Electron and Light Microscopic Investigations of Follicular Epithelium in Vitellogenic Oocyte of Zebrafish (Danio rerio)

The zebrafish (Danio rerio) is an extremely dynamic organ in which follicles undergo asynchronous development. The oocytes of zebrafish ovary are observed in various phases. The oocyte development of zebrafish was divided into four stages (primary growth, cortical alveolus-previtellogenic, vitellogenic and mature oocyte). Zebrafish follicles contain only a single layer of granulosa cells that are separated from the oocyte by the vitelline envelope (zona radiata). The follicular epithelium and theca of oocytes in zebrafish differentiates during the primary growth phase. Histological analysis revealed that the zona radiata is formed during the vitellogenic growth stage. Specializations associated to the outher layer of the zona radiata may be related to the egg’s adherence to the substrata. We conclude that cytological characteristics of follicular cell and oocytes don’t differ from those described in other teleosts species.