Dichlorvos toxicity on hemato-biochemical, histopathological, and behavioral parameters in the grass carp (Ctenopharyngodon idella).

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 (Ctenopharyngodon idella) 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 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 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.