The reproductive cycle in winter flounder, Pseudopleuronectes americanus (Walbaum)

The reproductive status of winter flounder was analyzed in individuals collected at regular intervals throughout the year. Although spawning occurred in May–June, sperm could be activated in January, and male gonadosomatic indices in November were approximately twice those recorded immediately before spawning. Oocyte recruitment occurs close to spawning, and oocyte changes are compatible with a 3-year cycle. Vitellogenesis of the oldest year class of oocytes is initiated during the summer feeding season and maintained over the nonfeeding winter season. Some females after spawning do not enter the vitellogenic stage but overwinter with two year classes of immature oocytes. This nonreproductive phase in females in related to condition rather than age. Nonreproductive males also occur in the population sampled and in the fall there was a trend towards an increased number with advancing age. The protracted gametogenesis in winter flounder demonstrates the need for caution when assessing spawning condition and reproductive capacity of some fish stocks.