Abstract: In this study, the preventative efficacy of Sanhuanglian Powder against artificially induced Streptococcus agalactiae infection in tilapia was assessed, and the large-scale clinical application effect and safety of Sanhuanglian Powder with recommended dosage of 13.2 g/kg feed in production was evaluated. A total of 3 groups including Sanhuanglian Powder experimental group, traditional Chinese medicine control group, and blank control group were included in this study, and there were 300 tilapia in each group. After a 7-day continuous administration, 30 fishes were randomly selected from each group for the measurements of weight gain rate, organ index, blood physiological and biochemical indicators as well as liver antioxidant indexes. On the 8th day after medication, the fishes were challenged with Streptococcus agalactiae by artificial cohabitation infection, and the protection rate was calculated on the 14th day after the challenge. The results showed that after the 7 days administration, compared with the blank control group, Sanhuanglian Powder experimental group had obviously increased weight gain rate, organ index and multiple liver antioxidant indexes, and had no obvious abnormality in blood physiological and biochemical indicators generally. The protective rate of Sanhuanglian Powder against the artificially induced Streptococcus agalactiae infection in tilapia was 43.67%. In conclusion, Sanhuanglian Powder can improve the immune resistance and reduce the mortality rate of tilapia caused by Streptococcus agalactiae infection.

Key words: Sanhuanglian Powder；tilapia；Streptococcus agalactiae