Fish seems like an okay name to me. Just plain "Merfolk" doesn't sound interesting enough, but calling them Fish still establishes some sense to the name, until a new deck is created that is still called Fish, but doesn't use Merfolk...
Parfait seems like a great name. It DOES mean "perfect" after all, and what deck doesn't want to be perfect?
Trix is a silly name. It came from the rabbit on Illusions of Grandeur. I don't like the cereal and I don't think it's a good name for a deck either, but at least it's named for something that actually has something to do with the deck, rather than some guy I don't know...