Bulgarian Journal of Veterinary Medicine, 2017, 20, No 2, 141–150 ISSN 1311-1477; DOI: 10.15547/bjvm.965 Original article HAEMATOLOGICAL, BLOOD BIOCHEMICAL AND HISTOPATHOLOGICAL EFFECTS OF SUBLETHAL CADMIUM AND LEAD CONCENTRATIONS IN COMMON CARP M. K. KHALESI 1 , Z. ABEDI 1 , S. BEHROUZI 2 & S. KOHESTAN ESKANDARI 1 1 Sari Agricultural Sciences and Natural Resources University (SANRU), Sari, Iran; 2 Caspian Sea Ecology Research Center, Iranian Fisheries Research Organization, Iran Summary Khalesi, M. K., Z. Abedi, S. Behrouzi & S. Kohestan Eskandari, 2017. Haematological, blood biochemical and histopathological effects of sublethal cadmium and lead concentra- tions in common carp. Bulg. J. Vet. Med., 20, No 2, 141–150. 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 al- most 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 re- sponses can be secondary to low heavy metals concentrations reflecting the trigger of stress reactions in affected fish. Key words: cadmium, common carp, haematology, histopathology, lead INTRODUCTION Cadmium (Cd) is considered as one of the most toxic contaminants in polluted wa- terways, causing toxicity at any level of the ecologic stratum (Rashed, 2001). Even at sub-lethal concentrations, cadmium has a cumulative effect and causes serious physiologic disturbances in fish, such as anorexia as well as effects on the blood cells (Witeska, 1998; Cicik & Engin, 2005). Particular attention, therefore, must be focused on fish because of their high affinity for cadmium (De Conto Cinier et al., 1999). Lead (Pb) is a non-essential and non-beneficial element known to alter