Over about 3 to 4 months there has been a lump growing on my diamond tetra and it at this point has become so large I it is killing the fish. It wasn't too noticeable at first.
It seems to be just beginning in other ones as well but haven't gotten as large yet.
Thought maybe it was just a distended stomach so tried changing foods in hopes they weren't sucking air or anything.
It is hard to the touch.
Here are some images.