Relationships between serum levels of gonadotropin, oestradiol-17β, and vitellogenin in the control of ovarian development in the rainbow trout

摘要: Abstract The present study investigates the effects of seasonally changing photoperiod regimes on levels serum gonadotropin, oestradiol-17β, and vitellogenin (as indicated by phosphoprotein phosphorus calcium measurements) time spawning female rainbow trout ( Salmo gairdneri ). This included a control regime also seasonal cycles in which increasing decreasing components were maintained but compressed into 6- 9-month periods. Spawning fish occurred mid-January at same as outside ponds under ambient conditions, whereas it was advanced approximately 12 6 weeks, respectively. Under both experimental regimes, primary change an increase gonadotropin during early stages ovarian development, after reduced. followed increased oestradiol-17β became particularly pronounced period exogenous vitellogenesis. These changes appeared to stimulate production release liver evidenced increases levels. Subsequently, remained high until complete. During later development oestradiol fell, thus signalling, probably negative feedback mechanism, further larger presumably required for final oocyte maturation ovulation. sequence endocrine similar shortened cycles, although modifications apparent their timing duration, resulting earlier times.