Characterization of oocyte development in hatchery-reared burbot

Burbot Lota lota are an emerging aquaculture species. To aid in predicting the natural and hormonal-manipulated timing of ovulation and for ensuring maximum viability of eggs at spawning, this study describes oocyte maturation of hatchery-reared burbot from vitellogenesis through ovulation. At a temperature of 4°C, visual polarization of the oil globule occurred 7–13 d preovulation. The lack of uniformity in individual oocyte development was observed and persisted until approximately 2 d before ovulation, at which point complete polarizationwas observed in all oocytes and a condensed blastomere was observed along the inner chorion. These preliminary observations imply that implantation of gonatotropinreleasing hormone (GnRH) decreased the final maturation stage of oocyte development by 2–4 d and may aid in initiating the maturation process, the induction of which appeared to be a threshold for either a female’s progression to ovulation or nonovulation and atresia. Although additional investigation may be needed to fully maximize egg fertilization success and optimize timing related to intensive spawning practices, this study lays a foundation for further investigations and provides a reference for assessing oocyte development and predicting ovulation for this species.