The present study investigated the effects of acute toxicity of malathion on behavioral and haematological parameters in the cyprinid Capoeta damascina. The specimens were collected from the Kordan River, Karaj, Iran in August, 2014 and were exposed to different concentrations of malathion at the laboratory (24, 48, 72 mg L‑1) based on 96h-LC (10; 30; 50; 90) which was 6.08 (5.22-7.18) mg L-1. The animals were then exposed to 0.76, 1.00 and 1.52 mg L-1 of malathion for 10 days. Blood samples were collected in days 1, 5 and 10. Red blood cell (RBC), white blood cell (WBC), hemoglobin (Hb), hematocrit (PVC), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) were measured. Behavioral abnormalities were observed in fishes exposed to high levels of malathion. The specimens exposed to malathion had significantly lower RBC, WBC, Hb, PVC but higher MCV and MCH than those of the control group. No significant difference was detected in MCHC the exposed and control specimens. Hematological parameters (except MCHC) were significantly correlated with exposure time. In conclusion, malathion showed extensive haematological effects on C. damascina that might be used as bioindicator of this pesticide in flowing waters.
