IMO depends on the datnoid /arowana. i have a dat that is about 9 inches and is the nicest fish which would never touch or bully my other fish no matter the size. on the other hand i have another datnoid 3 to 4 inches which i had to catch and separate from my 6 inch tems and orinos because it constantly chases the bass, to the point that the bass gets scars.... tried rearranging the decor in my tank but still the same. the fish is just too damn aggressive. i dont think that there is a sure answer to your question except watch your fishes and at the first sign of aggression separate them.
