Direct and circulatory paths of Permethrin (NRDC‐143) causing histopathological changes in the gills of rainbow trout, Salmo gairdneri Richardson

Rainbow trout were exposed to sublethal concentrations of Permethrin in water (0.09, 0.18 and 0.35 μg l−1) and in food (85, 180 and 350 μg kg−1 dry diet) in 20–0 day experiments. Histological changes in the gills included epithelial separation or necrosis, mucus cell hyperplasia, clubbing of epithelial cells or hyperplasia and fusion of adjacent secondary lamellae. These changes were noted in all fish, suggesting that the pesticide or its metabolites reached the gills not only directly through the water, but also indirectly via the circulation.