Influence of oral administration of 3,5,3'-triiodo-thyronine on growth, digestion, food conversion and metabolism in the underyearling red sea bream, Chrysophrys major (Temminck & Schlegel)

The effect of inclusion of 3,5,3'-triiodo-～-thyronine (T₃) in the diet was examined in underyearling red sea bream Chrysophrys major (Temminck & Schlegel). The treatment brought about increases in growth rate, appetite, food conversion efficiency and activities of intestinal enzymes including leucine nitroanilidase, alkaline phosphatase, α-glutamyltransferas, α-amylase and disaccharidase. There were no changes in the muscle content of water, protein, lipid and glycogen. Liver glycogen content was elevated, as well as activities of the hepatic enzymes glycogen phosphory-lase, glycogen synthetase, glutamate-pyruvate transaminase, fructose- 1, 6-diphosphatase and glucose-6-phosphatase. The serum concentrations of total protein, albumin, globulin, α-amino acids. glucose, ammonia and calcium were increased by the treatment whereas the serum concentrations of free fatty acids, cholesterol and triglyceride remained unaltered. The results suggest that in the red sea bream T, stimulated protein and carbohydrate but not lipid metabolism and that the hormone promoted growth by improving appetite, digestion and absorption.