Vitamin C is essential for fish diets because many species cannot syntethize it. This vitamin is needed for bone and cartilage formation. Moreover, it acts as antioxidant and improve the immunological system. The present work investigated the effects of vitamin C diet supplementation to spotted sorubim (Pseudoplatystoma coruscans) fingerlings by frequency of bone and cartilage deformation. Ascorbyl poliphosphate (AP) was used as source of vitamin C in the diets for spotted sorubim fingerlings during three months. Six diets were formulated: one diet control (0 mg/kg of vitamin C) and 500, 1,000, 1,500, 2,000 and 2,500 mg AP/kg diets. Fishes fed without vitamin C supplementation presented bone deformation in head and jaws, and fin fragilities. Thus, 500 mg AP/kg diet was enough to prevent deformation and the lack of vitamin C supplementation worsening the development of fingerlings.