Steph, I'm so sorry about your babies. :( *hugs*
The bacteria flexibacter columnaria - also known as cotton-mouth, mouth rot, mouth fungus, or just plain columnaris - is pretty much the one to blame for tissue eating. There are other bacterias that cause ulcers and lesions but generally, it's acute columnaris that causes that severe tissue necrosis. There are also some fungus and parasites that can cause tissue damage but usually it's bacteria that deals the finishing blow.
I'm like a typing encyclopedia of yucky fish trivia.
Tisia, aaaah, now there's an idea. :) Your fry are looking so adorable too. :D
Gossip, I always tell my mom this quote out of the movie Driving Miss Daisy. "Sometimes I don't think you got the sense God gave a lemon."