Molecular interactions and biomarker responses to pharmaceutical contaminants in aquatic species.

Pharmaceutical residues are increasingly detected in freshwater systems, yet mechanistic links between sub-lethal exposure and organ-level injury in fish remain limited. This study assessed 21-day effects of carbamazepine (CBZ), diclofenac (DCF) and fluoxetine (FLX) on Labeo rohita using integrated hepatic and renal biomarker panels supported by molecular docking. Fish were exposed to sub-lethal concentrations under semi-static conditions, and responses were quantified using standard biochemical assays. Hepatic markers included cytochrome P4501A activity (CYP1A/EROD), uridine diphosphate-glucuronosyltransferase (UGT), glutathione S-transferase (GST), antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx)], redox balance [reduced/oxidized glutathione ratio (GSH/GSSG)] and oxidative damage indicators such as malondialdehyde (MDA). Renal endpoints comprised organic anion transporters (OAT1/OAT3), cyclooxygenase-2 (COX-2), caspase-3, kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), N-acetyl-β-d-glucosaminidase (NAG), creatinine and urea. Homology models of CYP1A, COX-2, serotonin transporter (SERT), heat-shock protein 70 (HSP70) and vitellogenin (Vtg) were validated using QMEAN and docked with CB-Dock2. Responses ranked DCF > CBZ > FLX. Diclofenac caused the strongest biotransformation induction, antioxidant suppression, oxidative damage and renal injury, whereas CBZ induced moderate health effects and FLX produced mild changes. Findings highlight biomarker-anchored evidence of pharmaceutical risk to carp health and offer practical indicators for freshwater monitoring.