Effects of physical properties of diets on evacuation time of digesta and plasma free amino acid patterns in yellowtail

The periodical changes of feed digesta contents in the digestive tracts and plasma free amino acid levels of yellowtail, Seriola quinqueradiata (avera ge weight 690 g) were investigated at 0, 3, 6, 12, 18, 24, 30, and 48 h aft er feeding on three different types of diets. The diets were: (i) extruded pellets prepared using a large-sized twin screw extruder (SDP); (ii) pellet s processed using a small-sized twin screw extruder (EP); and (iii) single moist pellets (SMP). Three types of experimental fish meal diets were formu lated so as to have an almost similar ingredient composition, and were supp lemented with crystalline methionine, lysine, and tryptophan. Digesta conte nts in the stomach of fish fed the SDP diet during the experimental period were highest, whereas fish fed the SMP diet were lowest, and the stomach di gesta evacuation time was different for the different types of diets. This might be caused by the differences in the chemical and physical properties of the diets. The evacuation times of the feed digesta contents of the stom ach influence those of the intestine. Three crystalline amino acids added t o the diets seemed to be absorbed effectively into blood plasma immediately after feed intake irrespective of the diet types. Periodical changes in th e plasma levels of methionine seemed to be linked to the feed digesta conte nts of the stomach. Therefore, it is suggested that utilization of suppleme nted methionine might be affected by diet characteristics which, in turn, i nfluence the stomach digesta evacuation times.