Clowfish are all born male?

The most dominant male becomes female if necessary. 

A lot of people know the famous clown anemone-fish, known as clownfish. These orange and white fishes live together in reefs and most of them are small. Almost 4.3 inches (11 centimeters) is their regular size. However, a couple of them are slightly bigger than the others. Naturally all clownfish are born male, but they have hermaphrodite’s features. Only one female is allowed on each group at the same time and only the most aggressive male of the group can breed with her. When the unique female dies, the actual male who was allowed to breed turn himself as the new female of the group and the most aggressive male available fill that spot. This change of genre is irreversible. The rest of the males in the area are not allowed to breed with the available female.

This changing process is a peculiar ability this fish has. When the female dies, the actual dominate male gain weight and size. Now as female, this fish will breed with the most dominant male available until something happens to one or the other. Those fishes lay thousands of eggs near to their anemone which they use as home. Some theories state that this ability happens because clownfish do not use to leave their anemones, so it would be hard to find breeding partners. 

Sources: Huffington post, National Geographic and Today I found out