Difficult to say. Somebody else contacted me today with a very similar problem. Friend of mine had an Oscar which they unfortunately had to be put down . This fish was acting very similar to yours, it wasn't sitting straight in the water, it was actually sitting vertically. . I suppose there could be a possibility that there is a problem with the fishes swim bladder. Swimbladder disorders can certainly cause fish real problems. Unfortunately, it is quite difficult to cure. As for these swelling behind the fins, that isn't really a particularly good sign out you just don't know what's going on underneath, I have got to be honest with you, I'm really not sure. Like I said, I would hazard a guess that there is a swimbladder problem if the fish can't right itself properly. To get a proper diagnosis, you would have to visit a vet who specialises in fish. I will post another message tomorrow after I have had a good look through my fish health book. There may be something we can do to try and help. I really don't think the outlook is good unfortunately. Have you tested the water. I have to tell you that your tank is grossly overstocked with that algae eater. Those fish are incredibly messy and will turn water to crap in no time at all. Doubling up the Oscar, I dread to think what sort of bio load is being produced. You have to remember that poor water conditions is one of the main contributions to ill health. However, I am certainly not saying that this is what is causing your problem. Test the water, ammonia/nitrite/nitrate and post the results
