Hermaphrodite

A few species of vertebrates (mostly fish), and some species of crustaceans (barnacles and shrimps) change sex during their lifetime.

Sequential hermaphroditic fish, such as the bluehead wrasse, undergo protogyny, changing sex from female to male. Other species, such as the sea perch, Pagellus acurne, undergo protandry, changing sex from male to female. A third group of fish, such as the sea bass, undergoes both protogyny and protandry, and can do so repeatedly. One of the most dramatic sights in nature is the mating of the sea bass Serranus subligarins. When two female sea bass meet to mate, one undergoes protogyny, changing color from a deep blue to bright orange with a white stripe. After fertilization, both fish then switch sex (and coloring) and then mate again.

The sex changes of sequential hermaphrodites depend on social factors. For example, bluehead wrasse live in large colonies where only the largest fish are males. The others must remain female until the males die. Only then can some of the females (usually the largest) change from female to male. Other factors influencing protogyny and protandry are hunger, the amount of salt in the water (salinity), social behaviors, and the ratio of males to females in the population.