Toxicological Effects of Lead and Zinc on the Antioxidant Enzyme Activities of Post Juvenile Clarias gariepinus

Toxicological effects of sub lethal concentrations of lead and zinc salts (Pb(NO3)2 and ZnCl2) on the antioxi- dant enzymes of post juvenile Clarias gariepinus in laboratory bioassays was investigated, using the liver. Oxidative stress enzymes and substrates (Glutathione-S-Transferase (GST), Glutathione (GSH), Superoxide dismutase (SOD), and Catalase (CAT) ) showed irregular activities during the first two weeks of the experiment, but a significant variation (p<0.05) from levels detected in controls after 28 days in fishes exposed to both metals. Increased levels of GST-GSH and reduced levels of SOD and CAT occurred in fishes exposed to ZnCl2 as compared to control while there were no variations in the levels of Malondialdehyde (MDA). In fishes exposed to Pb(NO3)2 however, GST-GSH, SOD, CAT and MDA all reduced when compared to control. There is need for more research on the oxidative defense response of Clarias gariepinus to persistent levels of high concentrations of heavy metals .There is also a need for comparison of existing field and laboratory studies so as to fully exploit the bio markers of oxidative stress as indicators of environmental pollution in tropical fresh water systems.