Effects of dietary leucine on growth performance, feed utilization, non-specific immune responses and gut morphology of juvenile golden pompano Trachinotus ovatus

• Dietary leucine requirement of juvenile Trachinotus ovatus was determined.
• Dietary leucine improves growth performance, food intake and protein deposit rate of juvenile T. ovatus.
• Dietary leucine improves non-specific immune response of juvenile T. ovatus.
• Dietary leucine has a positive influence on the gut morphology of juvenile T. ovatus.

The effects of dietary leucine on growth performance, feed utilization, non-specific immune responses and gut morphology were studied in juvenile golden pompano (Trachinotus ovatus) using 8-week feeding trials. Six isonitrogenous and isolipidic diets were formulated to contain six graded levels of dietary leucine (16.2, 20.9, 26.0, 30.7, 35.9 and 41.0 g kg− 1 leucine of dry diet). Each diet was randomly assigned to triplicate groups of 20 juvenile fish (5.76 ± 0.06 g). Maximum weight gain rate (WG), specific growth rate (SGR), feed intake (FI), protein efficiency ratio (PER), microvilli numbers and microvilli length in foregut and midgut were recorded at 30.7 g kg− 1 dietary leucine. Protein deposition ratio (PDR), hemoglobin (HGB) and hematocrit (HCT) were found to be optimal in fish fed with 35.9 g kg− 1 leucine of diet. Dietary leucine levels had a significant effect on serum superoxide dismutase (SOD), malondialdehyde (MDA), lysozyme (LZY) and total antioxidant capacity (T-AOC) (P < 0.05). Intestinal microstructures were positively affected by dietary leucine at the optimal levels of 26.0 and 30.7 g kg− 1, significantly (P < 0.05) increasing microvilli numbers and microvilli length in foregut and midgut. Based on the growth performance, feed utilization, proximate composition, serum enzyme activities and gut morphology, the optimum dietary leucine level for optimal growth of juvenile golden pompano was 29.3–32.9 g kg− 1 of the dry diet, corresponding to 71.5–80.2 g kg− 1 of dietary protein.Statement of relevanceThe study indicated low or excess amount of dietary leucine decreased growth performance, serum total antioxidant capacity and had a significantly negative effect on gut morphology. The optimum dietary leucine level for juvenile golden pompano was 2.93–3.29% of the dry diet. The results provide a theoretical basis for the designing of feed formulation for golden pompano (T. ovatus).