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Oxytetracycline depletion from skin-on fillet tissue of coho salmon fed oxytetracycline medicated feed in freshwater at temperatures less than 9 degrees C

Meinertz, J. R., Gaikowski, M. P., Stehly, G. R., Gingerich, W. H., and Evered, J. A., 2001, Oxytetracycline depletion from skin-on fillet tissue of coho salmon fed oxytetracycline medicated feed in freshwater at temperatures less than 9 degrees C: Aquaculture, v. 198, no. 1-2, p. 29-39.

Abstract

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, I 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.

Keywords

oxytetracycline, salmonid, depletion, fillet tissue, rainbow-trout, chinook, fish