Started a few (2) years ago on one fish thought it was some kind of fish tumor and it wasn't dangerous to my other fish but now 6 of the 17 fish in my pond have it.I'll post pictures please help, I'm kind of stumped with this one. They are not flashing or gasping, What is this thing? It kind of looks like a bubble but starts out looking like a small sore on them. I've included pictures, please help me out