Fisheries Laboratory, Kinki University, Wakayama 649-5145, Japan
A new backcross sea bream (RF1), red sea bream (RSB) Pagrus major ×F1 (RSB ×crimson sea bream Evynnis japonica ), and RSB, weighing 107g on an initial mean body weight, were given a commercial diet at a daily feed intake of 1.2% body weight for 80 days. The RF1 steadily grew but showed lower final mean body weight, feed efficiency, protein efficiency ratio, apparent protein retention and final gastral and enteral organ-somatic indices than the RSB. The RF1, on the other hand, had higher apparent lipid retention, hepatosomatic index, lipid contents of abdominal cavity, carcass and hepatopancreas, and enzyme activities of hepatic aspartate aminotransferase, alanine aminotransferase, glucose-6-phosphate dehydrogenase, and fructose-1,6-bisphosphatase on the final day of the rearing period. No significant differences between RF1 and RSB were found in final hematocrit value, hemoglobin content, plasma total protein level, and blood glucose. These results indicated that RF1 was characterized by slightly lower growth performance than RSB, due to small digestive organs and excessive amino acid utilization for energy expenditure, gluconeogenesis, and lipid synthesis.