These new females are probably not as reproductively successful as a normal female, but a sex change has taken place. There is one other type of hermaphroditism that is expressed in at least one fish species. This diminutive killifish is not much to look at, but its method of reproduction is amazing to see. Sexual determination in non-hermaphroditic fish is not as cut and dry as it is with humans. We have a set of chromosomes designated the sex chromosomes.
Fish often have sex genes that exist on chromosomes other than the sex chromosomes.
Sexual determination is based upon the balance between the number of female sex determinants and male sex determinants in the fish's entire genome. If there are more male genes that female genes then the fish will be male, and vice versa. Environmental conditions have been shown to play a role in sex determination, or in the appearance of secondary sexual characteristics. Pelvicachromis pulcher is well known as a species of West African dwarf cichlid that can have the sex ratio of an entire spawn skewed by pH. Behavioral response to aggression in cichlids, especially dwarf cichlids of the genus Apistogramma , can suppress the expression of secondary sexual characteristics in sub-dominant males. Apistogramma species that get sneaker males, fish that look like females but breed like males, in groups that have a dominant male in them are an example of this phenomenon.