ABSTRACT
The study conducted to evaluate the toxicity of cassava mill effluent on Clarias gariepinus fingerlings with emphasis on physicochemical characteristics of the effluent, effect on the level of enzyme activity and histopathology of the gills and liver, using fingerlings of African cat fish (Clarias gariepinus). Samples of Cassava effluent were collected from a cassava processing factory and characterized using standard procedures. The test organisms were obtained from the Fisheries Department of the University of Benin, acclimatized, and subjected to histopathological and biochemical analysis. After series of range finding test, the fishes were exposed to lethal concentrations 0.00 ml/L (control), 0.001 mg/L, 0.003 ml/L, 0.005 ml/L and 0.007 ml/L of cassava mill effluent for 96hrs in a static renewal bioassay procedure. The experiment was set up in triplicates. Respiratory disturbance, erratic swimming, loss of equilibrium, lethargies and sudden fish death were observed in the exposed fish and these varied greatly with differences in concentration of the toxicant. Mortality also increased with an increase in concentration and duration of exposure. The pH of the effluent was 3.82 while temperature was 25°C. The value of Chloride, total alkalinity, total hydrocarbon and nitrate in the effluent was 187.20, 15.36, 18.48 and 3.052mg/l respectively. The value of copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd) and chromium (Cr) in the effluent was 0.09, 0.24, 0.01, 0.01 and 0.02mg/l respectively. Also, total suspended solids (TSS), dissolved oxygen (DO) and biological oxygen demand (BOD) was 680.23, 38.61 and 185.60mg/l respectively. A statistically significant concentration dependent increase in the activities of the enzyme amylase, ALP, ALT, AST, GPx, MDA and SOD, as well as a decrease in the activity level of catalase in Clarias gariepinus treated with cassava mill effluent compared to the control group (P<0.05) was observed. The liver of the control fish showed normal parenchyma appearance of hepatocyte with normal staining patterns of the cell. In the treated fishes, there was congestion of central vein, vacuolation of hepatocyte, oedema, cellular infiltration and cellular necrosis. The gills of the control fish showed normal cell and tissue structure with the entire length of the filaments and lamellae lined by normal epithelial cells and chloride cells were large, scattered along the filaments. Histopathological alterations such as hemorrhage, lamella fragmentation, chloride cell damage, loss of lamella, necrosis and hemorrhage. The study revealed that cassava mill effluent is toxic to Clarias gariepinus fingerlings, therefore, indiscriminate discharge of this effluent to the surrounding should be discouraged.
