I once had a very cute one-eyed ranchu goldfish called
Jojo the Dog-faced Boy. I love ranchus and the way they wiggle.
A friend once had a betta called Chakotay, from
Star Trek Voyager. It suited him.
I've had other fish called
Fifi Lemieux, Mystery, and
Benoît.
If I had to follow your rule I might pick something like.... Chilchuck
Wallace Popple aka "Chilly
Willy".