Growing Conditions and System Productivity in a Closed-Loop Aquaponic System Under Varying Stocking Density

Aquaponics is an integrated form of a multi-commodity production system that combines a recirculating aquacul-ture system with the hydroponic cultivation of crops using the same water via recirculation using pumps. However, the ideal density of cultured aquatic species and the suitable fish/plants/fish feed combinations applicable under aquaponics must be established to determine its impact on the system's performance, including the local growing conditions that could affect its productivity. Eighteen aquaponic systems following a closed-loop water recircula- tion method were established for the production of red tilapia, giant river prawns, lettuce, and duckweed. The study aimed to establish the ambient growing condition, water quality, and productivity of the system subjected to different stocking densities of fish (RT24 - 24 fish/m3, and RT48 - 48 fish/m3) and prawn (P0 - zero prawn, P12 - 12 prawns/m2, and P25 - 25 prawns/m2. Results show that with an ambient air temperature and humidity ranging from 30-35 degrees C and 52-71% during the production, the obtained water quality conditions in the system were: water tem-perature 27-30 degrees C; dissolved oxygen (DO) 2.8-3.3 mg/L; pH - 8.3; total ammonia nitrogen (TAN) close to 0, Nitrite - 0; Nitrate - 40 to 160 mg/L; total dissolved solids (TDS) - 580 mg/L; and a daily water loss of 1.47% which were within the tolerable growth conditions of the different species. The stocking density of 24 fish/m3 and 12 prawns/m2 resulted in better growth and yield performance of the cultured aquatic species. However, the stock- ing densities had no significant effect on the growth and yield of lettuce and duckweed.