The effects of water soluble fraction (WSF) of crude oil from Afiesere oil field on haematological and biochemical parameters in juveniles of Clarias gariepinus were studied. The 96 h-LC50 of crude oil determined by probit regression was 224.74mg/l. Fish were exposed to 4 sub-lethal concentrations (30, 45, 60 and 75% of the LC50 corresponding to 67.42, 101.13, 134.84 and 168.56 mg/l respectively) of the oil and a control. After 84 days of exposure, blood was collected and used for haematological and biochemical analyses. Result showed a significant (p<0.05) reduction in the values of red blood cells, packed cell volume and haemoglobin with no definite trend in the values of computed haematological indices. Glucose content (mg/dl) increased significantly (p<0.05) from 289.00 in control to 384.67 in the highest concentration indicating the occurrence of gluconeogenesis to supplement additional energy needed to meet the increased metabolic demands. A significant (p<0.05) inverse relationship between the concentration of crude oil and values of total protein, albumin and globulin was also observed. The mean plasma alanine aminotransferase (ALT), alkaline phosphatase (ALP), aspartate aminotranferase (AST), creatinine and urea activities of all the affected set of fish, which have been exposed to sub-lethal concentrations of the crude oil were significantly higher (p<0.05) in comparison to their respective control. The upsurge in the activity of these enzymes is a direct reflection of alterations in the hepatic structural integrity and kidney disorder. The results revealed that WSF of crude oil can negatively affect the haematological and biochemical parameters of fish causing various disturbances. It is hereby recommended that all stakeholders in crude oil exploration, exploitation and transportation should adopt adequate measures aimed at stopping oil spillage into our environment.

Keywords: Toxicity, Crude oil, Blood, Stress response, Fish