Hi Katie Bugg: If your Oscars stopped fighting, then maybe that's it, one of them established dominance and the other accepted it. In my limited experience, my two youngsters, at 5" and 3.5" then, displayed some nasty aggressive behavior and I ended up splitting them for a few days. Afterwards, I brought them together and nothing really serious happened. Note that the first time they met they were in a tiny tank for them, a 26UKgal tall tank (I was waiting for their home tank to arrive).
If you didn't see the aggression when it happened, it could be that the injured one bruised with something in the tank while moving around fast, as the issues between them were being settled. That said, in my particular case, almost three months later, they paired-off and are parenting their first fry as I write these lines.
What tank size do you keep yours? Do you have some driftwood or stones that they could use as landmark for taking over/claiming some tank territory? Since it is impossible to tell male from female until they actually lay and fertilize eggs, keep in mind that if aggression goes out of hand and one or both is/are getting really hurt, you may have a rare, but not unheard of, case of two particular Oscars being not-compatible to share a tank at all. Hope that's not your case.
If your water parameters are in check, they usually heal in no time from this type of lesions, at least mine did.
Pepe
Santo Domingo
