Effect of sublethal concentrations of cypermethrin on some haematological parameters of the freshwater fish Oreochromis niloticus in static bioassay

Abstract

Study was carried out to determine the haematological responses of Oreochromis niloticus exposed to cypermethrin. Juveniles were exposed in aquaria of 20 l capacity containing 0.0005, 0.001, and 0.002 mg/l sublethal concentrations of cypermethrin. Haematological analysis of the blood of fish examined showed that Red blood cell counts (RBCC), and haemoglobin (Hb), and packed cells volume (PCV) decreased significantly (P < 0.05) as the concentration of the toxicant increase. The mean corpuscular volume (MCV) significantly (P < 0.05) increased with fish exposed to 0.001 mg/l concentration of the toxicant when compared with control value, but were lower significantly (P < 0.05) with those fish in the highest concentration (0.002 mg/l) concentration. Mean corpuscular haemoglobin (MCH) and Mean corpuscular haemoglobin concentration (MCHC) between the control and the exposed groups did not vary significantly. White blood cell counts (WBCC) increased significantly (P < 0.05) as the concentration of the toxicant increased. Similar trends were observed during week 6 exposure periods, RBCC, Hb, and PCV values of fish reduced significantly (P < 0.05) with fish exposed to ≥ 0.001 mg/l concentrations. MCV of fish recorded significant higher (P < 0.05) values in exposed groups at concentrations ≥ 0.001 mg/l. Values were highest with fish exposed to 0.001 mg/l and lowest in the highest concentration (0.002 mg/l, while MCHC values were not significant with exposed fish compared to the exposed groups. Percentage neutrophils of the control fish were significantly lower (P < 0.05) than those exposed to ≥ 0.001 mg/l sublethal concentrations of cypermethrin, but significantly higher (P < 0.05) than fish exposed to 0.0005 mg/l. Percentage lymphocytes of the control group were significantly lower (P < 0.05) compared to fish exposed to 0.000 and 0.001 mg/l concentrations of the toxicant. No traces of basophils, eosinophils, and monocytes found.