THE DISPOSITION OF C-14 FLORFENICOL IN ATLANTIC SALMON (SALMO-SALAR)

The absorption, distribution, metabolism and excretion of C-14-labelle d florfenicol in Atlantic salmon held in sea water at 8.5-11.5-degrees -C were studied by means of whole body autoradiography (WBA), liquid s cintillation counting (LSC) and high performance liquid chromatography (HPLC). Uniformly ring-labelled C-14-florfenicol was mixed in capelin oil, and coated on ordinary fish feed. Each of 28 fish (139.6 +/- 18. 4 g) was gavaged with a single dose of 10 mg/kg bodyweight of florfeni col, corresponding to 119.05 muCi/kg bodyweight. Whole fish were sampl ed from 3 h to 56 days after administration, and were analyzed by WBA and LSC. Muscle samples from fish sampled 6 h to 3 days after administ ration were analysed by HPLC, and LSC of fractions of the eluate. Peak radioactivity levels were detected in most tissues at 12 h after admi nistration (3 days in the kidney), and declined thereafter. The radioa ctivity in the brain was low compared with that in muscle and blood, s uggesting that the passage of the blood-brain barrier by florfenicol o r its metabolites is limited. Radioactivity levels in blood and muscle were similar at all times. Accumulation of radioactivity could be see n in the kidney and the choroidea of the eye, indicating a possible af finity to melanin. The radioactivity was excreted both via urine and b ile. There were trace amounts of radioactivity in skin, liver and kidn ey tissues of fish sampled 56 days post administration, while no radio activity was detected in any blood or muscle samples taken later than 28 days after administration. The fraction of parent florfenicol in mu scle decreased from approximately 90% (6 h) to about 20% (3 days), whi le the fraction of florfenicol amine increased from about 7% to about 70% during the same period. Other metabolites were detected, but were quantitatively of minor importance. The results strongly suggest that florfenicol is rapidly metabolized in the body of Atlantic salmon, and that the dominant metabolite is florfenicol amine.