I have the same hoplias malabaricus species as the one in the picture Bullterrier posted. It has been housed for about 6 months in a 150 gallon with a leporinus fasciatus, a species of tandanus (eel-tailed cat, but not quite sure which!) and a pike cichlid (crenicichla johanna). They are all about the same size, approximately 8-10 inches. I would not say they get along wonderfully, but they all respect each other and there is very little bickering. The tank is filled with a large amount of driftwood and large rounded rocks, which offers plenty of boundaries and reduces squabbling. The wolf fish tends to hover or lay parallel to a piece of wood and appear to blend in with it. Definitely an ambusher, but will occasionally make quick chase attempts halfway across the tank. It will take any live fish that can fit in its mouth and also smaller crayfish.