Total aromatic amino acid requirement, phenylalanine requirement and tyrosine replacement value for fingerling...

A series of experiments was conducted to determine the aromatic amino acid requirement, the tyrosine replacement value for phenylalanine and the phenylalanine requirement under conditions of adequate tyrosine for fingerling channel catfish. Effects of excessive dietary levels of tyrosine were also investigated. The studies were conducted utilizing casein and gelatinbased diets supplemented with crystalline L-amino acids to correspond to the pattern of 24% whole egg protein. Based on 8-week growth studies, the total dietary aromatic amino acid requirement for fingerling channel catfish was approximately 1.20 +/- 0.06% (50% of the dietary protein) of which about 50% could be supplied by tyrosine. The phenylalanine requirement per se, based on growth and feed efficiency, was determined to be 0.47 +/- 0.02% and 0.49 +/- 0.02%, respectively. High dietary levels of tyrosine (up to 10%) did not adversely affect performance of fingerling channel catfish. It appears that neither serum-free phenylalanine nor serum-free tyrosine can be used to accurately predict dietary aromatic amino acid adequacy for the fingerling channel catfish.