Masked Swallowtail Angel - Genicanthus semifasciatus

Masked Swallowtail Angel (Genicanthus semifasciatus)

The Masked Swallowtail Angel is an elegant marine angelfish admired for its streamlined body shape, graceful swimming style and striking sexual differences between males and females. Unlike many larger angelfish, Genicanthus species are primarily open-water planktivores rather than coral grazers, making them one of the more dependable choices for reef aquariums. Peaceful, active and highly attractive, this species is best suited to spacious, mature marine systems with excellent water quality and plenty of open swimming room.

Common Name:
Masked Swallowtail Angel, Japanese Swallowtail Angelfish

Scientific Name (Latin):
Genicanthus semifasciatus

Maximum Size:
Approximately 20–22 cm

Water Type:
Marine

Origin / Natural Habitat:
The Masked Swallowtail Angel is associated with deeper reef slopes and offshore reef environments in the western Pacific.

It typically inhabits open water close to reef structure, where it feeds on plankton while remaining near caves and overhangs for shelter.

Water Parameters:
Temperature: 24–26°C
pH Range: 8.1–8.4
Salinity: SG 1.024–1.026
Nitrate: Low and stable
Ammonia/Nitrite: 0 ppm

Temperament:
Peaceful to Semi-Aggressive

The Masked Swallowtail Angel is generally peaceful towards unrelated marine fish and is considerably less territorial than many other angelfish.

Males may become competitive towards other Genicanthus males, particularly in smaller aquariums, while females are usually more tolerant.

Diet:
Omnivore / Planktivore

The Masked Swallowtail Angel naturally feeds largely on planktonic foods within the water column.

In the aquarium, offer a varied diet including frozen mysis, enriched brine shrimp, finely chopped krill, marine pellets, flakes and quality angelfish foods.

Small amounts of algae-based and spirulina-enriched foods can also be included regularly.

Minimum Tank Size:
Approximately 450 litres

Its active open-water swimming behaviour means the Masked Swallowtail Angel requires substantial horizontal swimming space.

Behaviour & Activity:
The Masked Swallowtail Angel is an active daytime swimmer that commonly spends much of its time in the middle and upper areas of the aquarium.

Provide generous open swimming room alongside caves, overhangs and secure rockwork.

Males and females differ noticeably in colouration and pattern, and established groups may form a social hierarchy.

Reef Safe:
Reef Safe

The Masked Swallowtail Angel is generally considered reef safe and is one of the safer angelfish choices for coral-rich marine aquariums.

Because it feeds primarily from the water column rather than grazing heavily on coral tissue, it is much less likely to damage healthy corals or clam mantles than many other angelfish.

Special Requirements or Care Notes:
Provide a large, mature marine aquarium with excellent filtration, strong oxygenation and substantial open swimming space.

Several smaller feeds throughout the day are beneficial due to its active swimming behaviour and plankton-based feeding habits.

Avoid highly aggressive tankmates that may intimidate the fish or prevent it from feeding comfortably.

If keeping more than one Genicanthus angelfish, provide ample space and carefully consider the sex and size of individuals being introduced.

Stable water chemistry and regular maintenance are important for maintaining healthy body condition and strong colouration.

A secure lid is recommended, particularly during acclimation, as active marine fish may jump when startled.

Suitable for:
Intermediate

Availability:
Availability can vary depending on season, sex and supplier.

All images are a visual representation of the fish you will receive, made to be as accurate as possible. Please note that Mother Nature is a wonderful thing, and variation in patterns and colours will occur — that is part of the unique beauty of these animals.