Characterizing the effects of dietary and endogenous factors on amino acid requirements of fish

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High commodity prices created a strong impetus for feed manufacturer to focus on improving cost-effectiveness of fish feeds. Fish feed manufacturers have significantly reduced fish meal level and have been relying more heavily on more economical protein sources in their feeds. This increased reliance on protein sources with different (poorer) amino acid profiles has brought about the need to pay greater attention to the essential amino acids (EAA) requirements of fish. A critical review of the literature reveals very significant gaps in our understanding of amino acid nutrition of fish. There is a multitude of opinions as to the optimal levels and best mode of expression of essential amino acid (EAA) requirements for fish. This situation often limits the ability of feed manufacturers to meaningfully improve the cost-effectiveness of feeds and/or adapt feed formulations to a changing commodities market (e.g. relative low price of protein sources compared to lipid sources). The root cause of the conflicting views appears to be our poor understanding of the effect of endogenous (e.g., species, life stage) and dietary factors on EAA utilization and requirements of fish. The regulation of amino acid catabolism of fish may also be slightly different from that of monogastric terrestrial animals. The adaptation of models developed for swine and poultry to fish nutrition resulted in poor predictions, notably for large rainbow trout.