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The present study was undertaken to examine the DNA damage in peripheral blood erythrocytes of Cyprinus carpio under the binary exposure of bifenthrin and chlorpyrifos by using single cell gel electrophoresis (SCGE). Limited efforts have been made to study the genotoxic effect for long duration period. Therefore, the present investigation was aimed to assess the genotoxicity of pesticide mixture to the freshwater carp, Cyprinus carpio at sub-lethal concentration exposure (33% LC50). At first 96-hr LC50 value of pesticide, the mixture was determined for Cyprinus carpio in a static system and then sub-lethal concentration was calculated and fish was exposed to this sub-lethal concentration of the mixture in glass aquaria for 70 days (five fortnights) at constant laboratory conditions. Peripheral blood erythrocytes were taken on a fortnightly basis for the time-dependent DNA damage assessment in-terms of percentage of damaged cells, genetic damage index and a cumulative tail length of comets. Concentration-dependent increase in the percentage of DNA damaged cells were observed up to a 4th fortnight, followed by a slight decrease in the 5th fortnight. Similarly, statistically significant time-dependent DNA damage was observed in terms of percentage of damaged cells, genetic damage index and a cumulative tail length of comets in treated fish (at 33% of LC50) as compared to control groups. The results supported the use of SCGE for evaluating the toxicity of pollutants which may be used as part of environmental monitoring programs.

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During present study, the copper (Cu) mediated oxidative stress was measured that induced DNA damage by concentrating in the tissues of fish, Catla catla (14.45±1.24g; 84.68±1.45mm) (Hamilton,1822). Fish fingerlings were retained in 5 groups for 14, 28, 42, 56, 70 and 84 days of the exposure period. They were treated with 2/3, 1/3, 1/4 and 1/5 (T1-T4) of 96h lethal concentration of copper. Controls were run along with all the treatments for the same durations. A significant (p < 0.05) dose and time dependent concentration of Cu was observed in the gills, liver, kidney, muscles, and brain of C. catla. Among organs, the liver showed a significantly higher concentration of Cu followed by gills, kidney, brain, and muscles. Copper accumulation in these organs caused a significant variation in the activities of enzymes viz. superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). The SOD activity varied significantly in response to the exposure time of Cu as 56 > 70 > 42 > 84 > 28 > 14 days while CAT activity exhibited an inverse relationship with the increase in Cu concentration. POD activity showed a significant rise with an increase in Cu exposure duration. Comet assay exhibited significant DNA damage in the peripheral erythrocytes of Cu exposed C. catla. Among four exposure concentrations, 2/3rd of LC50 (T1) caused significantly higher damage to the nuclei compared to control. Increased POD and SOD activity, as well as a decrease in CAT activity in response to Cu, demonstrates the involvement of a protective mechanism against reactive oxygen species (ROS), whereas increased ROS resulted in higher DNA damage. These above-mentioned molecular markers can be efficiently used for the biomonitoring of aquatic environments and conservation of edible fish fauna.