The effects of dietary Bacillus subtilis on immune response, hematological parameters, growth performance, and resistance of juvenile olive flounder (Paralichthys olivaceus) against Streptococcus iniae

We investigated the effects of different levels of dietary Bacillus subtilis (BS) on innate immunity, growth performance, feed utilization, and disease resistance of juvenile olive flounder. A control diet was formulated without probiotic, and three other diets were prepared adding different doses (1 × 107, 3 × 107, and 5 × 107 CFU/g feed) of BS (designated as Control, BS1, BS3, and BS5, respectively). Triplicate groups of fish (initial body weight, 25 g) were fed for 12 weeks. Fish fed BS‐containing diets showed significantly higher nonspecific immune responses than fish fed the control diet. Fish fed the BS5 diet showed significantly higher growth performance and feed utilization efficiency than fish fed the control diet. Fish fed the BS diets showed remarkably higher resistance against Streptococcus iniae than fish fed the control diet. These results indicate that BS supplementation at a dose of 5 × 107 CFU/g diet can improve innate immunity, growth performance, feed utilization, and disease resistance against S. iniae in olive flounder.