Abstract: Residues of florfenicol and its major metabolite florfenicol amine were detected in vivo in common carp （Cyprinus carpio） with body weight of （ 100＋ 10） g orally gavage administrated 3 times in a 24 h interval at a dose of 15 mg·kg^-1 body weight by high performance liquid chromatography tandem mass spectrometry to evaluate the withdrawal period of the drug at water temPerature of （ 18±1 ）℃. The contents of florfenicol and florfenicol amine were monitored in the muscles and skins 0.5h, lh, 2h, 4h, 8h, 12h, 24h, 2d, 3d, 5d, 7d, 10d, 15d, and 20d after the drug delivery. The results showed that the florfenicol in the common carp was metabolized in vivo rapidly, peak in 2-4 hours. There was more florfenicol and its metabolite florfenicol amine residues in the muscles than those in the skin, and the florfenicol contents in the muscles and skins higher than the florfenicol amine residues in the same tissues, showing rapid metabolism in the skin. The withdrawal period of the drug was found to be over 2 d according to EU standard and over 10d ac- cording to Japanese standard.

Key words: florfenicol, florfenicol amine, residue, liquid chromatography-mass spectrometry, common carp