Oita Institute of Marine and Fisheries Science, Kamiura, Oita 879-2602, Japan
Post-feeding changes of apparent protein digestibility (APD) and gastric digesta contents in one-year-old yellowtail Seriola quinqueradiata fed extruded pellets (EP), single moist pellets (SMP), and Oregon moist pellets (OMP) were compared to estimate the protein digestibility (EPD) of those diets between seasons.
APD of OMP were constant at 85-90% irrespective of the season and post-feeding time. APD of EP and SMP were 65-80% at the earlier time of post-feeding and 80-90% at the later time. In fish fed SMP, however, APD decreased in low temperature seasons. Gastric evacuation rates were slower in fish fed EP than in fish fed SMP and OMP throughout the seasons. Protein digestibility values estimated based on post-feeding changes of gastric digesta contents and APD were about 86-89% in fish fed OMP during all seasons. Though those values of fish fed EP were relatively high (83-84%) in low-temperature seasons (December and March), those values decreased from 84% to 69% in fish fed SMP as water temperature fell. These results indicate that EPD of SMP is lower than OMP for one-year-old yellowtail during the low-water-temperature periods, while that of EP is identical to OMP.