Based on my experience and others that I know, they are extremely aggressive. He was the last fish added to my tank, mostly wrasses, and he would chase the other fish non stop. He would never attack them, but he would force them into hiding. After a short period of time, I had to pull him from the tank. IMO, they are a beautiful hardy fish, but I would only get another one if it was going into the right environment (aggressive tank). I know that each fish is different, and hopefully, he works out for you.