Effect of salinity on growth of Nile tilapia (Oreochromis niloticus) and spinach (Spinacia oleracea) in aquaponic system using inland saline groundwater

This study was carried out to find suitable salinity for the best growth performance and survival of Nile tilapia (Oreochromis niloticus) with spinach (Spinacia oleracea) in an aquaponic system. The experimental design consisted of inland saline groundwater with salinities 3, 6 and 9 g L⁻¹ as treatments and freshwater as control, carried out in 12 identical aquaponics units with fish stocked at a biomass 1.3 kg m⁻³ and plants at a density 40 m⁻². Nile tilapia reared at salinities 9, 6 and 3 g L⁻¹ showed significantly higher (p < 0.05) feed efficiency ratio and protein efficiency ratio compared to freshwater. The feed conversion ratio of fish at salinities 9, 6 and 3 g L⁻¹ ranged between 1.31–1.43 and significantly differed from control. Final mean biomass were statistically similar at 9 g L⁻¹ (5 kg m⁻³), 6 g L⁻¹ (4.92 kg m⁻³) and 3 g L⁻¹ (4.68 kg m⁻³). Survival of O. niloticus was 100% in all the salinities tested. Spinach was harvested twice during the study, in the first harvest the yield was observed higher in freshwater followed by 3, 6 and 9 g L⁻¹, but in the second harvest, the higher yield was observed in 9 g L⁻¹ followed by 6 g L⁻¹, 3 g L⁻¹ and freshwater. Based on the overall production performance and water quality parameters, a salinity of 9 g L⁻¹ was found to be the best for the integration of Nile tilapia and Spinach in an aquaponic system.