Effects of dietary chito-oligosaccharide and β-glucan on the water environment and gut microbiota, intestinal morphology, immune response, and meat quality of Chinese soft-shell turtles (Pelodiscus sinensis). Effects of dietary chito-oligosaccharide and β-glucan on the water environment and gut microbiota, intestinal morphology, immune response, and meat quality of Chinese soft-shell turtles (Pelodiscus sinensis)

Chito-oligosaccharides (COS) and β-glucan are gradually being applied in aquaculture as antioxidants and immunomodulators. However, the effects of different levels of these prebiotics on the water quality and gut microbiota, intestinal morphology, non-specific immunity, and meat quality of Chinese soft-shell turtles remain unclear. To investigate the possible mechanisms, 3-year-old turtles were fed a basal diet containing different amounts of COS (0.1%, 0.5%, and 1%) or β-glucan (0.1%, 0.5%, and 1%). Gut microbiome of colon contents, colonic morphology, immunoenzyme activity of liver and serum, nutrient composition of muscle, and water environment were analyzed after feeding 2 and 4 weeks. The results indicated that COS and β-glucan altered microbial community composition and diversity in Chinese soft-shell turtles, and increased the relative abundance of Romboutsia, Paraclostridium, Terrisporobacter and Turicibacter, while decreased the abundance of Cetobacterium and Edwardsiella when compared with the control group. Furthermore, colon morphology analysis revealed that COS and β-glucan improved the length and number of intestinal villi, and the effect of high-dose β-glucan was more obvious. In terms of non-specific immunity and antioxidant capacity, both β-glucan and COS significantly improved liver and serum lysozyme activity and antibacterial capacity. COS significantly increased the total antioxidant capacity in the liver. Further, β-glucan significantly increased the activity of hepatic alkaline phosphatase, which closely related to the bacteria involved in lipid metabolism. Moreover, dietary supplementation with COS and β-glucan significantly enhanced the content of total amino acids, especially umami amino acids, in muscle tissue, with β-glucan exerting a stronger effect than COS. Additionally, these two prebiotics promoted the quality of culture water in paddy fields and reshaped the bacterial community composition of aquaculture environment. All these phenotypic changes were closely associated with the gut microbes regulated by these two prebiotics. In summary, the findings suggest that dietary supplementation with COS and β-glucan in Pelodiscus sinensis could modulate the gut microbiota, improve intestinal morphology, enhance non-specific immunity and antioxidant capacity of liver and serum, increase meat quality, and improve the culture water environment. This study provide new insights and a comprehensive understanding of the positive effects of COS and ꞵ-glucan on Pelodiscus sinensis.