Our Oscar ate a huge yabby and eversince he ate it, his been acting strange and he started off by doing summer saults and back flips inside the tank and keeps hitting himself like asif he doesn't know what his doing and now parts of his body is swollen because of it. He seems to be breathing fast and this morning i woke up his laying on the ground and once, laying upside down.... He also keep trying to swim up to the surface but when he goes half way, he does these summer saults and just falls to the ground.... Before he ate that yabby, i changed the water... maybe it had something to do with that.

Okay, first things first, you need to test the water for ammonia, nitrite, nitrates and pH. Fish will often dart about hitting themselves against the side of the aquarium if there are toxins in the water, or impurities. Well suggest you do is do several large water changes over the next few days and see if there's any improvement. There is of course remote chance that there is an internal parasite but I don't want to go down that road just at the moment

I think that maybe the answer... the water change that i did infected the oscar. Or white one just died and now one of the baby ones are doing the same. I changed the water after i took the white oscar out