Pharmaceuticals are a fast-emerging class of environmentally relevant contaminants of concern, due to their ubiquitous presence in surfaces waters consequent on human and veterinary use. Their relatively unknown effects on non-target organisms and probable deleterious effects on ecosystem health and complexity make it necessary to develop the use of simple early warning detection systems to validate their probable presences in the aquatic environmental niche.. In this paper we present the results of the effects on the gills exposure of a local catfish, Clarias gariepinus to four pharmaceuticals detected in the Lagos lagoon at concentrations exceeding determined no effect concentrations in literature. Histopathological changes observed included lamellar hyperplasia, hypertrophy, epithelial lifting, necrosis and atrophy. his study validates the continuing histological utility of fish gills as sensitive indicators of exposure to xenobiotics, and the inherent capacity of pharmaceutical residues in water to elicit detectable pathologies in various fish organs, even at extremely low concentrations.

Keywords: Pharmaceuticals, Clarias.gariepinus, Gills, histopathology