Abstract: In vivo pharmaeodynamics of high （50 mg·kg^-1 ） / middle （20 mg·kg^-1 ） / low （5 mg·kg^-1 ） concentration of florfenicol and chloramphenicol （ 10 mg·kg^-1, control group） were studied through negative control group （no bacterial infection or drug given） and positive control group （infected by bacterial but no drug given and by establishment of a pathological model in Siberia sturgeon （Acipenser baeri）infected by pathogenic bacterium Yersinia ruckeri. The cumulative mortality rates were found of 0% in negative control group and of 50% in positive control group three days after continuous oral administration of florfenicol, indicating that the pathological model was successful, the cumulative rate of 30% in low florfenicol group, 0% in middle florfenieol group, 0% in high florfenicol group, and 10% in treatment control group. After healing, no bacterial infection was found in the fish blood. The pathogenic bacterium Y. ruckeri was isolated from the liver and kidney of the experimental fish except negative control group, causing no death. The results showed that florfenicol had better effects in treatment of Siberia sturgeon infected by Y. ruckeri than chloramphenicol, and replaced chloramphenicol to treat bacterial diseases in fish.

Key words: Florfenicol, Yersinia ruckeri, Siberia sturgeon, pharmacodynamics in vivo