A JD I kept alone in a fairly new tank was the meanest fish I've ever encountered. Shortly after he was added to the tank, he ate the danios I cycled the tank with (by wedging their heads into his mouth and ramming their tails against the sides fo the tank). When he was about 2" long, I added a 3" Tiger oscar. They camped at opposite ends of the tank for a couple of days. On the third morning, they ate together. When i got home that afternoon, the oscar had been ripped into pieces lo larger than the gravel they were resting on. By the time he was 6" long, he would breach to take live foods from my hand.