Haematological and histopathological examinations of African mud catfish (<i>Clarias gariepinus</i>) exposed to petroleum wastewater

Abstract

Effects of petroleum refinery wastewater on Clarias gariepinus juvenile were investigated. Commercially obtained C. gariepinus fingerlings were acclimatized in a plastic tank (100 L capacity) of de-chlorinated tap water at 25±2°C for 14 days and fed with commercial feed pellet at 2% body weight of the fingerlings. Bioassay tests were carried out in four transparent plastics tank with nominal concentrations of 100 ml, 200 ml, 300 ml of the wastewater added to 40L of de-chlorinated tap water and only de-chlorinated tap water as control. Each tank contains twenty fish samples, while the assay was replicated three times concurrently. Following standard procedures, behavioural response, growth changes, haematological and histopathological tests were carried out on the samples. Significant reduction in the weight was observed in the fingerlings cultured with the wastewaters, while no significant difference occurred in the control fish. Highest values of Packed Cell Volume (PCV) (22), Haemoglobin (HB) (7.0), Red Blood Cell (RBC) (1.62) and endocochlear potential (EP) (5) were recorded for the control fish than exposed fish. On the other hand, Haptoglobin (HP), Mean Corpuscular Volume (MCV) and Mean Corpuscular Haemoglobin (MCH) were higher in the blood of exposed fish than in control. Histopathologically, exposed fishes showed no visible lesion in gills except from the thickening of the lamellae as the concentration of wastewater increases, indicating an increase in tissue disintegration. Similarly, gross tissue disintegration was observed in those fish exposed to 200ml wastewater as evidenced by the presence of large open spaces (hepatocytes) in the liver.