The Blue Ring or Blue-Ringed Angelfish is also known as the Annularis Angelfish. The Blue Ringed Angelfish is very territorial, so only one of the species should be kept in an aquarium. A tank size of at least 300 gallons is recommended for this size fish. Also, the Blue Ring should not be kept with other angelfish as they will fight aggressively. An angelfish should be introduced last in a community tank. Possible tank mates include Dwarf Angels, Wrasses, Damsel Fish, Clown Fish, Butterfly Fish, and Tangs. It should have hiding places and live rock for feeding. If your angelfish doesnt have adequate room, it will be more aggressive.