Did you know that some aquatic species can change from male to female and vice versa?
This phenomenon is called sequential hermaphroditism and describes a type of hermaphroditism that occurs in many fish, snails, slugs (yes, nudibranchs are hermaphroditic as well), and even some plants. We speak of sequential hermaphroditism when the individual changes its sex at some point in its life. Species that can undergo these changes from one sex to another do so as a normal event within their reproductive cycle that is usually cued by either social structure or the achievement of a certain age or size. Oftentimes this happens to ensure successful reproduction.
Clownfish are one of the most famous sequential hermaphrodites. Clownfish are all born male, but can change their sex to female if the necessity occurs. They for example change their sex from male to female when there is no other female to mate with or when they attain a certain size. (By the way, this would’ve changed the entire plot of Nemo.)
This phenomenon goes the other way as well.
Unlike clownfish that start life as males and transform into females, there are other species, such as the California sheephead, that start as female and transform into male.