Partial substitution of protein by a single amino acid or an organic acid in rainbow trout diets

Abstract

Performances of rainbow trout ( Salmo gairdneri) fed on experimental diets in which fish meal (42%) was supplemented (12%) either with a purified protein (casein or corn (maize) gluten), with a single amino acid (AA: alanine, aspartic acid or glutamic acid) or with an organic acid (OA: succinic acid or citric acid) were analysed. The voluntary food intake of fish fed the AA and OA diets was lower than that of fish fed either on a control commercial diet or on a protein-supplemented diet, but without large alteration in the efficiencies of protein and energy utilization. The protein and energy content of the liver, digestive tract and carcass, and the plasma glucose and amino acids levels were analysed. It was concluded that a part of the protein in the diet could be replaced by a single amino acid such as aspartic acid. These results are discussed in the light of the control of food intake by energy density of the diet.