I know this thread is from a while ago, and it was brought back from the dead but...
Titan-Ty (Ti), Ty-ty, his name
Kreios- Mister, Little Guy/Boy, his name
Deimos-Dye, Dice, Dicey, his name
Irene (RIP)-Girlie (I almost never called her Irene, only Girlie. But I didn't think that was a very good name so she had a "real" name XD )
Also, I call all of my males "Buddy" and/or "Buddy-boy"
EDIT: I seem to recall also calling one or more of my fish "Dumbo" or something of that nature. Don't ask why, I don't know.