I don't know how aggressive, it isn't with other fish. He come from a very small tank, 2 foot, could barely turn around, and was an only fish, I have him in a 3 foot, still too small, but best I can do till I get the 5x2x2 running.
i did have a 2" electric blue acara in the tank when I added the O, which I have sinced removed due to it starting to trim the Oscars fins. I was told that the Oscar has eaten other fish, I have no idea what they were or size, however it showed no agreeing to ward the electric blue. It does charge at the glass of the tank though when it sees it's own reflection, so I'm guessing there may be some aggression if I was to ad a similar fish, although tank size may help.
one of the questions I have is, would it be better to hold off adding the Oscar till after I add the other fish to the new tank? Rather than adding him first?