I have them in a 150g. There is a pecking order but they have been together for 2 years or so and do not do much more than take a nip out each others fins every once in a while. They were about 4-6" when I got them. Here is a pick of my largest out of water several months ago. He has grown about an 1" since and has gotten thicker.
They are well fed. The eat pellets which is great & Krill mostly. When it's feeding time, water changes or if I move decor around is the only time they are really aggessive with each other but never anything serious.