i wanna share my story, i bought two oscars a couple of days ago because i wanted to add some sort of cichlid to my arowana tank. the moment i added those two tiger oscars to my tank, they immediately chased my school of silver dollars. those guys are 4 to 5 inches. the oscars are roughly the same. then saw my flagtail and also chased him and bullied him. the flagtail is 10". then turned their attention to my silver aro, almost 14". they didn't mind the difference, they bit him and got his scales. so before they wrecked more havoc i just isolated them in my spare tank. my point is that you cannot just add anything to oscars because they are plain mean. you should always be careful in choosing. i'm not saying that this is always the case but most of the time they are just like that.