Growth, digestive enzyme activities, proximate composition and hemato-biochemcial responses of juvenile Nile tilapia (Oreochromis niloticus) reared at various stocking densities in a recirculatory aquaculture system

ABSTRACT This investigation aimed to assess the impact of rearing biomass on growth, digestive enzyme activity, and hematobiochemical indices of Nile tilapia in a tank-based recirculatory aquaculture system (RAS) for 90 days. Oreochromis niloticus (35.5 ± 0.24 g) were randomly stocked at the following densities: 80 fish/m3 (F80), 120 fish/m3 (F120), and 160 fish/m3 (F160) in triplicate. Ammonia, nitrate, nitrite, and CO2 were increased significantly as density increased and dissolved oxygen decreased (P < 0.05). A significantly increased weight gain, specific growth rate, growth efficiency, and protein efficiency ratio were recorded in F80 groups compared to F160 groups, whereas feed conversion ratio was decreased. Protease, amylase, and lipase activities were significantly lower as fish density increased. An improved (P < 0.05) red blood cell count, hemoglobin, and hematocrit were found in F160 groups. A considerably higher level of glucose, cortisol, triglycerides, total cholesterol, alanine, and aspartate aminotransferase were recorded in high-density tanks (P < 0.05). The crude lipid and carbohydrate contents were significantly lower in F160 groups. Hence, the outcomes of the present study indicated that stocking density 80 fish per m3 would be appropriate as it promotes the growth and health status of Nile tilapia cultured in RAS.