Histological changes in the gills of Clarias gariepinus (Teleostei: Clariidae) from a polluted South African urban aquatic system

A semi-quantitative histological assessment was used to investigate histological changes in the gills of Clarias gariepinus from Marais Dam and Rietvlei Dam near Pretoria, which receive effluent from sewage treatment plants and industries, as well as runoff from informal settlements. Results were compared to those from a laboratory-bred reference group of fish. Histological alterations were prevalent in fish from both impoundments, including circulatory disturbances such as telangiectasia and epithelial lifting, hyperplasia of mucous cells and epithelial cells between secondary lamellae, structural alterations in the form of fusion and branching of primary and secondary lamellae, and regressive changes in the form of intracellular alterations within gill epithelial cells. Significantly higher histological index values were calculated for fish from Marais Dam compared to those from Rietvlei Dam.