The present study was designed to determine the level of four toxic heavy metals: lead, cadmium, mercury and arsenic, in edible muscles of four fish species namely Tilapia nilotica (Tilapia), Synodontis guntheri (Kurungu), Heterotis niloticus (Bargi), and Clarias anguillaris (Catfish), harvested from three locations Alua Dam, Doron Baga and Dabamasara within the Lake Chad Basin of Borno State, Nigeria. The main objective was to investigate the possible effects of dry and rainy seasons and smoking of the fish on the concentration of the toxic heavy metals in the fish following wet digestion. The toxic heavy metals, expressed in parts per million (ppm), were detected in all the fish species sampled during the dry and rainy seasons from the three (3) inland waters investigated. The overall mean concentrations of the heavy metals were significantly higher (P0.05) in fresh fish samples harvested during the rainy season than the dry season. Significantly different variations were also observed within fish types and between locations in the concentrations of the four heavy metals. Smoking of the fish also resulted in significant increases (P0.05) of the metals, especially in lead and mercury concentrations in smoked samples during the two seasons. Cadmium and arsenic were the lowest recorded metals in both fresh and smoked fish during the two seasons and in all the locations. Washing the smoked samples with double distilled water resulted in significant reduction of more than 50% of the metals in the smoked fish, indicating surface contaminants. The sequence of the heavy metals concentrations in all the fish samples was Pb>Hg>Cd>As. The concentrations of the metals in both the fresh and smoked samples from all the locations during the two seasons were however lower than the internationally recommended threshold levels. Follow up studies were recommended while it was concluded that fish from Lake Chad basin are still safe for human consumption in terms of their heavy metal contents.
