How aquaponics turns fish food into lettuce

In aquaponics, fish waste releases ammonia into the water, bacteria living on a biofilter turn that ammonia into nitrate, and plants in a grow bed take up the nitrate as fertilizer. Cleaned water flows back to the fish, so feed going into the tank is effectively what feeds the plants.

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Fish tankFish eat pellets and excrete ammonia through their gills and waste. Left alone, that ammonia would soon become toxic to them.
BiofilterNitrifying bacteria colonize the rough surface of the filter media. One group turns ammonia into nitrite and another turns nitrite into nitrate.
Grow bedPlant roots take up nitrate and other nutrients, which cleans the water. The bed is sized to use what the fish produce.
Back to the fishA sump collects the cleaned water and a pump sends it back to the tank, so very little water is lost apart from what plants drink.
Fruiting cropsTomatoes and peppers need more nutrients per square meter than lettuce, so the same bed needs more feed and more fish.

The feed rate ratio

Aquaponic designers balance a system by the feed rate ratio: grams of fish feed per square meter of growing area per day. FAO guidance for small systems suggests about 40 to 50 grams for leafy greens and 50 to 80 grams for fruiting crops. This model uses 45 and 65.

Fish eat roughly 1 to 2 percent of their body weight per day during grow out, so the model divides the feed by 1.5 percent to estimate the fish biomass, then sizes the tank at no more than 20 kilograms of fish per 1,000 liters.

Try it: set a 4 square meter bed of leafy greens. The model calls for about 180 grams of feed a day and roughly 12 kilograms of fish, close to the FAO worked example. Now switch to fruiting vegetables and watch every number rise by more than 40 percent.

Fine tuning by testing

These ratios are a starting point. Growers test nitrate in the water: very low readings mean feed more, very high readings mean add plants or exchange some water. Ratios also shift with feed protein, fish species and temperature.

Sources

Plant and Pest Management in AquaponicsOhio State University South Centers (aquaculture workshop)
Integrated nutrient and feeding optimization strategies in aquaponics for sustainable urban food productionFrontiers in Sustainable Food Systems (open access)
Management of the aquaponic systemsFAO Fisheries and Aquaculture Department

How to cite this model

Avid Solutions International. (2026, November 11). How aquaponics turns fish food into lettuce [Interactive 3D model]. Avid Field Lab. https://avidsolutionsintl.com/explore/aquaponics-loop

Last updated November 11, 2026

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