Effects of feeding <italic>Bacillus subtilis</italic> on growth and intestinal microflora of hybrid sturgeon

China is the world’s largest sturgeon farming country. In recent years, the disease of sturgeon has been frequent, which has a serious impact on sturgeon farming industry. The sturgeon disease mainly occurrs in juvenile stages, especially the juvenile opening stage and the juvenile feeding stage, which are two sensitive stages in the breeding of sturgeon seedlings and it often results in massive death. How to improve the survival rate of sturgeon fry has become an important problem restricting the development of sturgeon industry. The effect of Bacillus in promoting the healthy growth of cultured animals is mainly reflected in three aspects: promoting the digestion and absorption of animal nutrients, regulating the micro-ecological balance of animal digestive tract, and enhancing the immunity and disease resistance of animals. Therefore, probiotics have attracted more and more attention as an effective feed additive and disease control substance. However, there are few reports on probiotics in sturgeon farming. In this study, the commercialized Bacillus subtilis with concentrations of 0.00%(control), 0.10%, 0.20% and 0.40% were added to the feed of juvenile hybrid sturgeon (Acipenser baeri ♀ × A. schrenkii ♂) for 90 days, with breeding time from August 23rd, 2018 to November 23rd, 2018. The application effect of B. subtilis were evaluated by observing growth performance, blood biochemical indices and the intestinal microbial flora of juvenile hybrid sturgeon. The results showed that the feeding rate and feed coefficient first decreased and then increased with the addition of B. subtilis but all significantly lower than that of the control group(P<0.05), and the addition of 0.22% into the feed could improve the feed utilization for sturgeon. Compared with the control group, the addition of B. subtilis to feed increased the serum glucose content, and the its content in 0.10% addition group was significantly higher than that of the control group (P<0.05). The analysis of intestinal microbial species composition among four groups showed that at genus level, Cetobacterium was the dominant bacterium in each experimental group. With the increase of the amount of B. subtilis, the content of Cetobacterium decreased, and the lowest proportion (74.29%) was obtained in the 0.40% group. While the content of Plesiomonas increased. When the amount of B. subtilis reached 0.40%, the content of Plesiomonas reached the highest 23.64%. Adding B. subtilis to feed can reduce the abundance of Streptococcus, Lactobacillus and Lactococcus. In conclusion, feeding different doses of commercial B. subtilis to hybrid sturgeon can significantly reduce the feeding coefficient, enhance the fish body’s ability to use blood sugar and fat and improve the intestinal microecological environment to a certain extent. The recommended dosage of B. subtilis (Gutcare^a, DSM32315) in sturgeon feed is 0.10%-0.20%.