The swallowtail angelfish, a member of the Genicanthus genus, stands out in the marine aquarium hobby for its reef-safe behavior and distinctive forked tail. Unlike many angelfish species, it does not pick at coral, making it a suitable addition to reef tanks. However, its size and swimming needs demand a large aquarium—at least 125 gallons—and a commitment to careful husbandry.
Native to the Pacific Ocean, this species is commonly found around Fiji, Indonesia, and the Vanuatu islands. In the wild, it inhabits moderate to deep waters on steep slopes, often seen in groups of one male with several females. This social structure is reflected in its behavior in captivity, where it can be kept as a mated pair or a small group of females with a single male.
Distinctive Appearance and Sexual Dimorphism
The swallowtail angelfish is also known as the blackspot angelfish due to a black spot on the male's breast. Males display a pale body covered with vertical red stripes, a forked yellow tail with blue edges, and a yellow band at the base of the tail. Females are blue, fading from darker at the head to lighter near the tail, with a mostly yellow dorsal fin and a white tail outlined in black. These clear differences make it one of the few angelfish species where males and females are easily distinguishable.
This species is a protogynous hermaphrodite, meaning all individuals hatch as females. If no dominant male is present, the dominant female will undergo a sex change to become male, a process that can take up to 30 days.
Tank Requirements and Compatibility
Given its active nature and potential to reach seven inches in length, the swallowtail angelfish requires a spacious tank of at least 125 gallons. It appreciates strong water movement during the day, which can be provided with pumps on timers, and well-oxygenated water is essential. A tight-fitting lid is necessary, as this fish may jump out of open aquariums.
In terms of tankmates, the swallowtail is generally peaceful and will not bother most fish. However, it may chase small planktivores like anthias. It should not be kept with aggressive species such as triggerfish, large angelfish, or most surgeonfish, as it can be dominated. Males will fight with other males of the same or similar species, so it is best kept alone, as a pair, or in a group of females with one male. Ideal tankmates include clownfish, blennies, gobies, chromis, butterflyfish, small lionfish, and eels.
Diet and Feeding Considerations
As a planktivore, the swallowtail angelfish feeds on zooplankton and algae in the wild. In the aquarium, it should be offered a varied diet of finely chopped shrimp, frozen brine and mysis shrimp, and marine algae-based foods like nori or spirulina-enriched pellets. It tends to gulp food from the surface, which can lead to swallowing air and temporary bloating. Feeding sinking foods can help prevent this issue.
Breeding the swallowtail angelfish in captivity is possible with the right conditions. Males perform elaborate courtship displays, including rolling onto their sides and quivering their fins, to entice females. Once a female is receptive, the pair will release eggs and sperm simultaneously.
For aquarists interested in this species, it is important to note that it is considered fragile and difficult to ship. However, a healthy specimen will often settle into aquarium life quickly. With proper care, the swallowtail angelfish can be a rewarding and visually striking addition to a large, well-maintained reef system.