Changes in the ovary of the Gulf killifish, Fundulus grandis (Baird and Girard), during seasonal and semilunar spawning cycles

Abstract

Annual and semilunar ovarian cycles were examined in a wild population of Gulf killifish, Fundulus grandis, from the Alabama (U.S.A.) coast of the Gulf of Mexico. Production of mature eggs was first observed in late February, with the main breeding season beginning by mid‐March and extending into August. The season was punctuated by shorter, typically semilunar, cycles of spawning activity and gamete development that became more pronounced as the season progressed. In September any remaining ovulated eggs and oocytes past the intermediate‐cortical alveolus stage underwent atresia, suggesting that the latter may be the final gonadotropin‐ independent stage of oocyte development in F. grandis. Seasonal proliferation of primary growth phase and cortical alveolus oocytes occurred in late autumn and early winter (October‐January). Vitellogenic oocytes first appeared in early February at the start of a month of intense and rapid vitellogenic oocyte growth prior to the March onset of a new breeding season.