ULTRASTRUCTURE OF SPERMATOZOA AND FERTILIZED EGGS OF ANGUILLA JAPONICA AND OBSERVATION ON THE FERTILIZATION PROCESS

This paper focus on the ultrastructure of sperm and egg membrane of Anguilla japonica,which was artificially induced by extraneous hormone,and an observation on the fertilization process by means of scanning electron microscope (SEM) and transmission electron microscope (TEM),so as to provide theoretical basis for breaking through the artificial reproduction of Anguilla japonica furthermore.The results showed that the spermatozoa of Anguilla japonica was composed of head﹑middle piece and flagellum.The sperm head which divided into back side and dorsal side was in the shape of erose pear.An undee membrane wrapped the sperm head.There was great interspace between the undee membrane and karyon.The karyon filled with electron density substance nearly occupied the whole space of the sperm head.Many nuclear vacuoles in different size irregularly distributed in the karyon.One large round mito-chondrion was in a cyst which was on the top of sperm head and had no acrosome.Middle piece of sperm which was wrapped up in an undee membrane connected with flagellum.Additionally,a rootlet lied dorsal side of spermatozoa threw out backward from the middle piece,forming “8+2”pattern.The rootlet front part of which extended to the mitochondrion could cut off the flagellum during fertilization process.There were many cytoplasma granules between the cytoplasma membrane and the karyon membrane.The sperm tail was composed of flagellum and tip of flagellum.The cross section of the flagellum which was composed of axoneme and microtube formed in a “9+0”pattern appeared to be round,no side fin.A great deal of ridge-hole complexes distributed on the surface of fertilized eggs,where no fertilization hole was found.Matured eggs were wrapped up in outer egg-shell membrane and inner vitelline membrane between which perivitelline space lied.Radiozone but no zone pellucida was found on egg-shell membrane.The radiozone was divided into three sublayers.Out layer formed with the ridge of ridge-hole complex.The middle layer was gauffer layer and the inner compact smooth layer.The hole of ridge-hole complex penetrated the whole radiozone and formed a mostoid structure at the bottom of the radiozone.Egg membrane not only protected eggs but participated in the fertilization process.The process of fertilization which happened pre and post 30 seconds after fertilization could divide into four phases: egg membrane attracting sperm; sperm anchoring on egg membrane; sperm karyon penetrating into egg membrane and holes on the surface closing.Only morphological changes of Anguilla japonica sperm and egg membrane were observed in this paper.The character and way of sperm penetrating into egg membrane need thorough research.