Withdrawal times of freshwater rainbow trout,Salmo gairdneri Richardson,after treatment with oxolinic acid,oxytetracycline and trimetoprim

Abstract. Oxolinic acid (OA), oxytetracyline (OTC) and trimetoprim (TMP) were investigated in whole gutted rainbow trout, Salmo gairdneri Richardson, and in their skin, muscle and blood, at 6, 12 and 18°C. Concentrations of drugs were measured by high-pressure liquid chromatography. It is recommended that withdrawal times for rainbow trout be based on whole gutted rainbow trout and not, as in earlier investigations, from residual concentrations in muscle. Any concentrations in rainbow trout feed were found to be stable during the pelleting process used and up to 81 days after pelleting. The absorption of the drugs in rainbow trout show different temperature dependencies. A quantitative comparison of our overall data from this work with individual results from earlier investigations was undertaken. Suggested withdrawal times for freshwater rainbow trout treated with these drugs are: for OTC, 90 days below 6°C, 70 days between 6 and 12°C and 60 days above 12°C; for TMP, 60 days below 8°C and 40 days above 8°C; for OA, 20 days at approximately 18°C.