Sequential Hermaphroditism

Sequential hermaphroditism is the ability to change sex during the life cycle. It is more common in fish than in any other vertebrate group and has evolved independently in dozens of families. Protogyny (female → male) is more common (e.g. wrasses, parrotfishes, groupers) and typically linked to size-advantage models: in harem-based species, a large male can monopolise fertilisations, so it pays to be female when small and male when large. Protandry (male → female) occurs in some sparids and is less common.

All large "dominant males" (supermales) in wrasse species such as the bluehead wrasse were born female and sex-changed after becoming socially dominant.