Residues of clenbuterol in tissues of the rainbow trout (Oncorhynchus mykiss).

There have been many studies on the efficacy of beta 2-adrenergic drugs as feed additives but no data are available at present on the use of clenbuterol in fish production. To evaluate the residues of clenbuterol in tissues of fish, 50 trout (Oncorhynchus mykiss) were fed for 21 days on a fish feed containing 5 ppm of the drug. The livers, muscles and skins of sample groups of fish were analysed by HPLC with visible spectrophotometric detection on days 15 and 21 of treatment and at intervals during a 30-day withdrawal time. Clenbuterol reached its highest levels in the liver (mean 440 ppb; SD = +/- 159; n = 5) on day 15 of treatment, with a slow depletion curve; 24 +/- 3 ppb was still present at the end of the withdrawal period. At this time, residues were still present in the edible tissues, i.e. muscle (5 +/- 1 ppb) and skin (7 +/- 3 ppb). Side-effects were noted during the first week of treatment.