hey, i've posted on another page about rb piranha tankmates....i have had a single r.b.p. for 3 years now in a 75 with a pleco, a frontosa and convicts. no one has fought, (except for maybe some baby convicts getting eaten)....the piranha is not even skiddish as they usually are. i think it is best for piranha to be in a school, but i took this guy from a friend who bought him not knowing he would grow so large. he seems healthy and happy after three years with his tankmates...if given the choice, i think piranha should be in a school, but if they are already singled out, then tankmates are possible....