Abstract: In this study, yellow grouper (Epinephelus awoara) were administered with a single dose (200 mg/kg) of sulfamethoxazole (SMZ) and sulfadiazine (SDZ) incorporated in the diet to investigate the distribution and elimination patterns of SMZ and SDZ in various fish tissues. Both sulfonamides were detected by high performance liquid chramotography-tandem mass spectrometry (HPLC-MS/MS) and quantified by the internal standard method. The results showed that SMZ concentrations in fish tissues were in the following order: liver 827.97 (μg/kg) > muscle (776.70 μg/kg) > blood (610.29 μg/L) > kidney (432.14 μg/kg) > gill (345.18 μg/kg), while SDZ concentrations in fish tissues were in the following order: liver (895.30 μg/kg) > muscle (660.55 μg/kg) > gill (431.88 μg/kg) > blood (419.56 μg/L) > kidney (310.67 μg/kg). The elimination half-life of SMZ in fish tissues was in the following order: kidney (26.65 h) > gill (21.00 h) > muscle (20.38 h) > blood (18.73 h) > liver (16.90 h), while that of SDZ in fish tissues was in the following order: kidney (31.50 h) > blood (27.72 h) > gill (24.75 h) > muscle (21.66 h) > liver (18.24 h). The elimination half-lives of two sulfonamides in liver were much shorter than all other tissues and they were metabolized at a faster rate in liver. On the contrary, the sulfonamides showed the longest elimination half-life and were metabolized at the fastest rate in kidney among the tissues tested. After simultaneous administration of single-dose SMZ and SDZ to fish living at (25 ± 2) ℃, the withdrawal period should last at least 3 days. In conclusion, our study provides a theoretical and experimental basis for reasonable application of SMZ and SDZ in fish farming.

Key words: yellow grouper (Epinephelus awoara), sulfamethoxazole, sulfadiazine, HPLC-MS/MS, metabolic patterns