A STUDY ON ULTRASTRUCTURE OF ZONA RADIATA DURING OOCYTE DEVELOPMENT OF ZEBRAFISH (Danio rerio)

Fine structures of the zona radiata in zebrafish, Danio rerio, is examined and compared. The zona radiata (called as zona pellucid in mammals), is a porous structure located between oolemma and follicle cell epithelium in fish, has various functions. The zona radiata is an inner connection surface that regulates essential transition from follicle cells to oocytes and from oocytes to follicular layer. In this study, it is aimed to examine changeable and distinct structure of the zona radiata during oocyte development in zebrafish, which is a member of teleosts fish family. The structure of zona radiata were examined using light and transmission microscopy. The structure of zona radiata showed a morphological difference among the different species. The zona radiata structure could not be seen under light microscope in the pre-vitellogenic phase, but it was seen as a thin line form at the edge side in the early vitellogenic phase. In the following phases, the tendency to become thicker zona radiata was observed. The existence of microvillus structures, which lie from the zona radiata to follicle cell layer and from this layer to the zona radiata, was observed by means of electron microscope. It was assumed that the oocyte ensures communication between two sides through microvillus structures.