Studies on Toxicological Effect of the Herbicide Paraquat Dichloride on the Air Breathing Singhi Catfish, Heteropneustes fossilis (Bloch)

Abstract

The habitats of air breathing freshwater catfish Heteropneustes fossilis are prone to oxygen deficiency and mostly contaminated with the organic and inorganic pollutants. But the fish is known for its greater adaptive capability even in adverse environmental condition and is regarded as champions in tolerating such type of aquatic environments. Therefore, it seems to be a suitable model for the study of toxicological effect of the paraquat dichloride (1, 1′-dimethyl-4, 4′-bipyridinium dichloride), a recognized contact herbicide which is highly noxious to humans and animals. The aim of this study was to investigate the toxicity of paraquat (PQ) when used in sub-lethal concentrations of 6 mg/L and 12 mg/L respectively, as determined from the LC50 value. The oxidative stress markers in liver, kidney and intestine of the fish; alanine aminotransferase, aspartate aminotransferase and alkaline phosphatise enzymes in the blood serum and haematological parameters of the fishes were evaluated at 6 h, 24 h, 48 h, 5 days, 10 days and 14 days post treatment with 6 mg/L and 12 mg/L of PQ. The results revealed the increased concentration of glutathione-S-transferase (GST), specifically after 10 days of treatment with 12 mg/L paraquat concentration, along with significant increase in the concentration of superoxide dismutase (SOD), catalase (CAT) and malondialdehyde after 14 days of PQ exposure (12 mg/L concentration), when tallied against the control. However, the concentration of non-enzymatic reduced glutathione (GSH) was decreased significantly in treated fishes after 14 days (12 mg/L concentration) as GST uses GSH as a substrate to detoxify substances, hence enabling more defence against ROS production in H. fossilis. Haematological indices like the RBC count and haemoglobin concentration manifested a significant reduction, while the WBC count significantly increased on exposure to both 6 mg/L and 12 mg/L concentrations of PQ as compared to control fish. These findings clearly indicated the increased concentration of antioxidant enzymes (SOD, CAT, GST) and reduction in non enzymatic GSH enabled the fish to survive during the PQ exposure period.