I separated my Oscar a few months ago in order to bring in some smaller fish. Three weeks ago I re-introduced it into the 240 gallon when I brought home some other big fish. Immediately my new 14 inch Rio Jaltpec Zonatus went after it. It didn't look like he was biting the Oscar, but clearly did not like it and was bumping it with it's head. This happened for about a day and then it stopped. When I put the Oscar in the tank I could see on it's side some skin color loss. It almost looked like scarring. Today when I eyeballed him, I could see it's skin on it's side was missing completely. I mean it looked pretty bad. If you look to the right, that's how it looked originally when I put him in. He is still swimming around OK and eating. Any thoughts on this?