Evaluation of protective role of selenium on mercury toxicity by oxidative stress parameters in gill and liver tissues of Oreochromis niloticus

In this research, to identify mercury (Hg) toxicity and whether selenium (Se) has any role in alleviation of this toxicity, it was investigated the alterations in oxidative stress parameters in tissues of Oreochromis niloticus. For this purpose fish were exposed to 0.01 and 0.05 ppm Hg and 0.01 ppm Hg+0.01 ppm Se and 0.05 ppm Hg+0.05 ppm Se for 4 and 21 days and gill and liver superoxide dismutase (SOD) and catalase (CAT) activities and malondialdehyde (MDA) levels were determined. It was observed significant changes in all analyzed parameters due to tissue, medium concentration and exposure period in the exposure of mercury alone and mercury+selenium mixtures. In the Hg alone, and in combination with Se especially in their higher medium concentrations, the gill and liver SOD and CAT activities significantly increased at 4 days (P˂0.05), while they significantly decreased at 21 days (P˂0.05). In the exposure of Hg and Hg+Se and in the both tissues, it not determined significant alteration in the MDA levels at 4 days (P˃0.05), while they elevated in their higher concentrations at 21 days (P˂0.05). In conclusion, it was determined the observed increases or decreases in SOD and CAT activities and MDA levels in O. niloticus were higher in the Hg alone than Hg+Se mixtures and selenium has a protective effect on oxidative toxicity of mercury. Keywords: Oreochromis niloticus, Mercury, Selenium, Antioxidant Enzymes, Malondialdehyde