Toxic impact of lethal concentration of lead nitrate on the gills of air -breathing catfish Heteropneustes fossilis (Bloch).

nitrate on the gills of air-breathing catfish Heteropneustes fossilis (Bloch). Vet. arhiv 72, 167-183, 2002. Toxicopathological impact of lethal concentration (925 mg/l) of lead nitrate on the gills of air-breathing catfish Heteropneustes fossilis was analysed. Following exposure the gills exhibited rapid alterations that include detachment and lifting of the epithelial linings from the surfaces of the gill filament (primary, PL) and respiratory (secondary, SL) lamellae. This led to extensive haemorrhage from the gills. Thus the quantity of blood flowing across the gills decreased substantially. Simultaneously, uncontrolled regeneration of the PL and SL occured, leading to extensive hyperplasia of the epithelial cells lining the PL, and SL. Consequently, the gill filaments appeared as a cylindrical solid mass of cells with very little or almost no free surface left on the SL for gaseous exchange. The goblet mucous cells also exhibited periodic fluctuations in their density and staining behaviour. The chloride cells showed periodic fluctuation in their number at different stages of exposure. The density of the chloride cells is inversely proportional to the thickness of the epithelial lining of the PL and SL. Due to prolonged exposure, the neighbouring SL fused together and the entire gills appeared as solid mass of undifferentiated cells. Subsequently, the ladder-like arrangement of the pillar cells-blood capillaries of the gills also collapsed, causing asphyxiation and the death of the fish.