Abstract: The enzyme activities of superoxide dismutase （SOD） in blood plasma and liver were analyzed 2 days after Enrofloxacin withdrawal in starlet （Acipenser ruthenus Linnaeus） and Amur sturgeon （Acipenser schrenckii Brandt） orally administrated for En- rofloxacin at a dose of 0, 20, 40, 60, 80 and 100mg/kg fish for 5 days to evaluate changes in SOD activities and mechanism of the drug metabolism in both sturgeon. There was SOD enzyme in both sturgeons at a different level and the SOD activities were found higher in the livers than those in the blood plasma no matter whether the drug was delivered or not. The SOD activities were found to be increased first and then decreased in the two tissues under the different drug delivery concentration, with the maximal value at the concentration of 40 mg/kg fish. In the blood plasma, hardly change in the SOD activities was observed through the period of drug delivery and there were higher SOD activities in the starlet than those in the Amur sturgeon. However, the SOD activities were fluctuated sharply through drug delivery in the liver, in which there significantly higher SOD activities in the Amur sturgeon than those in the starlet at a concentration of less than 40 mg/kg fish. It was the opposite case at a concentration of more than 40 mg/kg fish.

Key words: Enrofloxacin, Amur sturgeon （A cipenser schrencki Brandt）, starlet （A cipenser ruthenus Linnaeus）, SOD