Periodical changes of plasma free amino acid levels and feed digesta in yellowtail after feeding non-fishmeal diets with or without supplemental crystalline amino acids

Postprandial changes of free amino acid (FAA) concentrations in plasma and feed digesta contents were examined in yellowtail, Seriola quinqueradiata ( 220-280 g bodyweight) fed non-fishmeal diets either with or without supplem ental crystalline amino acids (lysine, methionine, threonine, and tryptopha n) in order to evaluate the availability of supplemental amino acids. Non-f ishmeal diets containing 30% soy protein concentrate as the major protein s ource were prepared in three diet forms: soft dry pellet, extruded pellet, and single moist pellet. The level of plasma FAA and feed digesta content w ere determined at 0, 3, 6, 9, 12, 18, and 24 h after feeding. Plasma levels of four supplemental amino acids in fish fed the non-fishmeal diets with E AA were higher than those of fish fed diets without EAA, suggesting that ye llowtail can efficiently absorb supplemental crystalline amino acids irresp ective of diet form. However, a remarkable difference was observed in the p eriodical patterns of these four amino acids between FAA derived from suppl ements and those from feed protein. Moreover, FAA patterns in fish fed the non-fishmeal diets with EAA were different from those of the control fishme al diet. Of note, methionine concentration was markedly high during the who le experimental period, resulting in an amino acid imbalance that may have caused lower feed performances in fish fed the non-fishmeal diets with EAA compared to the control fishmeal diet.