Seasonal changes of the amounts of growth hormone receptor (GHR) were investigated in black seabream (Acanthopagrus schlegeli). Serum growth hormone (GH), serum triiodothyronine (T3), gonadosomatic index (GSI), and ratio of RNA-DNA (R/D) in liver and white muscle in black seabream were also measured. The hepatic GH binding amounts of black seabream, which were lowest in June, were higher significantly in September and December than that in March and in June. Levels of hepatic GHR mRNA showed the similar variation manner with GH binding. GH binding amounts in gonad of black seabream were highest in September. In contrast to hepatic GHR, serum GH concentration of black seabream were highest in June. Serum T3 concentration of black seabream were lower in June and September than that in March and December. White muscle R/D showed sex specific seasonal variations. In male fish, white muscle R/D was higher in June than the other seasons, whereas there was no statistical seasonal difference in female fish. Liver R/D of female fish was higher in March than that of male fish in March and that of female fish in June and December. GSIs of both male and female fish were lowest in June and highest in December.
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