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Two experiments were conducted to determine the dietary requirement for vitamin C of young Tilapia aurea. In the first experiment, best growth and food conversion were obtained over 14 weeks on a diet which contained 50 mg/kg of vitamin C (other levels tested were 0, 100 and 200 mg/kg). In the second experiment, levels of 0, 25, 50, 65, 80, 95 and 110 mg/kg of vitamin C were employed and, again, growth and food conversion did not improve at dietary vitamin C levels above 50 mg/kg. Pathologic changes were observed in fish maintained on rations containing 25 mg/kg or less vitamin C. Gross changes included mild scoliosis and occasional hemorrhages of the fins, mouth and swim bladder. Histologic changes included shortening and thickening of gill lamellae and disorganization of chondrocytes in tips of gill filaments and bases of gill arches.