Halver et al. (1957) determined the essentiality of the 18 common protein amino acids by comparing the relative growth rates of Chinook salmon fed the basal and specific amino acid-deficient diet over a 10-week period. For each of the ten indispensable amino acids, groups of the deficient fish were split at 6 weeks, with one subgroup being continued on the deficient diet and the other subgroup fed the basal diet. In each of the subgroups shifted to the basal diet, the fish showed an immediate and substantial growth response to the complete diet. The results indicated that the following ten amino acids were indispensable for chinook salmon: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. All other species that have been studied to date have been shown to require the same ten amino acids.
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