Feed is an important factor in aquaculture with the individual ingredients being significant to the physiology of fish and to the condition of culture water. This study therefore investigated the effects of including onion at 0%, 1.02%, 2.05% and 3.07% in fish feed on the haematology of Clarias gariepinus and on water quality. The haematological parameters evaluated included red blood cell count (RBC), white blood cell count (WBC), packed cell volume (PCV), haemoglobin content, mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), and mean corpuscular haemoglobin concentration (MCHC). Furthermore, cholesterol and protein were determined using spectrophotometric-enzymatic and Bradford methods respectively. Albumin and glucose were determined using kits that detect albumin and glucose-oxidase reaction respectively. Globulin was calculated by subtracting the measured albumin value from the total protein. Water quality parameters evaluated were temperature, dissolved oxygen and pH
There was significant increase (P<0.05) in RBC, PCV and Hb but decrease in WBC in the fish fed diet containing onion (Table 1.0). The decrease in WBC became significant (P<0.05 when onion was included at 2.05%. However the value of the WBC spiked when the onion concentration was 3.07%. There was no significant difference in the value of MCV at the studied concentrations. The increase in MCH due to onion in feed became significant (P<0.05) at 2.05%. Value of MCHC followed the same trend as MCH (Table 2.0). There was decrease in cholesterol and glucose due to onion in feed (Figure 1.0). There was increase in total protein and albumin but decrease in globulin due to onion in the diets (Figure 2. 0). Lowest globulin was observed when onion was included at 2.05%. There was no significant difference (P>0.05) in the water quality parameters studied among the treatments (Table 3.0). Results from the study suggest 2.05% as a preferred inclusion level of onion in feed for African catfish.