Dietary nucleotide supplementation enhances growth and immune responses of grouper,Epinephelus malabaricus

Basal diet containing 0.5, 1.0, 1.5 and 2.0 g kg−1 mixture of inosine monophosphate (IMP), adenosine monophosphate (AMP), guanosine monophosphate (GMP), uridine monophosphate (UMP) and cytidine monophosphate (CMP) (1 : 1 : 1 : 1 : 1) (mixed-NT; Experiment 1) and 1.5 g kg−1 from each nucleotides and mixed-nucleotides (NT; Experiment 2) were fed to triplicate groups of grouper for 8 weeks. Basal diet without NT was used as control in both Experiments. In Experiment 1, fish fed the diet with 1.5 g mixed-NT kg−1 had higher (P < 0.05) weight gain (WG) than the control group. The superoxide anion (O2−) production ratio was higher in fish fed diets with 1.0–1.5 g mixed-NT kg−1 than the fish fed diets with ≤0.5 g mixed-NT kg−1. In Experiment 2, fish fed diets with nucleotides had higher WG than the control group. The O2− production ratio was higher in fish fed the diet with 1.5 g AMP kg−1, followed by fish fed diets with 1.5 g UMP and mixed-NT kg−1, and lowest in the control group. These results suggest that growth and immune responses were enhanced in grouper fed diet with 1.5 g mixed-NT kg−1 diet. Diet with 1.5 g kg−1 of AMP seems to be more beneficial on the immune responses in fish than other nucleotides.