Never heard of any problems unless you have a very aggressive Oscar! Which doesn't tend to happen as they are commonly peaceful pigs lol. My local petsmart has a 50ish gallon bowfront tank. Hey have at least 13 oscars in there! The owner is "growing them out" but he says he's keeping them in that tank! I tried to buy them and he said no! But there are albinos,ruby reds,tigers,reds,golds,and platinum oscars in there. It's horrible!
-Andrew