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Abstract
Amino acid profiles of various body tissues from juvenile and adult discus fish, Symphysodon aequifasciata, were compared. Results from whole-body tissue revealed significant difference (P < 0.05) between the levels of lysine, phenylalanine, alanine, aspartic acid, and serine among the two different fish sizes. Levels of arginine, histidine, leucine, methionine, phenylalanine, and threonine were also higher in muscle tissue of adult fishes. Analysis of gill tissues showed significant difference in levels of histidine, isoleucine, lysine, methionine, threonine, tryptophan, aspartic acid, glutamic acid, proline, and serine were significantly different among the different fish stages. This study also showed that among all ten essential amino acids, muscle had the highest levels of histidine, isoleucine, lysine, and tryptophan; gills had the highest level of arginine; while levels of methionine and threonine were higher in the intestinal tissue. Regression analysis between the calculated whole-body A/E ratio of discus juveniles and with quantitative dietary amino acid requirements of several fish species also showed significant correlation, with highest r values (> 0.90) obtained with tilapia, common carp, channel catfish, and Japanese eel. This profile may be useful as a preliminary reference index to evaluate suitability of various ingredients in terms of amino acid profile for development of economical diet for discus farming.