My Oscar was attack in the night by my other Oscar. the injured Oscar hasn't eaten in three days and his scales are falling off. http://i262.photobucket.com/albums/ii111/evila727/fish1.jpg

What should I do?

Hi evila727, wow that appears to be a fairly significant injury. The good news is oscars have amazing regenerative powers. The first thing to do is ensure your water is as pristine as possible, generally speaking clean water is the first step in most aquarium issues. To promote healing your nitrates should be as low as possible ( I would recommend no higher than 10 ppm). Also, depending upon what other tank mates your O has, a dose of salt will aid in osmoregulation. 1 tblspn per 5 gallons of water should do the trick. If the oscar begins to show any sign of infection treating the tank with pimafix and melafix is what I would do.

I would add a treatment thats treats fin rot or body sores to help things along