Just some thoughts - but that is one major beer belly! I doubt it is from eating flatworms. My guess is a blockage in the gut, ascites (fluid build up), or a tumour. Hard to say which, though. Ascites is usually due to a bacterial infection. If it was a bacterial infection, your fish would probably show other signs of septicaemia. Alternatively, it could be a fluid filled abscess - which wouldn't be good (as it could tear open any time). My guess is that's itââ"šÂ¬Ã¢"žÂ¢s a blockage in the gut. Any chance you can catch it? I suggest this as you may try a couple things to loosen up potential blockages such as feeding veggies (I know, tough with this type of fish) or putting the fish in a concentrated Epsom Salt bath? You might try doing a search to see what other ideas turn up for moving gut blockages. Lastly, if it is fluid build-up, you could also try draining it, but that would require specialist veterinary intervention. This would essentially involve catching and anaesthetising the fish and aseptically making a very small incision to see if the belly drains. Sorry I can't be more helpful, but like I said - just some thoughts.
