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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.

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Cyclopoid copepod, Dioithona oculata, is a common free-living euryhaline species in tropical and temperate waters having potential as live feed in marine fish larval rearing. Here, the effect of salinity on adult and naupliar survival, total population, population composition, clutch production, clutch size, development rate and adult longevity was investigated. Adult copepods survived the abrupt changes in salinities from 15 to 50 ppt (parts per thousand). The highest naupliar survival was at 30 ppt (86.33 ± 2.84%) and the lowest at 15 ppt (12.6 ± 2.34%). The highest production was at 30 ppt (883.0 ± 5.5 individuals/L) and the lowest at 15 ppt (49.0 ± 6.56 individuals/L). The proportion of nauplii was higher at salinities from 20 to 40 ppt, whereas the total population of copepodites and adults was significantly less at 15 and 45 ppt. The highest clutch production was observed at 30 ppt (8.6 ± 0.54 clutches)and the lowest at 45 ppt (2.6 ± 0.54 clutches). Maximum clutch size of D. oculata was recorded at 30 ppt (19.2 ± 2.94 eggs/clutch) and minimum at 45 ppt (7 ± 1 eggs/clutch) respectively. Development time from nauplius to adult was significantly (p < 0.05) longer at 45 ppt (12.72 ± 0.03 days) and shorter at 20 ppt (9.06 ± 0.02). Adult longevity was significantly higher at 30 ppt (27 ± 1.0 days) and lower at 45 ppt (11.3 ± 1.15). Salinity changes significantly affected the production performance of D. oculata. The optimum salinity for mass culture of D. oculata was found to be 30 ppt.