Abstract: The ultratructural changes of the yolk platelets in fertilized eggs and liver of cruclan carp (Carassius auratus gibelio) have been studied through electron microscopy. It was found that the structure of yolk platelets of fish eggs is different from that of amphibians. In fish eggs, the yolk platelets have no crystal main body but consist of noncrystal dark granular structure. Before first cleavage, some yolk platelets in the fertilized fish eggs began to degrade forming two kinds of vesicles, of which one is small and empty, while the. other is large, containing mitochondria and ribosomes. Around large vesicles, there are some lipid droplets in the forth of lamellar structure.The internal structure of mitochondria of the fertilized eggs is multiform, containing dark granules or lamellar lipid droplets.