Optimum dietary protein-to-energy ratio for juvenile whiteleg shrimp, Litopenaeus vannamei, reared in a biofloc system

An 8-week feeding trial was conducted to evaluate the optimum dietary protein-to-energy (P/E) ratio in juvenile whiteleg shrimp, Litopenaeus vannamei. Six diets were formulated with two protein levels (30% and 35%) and three digestible energy levels (16, 17.5 and 19 kJ/g diet) at each protein level (P-30(16), P-30(17.5), P-30(19), P-35(16), P-35(17.5) and P-35(19)). Fifty shrimp averaging 0.97 +/- 0.03g (Mean +/- SD) were randomly distributed in biofloc tanks and fed one of the experimental diets. Weight gain (WG), specific growth rate (SGR) and feed efficiency (FE) of shrimp fed the P-35(17.5) diet were significantly higher than those of shrimp fed P-30(16), P-30(17.5) and P-30(19) diets (p<.05). Results for non-specific immune responses showed that diet P-35(17.5) caused higher lysozyme activity in shrimp comparing to lower protein diets. Thiobarbituric acid reactive substances (TBARS) of plasma were lower for shrimp fed on diets consisting of higher protein and energy levels than shrimp fed on the P-30(19) diet. Analyses of digestive enzyme activities showed higher trypsin activities for shrimp fed on P-35(17.5) and P-35(19) diets comparing to P-30(16) and P-30(17.5) diets. Also, hepatopancreatic lipase activity of shrimp fed P-35(16), P-35(17.5) and P-35(19) diets were significantly higher than those of shrimp fed the other diets. In conclusion, based on the results for growth performance, biochemical parameters, immune responses, oxidative stress and enzyme activities, 35% protein and 17.5 kJ/g digestible energy (P-35(17.5)) could be considered as the optimum protein-to-energy ratio in the diet of juvenile whiteleg shrimp reared in a biofloc system.