Gill damage in the freshwater fish Gnathonemus petersii (family: Mormyridae) exposed to selected pollutants: An ultrastructural study

The histopathological effects of three heavy metals, cyanide and atrazine on the gill tissues of the mormyrid fish, Gnathonemus petersii, were determined primarily by electron microscopy. Replicate samples of fish were exposed for 6 hours to two concentrations of each toxicant in a continuous flow system comprising aerated, dechlorinated and heated water. Specific alterations to gill ultrastructure were found to be associated with each toxicant. Cadmium damage at 1.0 mg l(-1) was associated with the formation of large subepithelial spaces within the secondary lamellae and at 10.0 mg l(-1) with lamellar aneurism. Chromium caused epithelial hyperplasia at 1.0 mg l(-1) and extensive fusion of secondary lamellae at 10.0 mg l(-1). Copper exposure stimulated hyperactivity of mucous cells at 0.1 mg l(-1) which resulted in the accumulation of a thick layer of mucus on the gills at 0.5 mg l(-1). Cyanide caused desquamation of filamental epithelium at 0.05 mg l(-1) and shipping of the epithelium and underlying tissue down to the supporting cartilage at 0.10 mg l(-1). Atrazine damage was characterized by the presence of breaks in the gill epithelium at 0.50 mg l(-1) which developed into deep pits at 5.0 mg l(-1). This study demonstrates the potential of electron microscopy, in particular SEM, as a tool for detecting pollutant-induced damage to the surface of fish gills.