Biochemical Evaluation of Carbohydrate Metabolism in Fresh Water Fish Clarias batrachus exposed to Two Organophosphorus Insecticides

Author(s): Konda Ganesh

Abstract:

Agricultural pesticides frequently enter aquatic ecosystems and may affect non-target organisms such as fish. The present investigation evaluated the biochemical responses of the freshwater catfish Clarias batrachus following exposure to two organophosphorus insecticides, Dimethoate and Profenofos. Fish were exposed to sub-lethal concentrations of Dimethoate (1.846 mg L⁻¹) and Profenofos (2.100 mg L⁻¹) for a period of 15 days. After the exposure period, fish were transferred to pesticide-free freshwater for 12 days in order to assess recovery responses. Exposure to Dimethoate resulted in significant reductions in carbohydrate and glycogen levels across tissues, whereas Profenofos exposure produced variable alterations depending on the tissue examined. Metabolic intermediates such as lactate and pyruvate exhibited marked fluctuations under pesticide stress. Enzymatic activities related to carbohydrate metabolism also showed significant changes. Lactate dehydrogenase (LDH) activity decreased in liver, kidney, and muscle tissues but increased in gills. Dimethoate strongly inhibited succinate dehydrogenase (SDH) activity in all tissues examined. Malate dehydrogenase (MDH) activity was stimulated by both insecticides. Glycogen phosphorylase activity showed tissue-specific induction and inhibition patterns. Following transfer to pesticide-free water, partial recovery in biochemical parameters was observed, indicating the capacity of fish to restore metabolic balance after cessation of toxic exposure. However, recovery was slower in Dimethoate-exposed fish compared with those exposed to Profenofos, suggesting greater toxicity of Dimethoate. The results demonstrate that organophosphorus pesticides significantly disrupt carbohydrate metabolism in C. batrachus. These biochemical responses may serve as useful biomarkers for assessing pesticide contamination in freshwater ecosystems and highlight the potential ecological risk posed by organophosphorus insecticides to edible fish species.

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