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

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