Originally Posted by bruinsbro1997
I would not recommend a jack Dempsey for a thirty gallon, they get a foot long and require much more space to stretch IMO
7-8" is more typical, which is how most reference books list them. That shouldn't be a problem in a 30 long. (OP didn't state dimensions.)
Not that I'm pushing them; I only meant to cite examples of some often overlooked, tough, personality fish that a child might enjoy, which can often be found cheap at an LFS
or even at PetSmart. There are lots of others.
For myself, I'd have an Angelfish; Goldfish are beautiful, but too boring for my taste as a "pet". If I were buying for a boy, I'd probably opt for a Firemouth. Better yet, I'd make a list of candidates and let him choose the one he likes.