ABSTRACT
In fi shes sexuality ranges from gonochorism to unisexualism and selffertilizing hermaphroditism to sequential and serial hermaphroditism (Pandian, 2010, 2011). Even among the gonochores, a few individuals of Xiphophorus helleri are known to switch from female to male (Lodi, 1979). Modes of reproduction also range from sexual to gynogenesis and to hybridogenesis and each of these modes may involve external fertilization and oviparity, or internal fertilization and viviparity, which itself ranges from zygoparity to true viviparity. In fact no other vertebrate group offers as much diversity as teleost fi shes for the study of sex differentiation (Pandian, 2011). Hence this comprehensive account is restricted to oogenesis and related aspects alone; a descriptive account on the origin and differentiation of reproductive organs, system and related secondary sexual features may alone merit a title for a book.
