hmmm, I have lost a flower horn to the same sort of problem. Then a Oscar that we had for years swelled up. After loosing her the other day i decided to open her up and see if i could find what is the problem. I found that she was full of a fluid and a grey to black jelly subsance that had seemed follow her reproductive system. I still have one oscar that is developing the same thing. I think all fish so far have been female. They have all been digging pits when symtoms started. I am now left with what i think is 2 male and one female oscar that i have grown from babys to breed and im worried that it is too late for the last female i got.