Cytological observation of fertilization and analyse of the nurse eggs in Hemifusus tuba (Gmelin)

The cytological changes of nuclear behavior during the process of fertilization and early cleavage of Hemifusus tuba (Gmelin) were continually observed by fluorescent microscope. The numbers of eggs and embryos were also calculated for the whole embryonic development stages. The results showed that mature unfertilized eggs of H. tuba were oval and the average diameter was 0.33 ± 0.03 mm. The nuclear phase was at the metaphase of the first maturation division. At water temperature of 27-28℃, sperm penetrated into cytoplasm of egg 1h after fertilization. The fertilized eggs released the first polar body and the second polar body at 2~3 h. The female pronuclei and male pronuclei formed at 6 h, followed by the first cleavage. The second cleavage happened at 12-24 h, formed 4-cells. The study showed that the zygotes of H. tuba were asynchronous during meiosis and cleavage. In total, the fertilization ratio was about 43.14%, but the zygotes which could develop to 4-cell stage were only 5.70%. In a capsule, many eggs were not fertilized, or stopped developing, and both of them were inferred as the sources of nurse eggs which were consumed by developing embryos. The ratio of eggs unfertilized to eggs that stopped developing was 3 to 2. During the embryonic development, the number of eggs reduced significantly during the 1st to 6th day, only 0.48% of eggs developed to trochophore stage, and this ratio maintained until the juveniles left the capsules for natural environment.