Sex change in fish
Some fish change sex during their lives: clownfish from male to female, many groupers and wrasses from female to male.
Also: sequential hermaphroditism, protandry, protogyny
Sequential hermaphrodites start life as one sex and change to the other. Clownfish are protandrous: a group lives in one anemone, the largest fish is the breeding female, and if she dies the largest male becomes female. Many groupers, wrasses and parrotfish are protogynous, changing from female to male as they grow. That matters for fishing: taking the largest groupers removes most of the males. The barramundi, the Asian sea bass of Indian coasts, is usually male first and female later.