some fish change sex over the course of their life. this phenomenon is called "sequential hermaphroditism". in clownfish, smaller fish are male, and the dominant and largest fish in a group becomes female. in many wrasse the opposite is true—most fish are female at birth and become male when they reach a certain size. sequential hermaphrodites may produce both types of gametes over the course of their lifetime, but at any given point they are either female or male.