Innovative methods for analysis of reproduction may provide more information that can be used to conserve species of concern. We present data on oocyte development, batch size, and batch number of anadromous Alewives Alosa pseudoharengus in a lake-spawning population located in Connecticut. We sampled female Alewives as they arrived at the spawning habitat (uprunners) and females as they were leaving (downrunners). We estimated batch size by weighing all oocytes and performed image analysis on oocytes in subsamples of some ovaries, thereby estimating oocyte size-frequency distribution to define the number of batches. We performed both whole-mount and histological analysis on other ovaries to compare gravimetric and stereological estimates of batch size and to precisely characterize oocyte developmental stages. Uprunners had advanced oocytes at the ultimate stage of vitellogenesis and usually three additional less-developed batches. Postovulatory follicles and oocytes that were being resorbed were prevalent in downrunners but were absent in uprunners. Females spawned at least three batches in a season; however, downrunners had nearly as many batches as uprunners in their ovaries, indicating there was continuing recruitment and maturation of fresh batches. A numerical model of oocyte growth indicated that there is sufficient time for batches recruited at the beginning of the spawning season to develop and be spawned in the same season, indicating that fecundity is indeterminate. Accurate assessments of individual reproductive performance will require detailed consideration of within-season oocyte dynamics as opposed to relying on enumerating oocytes in prespawners.

Following the classic lines of evidence of Hunter et al. (Hunter, J. R., Macewicz, B., Lo, N. C. H., and Kimbrell, A. 1992. Fecundity, spawning, and maturity of female Dover sole Microstomus pacificus, with an evaluation of assumptions and precision. Fishery Bulletin US, 90: 101–128.) on the fecundity type of fishes (determinate vs. indeterminate), the stock of horse mackerel (Trachurus trachurus) in Atlantic Iberian waters (ICES Division IXa) was shown to exhibit a mixed picture. Total fecundity, the total number of secondary growth (SG) oocytes dropped during the spawning season and there were reproductively active individuals with a distinct size hiatus between primary growth (PG) oocytes and SG oocytes, while no massive atresia was observed in late-season spawners. All of these characteristics matched with evidence for determinate fecundity. However, daily decrease rate of total fecundity was lower than daily specific fecundity (i.e. the number of eggs produced daily per unit weight) by orders of magnitude which suggested that the stock of SG oocytes was replenished during the spawning period through de novo oocyte recruitment. In addition, the maximum number of batches in reproductively active females was lower than the predicted annual number of spawnings, while total fecundity in recent spawners—those containing post-ovulatory follicles—was not lower than the fecundity of the remaining reproductively active females. All of these results suggest that, despite the aforementioned mixed lines of evidence, the fecundity of horse mackerel is clearly indeterminate. We attribute these mixed characteristics to the fact that, unlike most typical indeterminate spawners, horse mackerel ceases to recruit new SG oocytes during the latter part of its spawning season.

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We analyzed ovarian dynamics of anadromous blueback herring, Alosa aestivalis, in Connecticut River with the principal aim of exploring oocyte recruitment and how it shapes the fecundity pattern. We examined the oocyte release strategy and analyzed spawning cyclicity by linking oocyte growth to the degeneration of postovulatory follicles. Females were accordingly classified as pre‐spawners, early and late active spawners, and oocyte recruitment intensity was compared among the different spawning phases. Oocyte recruitment occurred continuously and in parallel with spawning activity, a pattern which is diagnostic of indeterminate fecundity. However, both fecundity and oocyte recruitment intensity progressively decreased (tapered) throughout spawning, until the ovary was depleted of vitellogenic oocytes. There was no massive atresia of vitellogenic oocytes at the end of the spawning season, which is atypical of indeterminate spawners. We propose that tapering in oocyte recruitment and fecundity is an adaptation to the high energetic expenditure of the upstream spawning migration.

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. K E Y W O R D Salosines, anadromy, fecundity, oocyte recruitment, oogonia, semelparity