The hispathological changes in gills of Nile tilapia, Oreochromis niloticus, fingerlings exposed to 5.3 mg/l (96-h LC50) malathion are described. These changes include hypertrophy of epithelial cells after 3 h, epithelial lifting and destruction of the structural integrity of some lamellae after 24 h, multifocal fusion of adjacent lamellae after 72 h, and diffused epithelial lifting after 96 h. Partial to complete recovery was observed in gills after rearing in malathion-free water for 6. to 12 d
