Wouldn't Nemo actually be a girl - people who understand clownfish?

Clown fish are a species. In each community there is one fish that is bigger than all the rest, which becomes the woman. When the female dies, the next biggest steps up and becomes the female. So Marlin would become a female after coral died. But then Nemo is taken away, and is the only clownfish in the tank, therefore the biggest. So wouldn't Nemo become a female too?