When we got our pacu we put him in with our 2 oscars and they almost killed her and we had to trade them in. We have a couple of 2-3" convicts, a 6" Jack Dempsey, a 2" OB peacock, a 3" ghost knife fish, and a 3" blue acara. and they all love each other the knife fish espicially loves Kia (the Pacu) Our pacu is not that aggressive but will eat anything if it will easily fit in her mouth. Anyways hope this helps.