i would say the wolf cichlid is aka Dovii its hard to keep it with other fish seeing as they just kill for the hell of it, i have a 7cm one and it killed my jag witch was 12cm and had its fangs comeing out as well, the fish was made to kill the only other thing i can think of witch might kill it is the murry cod, but it gets to 150cm thats why.
I think that the nastyest fish that I have seen would have to be a GT And by the way the Peacock bass is a Cichild I have a bluegill and he is a very peaceful one but of course it all depends on the fishes attitude
My Pike Cichlid was ruler of my tank. I had to remove him because he was so aggressive that no fish would move from the corners of the tank. Extremely fast and powerful...
depends on the physical atributes of the particular species and the personality of the particular fish... one of a species may be laid back and another would be ready to kick a**