Accumulation and Anti-oxidant Enzymes as Biomarkers of Heavy Metal Exposure in Clarias gariepinus and Oreochromis niloticus

Abstract

This study investigated the accumulation of heavy metals in tissues (gill, muscle and liver) and changes in anti-oxidant enzyme activities of edible fish species as biomarkers of heavy metal exposure using laboratory bioassays. Post juveniles of Clarias gariepinus and Oreochromis niloticus were exposed to 10% 96hr-LC 50 values of Pb(NO 3) 2 and ZnCl 2 against each species respectively, for 30 days. The two fish species accumulated the heavy metals (Pb and Zn) in their liver, muscle and gill with the highest concentration of the heavy metals in the muscle as observed in results obtained. The biochemical studies showed that the in the level of reduced glutathione (GSH), and the activities of superoxide dismutase (SOD), glutathione-s-transferase (GST) in the liver of fish species reduced significantly (p < 0.05) for C. gariepinus exposed sublethal concentration of Pb and Zn while catalase (CAT) reduced significantly (p < 0.05) for C. gariepinus exposed sublethal concentration of Pb. Also, the reduction in GSH, SOD, CAT and GST was significant (p < 0.05) for O. niloticus exposed to Zn. However, the reduction in GSH, SOD, CAT and GST in O. niloticus exposed to Pb was not significant (p > 0.05) and the increase in the level of Malondialdehyde (MDA) in liver of the exposed fish species was not significant (p > 0.05) after the 30 days exposure period as compared to the control. The need for routine monitoring of aquatic ecosystems integrating field and laboratory studies to assess presence and accumulation of toxic pollutants especially heavy metals in edible fish species and use of antioxidant enzymes as biomarkers of exposures to such pollutants were discussed.