The Sgt. Major Damselfish is an aggressive fish, so usually only one should be kept per tank unless added at the same time. An aquarium of 50 gallons or larger will provide a suitable environment. Although very aggressive they are considered reef safe. They are good for beginner tanks because they are very hardy. The Sgt. Major Damselfish is a common fish at all our dive sites! They feed on a variety of meaty items, herbivore preparations, and flaked foods.