Effects of dietary Bacillus pumilus on the growth, intestinal health, lipid metabolism, and mTOR signaling pathway of juvenile coho salmon (Oncorhynchus kisutch)

This study investigated the effects of dietary supplementation with the probiotic Bacillus pumilus on coho salmon ( Oncorhynchus kisutch ). A total of 360 juvenile fish, with an average initial weight of 130.75 ± 1.33 g, were randomly assigned to four treatment groups, each with three replicates of 30 fish. The fish were then fed for 70 days using formulated diets containing four concentrations of B. pumilus : 0 (control group), 2 × 10 6 , 4 × 10 8 , and 8 × 10 10 CFU/g. We then evaluated growth, nutrient metabolism, immune-related serum biochemical markers, enzyme activity, gene expression, and muscle composition. Additionally, we assessed intestinal histology and microbiota composition. Our findings revealed that B. pumilus significantly improved growth, protein and fat metabolism, and immune function compared to the control group. It also had a positive effect on the structure and function of the intestinal microbiota. The group receiving 4 × 10 8 CFU/g showed the greatest improvements. Overall, B. pumilus appears to be a promising probiotic for enhancing the health and performance of coho salmon in aquaculture. • B. pumilus Rf8 significantly bolsters the growth of fish • B. pumilus Rf8 optimizes nutrient metabolism and deposition • B. pumilus Rf8 enhances both intestinal structure and immune function. • The ideal supplementation amount in the feed was determined to be 4 × 10 8 CFU/g.