The pharmacokinetics of enrofloxacin and its metabolite ciprofloxacin were investigated in the mud crab(Scylla paramamosain)kept at a salinity of 33 after a single oral gavage and intramuscular injection(10 mg/kg).The concentrations of enrofloxacin and ciprofloxacin in the main tissues (hemolymph,muscle and hepatopancreas)were simultaneously detected by HPLC.The parameters in hemolymph and tissues were calculated by non-compartment model based on statistic moment theory.The peak plasma enrofloxacin was fast reached after oral gavage and intramuscular injection.The peak time were 0.5 h and 1 min for oral gavage and intramuscular injection,respectively and the peak concentration of enrofloxacin was 12.90 and 31.86 μg/mL,respectively.Area under the concentrationtime curve (AUC)in hemolymph was 216.1 and 816.8 μg/(mL·h),respectively.Enrofloxacin was widely distributed in mud crab tissues.AUC of muscle and hepatopancreas were 445.9 and 817.6 μg/(g·h),respectively,following oral gavage and AUC of muscle and hepatopancreas were 554.7 and 2 573.7 μg/(g·h),respectively,after intramuscular injection.Compared with other aquatic animals,enrofloxacin was eliminated at a medium level.Half-life of elimination(t_1/2z)and body clearance(CL_z)were 26.45 h and 0.054 L/(h·kg),respectively,for oral gavage,and 57.02 h and 0.012 L/(h·kg),respectively,for intramuscular injection.The AUC ratios of ciprofloxacin and enrofloxacin in mud crab hemolymph,muscle and hepatopancreas were 6.68%,3.60% and 4.78%,respectively,following oral gavage,and the corresponding values were 4.16%,7.24% and 1.48%,respectively,after intramuscular injection.Enrofloxacin in mud crab metabolized less ciprofloxacin and enrofloxacin played a main role in the efficacy in the mud crab.The efficacy of enrofloxacin in mud crab was evaluated with C_max/MIC ratio and AUC_0-24/MIC ratio.Oral gavage of enrofloxacin at a single dosage of 10 mg/kg once every 24 h could yield good therapeutic efficacy on vibrio diseases.