| Sumario: | A critical review of the literature highlights significant discrepancies in the estimates and modes of expression ofamino acid requirements. Using lysine as a case example, this paper highlights some of these discrepancies andpotential limitations of current approaches.Published estimates of lysine requirements for rainbow trout varied from 1.3 – 2.9 % of the diet and NRC (1993)estimated lysine requirement at 1.8% of the diet. Results from recent studies and detailed data analysis suggest thatlysine requirement to maximize weight gain is about 2.3% of the diet in rainbow trout, where requirement tomaximize protein gain of this species appears to be closer to 2.7% of the diet. These estimates are significantlyhigher and appear more appropriate (robust) than the lysine requirement proposed by NRC (1993).Different modes of expression of lysine requirement are used, often interchangeably, in the literature. It is importantto understand that these different modes of expression are based on different assumptions and that the use ofdifferent modes of expression will result in dramatically different recommendations, especially since aquaculturefeeds are formulated to widely different nutritional specifications (protein, energy, etc.). Studies suggest thatexpressing lysine requirement as a function of digestible energy or protein contents of the diet is not appropriate.Studies have also indicated that “newer” approaches of estimating amino acid requirements (e.g., factorial aminoacid requirement, ideal protein concept), widely used in poultry and swine nutrition, may have significant pitfallswhen used in fish nutrition.
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