Effects of a superoptimal temperature on aquacultured yellowtail Seriola quinqueradiata

This study aimed to investigate the effects of a superoptimal temperature on growth, body composition, body size heterogeneity, and relationships among these factors in juvenile yellowtail. Fish (mean body weight = 24 g) were tagged individually and reared for 70days under two different water temperature regimes [optimal (25 degrees C) and superoptimal (30 degrees C)]. After rearing, fish reared at 30 degrees C showed lower survival, less food, feed and protein utilization, significantly lower growth performance, and a lower hepatosomatic index than fish raised at 25 degrees C. Variations in body indices among individuals were larger for fish reared at 30 degrees C than for fish reared at 25 degrees C. Mean whole body protein content was significantly lower in fish reared at 30 degrees C than fish reared at 25 degrees C. In addition, several glucogenic and/or aromatic amino acids were lower in fish reared at 30 degrees C than in fish reared at 25 degrees C. Whole body lipid levels tended to be lower in fish with lower body weight reared at 30 degrees C. These results suggest that fish raised at 30 degrees C will have lower growth performance, and lower concentrations of specific amino acids. Moreover, heterogeneity in body size and body lipid content is expanded by a superoptimal temperature.