Toxicity of five therapeutic compounds on juvenile salmonids

Toxicity levels of therapeutic compounds used in aquaculture may vary depending on fish size and species, water quality, concentration of the compound, and duration of exposure. Two different sizes (2.0 and 10.0 g) of three salmonids (rainbow trout Oncorhynchus mykiss, coho salmon 0. kisutch, and Chinook salmon O. tshawytscha) were given immersion treatments with formalin, potassium permanganate, copper sulfate, acetic acid, and hydrogen peroxide at different concentrations for 1 h. Mortality curves and doses lethal to 50% (LD50) and 2% (LD2) of test fish within 96 h were developed. Analysis of the data showed significant differences in some toxicity levels based on the size of fish within a given species; small fish often were more tolerant than large fish. Among species, some differences in tolerance were apparent. This study showed that fish size and species can affect toxicity and must be considered when developing treatment regimes for those compounds or when collecting target animal safety data for new animal drug applications.