Models of comparative acute toxicity of injectable erythromycin in four salmonid species

Abstract

We quantified and modeled the 96-h toxicity of commercially available injectable erythromycin, Erythro-200, to Atlantic salmon ( Salmo salar), cutthroat trout ( Oncorhynchus clarki), rainbow trout ( O. mykiss) and spring chinook salmon ( O. tshawytscha) in several trials to analyze the response within and across different temperatures and ages (sizes) of fish. Probit analyses of the dose response across these separate trials, including those conducted at different water temperatures, revealed no significant differences among the slopes of the mortality response for each species group. Median lethal doses (LD50) of erythromycin for the species and temperatures tested ranged from 350 to 1041 mg kg −1. We provided a general dose-response model for injectable erythromycin in all test species and size groups, with the differences in probit intercepts modified by species, temperature and size of fish. The toxicity–body size relationship for injectable erythromycin fits an allometric equation with a body weight exponent of 0.79 to 0.80. We observed some mortality at high dosages of the injectable drug carrier (PEG-400, ethyl acetate and absolute ethanol) in all species tested and we estimated the LD50=4.71 ml kg −1 for yearling chinook salmon at 12 °C.