I have a Hawaiian trigger and he does it all the time. I notice it most when he's going for food and others are close by also when I put nori in the tank. It may be some kind of warning or excitement when others get close or he is startled. Also his tail fin straightens out. I am also training him to meat out of my hand and if I move to quickly he raises the trigger.
Originally Posted by Jam1e
it's to show that he's the boss and to show that he can't be eaten becuase he looks bigger
Not only does he look bigger but he is bigger. In my tank he is not the boss, the boss is the 1.5 inch Maroon clown. No one, not even the trigger messes with her and he stays away from her.