If your arowana is not overly aggressive (like my one) I have flagtail (if you have rays then flagtail not a good idea in my experience with brown rays.. he leaves black rays alone) clown loaches, rays, geos, electric blue acaras, datnoids, severums or any mild mannered cichlid that is not aggressive towards the aro
Then you should be fine with almost any fish that doesn't become aggressive towards the Aro
I don't know how big yours is, if he is small, the character could still change as he gets bigger.
I don't have a problem with mine
My son has a small chilli red, she is about 20cm, and she has a different character and is very cheeky towards tank mates, we will see how she turns out as she gets bigger