The present study was undertaken to investigate the adverse effects of mercuric chloride (HgCl2) overload in the fish Channa punctatus. Two sublethal test concentrations of HgCl2 (1/20th and 1/10th of 96 h LC50 i.e., 0.03 mg l−1 (low concentration) and 0.07 mg l−1 (high concentration), respectively, were used for exposure. Blood, liver and kidney tissues of the control and exposed specimens were sampled at intervals of 15, 30, and 45 days to assess alterations in oxidative stress, genotoxicity haematological parameters and histopathology. Significant changes in Hb%, RBC count, WBC count, antioxidant enzyme activity, i.e., superoxide dismutase (SOD), catalase (CAT), glutathione (GSH) and glutathione reductase (GR), were recorded. Micronuclei (MN) induction, nuclear abnormalities (NAs) and histopathological alterations were also observed in the exposed fish. Significant (P < 0.05) increase in the activities of SOD, CAT, GSH and GR was observed. After 45 days, a decrease in the level of GSH and GR was noticed which suggests an undermined anti‐oxidative defence system in the fish exposed to HgCl2. Histological examination of the liver and kidney showed serious tissue injury and histological alterations. Significant increases in MN and NA frequencies reveal the DNA damage in erythrocytes of fish, and haematological changes show the toxicological potential of HgCl2. The observed changes in the antioxidant defence system, genotoxicity and haematological and histological changes in the present study provide the most extensive insight into HgCl2 stress in C. punctatus.

The current study was strived to investigate the adverse effects of Mercuric chloride (HgCl2) overload in the fish Channa punctatus. Two sub-lethal test concentrations of HgCl2 viz., 1/20th and 1/10th of 96 h LC50 i.e., 0.03 mg/L and 0.07 mg/L, respectively, were used for exposure. Blood, liver and kidney tissues of the control and exposed specimens were sampled at intervals of 15, 30 and 45 days to assess alterations in oxidative stress, genotoxicity haematological parameters and histopathology. Significant changes in Hb%, RBC count, WBC count, antioxidant enzyme activity viz., super oxide dismutase (SOD), catalase (CAT), glutathione (GSH) and glutathione reductase (GR) were recorded. Micronuclei (MN) induction, nuclear abnormalities (NA) and histopathological alterations were also observed in the exposed fish. Significant (p < 0.05) increase in activities of SOD, CAT, GSH, GR and after 45 d decrease in the level of GSH and GR suggest an undermined anti-oxidative defence system in the fish exposed to HgCl2. Histological examination of liver and kidney showed serious tissue injury and histological alterations. Significant increase in MN and NA frequencies reveal the DNA damage in erythrocytes of fish and haematological changes show the toxicological potential of HgCl2. The observed genotoxicity, biochemical, haematological and histological changes in the present study provide the most extensive insight of HgCl2 stress in Channa punctatus.