I love my Oscars, they are definitely my favourite fish, but heck do they have a lot of health problems? swollen abdomens crops up time and time again. there are various factors that can account for this symptom. Remember that a swollen abdomen is a symptom, not a disease or an illness. For this reason, it is extremely difficult to diagnose or cure. it could be something as simple as a digestive problems such as constipation. However, a blocked intestine can be very serious indeed.
Other reasons for swollen abdomen is parasitic infestation, bacterial infection, organ disease. So can see that diagnosis is virtually impossible in many cases. I would suggest that you treat the tank with a broad-based bacterial medication, it's worth a try. however, I don't hold much hope it would work. Also try the same with a parasitic medication. The best thing to do is try and get the fish to injest medication, preferably that has been given to you by a vet. unfortunately in many cases, the fish stops eating so getting medication and side is impossible. It's sad to say but in a lot of these cases, the sad situation is in the lap of the gods. Either the fish gets better, or it doesn't.
If the fish are still eating, try it with peas and see what happens. is the fish breathing heavily at all? that's about as much advice as I can give you at the moment. Any chance you can get some video, or even some good photos?
