Finding Nemo's Real Story
All clownfish are born male, and can permanently change to female — meaning in Finding Nemo, Marlin would have become Nemo's mom.
Clownfish (*Amphiprioninae*), made famous by Finding Nemo, have a fascinating secret: they can change sex, and all individuals are born male.
In a clownfish group living in an anemone, there's a strict hierarchy: - One dominant female (the largest fish) - One breeding male (the second largest) - Several smaller non-breeding males
When the female dies, something remarkable happens: the breeding male transforms into a female over the course of a few weeks. His behavior changes, hormones shift, and his reproductive organs transform. The largest of the remaining males then becomes the new breeding male.
This transformation is permanent and irreversible — once a male becomes female, she cannot change back.
Biologically speaking, this means Finding Nemo has a major plot hole. When Coral (Nemo's mother) dies at the beginning of the film, Marlin (the father) would naturally have become female. One of Nemo's brothers would then have become Marlin's new mate.
This system, called protandrous hermaphroditism, ensures there's always a breeding pair without having to leave the safety of the anemone to find a mate. Many fish species can change sex — it's much more common in the ocean than on land.