That is true confirmed even if the Arowanas were male and female doesn't mean they will pair. Definitely a fight can erupt which I had tried many many times, this was the only pair that didn't. The size of the tank definitely matters also. I don't know about two Asian but I have housed 3 Asians a hbrtg, crossback and chilli for about 3-4 years. Got them at 6-7 inches now their about 20 plus inches I would say with the chilli being the biggest. I housed them in a 120gallon. I find that a odd number works a lot better