My Clowns must be the exception to this rule! As with adding any fish to an established tank you always run the risk of them fighting! I had 4 clowns (two Black Storm, one Wyoming White and an Ocellaris Clown) that were all added together! 8 months later I added a Snowflake, two Half Naked and a Platinum Clown) which have all been together now for about 10 months! I have never seen them fight! Oh sure, they may run the others away from their territory but they do that with any fish that comes near! I also have a very large Long Tentacle Anemone in the tank and 7 of the 8 clowns host! 1 does not show any interest! Bottom line is, you never know how they will react with each other! I have been lucky that mine have not yet begun to fight! I did have another clown in a different tank that would fight anything that you put in new! It is now in a tank by itself or as I call it, solitary confinement!