Evaluation of free essential amino acid in muscle of Nile tilapia (Oreochromis niloticus), as a basis of amino acid requirement for growth.

Abstract

The free essential amino acid levels in muscle of young Nile tilapia (Oreochromis niloticus) after feeding graded amounts of a corresponding test amino acid were measured in 9 separate experiments to determine if free amino acids indicate requirements for growth. Data were analyzed by the broken line regression method. Breakpoints for free threonine and free isoleucine were near the threonine and isoleucine requirements for growth. Breakpoints for free lysine, free histidine, and free valine were much higher than the lysine, histidine, and valine requirements for growth, respectively. Levels of other free essential amino acids in muscle behaved erratically or increased linearly as the dietary test amino acid increased. Amino acid requirements as estimated by levels of free essential amino acids in muscle did not consistently confirm amino acid requirements for growth of Nile tilapia.