Dietary zinc requirements of juvenile grouper, Epinephelus malabaricus

• Dietary Zn requirements of juvenile grouper were 29–34 mg/kg diet.
• Dietary supplementation of Zn sulfate enhanced the growth of grouper.
• Dietary Zn levels, as low as 10 mg/kg, did not affect grouper's immune responses.

Optimal dietary requirements of the juvenile grouper Epinephelus malabaricus for zinc (Zn) were investigated in an 18-week feeding trial, in which immune responses of the fish to the zinc treatments were also evaluated. In the feeding trial, the basal diet with egg white powder and mackerel muscle meal as the protein sources had a crude protein level of 52% and a residual zinc concentration of 10.0 mg/kg diet. Zn of graded levels (0, 4, 8, 12, 24, 36 and 140 mg Zn/kg diet as zinc sulfate) was added to the basal diet and fed to experimental fish with an initial mean weight of 5.9 g. The results showed that dietary zinc significantly affected the growth of the fish, but not the survival. The non-supplemental group showed a weight gain significantly lower than that of the supplemental groups. Zinc concentrations in fish serum, muscle, vertebrate and scales were increased with increasing Zn levels in diets. The dietary treatments did not significantly affect nonspecific immunity parameters including macrophage phagocytosis, alternative complement pathway activity (ACH50), agglutination titer and lysozyme activity as well as erythrocyte superoxide dismutase activity. Broken-line analyses based on the weight gain and body tissue zinc concentrations indicate that the optimal levels of dietary zinc for the juvenile grouper ranged between 28.9 and 33.7 mg/kg diet.