Supplementation of a semipurified casein diet for catfish with free amino acids and gelatin.

Semipurified diets with casein as the sole protein source were supplemented with gelatin, arginine, cystine, methionine or tryptophan, and fed to channel catfish (Ictalurus punctatus) fingerlings. Increasing the arginine level from 1.1% to 1.7% of diet by the isonitrogenous substitution of gelatin for casein resulted in a significant enhancement of growth. However, the addition of free arginine, cystine, tryptophan or methionine to casein had little effect on growth or food conversion. These data substantiate a previous report that suggested catfish were similar to carp in their inability to utilize free amino acids.