The only thing I ever kept with my Red Belly Piranha were Plecos. Had two in a 55 with four nice sizr Rbps. They grew up with one another. One day when I was near the tank, one of the rbps decide to take a bite out of one of the plecos. Before I could do anything, the Rbp bit off half of the plecos head. I reached my hand into the tank, but it was too late. Damn shame, because they coexisted for so long. Never had that problem with my other pleco.