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

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<jats:p>Hourly variations in oocyte stages were characterized by size class and histological examination inassociation to the daytime tidal cycle for the Hawaiian saddleback wrasse, <jats:italic>Thalassoma duperrey</jats:italic>. 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.</jats:p>

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