Development of Non-fish meal diet for fish

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This research was conducted to gather some basic information necessary for the development of non-fish meal dry diets for yellowtail. For the improvement of dietary value of non-fish meal diets supplementation of essential amino acids (EAA) is necessary, taking into consideration that their absorption into plasma must be synchronized with those derived from dietary protein for their effective utilization. Therefore, postprandial changes of FAA in plasma and feed digesta were examined in yellowtail by feeding them three types of diets {(soft-dry pellet (SDP), extruded pellet (EP), and single moist pellet (SMP)}, all having almost the same formulation with or without supplemental EAA.The supplemental EAA were found to be efficiently absorbed by yellowtail improving feed performances differing between diets, being highest for the SDP and lowest for the SMP group. However, the growth performance of fish fed the non-fish meal diets with EAA were inferior to those of fish on the control fish meal diet, in spite of the fact that the former were fortified with EAA to simulate the levels of the control diet. Although supplemental EAA were efficiently absorbed, the plasma methionine levels were markedly higher than those of fish fed the control diet. This may have caused an amino acid imbalance may have lowering the feed performances. For effective utilization, absorption of supplemental crystalline EAA into plasma must be synchronized with those derived from dietary protein, and this was found to be closely related to evacuation timing of the diet from the stomach. Thus the utilization efficiency differed between types of diets based on their physical properties such as hardness.