Hormonal regulation of the European sea bass reproductive cycle: an individualized female approach

Abstract

Fifteen tagged female sea bass Dicentrarchus labrax were sampled weekly from September to April and plasma vitellogenin (VTG), testosterone (T), 17β‐estradiol (E2), and two potential maturation inducing steroids (MISs): 17,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20βP) and 17,20β,21‐trihydroxy‐4‐pregnen‐3‐one (20βS) assayed. An oocyte sample was obtained via intraovarian cannulation at each sampling time from every female and the stage of development of the most advanced clutch of oocytes determined and related to VTG and hormone plasma levels for each female. The mean number of ovulations per female was 1·75+0·25 when those females that did not present ovulations were excluded and up to 4 ovulations detected in some females. The highest plasma levels of T (c. 6 ng ml‐1) were observed during postvitellogenesis and the beginning of maturation while maximum plasma levels of E2 (>5 ng ml‐1) were obtained during late vitellogenesis. VTG plasma levels increased throughout vitellogenesis peaking (c. 2·5 mg ml‐1) at postvittelogenesis. For the first time significant changes of plasma progestogens were detected in European sea bass during the sexual cycle. The highest plasma level of 17,20βP (c. 1·1 ng ml‐1) was observed during postvitellogenesis while the highest level of 20βS (c. 1·4 ng ml‐1) coincided with final maturation. These results suggest that 17,20βP and 20βS play a role in the early and final maturation, respectively, in the European sea bass.