Influence of oral administration of estradiol-17β and testosterone on growth, digestion, food conversion and metabolism in the underyearling red sea bream, Chrysophrys major.

Estradiol-17β (E2) administered in the diet to the red sea bream Chrysophrys major did not affect appetite, food conversion efficiency, protein efficiency ratio and specific growth rate. Serum concentrations of total protein, albumin, globulin, vitellogenin, α-amino acids, total lipid, free fatty acids, cholesterol and calcium were elevated. The hepatosomatic index was also increased. Activities of hepatic enzymes including lactate dehydrogenase, isocitrate dehydrogenase and glutamate-pyruvate transaminase were higher than found in untreated control fish. Intestinal activity of leucine aminopeptidase was augmented. However, there were no changes in muscle water, protein, lipid and glycogen content. In contrast, testosterone (T) given by the same route increased appetite, food conversion efficiency, protein efficiency ratio and specific growth rate. There were no alterations in serum protein and calcium concentrations but serum glucose, ammonia and triglyceride levels were elevated. Hepatic glycogen content was increased. The activities of hepatic fructose- 1,6-diphosphatase, glucose-6-phosphatase and glycogen synthetase and intestinal activities of alkaline phosphatase and τ-glutamyltransferase were higher than noted on control fish. The results reveal that estradiol-17β and testosterone exerted different metabolic effects in the red sea bream and they suggest that testosterone exerts its anabolic actions by increasing appetite, food conversion efficiency and activities of digestive enzymes.