Effects of Lethal and Sub-Lethal Diclofenac Exposure on Enzymatic Activities in Heteroclarias and the Ameliorative Role of Neem Leaf Supplementation

Abstract

This study examined the lethal and sub-lethal effects of diclofenac on juvenile hybrid catfish (Heteroclarias) over 8, 15, and 30 days of exposure, focusing on behavioural and biochemical responses in blood, gill, and liver tissues. Exposed fish showed dose-related behavioural disturbances such as erratic swimming, surface gasping, and altered pigmentation, with effects becoming more pronounced over time. Biochemical analyses revealed significant changes in aspartate aminotransferase (AST), alanine aminotransferase (ALT), acetylcholinesterase (AChE), lactate dehydrogenase (LDH), superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), and malondialdehyde (MDA). Enzyme responses varied across tissues and exposure durations, indicating physiological stress and oxidative imbalance. Dietary supplementation with neem leaf (Azadirachta indica) reduced several of the observed biochemical disruptions and improved behavioural stability in exposed fish, suggesting a protective role against diclofenac-induced toxicity. These findings demonstrate that diclofenac can adversely affect aquatic organisms even at sub-lethal concentrations and highlight the potential of plant based dietary additives as a mitigation strategy. The study emphasizes the ecological risks posed by pharmaceutical contaminants in freshwater systems and supports the need for improved environmental monitoring and management.