Clown fish starts off as males and turn into females

Clownfish, also known as anenomefish, are sequential hermaphrodites and live in very regimented schools made up of all males and one female.  The group is made up of a hierarchy with the female fish being the dominant and generally the largest fish in a given group.  The second in command of the group is usually the largest male, who is also generally the most aggressive male of the group.  This male will pair off with the female to breed.  The rest of the males in the area will not breed with the female.

Upon breeding, the female will lay sometimes thousands of eggs close to their home, usually on a rock or coral.  The two will then take turns guarding the eggs until they hatch around a week later.

If the female dies, the dominate male will then begin to gain weight and will become the female of the group.  It will then choose a breeding partner among the available males, which is usually the largest male available.  The two will pair off and breed together until something happens to one or the other, at which point the cycle begins again.