Toxicity of Erythromycin, Oxytetracycline, and Tetracycline Administered to Lake Trout in Water Baths, by Injection, or by Feeding

Abstract

The toxicities of three antibiotics, each administered by three routes at doses up to five times the recommended concentrations, were determined in lake trout (Salvelinus namaycush). In water bath exposures, erythromycin phosphate was considerably less toxic than oxytetracycline hydrochloride (OTC) or tetracycline hydrochloride (TC); however, the toxicity of all three antibiotics was low. Injections of erythromycin produced no deleterious effects, even at concentrations four times the standard dose rate. Injections of OTC produced adverse effects and mortality at high treatment rates. A water-soluble form of TC was judged unsatisfactory for injections because of its low pH (2.5). In feeding studies, the palatability of erythromycin-treated feed was poor, but that of OTC- and TC-treated feeds was acceptable. Weight gains (as percent of original weight) for fish offered the erythromycin-treated diet ranged from 144.7% at the recommended therapeutic concentration to 111.6% at five times the recommended concentration, compared with nearly 300% for untreated fish or for those treated with OTC or TC in the diet. Concentrations greater than those recommended for treatment were not toxic to lake trout when fish were exposed in water baths to any of the three drugs, when they were injected with erythromycin, or when they were fed diets treated with OTC or TC.