I keep mine sola, cool looking fish that stays motionless on top. I picked up mine from a dozen in a lfs tank, all showed damage on their nose from jaw locking or banging on the glass. PTC are nasty fish towards their own kind, but peaceful to other fish. Like any tetra, they have visible sharp teeth In their mouth. There are 2 species of PTC under the same name, so find out what you have.