Articles

Heavy metal contamination has become a pressing environmental concern in freshwater ecosystems, particularly in river systems impacted by industrial discharge, agricultural runoff, and domestic effluents. In rivers of Punjab Pakistan, elevated concentrations of chromium, lead, cadmium, nickel, and manganese have been reported in water and fish tissues, especially in commercially important species such as Labeo rohita and other cyprinids. These non-degradable metals bioaccumulate in fish through direct absorption and trophic transfer, disrupting physiological and biochemical processes. A principal mechanism of toxicity involves excessive production of reactive oxygen species (ROS), leading to oxidative stress when antioxidant defenses are overwhelmed. ROS-induced lipid peroxidation, commonly assessed via malondialdehyde (MDA) levels, damages cellular membranes, proteins, and DNA. Fish counteract oxidative stress through integrated antioxidant systems, including enzymatic components (superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and glutathione-S-transferase) and non-enzymatic molecules such as glutathione and vitamins C and A. However, responses are dose-, tissue-, and species-specific, often showing adaptive enzyme induction at low metal concentrations and system failure at higher exposures. Biomarker-based assessments, including enzyme activity assays and metal accumulation analyses, provide valuable tools for ecological risk evaluation. Monitoring antioxidant responses in sentinel fish species offers an effective early warning framework for pollution management and conservation strategies in contaminated freshwater basins.