Effects of dietary immunostimulant combination on the growth performance, non‐specific immunity and disease resistance of cobia, R achycentron canadum ( L innaeus)

The aim of this study was to examine the effects of the immunostimulant combination ( IC ) containing β‐glucan, A3α‐peptidoglycan, vitamin C and vitamin E on the growth performance, non‐specific immunity and protection against Vibrio harveyi infection in cobia ( Rachycentron canadum ). Fish were fed diets containing six graded levels of IC (0, 1, 2, 3, 4 and 5 g kg −1 diet) for 8 weeks. The results showed that the survival rate ranged from 81.1 to 84.4% with no significant difference among all the groups ( P  > 0.05) after the feeding experiment. Dietary IC significantly increased the specific growth rate ( SGR ), serum lysozyme, alternative complement pathway ( ACH 50) activity, phagocytosis percentage ( PP ) and respiratory burst activity of head kidney macrophages of cobia. Moreover, feeding of supplemented diets containing 3.0 g kg −1 IC resulted in significantly lower mortality against the pathogens, V. harveyi compared with the control group. To elevate the growth and immune resistance ability of cobia, the optimal dose of dietary IC administration, determined by second‐order polynomial regression analysis was 3.43 and 2.71 g kg −1 diet, respectively, on the basis of the SGR and mortality after challenge with V. harveyi .