The Damselfish, is an extremely popular marine fish because it is readily available and because it is very hardy. Although we don't recommend it, many hobbyists use this fish to cycle new saltwater tanks. They can be very belligerent with other fish in the tank, especially new arrivals. They are very bold and can hold their own with larger fish and may even go after your hand if it approaches their territory. They didn't get the memo about them only being a few inches in size. As mentioned previously, Damsel fish will develop their own territory in the tank. Having live rock in your aquarium will help make them comfortable and it will provide them with hiding places. You can get away with keeping multiple Damselfish in the same tank if you introduce them at the same time. Because of their "anger management" issues it is a good idea to introduce them last into your setup. Damselfish are not very picky when it comes to fish food and should accept most foods that you give them. Try to give them a varied diet of live, frozen, freeze-dried and vitamin-enriched flake foods. They seem to be very resistant to most saltwater fish disease .