Effects of dietary sodium alginate and Lactobacillus reuteri on the growth, antioxidant capacity and intestinal health of largemouth bass (Micropterus salmoides)

Functional polysaccharides and probiotics are recognized for their ability to increase the growth and health of fish, but research on the combined impacts of these two compounds on aquatic organisms is limited. Hence, the aim of this study was to investigate the effects of single or complex sodium alginate and Lactobacillus reuteri on the growth, antioxidant status, immune function and intestinal health of largemouth bass (Micropterus salmoides). Four diets, CT for the control, SA for low molecular weight sodium alginate (10 g/kg), LR for L. reuteri (108 CFU/g), and ALR for SA+LR, were used to feed the fish (initial body weight of 4.68 ± 0.03 g) for 60 days. Our results revealed that the fish feed conversion rates and viscerosomatic indices of the SA and ALR groups were significantly lower than those of the CT group; the SA, LR and ALR groups presented significantly greater whole-fish crude protein and protein efficiency, and the highest values were found in the LR and ALR groups. Compared with those in the CT group, the aminotransferase activity and blood lipid levels of fish in the LR and ALR groups decreased, liver antioxidant enzyme CAT level was increased, and the MDA level decreased. In addition, the LR and ALR groups presented significant increases in muscular thickness and villus height and improved immune status by increasing intestinal barrier integrity and decreasing proinflammatory cytokine expression. For the intestinal microbiota, the dietary LR and ALR groups presented increased abundances of Firmicutes and Lactobacillus. The abundances of Fusobacteria and Cetobacterium increased in the SA group. In summary, SA and LR promote intestinal health by increasing the antioxidant capacity, improving the abundance of beneficial intestinal flora, and decreasing the levels of intestinal proinflammatory factors, which ultimately promote the growth of largemouth bass.