The synergistic effects of dietary protein and stocking density on performance, digestive enzymes, and hemato-biochemistry parameters of juvenile striped catfish (Pangasianodon hypophthalmus)

This experiment was designed to examine the impacts of different dietary protein levels (DPLs) and their interaction on the growth and some physiological indices of juvenile striped catfish, Pangasianodon hypophthalmus, reared at different stocking densities (SDs) for 15 weeks. A total of 1440 striped catfish (initial weight = 10.0 ± 2.2 g) were randomly allocated into six equal treated groups (three replicates per treated group). Fish were fed two DPLs of 25 % and 30 % and reared under different SDs of 20, 40, and 60 fish/m3. The obtained results indicated that with increasing DPL, growth parameters, and digestive enzyme activities, the liver function enzyme activities, serum protein constituents' levels, and concentrations of thyroid hormones significantly increased, while levels of serum glucose, total cholesterol, and triglycerides remarkably decreased. On the other hand, increasing SD negatively affects growth, digestive and liver enzyme activities, some hematological parameters, and fish-body chemical analysis. The interaction between DPLs and different SDs significantly improved the most estimated parameters with increasing DPLs despite intensifying SDs. In general, afforded striped catfish diets containing 30 % DPL and stocked at 20 fish/m3 presented the best performance, consumed feed efficiency, and health status. Thus, the interaction between DPLs and SDs demonstrated the favorable benefits of increasing DPLs by diminishing some of the adverse impacts generated by high SDs, which may subsequently lead to high production and increased revenues for fish farmers.