Its true that many Piranhas (including RB's) are skittish, shy and timid. However, rhoms, both peruvian and venezuelan, (among others like black diamonds, elongatuss, altuvie, irritan for example, in fact, any Serrasalmus piranha is highly aggresive and suggested as single speciman tanks) are very, very, very aggressive and active. A buddy of mine had once had a peruvian rhom in a huge tank, 125g I believe, and it would growl when you enter the room (a growl that could be heard 20+ feet away). The water would vibrate and drip out if the level was high enough. He would attack the glass trying to get the dog that would trot by. He would follow me viciously as I mover around the tank. It was an amazing thing, I cared for it while he was on vacation and I had to use a seperater (a home made one with steel mesh) to clean the tank. If you see the jaws on that guy and the look of the red eye, you would be amazed. It complete tore up his tank; fake plants, heater, airline tubing, structures, filters, etc.... If something was in his path, it was gone the next hour, if not then. After gvacing I would move rocks around, you could hear the rocks scrape the glass as he pushed all obstructions into the corner. His nose had a permant dent that was formed from ramming the glass and decor and rocks....Completely crazy and aggressive beyond belief. The most common thing is that the most aggressive piranha is the one that is the starving. A red belly would not hesitate to tear into anything if he was hungry enough. Just a little info I thought I'd share.