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2.1.2 Amino Acid Requirement
Cowey and Tacon 1983 suggested that the indispensable amino acid requirements of a fish should be related, or even governed, by the pattern of
amino acids present in muscle tissue. Imbalances in the amino acid profile of the diet may depress feed intake and reduce efficiency of utilization of essential
amino acid. Harper et al. 1964 suggested that plasma amino acids stimulate the synthesis or inhibit the breakdown of proteins in the liver which implies a
decreased supply of the limiting essential amino acid in tissues. Consequently, the free amino acid pattern of plasma and tissue becomes imbalanced which is
detected by the appetite regulating system in the brain. As a consequence, feed intake is reduced and this reduction on feed intake is at the origin of the growth
depression effect of amino acid imbalances. The ideal protein concept is based on the idea that there should be a direct
correlation between the whole body amino acid pattern of the animal and the dietary amino acid requirements of the animal. This is essentially with the same
AE ratios indispensable amino acid contenttotal indispensable amino acid content. The AE ratios have been used as a means to estimate the requirements
of all indispensable amino acids when only one is known by comparing the AE ratio of indispensable amino acid to the AE ratio of the known same amino acid
Wilson 2002. Changes in the feeds amino acid composition should be made in a way that
did not alter the relative ratios of amino acids. In other words, the ideal protein concept is built on the principle that amino acids are required and supplied in
specific proportions to each other. Growing fish fed on such a diet would use a few amino acids for energy. The amino acids would be used efficiently for
maintenance, health, and synthesis of proteins. This, will result in a maximum feed efficiency and growth.
Lysine is one of the ten essential amino acids which can be used as the amino acid reference. There are several reasons for selecting lysine as a referent
amino acid. First, lysine major function in the animal body is protein tissue deposition; therefore, its requirement is not influenced by other metabolic roles.
Second, depending on the fish species and type of ingredients, lysine is usually
6 the most or second most limiting amino acid; thus more is known about the
requirements for lysine than other amino acids Miles Chapman 2007.
2.2 Patin Pangasianodon hypophthalmus
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