Let's just say it involves child-parent relations that would make Oedipus blush.
Father and mother clownfish are tending to their clutch of eggs at their sea anemone when the mother is eaten by a barracuda. Nemo hatches as an undifferentiated hermaphrodite (as all clownfish are born) while his father transforms into a female now that his female mate is dead. Since Nemo is the only other clownfish around, he becomes a male and mates with his father (who is now a female). Should his father die, Nemo would change into a female and mate with another male. Although a much different storyline, it still sounds like a crazy adventure!
Cooney says he won't be surprised if Pixar robs us of the scientifically accurate version of the Nemo sequel, Finding Dory – then again, the studio apparently did change the movie's ending thanks to the devastating Blackfish documentary. No small victory there.