Allometric scaling exponents for individual amino acids differ significantly from that of protein in juvenile barramundi (Lates calcarifer).

An experiment was conducted to assess the effect of fish size on losses of crude protein and amino acids during a period of fasting in barramundi (Lates calcarifer). Fifteen fish within six size classes (10.5 +/- 0.23 g; 19.2 +/- 0.19 g; 28.3 +/- 0.08 g; 122.4 +/- 0.17 g; 217.6 +/- 0.62 g; 443.7 +/- 2.56 g) were housed in triplicate 600 L tanks, provided with 30.0 (+/- 0.2) 0C seawater and held under a photoperiod of 12 h light:12 h dark using artificial lighting for a period of 21 days, during which time they remained unfed. Losses in crude protein and individual amino acids over this period, relative to the geometric mean weight of the animals, were used to calculate allometric scaling exponents for each parameter. Contrary to previous assumptions, live weight exponents for the loss of the ma-jority of the proteinogenic amino acids differed significantly from that of crude protein, with most being higher, while that of the branched chain amino acids and cystine were lower. Additionally, that of the sum of all pro-teinogenic amino acids was significantly higher than of crude protein, suggesting an influence of fish size on utilisation of non-protein nitrogen. The use of these individual amino acid-specific weight exponents may correct for changes in individual amino acid requirements in barramundi more accurately than use of the protein weight exponent commonly used in feed utilisation modelling.