Integrated nutrient and feeding optimization strategies in aquaponics for sustainable urban food production and water conservation

This study investigated how different fish feed inputs (20, 40, and 60 g/m 2 ) influence water quality, nutrient availability, and the growth performance of tilapia ( Oreochromis niloticus ) and lettuce ( Lactuca sativa ) in a recirculating aquaponic system. Understanding optimal feed levels is essential for improving nutrient recycling and overall system productivity. Tilapia were stocked at a density of 80 fish/m 3 with an initial weight of 85.43 ± 2.54 g. Fish were fed commercial pellets twice daily at 20 and 40 g feed/m², and three times daily at 60 g feed/m². Water quality parameters, nutrient concentrations (macro- and micro-minerals), fish growth metrics, proximate composition, and lettuce biomass and nutrient content were recorded throughout the study. Data were statistically analysed to determine significant differences among treatments. Increasing feed inputs significantly affected system water chemistry. At 60 g/m 2 , pH declined from 7.74 ± 0.22 to 6.35 ± 0.01, while electrical conductivity, total dissolved solids, and nitrogenous compounds (ammonia, nitrate, nitrite) increased ( p < 0.05). Dissolved oxygen decreased to 4.15 ± 0.14 mg/L at the highest feeding level. Macro- and micro-minerals (Ca, K, Mg, P, Mn, Mo, Zn) increased in both the water and plant tissues as feed input increased. Tilapia fed 60 g/m² exhibited the greatest growth performance, with a final weight of 768.30 ± 17.60 g, a specific growth rate of 1.89 ± 0.10%, and the lowest feed conversion ratio of 1.67 ± 0.07%. Higher feeding also enhanced the proximate composition of the fish. Lettuce grown under 60 g feed/m² produced the highest biomass (14.51 ± 3.82 kg/m 2 ) and showed improved protein and mineral content. Feeding at 60 g feed/m 2 strengthened nutrient recycling, fish performance, and lettuce productivity without exceeding acceptable water quality limits. The enhanced mineral availability and plant uptake indicate strong nutrient coupling between the aquaculture and hydroponic components. Overall, feed optimization is a key driver of balanced aquaponic performance and sustainable nutrient utilization. Future studies should investigate higher feed levels to identify the maximum effective feeding rate.