We are fortunate in having over 300 gorgeous Damselfish species to choose from, but not for the reasons that may first jump to mind. We need ample choices because many of these 3-4 inch beauties are real terrors in the aquarium (i.e. the well-named Blue Devil), able to intimidate fish many times their size. Fortunately, a good number are also reasonably well-behaved, and most fans agree that their colors and hardiness offset their sometimes difficult personalities.