Supplementing the diet of pompano Trachinotus ovatus with MacroGard® to increase innate immunity, intestinal microbes, growth and ammonia tolerance

Abstract

The present experiment aimed to analyse the advantages of diets containing 0.05%, 0.10% and 0.20% β-glucan on improving the non-specific immunity response, intestinal Vibrio, total aerobic bacteria,growth and ammonia resistance of pompano, Trachinotus ovatus (28.68 ± 0.23 g). After four weeks of diet feeding, the phagocytic index (PI), phagocytic ratio (PR), and serum lysozyme (SL) of pompano increased when adding β-glucan to their diet. The greatest immune response was observed in the pompano fed the feeds containing 0.05% and 0.10% of β-glucan (P≤0.041). Further, on day 28, the total intestinal bacteria were remarkably rose (P≤0.017) in the pompano those were fed 0.05%–0.10% of β-glucan. However, the Vibrio density and the proportion of Vibrio to the aerobic bacteria were considerably higher in pompano fed the basal (P≤0.045). Also, the pompano that offered dietary β-glucan grew faster than the pompano in control. On days 14 and 28, the β-glucan concentration and fish immune response (PR, PI, SL) correlated positively (r≥ 0.379, P≤0.012). Moreover, on day 28, the total intestinal bacteria showed a profound correlation with the β-glucan level (r = 0.312, P = 0.012). However, the Vibrio to total bacteria ratio increased as the Vibrio count was corresponded negatively to the β-glucan quantity (r= −0.528, P≤ 0.001). On day 28, the β-glucan addition was highly correlated to the phagocytic index (PI) and intestinal Vibrio. The predicted optimum levels of β-glucan to maximise responses of pompano were 0.121% and 0.122% of β-glucan for PI and intestinal Vibrio, respectively. Moreover, under stress ammonia, the pompano that was given β-glucan diets gained better survival rates and lower relative risks than pompano fed the base diet. In conclusion, the 0.05% to 0.10% β-glucan diet could boost the immune activity, improve intestinal microbes, enhance the tolerance capacity to the ammonia of the cultured pompano, T.ovatus.