Adult female zebrafish; H&E staining Oocytes are lined by two layers, an internal granulosa cell layer and an external theca layer.

The granulosa cell layer develops gradually with the growing oocyte. Early previtellogenic oocytes are accompanied by flat epithelial granulosa cells, granulosa cells with larger oocytes have a higher appearance.

The theca cell layer is composed of stroma cells and contains capillaries. The theca layer is continuous over neighbouring oocytes. Note radial striation in the zona radiata of large vitellogenic oocytes.