ABSTRACT
This chapter focuses on discussing the understanding of major strategies employed by fishes at fertilization, particularly morphological, physiological and molecular biological features of the gametic devices for external fertilization which occurs in most teleosts. The size, the number of the layers, and also the toughness of the egg may be related to the evolutional adaptation of each species to the environment for spawning, fertilization and hatching. The pit region appears likely to have a role in fertilization. The chapter discusses each step from sperm-egg recognition to successful fertilization involving establishment of the polyspermy block. The fertilization steps are: sperm-egg recognition and fusion of the sperm plasma membrane and oocyte plasma membrane; acrosomal reaction in the sperm; egg activation and cortical reaction in the egg fused with a spermatozoon; Penetration of the sperm nucleus into the oocyte; polyspermy block during the fertilization process.
