Histological alterations observed in the gills and ovaries of Clarias gariepinus exposed to environmentally relevant lead concentrations.

Sublethal levels of pollutants usually cause biochemical or physiological effects at the subcellular level in an organism. Death is too extreme a criterion for determination of whether a substance is harmful or not; it is therefore important to find biomarkers of health and sublethal toxicant effects. In the 11 local-government areas of Ibadan, a large metropolitan area in Nigeria, previous studies of lead levels in surface water and fish ponds revealed surface water levels in ranges of 0.5-2.35 mg/L (mean = 0.76 mg/L) during the dry season and 1.15-2.20 mg/L (mean = 1.34 mg/L) during the rainy season, and a range of 1.09-2.9 mg/L (mean = 1.88 mg/L) in fish ponds. In the study reported here, Clarias gariepinus was exposed to environmentally relevant concentrations (0.0, 0.05, 0.1, 0.5, and 1 mg/L) of lead nitrate over a period of eight weeks. The goal was to assess histological alterations in the gills and ovaries. The lesions observed in the gills included epithelial hyperplasia, atrophy and fusion of gill filaments, and marked degeneration and necrosis of the epithelial cells, with hemorrhages and marked disorganization and rupture in the secondary lamellae. In the ovaries, diffuse mild degeneration and necrosis of the follicles were initially observed; subsequently, the groups exposed to higher concentrations of lead nitrate showed marked severe degeneration of ovarian follicles. The results of this work clearly indicate that lead has adverse effects on the gills and ovaries of Clarias gariepinis. The severity of lesions caused by lead nitrate was positively correlated with the concentration.