well at first i had some trouble with my tank mates they were 1 silver aro x 20cm---
2x 13 cm silver dollars,2 x 8cm archers & 2 x 8cm oscars.
tank size 4x2x2

my silver arowana became aggressive but only because the archers competed for food with my arowana,,now a few days later they are all good friends.
and most definately arowanas will eat anything thats fits in their mouth or even slightly larger too.
cheers chris