Mercury is a widespread heavy metal that causes a stable and prolonged environmental pollution. Low concentrations of inorganic and organic mercury compounds are found in almost all water bodies. The high level of mercury bioaccumulation is a cause of tissue-specific toxicity, including neurotoxicity. Absorbed in nervous tissue mercury can cause brain disorders both in neural and glial cells. The brain of fish is considered one of the most susceptible targets for cytotoxicity of mercury in

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... ic ecosystems. Taking into account that different forms of mercury have widespread distribution and exhibit a strong neurotoxic effect, the assessment of mercury cytotoxicity in the brain of fish is relevant and extremely important. Rainbow trout Oncorhynchus mykiss was exposed to mercury chloride in the dose range of 5-20 μg/L for 60 days to study the chronic exposure of low doses. In this paper, we studied the influence of inorganic mercury on oxidative stress, DNA repair proteins – ERCC1 and PARP1 in the trout's brain. The results obtained have shown that the chronic effect of inorganic mercury causes dose-dependent oxidative stress in the fish brain. In addition, low concentrations of mercury (10 and 20 μg/L) caused a decrease in the content of ERCC1 in the brain of fish. On the contrary, the same doses have caused an increase in PARP1 expression. That is the chronic influence of low concentrations of inorganic mercury has a negative effect in the fish brain. Observed results showed that inorganic mercury has a potential for suppressing DNA repair and, therefore, increases the instability of genome. Thus, ERCC1 and PARP1 can be considered as the sensitive biomarkers of mercury cytotoxicity in the fish brain. A further study of mercury neurotoxicity is needed to find out the hazard of mercury environmental pollution as well as a validation of biomarkers of their impact.