Oxytetracycline (OTC) is a broad spectrum antibacterial agent approved in the USA for treating certain bacterial diseases in salmonids cultured in freshwater at temperatures greater than or equal to 9??C. This study was conducted to provide the information necessary to expand the OTC label to include treatment of diseased salmonids cultured in freshwater at temperatures below 9??C. The study was designed to treat juvenile coho salmon (Oncorhynchus kisutch) with OTC-medicated feed and determine the depletion of OTC from the skin-on fillet tissue. Oxytetracycline depletion was evaluated in juvenile coho salmon (weight range, 13-62 g) fed OTC-medicated feed at a rate of 88.2 mg OTC/kg body weight/day for 10 days. Pairs of skin-on fillets were taken from individual fish on days 4 and 10 during the treatment phase and on days 1, 4, 8, 14, and 19 during the depletion phase. Water temperatures during the study period ranged from 4.1??C to 8.5??C. The OTC concentrations in medicated feed and skin-on fillets were determined with high-performance liquid chromatography methods. The maximum mean OTC concentration in fillet tissue was 932 ng/g, 1 day after the last treatment and decreased to 32 ng/g 19 days after the last treatment. The log-linear loss of OTC from the fillet tissue was biphasic with a terminal phase half-life of 4.9 days.
Additional Publication Details
Oxytetracycline depletion from skin-on fillet tissue of coho salmon fed oxytetracycline medicated feed in freshwater at temperatures less than 9??C