paOol that is not true. Just because pirahnas are from the same "family" or genus does not mean they can be kept together. For example only two species of the genus Serrasalmus can be kept together with somewhat success, Geryi and Spiloplurea (sp?). Mixing other species of this genus with each other or the previous mention two species will most certainly end in the death of one or more fish. Conversly members of the genus Pygocentrus can be kept with each other. However, even then death due to aggression is almost a garuntee in the longrun.