I would agree w/ exodons or wolf fish in the 55.. 125-180 I'de lean towards some of the larger SA cichlids. Dovii and Odoe's come to mind but I've never personally owned either of these and i believe the Odoe would need larger?.. possibly the Dovii too. a single male or pair of the other SA cichlids would also fit the bill I think. Piranha's as well, there are many species out there. flowerhorns also have a rep, but personally i'm not fond of hybrids.