Key words: sustainability, nutrient analysis, biofiltration

The aquaponics system offers a sustainable alternative to producing healthy foods to address health disparities and food scarcity in abandoned and often disturbed urban lands (food deserts). Aquaponics combines aquaculture and hydroponics facilitating natural biochemical cycles to grow fish and vegetables. It uses recirculating water, generating little solid or liquid waste than traditional production methods. The system conserves water and does not require soil, synthetic fertilizers or pesticides to grow plants or control pests.  

Tilapia (oreochromis niloticus) was used to grow green lettuce and red lettuce (lactuca sativa) operating a replicated aquaponics pilot plant system in a 6 m X 6 m greenhouse space. Nutrients are provided to the lettuce plants from natural waste generated by tilapia, which are given a constant feed based on 3% body weight from juvenility to maturity.  Biofilters transformed fish waste into essential nutrients for the plants. Ammonia (NH₃), which is prevalent in fish waste (urea), is converted into nitrite (NO₃^-) and nitrate (NO₂^-) absorbed by lettuce roots. Chelated iron was added to enhance plant growth.   

Over a growth period of seven weeks, red and green lettuce was greatest in systems that had high concentrations of NO₃^- and NO₂^-. Red lettuce reached a maximum leaf length of 26 cm, while green lettuce reached 20 cm. Wet and dry leaf above-ground leaf biomass was also greater in those systems. Wet weights of 14 (seven red and seven green) randomly selected lettuce heads reached a maximum of 700 grams, and dry weights on seven selected leaf samples from the heads reached a maximum of 1 gram. The aquaponics biomass was 25% greater than that of hydroponics. It is possible to have a large yield with minimal input in an aquaponics system. Tilapia fish were able to provide nutrients essential to the growth of lettuce.