Effects of Dietary Isoleucine Levels on the Growth Performance, Feed Utilization, and Serum Biochemical Indices of Juvenile Golden Pompano, Trachinotus ovatus

Abstract

A 56-day growth trial was conducted to determine the isoleucine requirement of juvenile Trachinotus ovatus. Six diets with different concentrations of L-isoleucine (13.2, 15.7, 18.2, 20.7, 23.2 and 25.7g/kg dry diet, defined as diet Ile-1, diet Ile-2, diet Ile-3, diet Ile-4, diet Ile-5 and diet Ile-6, respectively) were formulated to contain 430g/kg crude protein with fish meal, soybean meal, peanut meal, and pre-coated crystalline amino acids. Each diet was randomly assigned to triplicate treatments of 20 fish (initial body weight 6.36±0.03g) in seawater floating net cages. Results indicated that weight gain increased with increasing isoleucine concentrations up to 18.2g/kg, whereas diets containing higher isoleucine concentration reduced the growth performance significantly (P<0.05). The highest muscle protein content, protein efficiency ratio, body protein deposition, viscerasomatic index, hepatosomatic index, and lowest feed conversion ratio, serum AST activities were also found in 18.2g/kg dietary isoleucine treatment (P<0.05). The highest lipid content of whole fish was found in 15.7g/kg dietary isoleucine treatment (P<0.05). Survival rates in treatments Ile-5 and Ile-6 were significantly lower (P<0.05) than those in other treatments. Results of polynomial regression based on weight gain, feed conversion ratio, protein efficiency ratio and body protein deposition indicated that the optimal dietary isoleucine requirement for Trachinotus ovatus reared in seawater floating netcages was 17.39-17.50g/kg isoleucine of dry diet, correspondingly 40.4440.70g/kg of dietary protein.