CichlidFish.com - Fish That Think.

I have 4 12" oscars in a 125 gallon tank. They are about five years old. One of them just recently started staying upside down on the bottom of the tank. He does go right side up sometimes,he eats, but it seems when he does come up he fights with the others. I don't know if they are males or females. Has this ever happened to anyone?

Sounds like its a swim bladder problem. Possible an infection, or maybe a diet problem.

I had the exact same thing happen to my Oscar last year!
She went upside down and not eating and barely breathing for three or four weeks! I put her in her own 30 gal tank and treated with whatever anyone would tell us. No one ever answered the question of what it was but for almost a month she was almost dead and then one day she flipped back over and started swimming. I have no clue what meds worked because I was to the panicked point of adding everything I could find that might help. I thought I would wake up to her dead every morning.

She has been fine for at least 6 months now. It was weird but don't give up until the fish does. I had vets and experts from all over saying there was nothing to do she was as good as dead. Not true. Though with two large Oscars in my 55 I started vacuuming twice a week instead of just once. Just paranoid I guess.

probably internal. try a parasite med. check temp. of water too. water that is too cool can case swim bladder issues.