Adult Clarias gariepinus
of mean weight and mean standard length of 450 ± 50gm and 34 ± 5 cm respectively were allotted to aquaria at 10 fish per group (A-D) in replicates, based on the dose of cassava wastewater (CWW) to be administered (2, 5, 10 and 15 mls) respectively. Group E served as the control. The different doses were administered to the various groups for three consecutive days. After 96 hours, no mortality was observed in the control (Group E) and the group (Group A) injected with 2mls of cassava wastewater (CWW), 20% mortality was observed in the group that were injected with 5mls (Group B) and 50% mortality was observed in the 10mls group (C). None survived (100%mortality) in the group that was injected with 15mls CWW. Haematological changes in groups A, B and C includes: Anaemia marked by significantly low (at p< 0.05) PCV, Hb and RBC (in B and C alone). MCV values were significantly low in all the experimental groups relative to the control; MCH value was significantly low in Group A, while MCHC was significantly low (p< 0.05) in groups B and C. The total white blood cell (WBC) count was significantly higher (p< 0.05) than the control in all the experimental groups. Histopathological lesions were marked in the fish injected with the higher dose (10ml), the fish revealed severe necrosis, hypertrophy and vacuolation of hepatocytes. Other observation during the experiment includes reduced activities (swimming), haemorrahagic patches on the ventral surface of the fish, general discoloration and anoxia.