Timecourse of oocyte development in saithe Pollachius virens

Abstract

Wild caught North Sea saithe Pollachius virens were monitored for growth, sex steroid profiles and oocyte development pre-spawning and measured for egg size and group fecundity during the spawning season in the laboratory. Vitellogenesis commenced in late October-early November, at a leading cohort size (C ) of c. 250 µm, after which oocytes grew rapidly in size until spawning started in February. Notably, a distinct cortical alveoli stage was virtually absent with yolk granules observed in developing oocytes at the very beginning of vitellogenesis. Little atresia was observed pre-spawning, but atretic re-absorption of remnant oocytes containing yolk granules was found in all females immediately post-spawning. As expected, concentrations of sex steroids, oestradiol-17β (females), testosterone (both sexes) and 11-ketotestosterone (both sexes), increased pre-spawning before dropping post-spawning. The present experiment provides the first validation of sex steroid levels in P. virens. Post-ovulatory follicles were visible in histological sections from female gonads 9-11 months post-spawning, but then disappeared. Spawning commenced around a C of c. 750 µm (700-800 µm). Hydrated oocytes (eggs) measured between 1·04 and 1·31 mm (mean = 1·18 mm) with decreasing sizes towards the end of spawning. The average estimated realized fecundity was c. 0·84 million eggs (median female total length, L = 60 cm). Spawning lasted from 13 February to 29 March.

Egg size and density estimates for three gadoids in Icelandic waters and their implications for the vertical distribution of eggs along a stratified water column

“…For haddock, the range of diameters (1.31-1.57 mm) encompassed and extended upon the range (1.37-1.53 mm) found by Trippel and Neil (2004) for the northwest Atlantic haddock. Whilst for saithe, the mean (1.21 mm) and range (1.08-1.34 mm) were similar to the values (1.17 mm, 1.04-1.31 mm) found by Skjaeraasen et al (2017) for the North Sea stock.…”

Tracking oocyte development and the timing of skipped spawning for north‐east Arctic haddock (Melanogrammus aeglefinus)

“…Skjæraasen et al . (2017) elaborated on whether the laboratory settings associated with their study could have shifted the timing of vitellogenesis, but along with the results from the present study, this discrepancy could indicate potential real species differences in the onset of vitellogenesis between gadoids.…”

“…The reason why M. aeglefinus would progress into the CAO phase earlier than G. morhua , despite entering vitellogenesis later and subsequently spawning later in the spring, appears evasive. Still, the first appearance of EVO in the present study (October 27) resembles that of a recent study of the North Sea saithe ( Pollachius virens ; L. 1758) (Skjæraasen et al ., 2017), showing initiation of vitellogenesis in late October–early November, nearly a month later than in cod. Skjæraasen et al .…”

Reproductive ecology and size-dependent fecundity in the petrale sole (Eopsetta jordani) in waters of California, Oregon, and Washington

“…In most fish, this oocyte stage is a distinct one that occurs prior to the appearance of vitellogenin; however, in petrale sole in our study, cortical alveoli appeared at the same time as the vitellogenin. Although rarely documented, the lack of a cortical alveolar stage has been observed in pollock (Pollachius virens) (Skjaeraasen et al, 2016). This observation has little relevance in the context of our study; however, it is important to note that, although many aspects of oogenesis and reproductive biology can be generalized across teleosts, a great variety of reproductive patterns exist.…”

“…1.03x, University of Amsterdam, available from website) and associated modified macros (available from website) for image analysis software ImageJ (vers. 1.50i, National Institutes of Health, available from website; Schneider et al, 2012). Automated measurements recorded from damaged oocytes or detritus were manually removed.…”