In Disney’s animated movie Finding Nemo, the animators forgot to tell you one thing about clownfish: they can change gender!
Clownfish live in a group consisting of a breeding pair of male and female, as well as some non-breeding males. There is strict hierarchy based on size: the largest is the female, next largest is the male, and then the non-breeding males.
If the female dies (or gets fished, I suppose), the male will change sex and become the female! Then the largest of the non-breeding males will get a promotion to become the breeding male.