The effect of stocking density on growth and survival of post fry of the African mud catfish, Clarias gariepinus, was investigated. C. gariepinus post fry were stocked at the rate of 5, 10, 15, 20, and 25 post fry/litre of water. The post fry were fed to satiation four times daily with crumbles of a commercial catfish feed. The survival, mean total length, mean body weight, condition factor, specific growth rate and performance index were found to be density dependent. Survival rate ranged from 29.7 ± 7.4 to 56.6 ± 33.3%, while specific growth rate was between 0.00143 ± 0.0014 to 0.00702 ± 0.0044. Optimum growth and survival rates were recorded at stocking densities of 5, 10, 15 post fry/litre of water. However, the determined optimum stocking density for rearing of C. gariepinus post fry in tanks is 15 post fry/litre of water. It is concluded that increased density impacts on growth and survival of the fish, a consequence of increased activity (frequent surfacing, feeding and swimming) and aggressiveness.