cool-critters:

Pink skunk clownfish (Amphiprion perideraion)

The pink skunk clownfish is a species of anemonefish from the skunk complex that is widespread from northern Australia through the Malay Archipelago and Melanesia. Like all anemonefishes, it forms a symbiotic mutualism with sea anemones and is unaffected by the stinging tentacles of the host. It is a sequential hermaphrodite with a strict size-based dominance hierarchy;
the female is largest, the breeding male is second largest, and the
male nonbreeders get progressively smaller as the hierarchy descends. They exhibit protandry,
meaning the breeding male changes to female if the sole breeding female
dies, with the largest nonbreeder becoming the breeding male.

photo credits: Jenny

,
Michael McComb,
Nhobgood

A lot of other clownfish do the same thing as far as sexes. If you want to breed clownfish, you just get two juveniles and let them sort themselves out, one will become female. If the only ones available are adults, you get a big one and a much smaller one, and the big one is either female or will become female.