss of all his possessions. This phase represented a time of profound adversity and personal setbacks for Dr. McMurtry, testing his resilience in the face of health issues, financial constraints, and personal loss.

42.25. Revival and Recognition

Without institutional backing, sufficient income, or the widespread use of the internet, Dr. McMurtry was no longer able to support the dissemination of iAVs, leading to its temporary obscurity. However, in 2014, he engaged in a discussion on the Aquaponics Nation forum, which ultimately brought greater visibility to his work.

Over the next six years, Dr. McMurtry and Gary Donaldson, the forum’s administrator, continued to volunteer their time to promote iAVs, which might otherwise have remained obscure.

42.26. FAO’s Missed Opportunity in Gaza

In 2012, the Food and Agriculture Organization (FAO) launched a traditional aquaponic pilot system in Gaza, expanding it in 2013. This initiative demonstrates a concerning disregard for existing research and expertise in the field.

Several decades later, Dr. McMurtry learned that FAO was promoting and sponsoring flood-and-drain (F&D) gravel-media (Speraneo) ‘aquaponics’ in Gaza, Palestine. While he liked to believe that many people were significantly advantaged by these efforts, he does not believe that they truly were. Whatever the outcomes were, regardless of the beneficiaries’ felt satisfaction (or dismay), any benefit they would have accrued as a result of their (and FAO’s) efforts would assuredly have been at least an order of magnitude (or several) greater if FAO had listened to the inventor of record and the investigating scientists at North Carolina State University (NCSU).

Despite the well-documented advantages of iAVS and its extensive research conducted by Dr. McMurtry and his team at North Carolina State University, FAO did not incorporate iAVS into its projects nor consult with Dr. McMurtry. The organization completely ignored the iAVS research and its contributions to aquaponics.

Dr. McMurtry is widely recognized as the inventor of what is now commonly referred to as “aquaponics.” The categorical omission of iAVS and Dr. McMurtry’s contributions from FAO’s efforts displays a lack of professional integrity and competence. This failure to recognize the historical context and scientific foundations of aquaponics undermines the credibility of FAO’s work and raises questions about the thoroughness of its approach.

Had FAO acknowledged and incorporated the extensive iAVS research and consulted with Dr. McMurtry, their impact in Gaza could have been significantly greater – potentially by an order of magnitude or more. This oversight also deprived beneficiaries of the most effective and well-researched aquaponics methodologies, highlighting a missed opportunity to implement truly optimal solutions for food-insecure communities.

42.27. Critical Analysis of “Aquaponics Food Production Systems” Paper

In 2019, the paper titled “Aquaponics Food Production Systems” was published, but it exhibited significant gaps in its research.

The authors failed to explore the origins of what is now referred to as aquaponics, neglecting to provide essential context regarding the individuals, timeline, locations, motivations, and methodologies that shaped both major categories of this field, nor the impetus behind continuing efforts to disseminate authentic implementations. This significant omission raises serious questions about the paper’s thoroughness and objectivity.

Most notably, the authors omitted any mention of the most extensively researched, documented, and published methodology associated with aquaponics – known as iAVS – which has been part of the academic conversation since 1986. This methodology, invented, developed, and documented from 1985 at North Carolina State University under the leadership of Dr. Mark McMurtry and a comprehensive team of highly respected investigators, has been the subject of formal, peer-reviewed research.

The categorical omission of iAVS and of the widely attributed inventor/researcher of what is now termed to be “aquaponics” – namely Dr. Mark McMurtry – displays a calloused disregard for fact, history, evidence, and the absence of professional competence and integrity. This blatant oversight by the authors raises concerns about the completeness, integrity, and potential bias of their work.

While traditional aquaponic systems have evolved in recent decades, several key challenges remain unresolved. These include the need for energy-efficient systems and optimized nutrient recycling. The iAVS research effectively addresses these challenges; however, it appears that this research has been ignored by the Food and Agricultural Organization (FAO). Consequently, substantial time, effort, and resources have been expended on attempting to resolve issues that have already been effectively addressed.

Traditional aquaponic systems are being further complicated – leading to increased costs, complexity, management, space, and labour – by introducing mineralization components and sludge bioreactors containing microbes that convert organic matter into bioavailable forms, despite the fact that iAVS is already designed as a soil-based system with a much larger variety and diversity of microbes. This raises questions of whether the omission of iAVS in the FAO paper is a result of deliberate bias, given the system’s unparalleled legacy of research and publication.

42.28. Modern Research

Although identified as flawed, research by El Essawy et al. (2019) and El Essawy (2017) explored the potential of the Integrated Aqua-Vegeculture System (iAVs) as a sustainable alternative to new land reclamation and conventional agriculture in Egypt. Their comparison suggested iAVs was effective, utilizing minimal water and energy to produce high-quality, safe organic food, while also reportedly yielding more crops with greater variety at approximately 20% lower capital and operational costs than conventional methods, according to their economic feasibility analysis (Yacout 2025).

43. Conclusion

iAVs was designed to provide reliable, resource-efficient nutrition in challenging environments, particularly in harsh climates. Its goal is to demonstrate a sustainable method of food production that minimizes harm to the planet’s biosphere and ecology. Unlike traditional aquaponic systems, which have proven economically unsustainable and biologically dependent on external inputs, iAVs operates with true sustainability, requiring fewer resources and external dependencies.

43.1. Goals and Key Principles

The primary objective of iAVs is to empower individuals and communities by teaching them how to sustainably produce their own food. This system is especially beneficial in regions where conventional agriculture struggles due to environmental limitations like degraded soil, limited water availability, and pollution.

Key Principles of iAVs:

Empowering Self-Sufficiency: iAVs enables individuals and communities to develop sustainable food production systems, addressing urgent needs for food security and health.
Call for Global Support: Participation from individuals worldwide is encouraged to foster informed discussions and implement ultra-efficient resource management in food production.
Education as Empowerment: By educating people on sustainable food production, iAVs promotes self-reliance and food security, empowering communities to meet their nutritional needs.
Community Engagement: The success of iAVs relies on collective involvement. Contributions from individuals help expand the reach and benefits of this innovative system.
Advocating for Informed Action: iAVs supports evidence-based research in food production that maximizes resource efficiency while preserving environmental integrity.
Commitment to Scientific Evidence: iAVs emphasizes the importance of factual information and the scientific method in developing sustainable food production systems.

By adhering to these principles, iAVs contributes to a more adaptable, sustainable, and secure global food system tailored to meet the diverse needs of communities worldwide.

43.2. The Benefits of iAVs

iAVs offers several key advantages that make it a groundbreaking solution for sustainable agriculture:

Lower Capital Requirements: iAVs is less capital-intensive with reduced equipment costs and requires less specialized knowledge, making it accessible to a broader audience.
Reduced Technical Complexity: The system’s simplicity reduces operational risks and enhances reliability.
Lower Operating Costs: With lower energy demands and minimal external inputs, iAVs operates efficiently.
Minimal External Inputs: The system’s self-sufficiency reduces reliance on external physical or informational inputs.
Global Adaptability: iAVs is scalable and adaptable for use in less developed countries (LDCs) as well as urban settings like rooftops in mega-cities.
Enhanced Oxygenation: By providing significantly more oxygen to aerobic microbes, iAVs enhances plant nutrient assimilation and ecosystem health.
Resource Efficiency & Zero Waste: iAVs reduces resource consumption (water, energy) and generates zero waste by utilizing both soluble and solid fish waste fractions, contributing to a circular economy.
Wider Crop Range & Higher Yields: It supports a variety of plant species with higher nutritional value and yields, even in difficult environments.
Reduced Pollution: iAVs minimizes pollution by reducing toxins associated with industrial processes like styrene production.
Increased Profitability & Efficiency: With faster returns on investment and reduced operational effort, iAVs offers greater efficiency without requiring extensive technical expertise. The ability to produce two commodities (plants and fish) simultaneously can make the system more economically efficient than conventional cultivation (Andriani & Zahidah, 2019).
Independence from Economic Systems: iAVs functions independently of specific economic models or infrastructures, making it viable even without access to developed markets or fiat currency.

These advantages position iAVs as a transformative tool for sustainable food production across diverse contexts worldwide.

43.3. Potential for optimization

iAVs offers numerous opportunities for optimization, encompassing various aspects of its design and operation. Key areas for improvement include:

Plant Selection and Cultivation: Experimenting with different plant species to identify those best suited to the system’s conditions.
Irrigation Regimes: Testing intermittent irrigation schedules to determine the most efficient water delivery methods.
System Ratios: Adjusting the ratio of fish tank volume to sand biofilter volume within the established upper and lower limits to refine performance.
Fish and Feed: Exploring the effects of fish species and feed composition on nutrient availability for plants.
Other Variables: Investigating additional factors, such as environmental controls and supplementation, to enhance productivity.

When attempting to optimize or modify iAVs, it is essential to begin with a standard baseline model. This serves as a control system, enabling users to identify potential issues or opportunities for improvement. Without this baseline, it becomes impossible to determine whether a proposed change constitutes a genuine enhancement or simply introduces new challenges.

43.3.1. Modern Approach

Dr. McMurtry has said that if the iAVs research were conducted today in a Western context, he would likely incorporate advanced technologies such as computer-monitored controlled environment agriculture (CEA), dynamic stocking management, staggered crop rotations, and high-density fish stocking. Additional measures could include ultraviolet (UV) sterilization to prevent viral outbreaks, supplemental lighting, CO2 enrichment, humidity regulation, positive pressure ventilation for cooling, and integrated pest management (IPM) using beneficial insects and plants.

43.4. Open-Source Knowledge and the Future of iAVs

Since its inception, iAVs has been an open-source system available for anyone to adopt. This philosophy encourages widespread use, particularly in regions facing food security challenges. However, ensuring that the necessary knowledge is accessible remains a challenge. The future success of iAVs depends on the global community’s willingness to take ownership of its development. While the original creators laid the foundation, researchers, practitioners, and educators now hold the responsibility for its continued evolution.

iAV needs sponsors and supporters from a diverse range of disciplines to drive progress and innovation. These fields include aquaculture sciences, aquatic ecology, and horticultural science, where expertise can enhance sustainable practices. Applied genetics and soil ecology are crucial for improving crop resilience and soil health. Specialists in hydrology and water conservation are essential for managing our water resources efficiently, while microbiologists can help understand and utilize beneficial microorganisms. Nutritionists with expertise in aquatic, botanical, and human nutrition play a vital role in promoting health and well-being. Integrated pest management experts are needed to develop eco-friendly pest control methods. Additionally, professionals in controlled environmental engineering and management can optimize growing conditions for various species. Contributions from those in eco/biological synergism and systematics, as well as dynamic systems management, are important for creating balanced ecosystems. Phycologists bring valuable insights into algae and their applications. Furthermore, expertise in the marketing and distribution of perishable commodities ensures that products reach consumers efficiently. Finally, advancements in post-harvest technologies and food safety regulation are critical for maintaining quality and safety standards. Together, these disciplines can make significant contributions to our shared goals.

44. Recommended Resources

Greenhouse Operations & Management – Paul V. Nelson
Soil Microbiology & Health – Elder A. Paul
Teaming With Microbes
Teaming With Nutrients
Knotts Handbook for Vegetable Growers
Growing Great Tomatoes by Robert Pavlis
Seed Germination Theory and Practice, by Dr. Norman C. Deno
Botany Primer
The Science of Plants
Introduction to Soil Science
From Growing to Biology
Square Meter Gardening – https://theswissbay.ch/pdf/Books/Survival/Farming,%20Animalraising,%20Homesteading/Farming+gardening/Gardening/square%20foot%20gardening/All%20New%20Square%20Foot%20Gardening.pdf
Constructing Shade Structures: Small Area Vegetable and Fruit Production – https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2930&context=extension_curall
Greenhouse Manual – An Introduction for Educators – https://www.usbg.gov/sites/default/files/usbg-greenhouse_manual.pdf
Propagating Crops from Seed, and Greenhouse Management – https://agroecology.ucsc.edu/about/publications/Teaching-Organic-Farming/PDF-downloads/1.3-propagation.pdf
Greenhouse Cucumber Production – https://www.lls.nsw.gov.au/__data/assets/pdf_file/0020/1201727/Cucumber-book-2019_LOW_RES.pdf
Improving greenhouse systems and production practices – https://ausveg.com.au/app/data/technical-insights/docs/VG07145.pdf
Greenhouse Vegetable Production – https://pubs.nmsu.edu/_circulars/CR556.pdf
Greenhouses for Homeowners and Gardeners – https://bpb-us-w2.wpmucdn.com/u.osu.edu/dist/9/24091/files/2016/10/NRAES-137_Web-1eiwt4v.pdf
DIY Greenhouse Instruction Manuals – https://www.bootstrapfarmer.com/pages/instruction-manuals
Scientific Enquiry – https://youtu.be/Z-OBmSq8lU4
Soil Bulk Density – https://youtu.be/2UTwNJqmv0w
Introduction to Silicate Minerals – https://youtu.be/mqXUytwB3uQ
Soil & Water – https://youtu.be/m4iHBy5PNY4
Water Movement in Soil – https://youtu.be/ego2FkuQwxc
Mastering Freshwater Aquarium Ecosystems – (Lots of Ads, need a better version) http://www.aquaworldaquarium.com/ebooks/MFAE/004_WaterTesting.html
Water Quality Management for Recirculating Aquaculture – (Download) https://store.extension.iastate.edu/Product/14271.pdf
Theory and Practice of pH Measurement (Advanced Guide) – https://www.emerson.com/documents/automation/manual-theory-practice-of-ph-measurement-en-70736.pdf
Guide to pH Analysis (Advanced) – https://hannainst.com.au/wp-content/uploads/2024/03/guide-to-ph-analysis-for-lab-ebook.pdf
Aquarium Science – https://aquariumscience.org/
Square Meter Gardening – http://www.terraperma.com.au/uploads/1/9/1/3/19138605/terra_perma_-_sfg_workshop_notes_final_2.pdf

45. Acknowledgements

I express my heartfelt gratitude to Dr. Mark McMurtry for his invaluable contributions to the development of iAVs, and with his assistance with writing this book. I honor the memory of Gary Donaldson, whose pioneering work and dedication significantly shaped the path of this study, despite his passing before its completion. I sincerely appreciate Alex for his crucial assistance with funding and support, which facilitated this work. Lastly, I thank my family and friends for their patience and understanding throughout the writing process, which greatly contributed to the completion of this paper.

45.1. Acknowledgment of Key Support and Mentorship

The development and success of iAVs was significantly influenced by the support, guidance, and encouragement of several key senior faculty members. While the conceptualization and effort behind iAVs were primarily driven by Dr. Mark McMurtry, it was the academic freedom, political backing, and opportunities provided by others that enabled the project to flourish.

Among the primary supporters were Paul V. Nelson, a highly respected figure in Horticultural Science, Douglas C. Sanders, a well-known horticulturist (now deceased), and Merle H. Jensen, a polymath who was directing the Environmental Research Laboratory (ERL) at the time. These individuals, along with many others, played critical roles in nurturing and advocating for the iAVs concept.

Dr. McMurtry considered himself fortunate to have been mentored and supported by such distinguished individuals throughout his research journey.

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The iAVs Handbook

1. Preface

2. Introduction to iAVs

2.1. Background

2.2. What is iAVs

2.3. How Does iAVs Work?

3. Quick Guide: iAVs in 10 Simple Steps

4. Site Selection

4.1. Utilities and Ease of Accessibility

4.2. Ground Stability and Flood Prevention

4.2.1. Site Preparation for Stability:

4.2.2. Flood Prevention:

4.3. Protection from Extreme Weather

4.4. Security Measures

4.5. Aesthetics: Visual Appeal and Practical Benefits

5. Climate

5.1. Weather Considerations

5.2. Sunlight and Shade

5.3. Temperature

5.3.1. Temperature Requirements for Freshwater Fish

5.4. Humidity

5.5. Climate Variations

5.6. Arid/Desert Climates

5.7. Temperate Climates

5.8. Tropical/Monsoon Climates

6. Light

6.1. Sunlight

6.2. Orientation

6.3. Seasonal Adjustments

6.4. Staggered Planting

7. System Size & Layout

7.1. Lo-Tech vs Hi-Tech iAVs

7.1.1. Lo-Tech Version

7.1.2. Hi-Tech Version

7.2. Core Ratios: Fish Tank to Biofilter Volume and Area

7.2.1. Fish Tank to Biofilter Volume Ratio (V:V): 1:2

7.2.2. Fish Tank to Biofilter Area Ratio (V:A): 1:6

7.3. Flexibility in System Layout

7.4. Layout

7.4.1. Key Considerations for Layout Design

7.5. Water Circulation Layouts: Gravity-Fed vs. Sump Systems

7.5.1. Gravity-Fed Layout (Preferred Option)

7.5.2. Sump Tank System

7.6. Biofilter Positioning Options

7.6.1. In-Ground Biofilters (Preferred Option):

7.6.2. On-Ground Biofilters:

7.6.3. Above-Ground Biofilters:

7.7. iAVs Layout Options

8. Fish Tank

8.1. Introduction: The Central Role of the Fish Tank

8.2. Optimal Fish Tank Design: Shape and Geometry

8.2.1. The Catenary Shape: Advantages and Creation

8.2.2. How to Dig and Shape a Hole into a Catenary

8.3. Fish Tank Placement and Practical Considerations

8.3.1. Fish Tank Placement in an iAVs (In-ground vs. Above-ground)

8.3.2. Protecting Fish Tanks with Netting and Covers

8.3.3. Optimizing Fish Tank Design for iAVs (Summary of Key Design Elements)

9. Biofilter

9.1. Dimensions

9.1.1. Length

9.1.2. Depth

9.1.3. Width

9.1.4. Shape

9.2. Slope

9.3. Materials

9.4. Multiple Biofilters per Fish Tank

10. Liners

10.1. Types of Liners

12. Water

12.1. Introduction

12.2. Water Sources

12.2.1. Rainwater

12.2.2. Mains or municipal supply

12.2.3. Rivers and lakes

12.2.4. Wells and ponds

12.2.5. Reverse Osmosis (RO)

12.3. Water Use

13. Managing pH in iAVs

13.1. Ideal pH for iAVs

13.2. Temperature