Chrysiptera parasema, also known as yellowtail damselfish, yellowtail blue damsel, goldtail demoiselle, and other variations, is a popular saltwater aquarium fish from the Indo-Pacific. It was described by Fowler in 1918. Appearance C. parasema is a small marine fish that reaches 2.8-3 inches in length. It has a spiny dorsal fin and is laterally compressed. Coloring C. parasema is blue with a distinctive yellow caudal fin (tail fin). The yellow coloring may extend up to the back of the anal and dorsal fins, especially in species from Papua New Guinea. These fish may also have yellow pelvic or pectoral fins. However, yellow is never found on the backs or bellies of Yellowtail Blue damsels. A yellow belly likely indicates that the fish is actually an Azure demoiselle, whereas yellow areas on the nose or chin may indicate that it is a Blue Devil damsel. Habitat Yellowtail Blue damsels prefer densely populated coral groupings in sheltered lagoons and inshore reefs, and generally remain between at a depth of between 3–52 feet (1–16 m). Breeding and reproduction In the wild, male C. parasema have their own territories, located near a nesting site. Each territory contains eggs from previous females. The females will swim around inspecting each male and its territory before choosing one based on its size and the number of eggs in its territory. As a part of the evaluation, the female will display a light ring around her eyes, and the male will respond with its own displays. The next day, the female will spawn with the chosen male. An individual male can have up to 10,000 eggs from different females. Males often abandon their territories to claim territories with more eggs, as this makes them appear more favorable to the females. The eggs hatch after up to 4 days, depending on temperature, and the male is responsible for guarding and caring for the eggs. The subsequent larval stage can take 10 to 50 days. Behavior and diet Chrysiptera parasema contain chromatophores and can change color in response to external stimuli. When stressed, they can turn darker to conserve energy. Adults are usually found alone or in pairs, while juveniles are more likely to remain in small groups. C. parasema are omnivores. In nature, they feed on plankton, algae, and small benthic crustaceans. In the aquarium Chrysiptera parasema is a popular fish in the saltwater aquarium hobby. Because of its