Effects of Bacillus Subtilis Supplementation on Growth Performance, Immunity, and Intestinal Health of Juvenile Salmo Trutta Fario

Abstract

Bacillus subtilis (BS) is a widely used feed additive in aquaculture that improves growth rates, feed conversion, and immunity in farmed aquatic animals. This study aims to explore the effects of different BS doses on the health and growth of juvenile Salmo trutta fario to determine the optimal dose of BS supplementation. The experiment consisted of a control group (CG), B1 group (0.25%), B2 group (0.5%), and B3 group (1%) with a 70-day feeding experiment. Then, the effects of BS on juvenile Salmo trutta fario growth parameters, blood biochemical indexes, liver antioxidant capacity, and intestinal health were investigated. The results showed that compared with CG, FBW, and WGR were significantly increased in the B2 and B3 groups, and CF was significantly decreased (P<0.05). Regarding blood biochemical indices, AST activity was significantly elevated in the B1 group (P<0.05), and ALP activity decreased considerably in the B3 group (P<0.05). Liver antioxidant analyses revealed that MDA content was significantly higher in the B1 group compared to the CG (P<0.05), whereas it was substantially lower in the B2 and B3 groups (P<0.05). The activities of SOD in B1 and B3 groups were significantly higher than those in the CG group (P<0.05), but there was no significant change between B2 and CG groups (P>0.05). There were no substantial changes in CAT and GSH activities in the B1, B2, and B3 groups compared with the CG group (P>0.05). Gut microbiota analysis showed that the OTU of the B1, B2, and B3 groups was higher than that of the CG group, but there was no significant difference in alpha diversity (P>0.05). Beta Diversity analysis showed that the clusters of microbial communities in groups B1, B2, and B3 were more similar than those in the CG group. Co-occurrence network analysis revealed a more complex and stable microbial community structure in the B2 group. In conclusion, dietary supplementation with Bacillus subtilis enhanced the growth performance, hepatic antioxidant capacity, and intestinal microbiota stability of juvenile Salmo trutta fario, and the effect of 0.5% BS was more pronounced.

Keywords: Salmo trutta fario, Bacillus subtilis, Growth parameters, Biochemical indicators, Antioxidant capacity of the liver, Gut microbiota1 Introduction