I know this is old but I have a pacu and a red devil together and yeah they fight from time to time but nothing to serious. But pacu are meant to be raised and then eaten . It’s not a forever fish no matter how big a tank you have. They get to big. My tanks only 100gal but that will allow the pacu to get big enough to feed my whole family. And if you think I’m weird for eating it you should know he is a food fish we’re it comes from and is quite tasty.