Red Bellies. pygocentrus nattereri. I stopped by and saw them today. The girl who took them in thought they were pacu. The one looked liked it tried to jump, and slammed into something good, but otherwise looking as good as can be expected being brought in a 10g tank. (They're in a 40 right now)
I know 2 isn't a good number to keep, but apparently some dude stopped by the store with the two of them in a 10g aquarium. We're there more? Who knows. They were suprisingly not skittish for piranha, I have to say. Usually my 4 year old scares most fish. (He just gets excited, not bad about it) but these two were just kinda hanging out.