Tryptophan and threonine requirements of fingerling channel catfish.

Growth studies, utilizing a 24% crude protein diet containing an amino acid pattern similar to whole egg protein, indicate that the tryptophan requirement for fingerling channel catfish (Ictalurus punctatus) is about 0.12% of the diet (dry weight basis) or 0.5% of the dietary protein. Similar studies indicate that the threonine requirement for the same fish is about 0.53% of the diet (dry weight basis) or 2.21% of the dietary protein. The dietary requirement of threonine was confirmed by serum free threonine analysis. A marked increase in serum free threonine occurred at a dietary threonine level of approximately 0.5% of the diet. None of the gross pathological changes previously reported for tryptophan deficiency in sockeye salmon and rainbow trout were observed in channel catfish.