The effect of dispensable amino acids on nitrogen and amino acid losses in Atlantic salmon ( Salmo salar) fry fed a protein-free diet

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The nutritional role of dispensable amino acids (DAAs) has been seldom studied in fish, while the metabolism of these species is orientated toward the oxidation of amino acids (AAs) for energetic purpose. The objective of this study was to characterize the role of DAAs in the absence of indispensable (I) AA supply in Atlantic salmon and to verify if, as in mammals they play a nutritional role under near maintenance conditions. Therefore we measured the effect of adding DAAs on nitrogen and AA losses in Atlantic salmon fry fed a protein-free (PF) diet. Fry were either starved or fed a PF diet or a DAA-supplemented (DAA-PF) diet for 30 days. The maintenance protein requirement estimated from the endogenous losses were 1.11, 1.58 and 0.65 g/kg BW/day for starved fish, fish fed PF or DAA-PF diets, respectively. The daily IAA and DAA losses of fish fed the DAA-PF diet were greatly reduced (− 55 and − 63%, respectively) compared to fish fed the PF diet ( P < 0.05), except for proline and serine for which the reduction was not significant. Among the DAAs, alanine and glycine losses were particularly reduced when fish were fed the DAA-PF diet compared to the PF-diet (− 74 and − 82% for alanine and glycine, respectively). Among the IAAs, methionine loss was the most reduced by the supplementation of the PF-diet with DAAs (− 72%). These results showed the indispensable role of DAAs under near maintenance conditions and their sparing effect on the use of alanine and glycine specifically.