Changes in tissue free amino acid concentrations in Atlantic salmon, Salmo salar L., after consumption of a low ration

Atlantic salmon (Salmo salar L.) with an average weight of 411 ± 16 g were fed after a period of 7 days without food and the free amino acid concentrations in the pylorus, liver and white muscle measured before and at 3, 6, 9, 15 and 24 h after feeding. There were few significant postprandial changes in tissue free amino acid concentrations. In the white muscle, concentrations of six indispensable amino acids were significantly (p < 0.05) higher after 9 (Ile, Leu, Phe, Thr) or 15 h (Val, Met). Individual feed intake was measured and there were significant positive correlations between amino acid intake and amino acid concentrations in white muscle free pools for total amino acids (p < 0.001), total indispensable amino acids (p < 0.001) and individual indispensable amino acids (Ile, Leu, Lys, Met, Phe, Val). These relationships were due to relatively low feed intake (0.28% body weight) that followed 7 days without feeding. The indispensable amino acid profile of the white muscle free pool was compared with that of standard proteins (the feed, whole body and white muscle), as well as with indispensable amino acids requirements. At different times one of two indispensable amino acids, Phe (at 0, 3, 6, 9, 15 h after feeding) or Trp (at 24 h after feeding), was present at the lowest relative concentrations compared to the other indispensable amino acids. This showed that although changes in tissue free amino acid concentrations following feeding were small the amino acid profile (relative concentrations) in the white muscle free pool changed. It is proposed that the lowest relative concentration of an indispensable amino acid in the white muscle free pool should be considered in relation to its potential to limit the efficiency of protein synthesis and retention.