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

Abstract

Abstract This study explored and evaluated the addition of the probiotic Bacillus pumilus Rf8 to Coho salmon (Oncorhynchus kisutch) feed. A total of 360 juvenile Coho salmon with an initial body weight of 130.45 ± 1.11 g were randomly divided into four treatment groups, with three replicates per group and 30 fish per replicate. Different concentrations of B. pumilus were added to the feed of the four treatment groups: 0 (control group), 2 × 106, 4 × 108, and 8 × 1010 cfu/g. The experiment lasted 70 days. Growth performance parameters, nutritional metabolism, immune-related serum biochemical indicators, enzyme activity, gene expression, and muscle composition were evaluated. Furthermore, intestinal histology and intestinal flora were assessed. The findings indicated that relative to the control group, B. pumilus Rf8 notably enhanced the growth performance, protein and fat metabolism, and immune status of the fish, effectively bolstering the structure and function of the intestinal microbiota. The “4 × 108 cfu/g concentration” group demonstrated a substantial advantage in juvenile fish. The B. pumilus strains identified in this study exhibit promising potential as probiotic feed supplements in Coho salmon aquaculture.