I have kept Arowanas and Peacock Bass together a couple of times. If your tank is tall enough you could probably keep Arowanas, some bass, and some stingrays together. Arowanas at the top foot, the bass in the midwater level and the rays at the bottom. I've kept Peacock Bass with Silver, Black and Jardini Arowanas in a 250 gallon (8" 2" 2") and a 360 gallon (8" 3" 2") with no problems. I have got a 12 inch Black Arowana with a 12 inch Temensis in my 360 gallon with no problems ever since I put them together (about 6 months now).