UTTAR PRADESH JOURNAL OF ZOOLOGY

The present study evaluated the toxic effects of the organophosphate (OP) pesticide Ethion (50% EC) on acetylcholinesterase (AChE) activity in the freshwater fish Catla catla and assessed its potential as a biomarker of pesticide induced neurotoxicity. An experimental laboratory based toxicological study was conducted at the Department of Zoology & Aquaculture, Acharya Nagarjuna University, Guntur, Andhra Pradesh, India, over a period of three months, involving both acute (lethal) and sublethal exposure trials. Fish were exposed to a lethal concentration of Ethion (2.8 µg/L for 24 hrs) and a sublethal concentration (0.28 µg/L) for 24 hrs, 4 days, and 8 days. AChE activity was measured in brain, muscle, gill, liver, and kidney tissues using standard biochemical assays, and behavioural alterations were also recorded. The results showed significant inhibition of AChE activity in all tissues, exhibiting a clear dose and time dependent pattern. Under lethal exposure (24 hrs), brain tissue exhibited the highest inhibition (44.59%) while the liver showed the lowest (31.83%). Sublethal exposure also resulted in consistent inhibition, with brain tissue (33.60%) being more affected than the liver (15.18%). Prolonged sublethal exposure further intensified enzyme suppression, indicating cumulative neurotoxic effects. In addition, behavioural abnormalities such as hyperactivity, erratic swimming, and impaired coordination were observed, correlating with the extent of AChE inhibition. These findings demonstrate that AChE activity serves as a sensitive and reliable biomarker of Ethion toxicity in C. catla, and they underscore the ecological risks posed by OP pesticide contamination in aquatic ecosystems. The study highlights the potential of integrating biochemical and behavioural endpoints to assess pesticide impacts and emphasizes the urgent need for stricter regulation and sustainable management of pesticide use in agriculture.