I started off naming one "Phantom" because it has an orange cape on its back, like what the Phantom of the Opera wears in the movie. Then I named the runt with funny colors Mortimer, after Mortimer Mouse, who is also a little odd looking. But it's turned out that Mortimer is the biggest fish now and a the only solid, shining orange, so his name doesn't fit very well anymore.
I decided to go ahead and name the rest after characters, also. The one that used to be the biggest is Grendel, as the threatening one of the bunch. Then I decided to go along with the villain theme and name the other one Heathcliff, just because that's such a cool name.
What of the last? It didn't have a name for the longest time, but last night I thought I should do something my brother would appreciate. I thought, maybe something from Star Trek. He'd like "Picard," but that didn't seem right. So I thought about who the villain is on the Enterprise. Q. Yes, Q is the name for the last fish. Not literary or even booky, but it fits.