Effect of Dietary Protein Level on Growth Performance, Protein Utilizat ion and Body Composition of Nile Tilapia Cultured in Low Salinity Water

The juveniles of Nile tilapia, Oreochromis niloticus (body weight 1.0±0.03 g) were reared in seawater tanks (35 liters each) in order to examine their optimum dietary protein r equirements. They were fed four isoenergetic (20.3 kJg -1 ) diets containing 25%, 30%, 35% and 40% protein at a daily ration of 5% body weight for 42 days. Fish fed diets of 35% and 40% protein produced higher weight gain and growth rate than those of the other diets. Broken line regression analysis yielde d an optimal protein level of 35%. Feed conversion and protein e fficiency were significantly higher at 35% and 40% protein diets than remaining diets. Fish whole body composition s howed that moisture, protein and ash content of the fish fed diets of 35% and 40% protein was significantly higher than that of f ish fed diets containing protein levels of 25% and 30% , although the lipid contents were lower. Fish fed 35% and 40% protein diets showed higher nitrogen gain and nitrogen retention efficiency than those fed on other diets. Based on the biological data, it was esti mated that the optimal level of protein for O. niloticus weighing between 1.0 g and 5.7 g was 35%.