This study investigated the growth and haematological response of Clarias gariepinus to different concentration of garlic supplemented diet for a period of 12 weeks. This study was carried out in 2011 in the premises of Fisheries Department, Delta State University, Asaba, Nigeria. The experimental diet was formulated to contain 0% (control), 0.5%, 1% and 3% garlic. Fish were sorted into four groups based on the diet and were fed 3% live body weight. Diets which contain garlic did not show a significant effect (P = 0.06) on the weight of C. gariepinus. However, fish fed diets containing garlic had a higher (P <0.001) total length compared to the control. Nevertheless, fingerlings fed 0.5% concentration of garlic in diet exhibited greater growth in terms of weight and length compared to fingerlings in all other treatment groups and the control. At the end of the experiment, the total red blood cell count (RBC), white blood cell count (WBC), haemoglobin (Hb) and packed cell volume (PCV) of fish in the garlic supplemented groups were greater (P <0.05) compared to the values prior to the commencement of the experiment and to the control. However, catfish fed 0.5% garlic diet were observed to have a higher value of RBC, PCV and Hb than the other concentrations. Increment in plasma protein was noted in catfish fed garlic supplemented diet than the control. This study demonstrates that garlic supplemented feed stimulates increment in both total length and haematological indices of fish. Supplementation of fish feed with garlic is therefore of high benefit in aquaculture as it boosts the ability of C. gariepinus to resist diseases.