No aggression at all. None from him or any fish towards him. I was curious if any of my fish would be aggressive since I have five tangs and various other fish. Everyone gets along great. I put him in the tank close to lights out and he went to a hiding place for that night. The next day he was swimming around the majority of the time and spent some time in his protected spot. The third day he has been swimming around the entire day and goes in his spot at night to sleep.