Sunfish are perciforms ("perch-like" fish), and so are cichlids. I love African cichlids as aquarium fish, but dear god they can be total assholes. Electric yellow cichlids (originally from Lake Malawi) are probably the least aggressive of all, but will still get territorial towards non-cichlid species.

Electric blue cichlids are the meanest little fuckers around, and if they out-compete their tankmates for food, they will go on little fishy murder-sprees. There are a few different species that have that common name; I had a pair of Johanni/Maingano electric blues ages ago when I still kept an aquarium, and one of them started getting too big. I had to move him to a separate tank so the other fish (mostly electric yellows; also had a pair of haplochromis obliquidens AKA "species 44" or "thick skin" in there) could catch up growth-wise. I had some ornaments in the quarantine tank, since they like to nest in them. Well, this little guy decided to dig out all of the gravel substrate underneath the ornament and turned it into a fucking bunker. My fish was a Hoxhaist. :hoxha-turt: