Japanese Swallowtail Angelfish

Geographic Origin and Biotope: Western Pacific, ranging from southern Japan (including Izu and Ogasawara Islands) to the northern Philippines and Taiwan. Inhabits deep outer reefs and current-swept channels at depths of 15 to 100 meters.

Taxonomy and Morphology: Member of the family Pomacanthidae. Grows to a maximum length of 21 cm. Slender body shape with a long, lyre-shaped caudal fin. Sequential protogynous hermaphrodite.

Social Behavior: Peaceful, active, and social water-column swimmer. Lives in harems led by a single dominant male. Spends the day in open water foraging for microscopic food.

Coloration and Sexual Dimorphism: Distinctly sexually dichromatic. Males display a bright yellow head and greenish-yellow flanks marked with numerous vertical black stripes. Females are plain grey-brown dorsally with black margins on the tail and a black forehead bar.

Aquarium Setup: Requires an aquarium of at least 500 liters with plenty of open swimming area and strong, well-distributed current. A secure lid is mandatory as they are highly prone to jumping.

Diet and Feeding: Planktivore. Feeds naturally on zooplankton. In captivity, it readily accepts frozen mysis, brine shrimp, finely chopped krill, copepods, and high-quality pellets.

Water Quality: Requires stable parameters. Temperature 20–25°C, pH 8.1–8.4, salinity SG 1.020–1.025, GH 15–25, and KH 8–12. High sensitivity to poor organic filtration.

Compatibility and Tankmates: Excellent for reef aquariums. Completely reef-safe; it does not harm corals or sessile invertebrates. Can be kept in pairs or small harems.

Aquarium Reproduction: Undocumented in home aquariums. Broadcast spawners in nature releasing pelagic eggs.

Risks and Diseases: One of the hardier Genicanthus species. Can contract marine ich (Cryptocaryon) if stressed or introduced into bare, coverless tanks.