Dietary supplementation with two host-associated Bacillus velezensis strains enhances growth, antioxidant, and gut health in Micropterus salmoides and Channa argus

Four week aquaculture experiment was conducted to evaluate the probiotic potential of Bacillus velezensis MS-3, isolated from Micropterus salmoides , and Bacillus velezensis CA-1, isolated from Channa argus , in both Micropterus salmoides and Channa argus . The two strains, MS-3 and CA-1, were prepared into MS-3 feed (8 ×10 6 CFU/g), CA-1 feed (8 ×10 6 CFU/g), and a composite probiotic feed (MS-3:CA-1 = 1:1, 8 ×10 6 CFU/g). At the end of the aquaculture experiment, enzyme activity assays, histological HE staining, real-time quantitative PCR, and 16S rRNA analysis of the gut microbiota were performed to assess the effects of MS-3 and CA-1 on weight gain, antioxidant activity, disease resistance, and the gut microbiota composition in Micropterus salmoides and Channa argus . The experimental results show that the addition of MS-3 and CA-1 to the feed promotes the growth of Micropterus salmoides and Channa argus , enhances their antioxidant capacity, increases the activity of immune-related and digestive enzymes, improves their overall immunity, and enhances intestinal structure and the composition of the gut microbiota. Additionally, the two strains of Bacillus velezensis from different host origins may exhibit host specificity. • The B. velezensis strains MS-3 and CA-1 enhance host growth and digestion. • The B. velezensis strains MS-3 and CA-1 can enhance the host's antioxidant capacity, immunity, and gut microbiota. • The B. velezensis strains MS-3 and CA-1, from different hosts, may possess host-specific properties.