Effect of Bacillus megaterium-Coated Diets on the Growth, Digestive Enzyme Activity, and Intestinal Microbial Diversity of Songpu Mirror Carp Cyprinus specularis Songpu

The present study was conducted to evaluate the effect of a Bacillus megaterium-coated diet on growth performance, digestive enzymes, and intestinal microbial diversity in Songpu mirror carp (Cyprinus specularis Songpu). The fish were manually fed two diets (a control diet and a B. megaterium-coated diet) three times daily until apparent satiation for 56 days. Compared with the control group, supplementation with the B. megaterium-coated diet enhanced the fish growth and significantly reduced the feed conversion ratio (P < 0.05). The activities of foregut amylase and lipase in the treatment group were significantly higher than those in the control group (P < 0.05). The activities of foregut, midgut, and hindgut proteases in the treatment group were all higher than those in the control group (P > 0.05). The results of sequencing the 16S rDNA genes of the microbiota through high-throughput sequencing showed that the diversity and abundance of the intestinal microflora increased along with Songpu mirror carp growth. The Songpu mirror carp fed a diet coated with B. megaterium displayed increased proportions of intestinal Bacillus and Lactococcus at the genus level, and both were significantly higher than those of the control group (P < 0.05). These results therefore suggest that dietary B. megaterium application can improve the growth and digestive enzyme activity of Songpu mirror carp and enrich the beneficial genus composition of its main intestinal microflora.