Wow its been a while since I posted here. Good to be back...Anyways,
I have a friend who owns a 10 footer. Inside are 8 asian arowanas and 6 silver arowanas. From what I have observed, it appears that interspecific (different) species of arowanas can tolerate each other, but are more aggressive toward members of the same species. Feuds break out between two silvers, or two asians, but never between a silver and an asian, regardless of size.
Based on this, I can make an assumption that maybe body shape has something to do with triggering aggressive behaviour among arowanas, but that is just an educated guess.