Pathology of lethal and sublethal exposure of fathead minnows, pimephales promelas, to cadmium: A model for aquatic toxicity assessment

Seventy‐six fathead minnows were exposed to 12 ppm cadmium for 96‐ h and examined histologically at 1‐wk intervals for 30 d. Thirteen fish (17.1%) died during the exposure period. Lesions associated with acute cadmium toxicity were epithelial necrosis of the skin, oral cavity, gills, olfactory organs, kidney, urinary bladder, ureters, gastrointestinal tract, and hemopoietic organ. The lesions were most severe in fish which died. Survivors had similar but less severe and less extensive lesions. Residual minimal to mild multifocal necrosis was observed In gastrointestinal, branchial epithelium and and hemopoietic tissue up to 29 d postexposure. Radiotracer studies in 50 fish using 115Cd demonstrated a rapid uptake and two phase elimination of cadmium by the fish. Rapid elimination of cadmium occurred within 7 wk and was correlated with lesions in the urinary epithelium. Slow phase elimination occurred for at least 3 wk and was correlated with persistant minimal necrosis in several tissues.