Certain biochemical responses in the air-breathing catfish Clarias batrachus exposed to sublethal carbofuran

Biochemical changes in the air-breathing catfish, Clarias batrachus (Linn.) exposed to a sublethal level of carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) at 0.5 ppm concentration in ambient water for a period of 30 days were assessed. A small reduction in growth rate was observed in the fish treated with 0.5 ppm carbofuran for 60 days although no mortality or any apparent symptom of toxicity could be noted. Studies were carried out on the activities of certain enzymes of intermediary metabolism viz., glucose 6-phosphatase, alkaline phosphatase, acid phosphatase, Na+, K+-ATPase, GOT and GPT in certain vital tissues of the fish exposed to carbofuran (0.5 ppm) for 30 days. Exposure to carbofuran resulted in sharp inhibition of acetylcholinesterase activity in brain of the fish which recovered rather rapidly after terminating pesticide treatment and maintaining the fish in clean freshwater. Ratio of the levels of calcium/phosphorus in serum showed significant diminution in experimental groups of fish compared to controls. Level of ammonia in serum of experimental fish was markedly increased while excretion of ammonia by fish showed concomitant decrease. The bioaccumulation level of the pesticide and its degraded product, 3-hydroxy-carbofuran in liver tissue was measured by gas chromatography. A rationale of the effect of carbofuran on metabolism vis-a-vis toxicity in the fish has been suggested.