Quantitative dietary leucine requirement of juvenile Pacific white shrimp, Litopenaeus vannamei (Boone) reared in low-salinity water

The experiment was conducted to determine the leucine requirement of juvenile Pacific white shrimp Litopenaeus vannamei (Boone) in low-salinity water (0.50-1.20 g L^-1). Six diets were formulated to contain 410 g kg^-1 crude protein with fish meal, peanut meal and precoated crystalline amino acids with different concentration of l-leucine (16.72, 19.60, 22.06, 24.79, 27.28 and 30.16 g kg^-1 dry diet). Each diet was randomly assigned to triplicate groups of 30 shrimps (0.38 ± 0.002 g), and the feed trial lasted for 8 weeks. The results indicated that the maximum weight gain was observed at 24.95 g kg^-1 dietary leucine group, whereas the diets containing higher leucine concentration conversely reduced the growth performance (P < 0.05). Moreover, the highest body protein content and body protein deposition and the lowest haemolymph AST and ALT activities were also found at 24.95 g kg^-1 dietary leucine group. With the increase in leucine in diets, a dose-dependent increase was found in body lipid content and haemolymph urea concentration. The polynomial regression calculated using weight gain, feed efficiency and body protein deposition indicated that the optimal dietary leucine requirement for L. vannamei reared in low-salinity water was 23.73 g kg^-1 leucine of dry diet, correspondingly 57.88 g kg^-1 of dietary protein.