Abstract:This study investigated the development and resorption of the oocyte of Cleisthenes herzensteini in the Yellow Sea, using light microscopy and morphometric methods. Oocyte development was divided into five phases, based on morphological criteria and nutrition accumulation. Oocytes in phase I were small, with little cytoplasm. In phase Ⅱ, oocytes were distinguished by the appearance of yolk nucleus near the cell nucleus. In phase Ⅲ, cortical vacuoles first appeared on the edge of the cytoplasm and then extended to the center, with the occurrences of crystalline yolk and double follicular membrane. Oocytes in phase Ⅳ were full of non-crystalline yolk, with the cell nucleus moving towards the animal pole and the zona radiate becoming thicker. In phase Ⅴ, the cell nucleus of the oocyte dissolved, and the hydrated oocyte was released from the follicular membrane. Ripe ovary that had not ovulated completely was in turn resolved, with the yolk absorbed and the zona radiate ruptured after the spawning season. In addition, this study showed that C. herzensteini was characterized by asynchronous oocyte development and batch spawning, based on histologic observations of the different stages of the ovary and the oocyte size-distribution method. The sizes (major axes) of the oocytes in the stage Ⅳ, Ⅴ, and Ⅵ-Ⅳ¢ ovaries had unimodal distributions, with the three modes at 0.45~0.55 mm, 0.60~0.65 mm, and 0.40~0.50 mm, respectively. Oocyte size distribution was bimodal for stage Ⅴ¢ ovary, the oocytes mainly distributed at both 0.50~0.55 mm and 0.90~0.95 mm, with the percentage of hydrated oocytes and small oocytes increased. The two dominant size groups of oocytes in the stage Ⅴ¢ ovary were well separated with a clear hiatus, and the oocytes in the larger-size group were all hydrated, which was in accordance with the characteristics of batch spawners. In the course of protecting C. herzensteini resources, we should take into account their reproductive characteristics.
