Groups of one to three of the same species is the rule, since two fish will result in one constantly terrorizing the other. Even though they are small do not underestimate their aggression. Avoid placing them with fragile species and watch for freyed fins, heavy breathing, hiding and other signs of aggression. The huge number of damsels makes detailed describtion of them out of the scope of this paper. Fortunately you can lump them into different categories for many species are just variations on a theme.
Lets look at five of the major damsel groups seen in the hobby.
The clownfish can all be readily identified by their conspicuous orange, white and black coloration. Like other damsels they can change sex as they age, with smaller specimens being males and the larger female. They breed quite readily in captivity if the water quality is good. While not mandatory, it is good to put them with an appropriate species anemone to insure good health and encourage interesting behavior. The domino and black and white striped damsels are both some of the most aggressive and hardy of the damsels.