Soy Protein Concentrate Dietary Substitution and Bacillus coagulans Supplementation Influence the Growth Performance, Digestive Enzyme Activity, Antioxidant Capacity, Gene Expression, and Gut Microbiota of Hybrid Grouper (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂)

This study evaluated the effects of soy protein concentrate (SPC) substitution for fish meal and dietary supplementation of Bacillus coagulans on the growth performance and biochemical responses of juvenile hybrid grouper (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂). Three experimental diets were designed, including 0% SPC substituting fish meal (NSPC0), 25% SPC substituting fish meal (NSPC25), and 25% SPC substituting fish meal supplemented B. coagulans to 108 CFU/g (BSPC25). As a result, BSPC25 significantly improved the final body weight (FBW), specific growth rate (SGR), weight gain rate (WGR), and condition factor (CF). Compared with NSPC0, BSPC25 significantly elevated the liver expression level of rapamycin target (TOR) gene, and NSPC25 and BSPC25 notably increased the content of malondialdehyde (MDA) in the liver. However, there was no significant difference in superoxide dismutase (SOD) activity, gut microbiota α-diversity, and β-diversity. In summary, 25% SPC substitution of fish meal together with B. coagulans dietary supplementation can significantly improve the fish growth performance by upregulating the TOR gene expression, providing important insights into the development of low-fish meal diets for hybrid grouper.