Evaluation and compare of yeast β-glucan and carboxymethylglucan to improve the immunity and gut health of turbot fed diet containing 400 g kg−1 of soybean meal

In carnivorous fish feed, soybean meal was widely used as the alternative protein source to fish meal, but its negative influence on fish immunity and gut health limits its application. Yeast β-glucan is a well-documented immunostimulant and prebiotic, and carboxymethylglucan has higher potential bioactivity. The present work was to investigate and compare the effects of yeast β-glucan and carboxymethylglucan on the immunity and gut health of turbot Scophthalmus maximus (with initial weight of 7.6 g) fed a diet containing 400 g kg⁻¹ soybean meal. Yeast β-glucan and carboxymethylglucan was respectively supplemented at the dose of 2 g kg⁻¹. Enteritis was observed in fish fed the soybean meal diet. Beta-glucan or carboxymethylglucan supplementation significantly increased serum lysozyme activity, and the concentrations of IgM, complement 3 and complement 4. These two additives significantly decreased the infiltration of leukocytes in the lamina propria and submucosa and the expression of inflammatory cytokine of il-8. Compared with β-glucan, the fish fed carboxymethylglucan showed higher growth performance, feed utilization, lysozyme activity, concentrations of IgM, complement 3 and complement 4 but lower enteritis severity and inflammatory cytokines expression (il-1β, il-8, tnf-a and tgf-β). The structure of intestinal autochthonous bacteria was also altered by dietary yeast β-glucan and carboxymethylglucan. In conclusion, the present work confirmed the beneficial influence of dietary yeast β-glucan and carboxymethylglucan on turbots suffering from soy enteropathy. And carboxymethylglucan showed better protective effects than β-glucan against soybean meal-induced intestinal inflammation on turbot.