Biology of Finfish and Shellfish

4.1.2 Types of reproduction

In fishes, generally the sexes are separate exhibiting bisexual reproduction, but sometimes they are hermaphrodites and rarely parthenogenesis is seen.

In bisexual reproduction, sperms and eggs are produced in male and female sex organs called testis and ovaries respectively. In hermaphrodites, both the sex organs are in a single individual and may develop simultaneously; such fishes are called synchronous hermaphrodites (e.g. Polynemus heptadactylus). But, they do not practice self fertilization. Most hermaphrodites show development of male gonads before female gonads (protandrous hermaphrodites e.g. Sparus spp.) while others show development of female gonads before male gonads (protogynous hermaphrodites Epinephalus diacanthus) so as to achieve cross fertilization.

Parthenogenesis is development of young ones without fertilization. This is reported from a tropical fish, Poeilia formosa. In parthenogenetic mode of reproduction mating with a male is required, but the sperm serves only one of its two functions, that of inciting or triggering the egg to develop. It does not take any part in heredity. The resultant young ones are always females (gynogenesis) with no trace of parental characters.