Annual cycle of plasma oestradiol-17β in the female trout Salmo gairdneri

Abstract

Levels of oestradiol in plasma of adult female rainbow trout Salmogairdneri were determined during the annual reproductive cycle using a radioimmunoassay. From January to June, during previtellogenesis and the period of endogenous vitellogenesis plasma levels were low (1,3 ! 0,2 ng/mi). At the beginning of the period of exogenous vitellogenesis, the cestradiol level rose and a maximum (16,9 ! 0,2 ng/ml) was reached at the end of vitellogenesis in November, some weeks before spawning. A positive correlation (r = 0,58) was established between plasma oestradiol levels and the gonadosomatic index. From enzymatic cytochemical studies it was concluded that the granulosa cells, as well as the interstitial cells in the ovary, are involved in oestradiol production.