Thanks alots for all your helps guys. Yeah, he's still little and act like a baby. Before my friend isolated him by himself in a 30 gals tank. Then when I got him, I put him together with my Pacu, but they didn't get along, he beat up my Pacu everyday ( The Pacu is bigger than him twice ), so that's why now I put him together with my parrot fish. He's chasing the small parrot fish all the time but he also get chased by the big parrot fish also. But I don't think he's happy when live together with other fish. I will figure out a way to isolate him again, he will have his own tank soon.
Thanks again guys.