So I did my research and common tank mate's for an arowana are fire eels. I've seen and heard of many being perfect tank mate's. So I got both and raised them from a young and small size. Apparently my arowana is a bit more aggressive than others. The arowana at the time was about a foot and a half long and the fire eel was quite longer. Well i came home one day to find the tail of my fire eel sticking out of my arowana mouth. Unfortunately I was too late and lost a gorgeous fire eel!