Guys, I hate to say it.....but Disney's clean on this one. Pixar is 100% responsible for all content creation, Disney is simply the distributor and marketer of the films.
That said, I think Pixar is clean on this one too. Parents dying, going on a lone journey, etc. is all part of children's stories. All of them. More than one person was bound to write a story about a clownfish. As someone that's had aquariums, I can honestly say clownfish are about the most interesting fish around.