Plasma concentrations of ovarian steroids in relation to oocyte final maturation and ovulation in female plaice sampled at sea

Blood plasma concentrations of free 17â-oestradiol, free testosterone and glucuronidated testosterone were strongly positively related to the percentage of vitellogenic oocytes remaining in the ovaries of plaice Pleuronectes platessa caught at sea—being at their highest in pre-spawning (stage IV) females (i.e. those in which the oocytes were close to fully grown, but had not yet entered the stage of final maturation). In contrast, the concentrations of free and sulphated 17,20â-P, 3á,17,20â-P-5â, and 3á,17,21-P-5â were at their lowest in stage IV females. Free 17,20â-P (the putative maturation-inducing steroid) became only slightly elevated (less than twofold) during spawning (i.e. in stage V and VI females with hydrated and/or ovulated eggs). Sulphated 17,20â-P and 3á,17,21-P-5â became slightly more elevated (three- to fourfold). However, sulphated 3á,17,20â-P-5â concentrations increased 30-fold and were at their highest in fish in which only 40% of vitellogenic oocytes remained in the ovaries. Sulphated 17,20â-P, 3á,17,20â-P-5â and 3á,17,21-P-5â concentrations were significantly positively related to hyaline oocyte batch size; and sulphated 17,20â-P and sulphated 3á,17,20â-P-5â were significantly negatively related to the degree of hydration of the hyaline oocytes. None of the steroid concentrations, however, was related to the time of capture. More ovulated females were found in the afternoon than at any other time of the day

Primary and secondary oocyte growth dynamics in anadromous semelparous allis shad Alosa alosa

We analysed the ovarian dynamics of the anadromous semelparous allis shad Alosa alosa for which our working hypothesis was that mature pre‐spawning females would have very low or even exhausted primary growth (PG) oocyte reserves; semelparity has been linked with the depletion of the pool of PG oocytes. To test this hypothesis, the PG oocytes were enumerated, their recruitment pattern to the secondary growth (SG) phase was analysed and their potential replenishment from the pool of oogonia was examined in females caught very close to the Mondego River mouth, in central Portugal and along the river. The development of the SG oocytes was also analysed, the fecundity (batch, total and annual) values were estimated and the intensity of atresia was quantified. Ovarian samples and histological sections were investigated in parallel. A dynamic recruitment pattern of PG oocytes to the SG phase was revealed, where all PG oocytes were recruited and were not replenished by oogonia. Annual fecundity was subject to down‐regulation due to atresia prior to spawning and its size was multiple times higher than the size of batch fecundity. Lack of population synchronicity in ovarian development and spawning migration was also observed. This multifaceted analysis of the ovarian dynamics of this species will contribute to management efforts for this critically endangered and economically important fish throughout its geographical distribution. The results reported in this study will also assist in unravelling the complexity of the early processes of oogenesis in fish