ABSTRACT
Egg envelopes are external, acellular structures of mature fish eggs. They remain in close connection with the developing embryo which provides it with permanent contact with the external environment. The structure of the egg envelope is adapted to the environmental conditions in which the egg develops. Egg envelopes play a variety of functions which change during embryogenesis. During egg activation it attracts spermatozoa and prevents polyspermy, protects the embryo againts mechanical damage, microorganisms and ensures gas axchange, regulates water balance, ensures anchoring to the substratum and constitutes a partial barrier for environmental pollutants. The structure of the egg envelopes is species-specific.
This chapter discusses in a comparative way the structure and the ultrastructure of different layers of fish egg envelopes, its thickness and resistance. The external and internal surface of the zona radiata, of the micropyle, and changes in the structure of the egg envelope during hatching and the egg capsule of elasmobranch fishes are also described.
