RÉSUMÉ
Fish samples of Tilapia nilotica obtained from Lake Maryout were used to investigate the relationship between heavy metals and biological effects due to the industrial contaminations in the lake. Samples were examined for the activities of acetylcholinesterase, alkaline phosphatase and glutathione S-transferase. Meanwhile, levels of cadmium [Cd] and mercury [Hg] were determined in both fish and water. Results obtained revealed that the activities of all studied enzymes were markedly inhibited. Maryout samples contained higher concentrations of Hg and Cd than Nozha samples. Marked differences in electrophoretic patterns of proteins prepared from Maryout and Nozha fish samples were found. The nutritional quality of Maryout fish proteins was lower than that of Nozha samples. Results obtained from field and laboratory exposures can give useful indication for a proper use of biochemical responses as biomarkers in monitoring heavy metal pollution