Not all fish are created equal ... if you do some searching on this site in the video lounge you will find a video titled '' RBP'S & OSCAR vs RAT " after seeing this video cichlid's and pirhana can live in the same aquarium provided space is there ..
if your asking who would win in a fight ?? well that again depend's on the fish..
I'am not saying a goldfish will kill a pirhana but one on one there is no reason a dovii could'nt kill a pirhana... size help's and there are large pirhana too...
Im assuming your asking what would happen if a Dovii and a piranha fought. I have no doubt the Dovii will destroy and murder any type of Piranha. Hands Down. Why do people continue to think Piranhas are the extreme killers. Dumb a s s OVERRATTED Piranhas.