I have an Azure in my 40 gallon and I've added fish to the tank after him. Azures are one of the least aggressive damselfish. Every fish has it's own personality so it's really hit or miss. Since the addition of my damsel I've added a midas blenny who quickly became the boss of the tank. A platinum clown that the damsel showed no interest in, a pygmy hawk that he didn't bother, a mandarin that he didn't bother either, and an orchid dottyback. He did go after the dottyback the first day but hasn't bothered him since. It's been months and my over crowded 40 gallon is very peaceful. It also has a sixline in it as well.