I had five in one tank for a period of 2 years. If anything, make sure to feed them! I went on vacation for 4 days, and came back to find that one was eaten up to the back of its head. It looked like a surgical cut... on top of that, it was still snapping at me when I pulled it out! Other than that, they used to freak out my GF b/c they would line up on the bottom of the tank, shoulder to shoulder, and stare at us. They would move in unision, changing their angle so that they were always watching us. It was messed up man. I will never keep those again. The staring thing... it made me nervous. They were plotting. I swear to god they were plotting.
Aside from all the evil plotting... they are Pacu's with teeth (dumb and ugly).