I would watch it closely, but if you don't have any problems with bullying or anything I say keep it nd good for you. I havn't seen anything like that before.
i have, it obviously one of the PACU species, google search pacu info or soemthing, or image search pacu, i am sure you will find it is a certain type of pacu, they come from brasil and in general south america, some species get HUGE, they are closely related to pirahna's but lack the teeth and the nasty dispostion, they are generally compatable but grow very big, and will eat most things that will fit in their mouth.
hope that helps.
kubora666
I have looked all over and it just doesn't look like a pacu to me. Maybe it is because it is smaller than most of the pictures of pacu that I have seen. The dorsal fin on a pacu just doesn't appear to go as far back as the dorsal in the picture. And a pacu just looks a little different in where the weight is distributed on the body. Pacu seems to be more heavy below the center line whereas this one seems to be a bit more meaty body above the center line.
And just so you will know this isn't my fish. I am just trying to figure it out for someone else.