Usama M. Mahmoud 1 , Imam A. Mekkawy 1,3 & Ahmed Th. A. Ibrahim 2 1 Zoology Department, Faculty of Science, Assiut University 2 Science and Math. Department, Faculty of Education New valley branch Assiut University 3 Biology department, Faculty of Science, Taif University, Taif, Saudi Arabia Correspondence and requests for materials should be addressed to A. Th. Ibrahim (Ahmedt1983@yahoo.com) Received 22 June 2012 / Received in revised form 12 September 2012 Accepted 14 September 2012 DOI 10.1007/s13530-012-0136-3 ©The Korean Society of Environmental Risk Assessment and Health Science and Springer 2012 Abstract The present investigation aimed to determine the tox- icological effects of mercury chloride on biochemical parameters of the widely consumed African catfish, Clarias gariepinus. Adult specimens of Clarias garie- pinus were exposed to sublethal concentrations (0.04 and 0.12 ppm) of mercury chloride for 7, 14, 21 and 28 days. Empirical data of results obtained were subjected to statistical analysis of variance (ANOVA) to test the effects of mercury, selenium, vitamin E and exposure periods. The mean values of Na + , Urea, Creatinine, AST, ALT and ALP were significantly in- creased from the control values, while mean values of K + , Glucose and Triglyceride were significantly decreased from the control values. Selenium and Vitamin E supplementation play appositive role in detoxification of mercury toxicity specially the low dose. The results suggest that mercury chloride can negatively affect the physiology of fish. It was observ- ed that supplementation of selenium and vitamin E decreases the toxic effect of mercury. Keywords: Mercury, Selenium, Vitamin E, Biochemical, Clarias gariepinus Introduction Fish are widely used to evaluate the health of aquatic ecosystems and physiological changes serve as bio- markers of environmental pollution 1 . Aquatic systems are exposed to a number of pollutants that are mainly released from effluents discharged from industries, sewage treatment plants and drainage from urban and agricultural areas. These pollutants cause serious dam- age to aquatic life 2,3 . The contamination of fresh water with a wide range of pollutants has become a matter of great concern over the last few decades, not only because of the threat to public water supplies, but also with the damage caused to the aquatic life. The river systems may be excessive- ly contaminated with heavy metals released from do- mestic, industrial, mining and agricultural effluents 4 . Pollutant effects on fish behavior have received in- creasing attention over the past decade. Several recent reviews on such effects have appeared including 5-10 . In Such reviews the treated fish behavioral categories included the behaviors associated with schooling, feed- ing, migration, aggression, fear, learning, phototropism and attraction to or avoidance of a chemical or tem- perature. Pitcher 11 gave a good overview of normal fish behavior. The resulting behavioral effects may inhibit an organism’s ability to capture prey, avoid predators, or successfully compete with others 12,13 . For example, a study of mosquito fish (Gambusia affinis) aqueous exposed to mercurial chloride demonstrated altered swimming activity and decreased swimming speed 14 . Similarly, Alvarez 15 noted concentration dependent effects of maternally-transferred MeHg in larval Atlan- tic croaker (Micropogonias undulatus), including de- creased response speed and increased response time to a vibratory stimulus. Mercury is generally found at very low concentrations and is very reactive in the environment. Total mercury levels are generally lesser than 10 ng/g in crustal mate- rials such as granites, feldspars and clays 16 , and in the range of 40 to 200 ng/g in soils and sediments that are not directly impacted by anthropogenic discharges. Generally, the majority of mercury in aquatic systems is inorganic forms (about 95 to 99%) and is found in sediments rather than the dissolved phase. This bio-magnification can cause high levels of Hg in top predator fishes and have a detrimental effect on humans and fish-eating wildlife 17,18 . Mercury concen- Biochemical Response of the African Catfish, Clarias gariepinus (Burchell, 1822) to Sublethal Concentrations of Mercury Chloride with Supplementation of Selenium and Vitamin E