The ways of yolk absorption and process of organofaction in Hucho taimen,Oncorhynchus keta,Silurus soldatovi and Silurus asotus were studied using the microscope technology.The results showed that the yolks of both H.taimen and O.keta were absorbed by the blood circulation and the early digestive tract.In S.soldatovi and S.asotus,the yolk was also absorbed by the blood circulation,but the location of absorption was different.About 60-70 days were needed for the yolks of H.taimen and O.keta to be completely absorbed.The yolks of S.soldatovi and S.asotus were absorbed faster,and the yolks were completely absorbed about 3-4 days.Of the four fish species,the yolk-sphere was absorbed first,and then the fat was absorbed.The relationship between yolk absorption and organ development were discussed.