Haematological, blood biochemical and histopathological effects of sublethal cadmium and lead concentrations in common carp

The present research aimed at examining the effects of common carp (Cyprinus carpio) exposure to sublethal concentrations of two non-essential heavy metals: cadmium (Cd: 8.4 mg/L) and lead (Pb: 6.2 mg/L) for 15 days to evaluate occurring biochemical and haematological effects. The examined parameters included haematocrit (Hct), haemoglobin (Hb), lymphocytes (Lym), neutrophils (Neu), total protein (TP), albumin (Alb), immunoglobulin M (IgM), glucose, red and white blood cells counts (RBC & WBC), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), and mean corpuscular haemoglobin concentration (MCHC). Exposure to both metals significantly (P<0.05) reduced the amounts of WBC and MCHC. MCV values decreased (P<0.05) after the Pb treatment but MCV estimates with Cd exposure showed no differences. MCH levels increased in both treatments (P<0.05) whereas Hct, Hb, RBC, Lym, and Neu following both metal exposures were almost similar to those in the control. IgM values were elevated in fish contaminated with both Pb and Cd (P<0.05). The exposed fish showed fusion of gill lamellae, vessel dilatation, hyperaemia, and hyperplasia of gill epithelial cells whereas muscle histology remained unchanged. The observed responses can be secondary to low heavy metals concentrations reflecting the trigger of stress reactions in affected fish.