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The cyano-metabolite of furazolidone (FZ), 3-(4-cyano-2-oxobutylidene amino)-2-oxazolidone, was isolated from the mixture of FZ incubated with the post-9000 g hepatic supernatant of grouper. Its structure was confirmed by mass spectrometric and nuclear magnetic resonance spectroscopic studies. Thereafter, the disposition of the cyano-metabolite in the orange-spotted grouper (Epinephelus coioides) after oral and bath treatment with FZ was investigated. Qualitative and quantitative analyses of cyano-metabolite in the fish were performed by high-performance liquid chromatography. Mean recoveries of the metabolite in serum, muscle, liver and kidney were 99.8 +/- 4.1, 98.6 +/- 3.5, 53.1 +/- 7.4 and 64.0 11.4%, respectively. Cyano-metabolite was mainly distributed in the serum and muscle rather than in the liver and kidney. After oral treatment of FZ, the peak cyano-metabolite concentrations, 167.2 ng x ml(-1) in serum and 283.2 ng x g(-1) in muscle, were reached at 5.1 and 6.7 h, respectively. The elimination half-life of cyano-metabolite was 4 h. During 24-h bath treatment of FZ, the maximum concentrations of cyano-metabolite, 258 ng x ml(-1) in serum and 204 ng x g(-1) in muscle, were found at 0.25 and 6 h, respectively. The half-life of cyano-metabolite was 0.5 h after transferring the fish to fresh seawater.