Histological and ultrastructural study of Zona Radiata in oocyte of common carp Cyprinus carpio (Linnaeus 1758)

Oocytes and fertilized eggs of teleosts are enclosed by a non-cellular envelope, the Zona Radiata (ZR). It has structural differences in various ecological and systematic groups of fish. Ultrastructural analysis has shown that ZR is formed during the previtellogenic stages. Morphological characteristics of ZR suggest various functional and ecological importance that are exhibited during oocyte development and adaptations to the released oocytes. In this research work, the structure of ZR in oocytes of Cyprinus carpio was investigated from its first appearance until final growth stage as matured ones. For this purpose, the left ovary was fixed in Bouin's solution. The histological slide preparations were studied by both light and scanning electron microscope. ZR was not observed in stage I and stage II of oocyte development. The onset of ZR appearance was in stage III which gradually increased in thickness until stage IV (vitellogenesis) and lowered in thickness during following stage V. Very fine outgrowths were observed growing from oolemma. ZR was shown porous on both inner and outer sides. Striations (pore-canals) were distinguished with crenated edges.