The oxytetracycline (OTC) label currently limits the administration of OTC to 
control specific diseases in salmonids and catfish. This residue depletion study 
was conducted to support the extension of the label to include all cool water 
fish species cultured at public aquaculture facilities. In this study, walleye 
averaging 59.1 grams each (in 17.5 ±1 °C water) were offered 3.87% of their 
total body weight per day of a slow sinking walleye diet (Walleye Grower 9206) 
top-coated with OTC (89.0 mg/kg/day OTC-HCl) for ten days. Fish were sampled 1, 
2, 3, 4, 7, 9, 11, and 14 days after the treatment and their skin-on fillets 
were analyzed for OTC-base concentration.
The maximum mean OTC-base concentration (721 ng/g) in the fillet tissues of 
walleye fed medicated Walleye Grower 9206 remained below the current OTC-base 
tolerance limit of 2000 ng/g. Loss of OTC-base from the fillet tissues was 
monophasic. Elimination half-life of OTC-base was 10.5 days. The OTC-base 
concentration representing the one-sided upper tolerance limit for the non-
central t-distribution of the data, at the 95% confidence level with a 99% 
confidence interval (1133 ng/g) was under the tolerance limit for OTC-base in 
fillet tissue.