How to Stop a Damselfish From Picking on Other Fish

Purchase damselfish that look bright, healthy and active. Try to obtain fish that are all about the same size to discourage them from bullying each other. Also look for fish that are about medium sized rather than very small or large; small fish are more likely to be sickly, and larger fish may be older and thus have more difficulty adjusting to a new environment.

Rearrange your tank decorations just before placing the new damsels in the tank to break down established territories that your other fish may be protecting. If you are experiencing aggression with damsels that are already in the tank, rearranging everything can give the community a clean slate from which to establish new territories.

Place plenty of corals and rock into the tank to create caves, crevasses, and hiding spots for fish that the damsels may be picking on. Adding lots of decoration also acts to break the line of sight if a damsel decides to chase after another fish, giving the damsel the impression that the perceived intruder has taken his leave.

Do not overcrowd your tank if you are stocking damselfish. Overcrowded tanks mean more opportunities for fish to come into close quarters with each other, which translates to more opportunities for picking on each other. Overcrowded tanks are also harder to keep clean, and less than pristine conditions can cause a high degree of stress in many saltwater fish. The combination of in-tank aggression and water conditions that are less than ideal can be deadly for some fish, and should be avoided.

Feed your damselfish frequently in small amounts. Fish which are receiving a steady supply of food will be less concerned about protecting what they view as their hunting ground, and therefore less likely to harass the other fish in the tank.