Nutrition of Salmonoid Fishes

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Abstract
Growth studies were conducted with chinook salmon fingerlings (Oncorhynchus tshawytscha) to determine the minimal requirements for isoleucine, leucine, valine and phenylalanine. A 41% protein diet containing an indispensable amino acid pattern similar to that found in whole egg protein was used as the experimental diet. Based on the dry diet, the salmon required about 1.6% of leucine, 1.3% of valine and 2.1% of phenylalanine (0.4% supplied by tyrosine). The isoleucine requirement appeared to be influenced by dietary leucine level, being about 0.9% with 1.50% of leucine, about 1.0% with 3.68% of leucine and about 1.1% with 6.00% of leucine. On the other hand, excess dietary isoleucine reduced growth rates when fed in conjunction with a slightly suboptimal level of leucine. Growth of the salmon fingerlings was reduced slightly below that with the control diet when 1.0% of isoleucine and 1.25% of leucine were fed; however, 3.00 and 5.0% levels of isoleucine with 1.25% leucine reduced growth to 67 and 60% of the control, respectively, presumably by increasing the leucine requirement similar to the way excessive leucine increases the isoleucine requirement.
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