Ultrastructure of Egg Envelope in the Sheatfish (Silurus soldatovi)

The surface structure of mature egg and change of fertilization envelope in embryonic development had studied in the Sheatfish (Silurus soldatovi). The surface of the mature egg envelope was very thin and adhesive when came into contact with water. The observation in SEM showed that the surface of the mature egg was covered by a membrane which was composed by thickness materials with even electron density. In high power lens, the surface of this membrane had some spheric or ridge bulges and imbricated extendedly structure arranged by flakes, which showed ribboned and reticular structure changed with embryonic development, the branch units were clear and uniform, the interspace among them had many trabecular structures. The ultrastructure of fertilization envelope egg could divided into four sub-layers according to morphology and compactness, the order of these layers from surface to inner is jelly coat, pellucida layer, zone radiata externa and zone radiata interna. The loosen sub-layer could be seen in layer pellucida inside, which was like spongy or branch and had many interspaces. The zone radiate externa was a compacted flake structure. The zone radiate interna was alveolate and very dense with the density of 1 pore/μm-2 microvilli pores, the inside of the microvilli pores had trabecular structures. The joint between zone radiata externa and zone radiata interna was compact.