Clownfish are transsexuals.  Clownfish live in a hierarchical society led by a dominant female. If this female were to die, she would be replaced by her mate. The male changes his sex and every other fish follows suit, moving up a rung on the social ladder. Clownfish also maintain a body mass 20% smaller than the fish that outranks it. 

To summarize – in Finding Nemo, Nemo’s dad should have become a woman and mated with his son after locating him!
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(via omgfactsofficial)