The protein requirement of grouper Epinephelus coioides at grow-out stage

The present study was conducted to investigate the protein requirement of grouper Epinephelus coioides at grow-out stage (initial weight of 102.8 +/- 1.02 g). Six iso-lipidic diets were formulated using white fish meal and casein as protein sources with graded levels of protein (350, 400, 450, 500, 550 and 600 g/kg). Grouper was hand-fed twice daily to apparent satiation in triplicates for 8 weeks. The results showed that lack of protein will lead to the declined of weight gain and specific growth rate and suitable protein not only improved growth, but also reduced feed coefficient rate. In addition, high-protein level diet significantly decreased the morphological index of grouper. For the body proximate composition analysis, the high-protein diets (500, 550, 600 g/kg) significantly increased the protein contents in the whole body and muscle which was contrary to as observed for the lipid content. High-protein diets significantly improved the total protein levels of plasma which were contrast to as observed in triglyceride contents. Moreso, the cholesterol content was observed to be significantly decreased after high-protein diet supplementation. The intestinal protease activity was observed to increase significantly with increasing protein supplementation whereas a decreasing trend was observed for the lipase and amylase activity with the highest going for the groups fed diets containing 350 g/kg protein as compared to the others. The liver alkaline phosphatase, superoxide dismutase and lysozyme activity increased with increasing protein level which later decreased. On the other hand, the acid phosphatase activity showed a significant downward trend. Based on SGR, the broken-line regression analysis showed that the optimum dietary protein level and digestible protein level of the grouper Epinephelus coioides at grow-out stage were 466.65 and 395.79 g/kg, respectively.