Water born environmental contaminants have been shown to exert pronounced effect on various aspects of fish physiology and sometimes lead to large scale mortality. The effects of Lead Nitrate and crude oil on the growth of the African catfish, Clarias gariepinus were studied. The acute toxicity tests lasting 96 hours were performed on Clarias gariepinus of mean weight 138±12 g and mean total length of 28±1.5 cm. The LD₅₀ of Lead Nitrate was 57.5 mg/l while the LD₅₀ of crude oil was 823.3 ppm. The experimental fish mean weights ranged from 126.0±3.22 g to 151.0±0.67 g and mean total lengths from 27.38±0.43 cm to 31.18±3.76 cm were divided into 5 groups A, B, C, D, E, of 20 fish each. Group A was kept as control (no treatment), Group B was exposed to 20 mg/l Lead Nitrate, Group C was given to 35 mg/l Lead Nitrate, Group D was administered to 300ppm crude oil, Group E to 600 ppm crude oil. The body weights of the fish were measured weekly. Percentage weight gain and feed conversion ratios were calculated. Treatment lasted for 70 days (10 weeks). The control group showed significant increase in body weight at P<0.05 while the treated groups showed significant reduction in body weight. Therefore, fish under the influence of these pollutants did not mature duly and was susceptible to diseases which lead to low productivity and nutritional value. Environmental protection laws must be enforced to prevent and control pollution of water bodies, thereby safeguarding public health.