Effect of Stocking Density on Sustainable Growth Performance and Water Quality of Nile Tilapia-Spinach in NFT Aquaponic System

In Saudi Arabia, there is a scarcity of water used for agriculture and human consumption. Therefore, the aquaponic technique needs to be considered. Aquaponics is a modern, environmentally friendly agricultural technology that combines hydroponics and aquaculture into one system. However, the key to a successful aquaponic system is optimizing the stocking density for the target species. This study estimates the effect of three stocking densities—3 kg/m⁻³, 6 kg/m⁻³, and 9 kg/m⁻³—in five replicates on the growth performance and water quality of fingerling Nile tilapia (Oreochomis niloticus), as well as the yield of spinach (Spinacia oleracea) grown in the nutrient film technique (NFT) aquaponic system. As for the planting density, 36 spinach plants are planted per m⁻² for each replicate. The experiment is set up for 8 weeks. The findings reveal that the average final body weight, weight gain, specific growth rate, and survival rate of Nile tilapia were significantly higher in the 3 kg/m⁻³ treatment. It is evident that the total yield of spinach increased as the stocking density increased (p < 0.05). Most of the water quality measurements are significant, pH values range from 6.74 to 7.47, dissolved oxygen is 4.33 to 6.35, ammonia is 0.13 to 0.17 mg/L⁻¹, nitrite is 0.045 to 0.089, and nitrate is 2.44 to 3.35. Therefore, to maximize the productivity of spinach and tilapia while achieving the maximum benefit from fresh water, it can be recommended to use the stocking density of Nile tilapia fingerlings in the range of 6 kg/m⁻³ in the aquaponic system.