<p>Organophosphate pesticides are widely applied in agriculture and may enter freshwater ecosystems through runoff and drift, posing risks to non-target fish. Yet, species-specific evidence integrating lethal and multi-organ sub-lethal endpoints remains limited for several aquaculture-relevant taxa. In the present study, the grass carp (<i>Ctenopharyngodon idella)</i> was selected as a representative freshwater cultured fish to evaluate the toxicological impact of technical grade dichlorvos (98.5%) using a multi-biomarker approach. The 96-hour median lethal concentration (LC₅₀) was determined to be 4&#xa0;µl/L. Fish were exposed to this acute concentration to assess behavioral, hematological, biochemical, and histological responses in the gills, liver, brain, and muscle tissues over 24–96&#xa0;h. Exposed fish displayed pronounced behavioral abnormalities, including hyperactivity, loss of balance and appetite, aggregation, excessive mucus secretion, discoloration, erratic movements, and surface swimming. Hematological indices indicated significant alterations, with a significant decrease in red blood cell count, hemoglobin concentration, hematocrit value, platelet count, and mean corpuscular hemoglobin concentration, whereas a significant increase in white blood cell count, mean corpuscular hemoglobin, and mean corpuscular volume occurred across the exposure period. Serum biochemistry showed elevated levels of aspartate aminotransferase, alanine aminotransferase, gamma-glutamyl transferase, urea, creatinine, blood urea nitrogen, and total bilirubin, alongside reductions in alkaline phosphatase, total protein, albumin, globulin, and the albumin-to-globulin ratio. Histopathological analysis revealed severe lesions in the studied organs. Overall, these results provide a multi-organ, time-resolved characterization of acute dichlorvos toxicity in grass carp, supporting its high hazard potential for non-target fish of economic and ecological relevance and reinforcing the need for safer pest-control alternatives.</p>