Dietary supplementation with host gut-derived Bacillus tequilensis (GCB-3) enhances growth, immune function, antioxidant capacity, and resistance to poly(I: C)-induced viral infection in grass carp (Ctenopharyngodon idella)

This study investigated the effects of dietary supplementation with host gut-derived Bacillus tequilensis (GCB-3) on growth performance, serum immunity, intestinal barrier function, antioxidant capacity, and resistance to poly(I: C)-induced viral infection in grass carp (Ctenopharyngodon idella). Fish were fed diets containing GCB-3 at doses of 0 (B0), 1 × 10⁶ (B6), 1 × 10⁷ (B7), 1 × 10⁸ (B8), and 1 × 10⁹ (B9) CFU/g for eight weeks. The B8 group showed significant improvements in final body weight, digestive enzyme activity, and serum immune markers compared to the control (P < .05). Intestinal barrier integrity was enhanced in the B8 group, as indicated by reduced serum levels of permeability markers (DAO, 5-HT, ET-1, d-LA) and upregulation of tight junction proteins and antimicrobial peptides (P < .05). Furthermore, the B8 group exhibited elevated antioxidant enzyme activities and gene expression in the hepatopancreas (P < .05). Following poly(I: C) challenge, the B8 group demonstrated lower serum AST, ALT, and γ-GT levels, as well as higher albumin levels, and reduced hepatopancreatic inflammation and apoptosis through the modulation of pro- and anti-inflammatory cytokines and apoptosis-related genes (P < .05). These results indicate that dietary GCB-3 at 1 × 10⁸ CFU/g improves growth, immunity, and intestinal health, and confers resistance to viral-like challenge in grass carp, supporting its potential as a probiotic agent in sustainable aquaculture.