Physiology of Finfish and Shellfish (2+1)

3.1.15. Sexual differentiation

A light press on the belly of most ripe fishes will bring the whitish milt or the eggs into view near the anus. However, fish also use other features to exhibit the sexes.

The characteristics of sexual difference or sexual dimorphism that enable identification of the sexes are classed as primary and secondary. Primary sexual characters are those that are concerned actually with the reproductive process. Testes and their ducts in the male and ovaries and their ducts in the female constitute primary sexual characters. The primary sexual characters often require dissection for their discernment which makes the secondary sexual characters often more useful. Secondary sexual characters are of 2 kinds- Those which have no primary relationship with reproduction act

- Those which are definitely accessory to spawning.