I got a green sunfish, which i got when i only had goldfish and carp in my tank.Since i upgraded my tank he's the only fish i kept "indoor".
Almost 7 inch now and yes, He is somewhat aggressive...
He's just a predator who does not allow any fish in his hunting-grounds.No real damage on my silver dollars,though .He keeps them nicely in a shoal .He annoys my big plecos by just hovering an inch over their heads and just checking them out.
He respects my red oscar and stays out of the way.