female intimate characteristics are substituted for male ones, or vice versa.
What's the substitution process all about?
Its as a result of sequential hermaphroditism observed in some species.
What's hermaphroditism?
It can change from a male to female (protandry), or from female to male (protogyny) or from female to hermaphrodite 
Any genetically related?
used for the medical procedures applied to intersex people.
You mean a specie can have both a male and females organs of reproduction?
Fish reproduction
Fish reproductive organs include testes and ovaries. In most species, gonads are paired organs of similar size, which can be partially or totally fused. There may also be a range of secondary organs that increase reproductive fitness. The genital papilla is a small, fleshy tube behind the anus in some fishes, from which the sperm or eggs are released; the sex of a fish often can be determined by the shape of its papilla.
Anatomy.
Anatomy Testes.
Most male fish have two testes of
Sex change
Sex change is a process by which a person or animal changes sex – that is, by which female sexual characteristics are substituted for male ones or vice versa. Sex change may occur naturally, as in the case of the sequential hermaphroditism observed in some species. Most commonly, however, the term is used for sex reassignment therapy, including sex reassignment surgery, carried out on humans. It is also sometimes used for the medical procedures applied to intersex people. The term may also be applied to the broader