Daytime changes in oocyte development with relation to the tide for the Hawaiian saddleback wrasse, Thalassoma duperrey

Abstract

Hourly variations in oocyte stages were characterized by size class and histological examination inassociation to the daytime tidal cycle for the Hawaiian saddleback wrasse, Thalassoma duperrey. Stage I (previtellogenic), stage II (vitellogenic) and stage III (hydrated) oocytes were identified as distinct clutches. During the autumn the profiles of oocytes stages showed rapid, group‐synchronous development from stage I to stage III. Concurrent increases in percentages of both stage III oocytes and the gonadosomatic index (GSI) were positively correlated to and occurred I h before the high tide. Increases in stage I and stage II oocytes 1 h after high tide indicated development of new clutches following a decline in stage III oocytes, and the appearance of post‐ovulatory follicles. The profile of stage II oocytes always exceeded 30% of the ovary. Lower GSI and percentages of stage III oocytes reflect significantly reduced reproduction in the summer: as in the autumn, both factors were significantly correlated, but neither variable showed a statistical relationship to the tide. Nevertheless, hydrated oocytes were found almost exclusively within 2 h of the high tide. The association of developmental changes with changes in tidal heights points to the importance of the tidal cycle or its underlying lunar influence as a predominant reproductive cue. These data show that developmental changes in oocytes occur more rapidly than observed in some more commonly studied temperate species which reproduce annually.