Channel catfish fingerlings were fed purified diets containing five levels (0, 20, 40, 80, and 120 mg/kg) and six levels (0, 3, 8, 20, 40, and 80 mg/kg) of riboflavin in separate 20 and 12 week feeding studies. The dietary riboflavin level required to provide maximal growth in channel catfish fingerlings was found to be approximately 9 mg/kg of diet. All fish fed unsupplemented diets (riboflavin content less than 0.1 mg/kg diet) demonstrated a short body dwarfism which was the result of arrested longitudinal growth of the vertebrae. This abnormality did not occur in groups fed 3 mg/kg or higher levels of riboflavin. No histological abnormalities were recognized in the liver, kidney, lateral muscle, gastrointestinal tract, gills, or bones of deficient fish.