Comparative study on fine structure of mature and fertilized eggs of silver carp (Hypophthalmichthys molitrix) and molly (Poecilia sphenops)



Zona radiate (ZR) is an acellular region which during early stages of oocyte development appear outer to oolemma and attains more thickness and complexity by the action of follicular epithelium and oolemma itself. The structure of ZR might help in recognition of egg type, fish habitat, spawning ground and exchanging routs for needful gases and nutrients. Microscopic studies of histological sections of oviparous silver carp (Hypophthalmichthys molitrix) and viviparous molly (Poecilia sphenops) revealed that ZR in mature oocytes was a simple layer with vestigial pore canals. ZR in post-fertilized eggs showed reduction in thickness and possessed different appearance. Based on mode of reproduction, pre and post- fertilized egg of both species presented notable and expected differences in ZR thickness and architecture.