PHARMACOKINETIC STUDY OF OXYTETRACYCLINE IN CULTURED RAINBOW-TROUT, AMAGO SALMON, AND YELLOWTAIL

The pharmacokinetics and tissue levels of an antibiotic, oxytetracycline, were determined after oral administration (100 mg/kg body weight) in cultured rainbow trout, amago salmon, and yellowtail. Oxytetracycline levels were determined by high-performance liquid chromatography. Serum levels of oxytetracycline in three fish species could not be fitted to compartment pharmacokinetic models with first-order absorption. The area under the serum concentration-time curve (AUC) were 32.1, 58.7, and 38.4 (mu-g.h/ml) for rainbow trout, amago salmon, and yellowtail, respectively. The mean residence time calculated from AUC were 50.3, 24.6, and 43.3 h for rainbow trout, amago salmon, and yellowtail, respectively. Biological half-lives (T1/2) of the serum were 23, 16, and 28 h for rainbow trout, amago salmon, and yellowtail, respectively. The T1/2 of muscle in yellowtail was shorter than those of the two salmonids. Oxytetracycline residues persisted in the liver of the three fish species. Elimination times were 22, 21, and 21 days for rainbow trout, amago salmon, and yellowtail, respectively.