I have a community tank with rays, arowanas, eels, knifes, gar, cichlids, datniods, bichers, p bass, and a few other odd balls. 400 gallon 8x4x20'' I have 3 silver aroawans 30'' 28'' 25'' and 1 black about 22''. Ever night I can hear them splashing around but they seem peaceful whenever I watch the tank. Occasional nips but nothing that would make me concerned. These fish are thick and can take a few nips. I have had all four together for the last 15 months. They where raised in separate 180 gallon tanks till they reached around 18 inches. There is a lot going on in the tank and therefore I think they don't single each other out. I know its always suggested to keep them solo or three+. good luck.