hmm... don't think that mix is a particularly good idea. we used to keep oscars and some other fish and in the end gave ALL the fish back to the fishshop coz watching our tank was like watching a battlefield.

we also have an arowana at the office, who used to share a tank with small garbage-fish (sorry, dunno the name for those fish that clean the aquarium) and one day our arowana picked up the poor garbage-fish and swam around with it in its mouth until the poor thing was so terrified. We had to change the garbarge fish for a much bigger one.