Effect of excess dietary riboflavin on growth of rainbow trout

Fingerling rainbow trout were fed semipurified diets containing graded levels of supplemental riboflavin (3, 35, 42, 49, 56, 63, 70, 100 and 600 mg/kg of diet) to determine if dietary riboflavin in excess of requirements decreases growth. In three trials with three sizes of fish (mean initial weights, 0.5, 3.2 and 4.3 g) and two water temperatures (8.3 degrees and 15 degrees C), no significant diet-related growth inhibition was detected. The results suggest that rainbow trout, like other animals, are insensitive to excesses of dietary riboflavin and that the growth depression reported by other workers was the result of some other dietary influence or of faulty experimental design.