PHYSIOCHEMICAL CHANGES IN TILAPIA (Oreochromis niloticus) DUE TO EXPOSURE OF PESTICIDE MALATHION

Abstract

Pesticide contamination is a major and persistent threat to freshwater and coastal aquaculture systems in Bangladesh, where organophosphate insecticides such as malathion are widely used and frequently detected in aquatic environments. Concurrently, climate change driven salinity intrusion is increasingly affecting freshwater and brackish-water habitats, potentially modifying pesticide toxicity and increasing physiological stress in fish. However, the combined impacts of pesticide exposure and elevated salinity on fish health and recovery capacity remain poorly understood. Sublethal malathion exposure disrupts hematological, biochemical, and genomic integrity in Oreochromis niloticus, and that elevated salinity may modulate these effects and delay post-exposure recovery. Juvenile tilapia were exposed for 28 days to a factorial combination of three malathion concentrations (0.7, 2.1, and 3.5 ppm; 10-50% of the 96-h LC₅₀ of 7 ppm) and three salinity levels (5, 10, and 15 PSU), followed by a 28-day recovery period in pesticide-free freshwater. Blood glucose and cholesterol were measured as indicators of metabolic stress, hemoglobin and RBC counts as measures of oxygen-carrying capacity and anemia, WBC counts as markers of immune activation, and cytogenetic endpoints (micronuclei and erythrocytic nuclear and cellular abnormalities) as sensitive indicators of genotoxic damage. Chronic malathion exposure produced clear concentration and time dependent alterations across all biomarker categories, with most effects becoming significant from mid to late exposure (Days 14-28; p < 0.001). RBC counts and hemoglobin levels declined progressively, while WBC counts, glucose, and cholesterol increased significantly (p < 0.001), indicating anemia-like conditions, immune activation, and sustained metabolic stress. Salinity alone acted as an additional stressor, and combined malathion-salinity exposure generally intensified physiological and genotoxic responses, particularly at higher malathion concentrations (3.5 ppm) and moderate to high salinity (10-15 PSU; p < 0.001). Genotoxic effects were pronounced, with micronuclei frequency and erythrocytic nuclear and cellular abnormalities showing marked elevation under high-dose combinations (p < 0.001). During recovery, most hematological and biochemical parameters showed significant improvement toward control values (p < 0.05), whereas cytogenetic abnormalities declined more slowly and often remained elevated after 28 days (p < 0.001), indicating delayed restoration of genomic integrity. Overall, the findings demonstrate that environmentally relevant, sublethal malathion exposure can xvii substantially disrupt physiological homeostasis and induce persistent genotoxic damage in O. niloticus, and that elevated salinity associated with climate-driven intrusion can modify and prolong these effects. The persistence of genotoxic damage despite apparent physiological recovery underscores the importance of considering multi-stressor interactions and recovery dynamics in environmental risk assessment. The integrated biomarker framework applied here provides a sensitive and effective tool for monitoring pesticide risks in salinity-affected aquaculture and coastal ecosystems.