Protective Effect of Humic Substances Against Oxidative Stress Caused by Lead in Liver of Nile Tilapia, Oreochromis niloticus (Linnaeus, 1758)

In this study, the protective effect of humic substance in the fish feed was investigated against the effects of subletal lead (Pb) concentration on the antioxidant enzyme system in Oreochromis niloticus. For this purpose, the fish which were affected by 1.5 mg/L lead nitrate Pb(NO3)2 medium concentration were fed with feed containing 0.2% of humic substance. Liver samples were taken at 4th and 10th days in this study, which included control group, humic substance (HM), Pb, and Pb + HM groups. The enzyme activity of liver tissue catalase (CAT) and superoxide dismutase (SOD) of O. niloticus and the level of malondialdehyde (MDA), a product of lipid peroxidation, increased significantly at 4th and 10th days in the group with subletal lead concentration compared with the control group. Compared with Pb and HM+Pb groups, it was determined that humic substance application decreased Pb toxicity on lipid peroxidation of liver tissue and did not cause a significant change in CAT and SOD activity. According to the results of the experiment, 0.2% humic substance added to the feed reduced toxicity of subletal Pb concentration on liver tissue lipid peroxidation.