It's a juvenile Queensland Grouper, Epinephelus lanceolatus. They dont really make good pets... punch the scientific name into Google images and you'll see why...
it's a grouper, everyone is right very bad choice...
Who told you that bichirs would attack an aro ??? they are out to lunch lol Or they were assuming you were talking about a small arowana. Mine ive with several bichirs ranging rom 10" up to 22-24". Bichirs are one of the few tank mates i'd recommend with an arowana.
also "fresh water groupers" are not a true fresh water fish, they also are far to large for any home aquarium.