Masked Swallowtail Angel
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Masked Swallowtail Angelfish (Genicanthus semifasciatus)
Overview
The Masked Swallowtail Angelfish (Genicanthus semifasciatus) is a striking marine angelfish endemic to Western Pacific reefs, including areas around Japan, Taiwan, and northern Indonesia. It is known for its distinctive black “mask” across the eyes, contrasting with a pale yellow to cream-colored body and lyretail-shaped caudal fin with subtle black markings.
Like other Genicanthus species, it is a mid-water, schooling angelfish that spends much of its time grazing on plankton and algae. Its peaceful temperament, smaller adult size, and striking appearance make it a desirable addition for intermediate to advanced marine aquarists, particularly in mature reef or FOWLR systems.
Aquarium Requirements
Minimum Tank Size: 300–400 litres (80–105 US gallons)
Temperature: 24–27 °C (75–81 °F)
pH: 8.1–8.4
Specific Gravity (Salinity): 1.020–1.025
Alkalinity: 8–12 dKH
Ammonia & Nitrite: 0 ppm
Nitrate: < 10 ppm
Aquascape:
Provide plenty of open swimming space with moderate water flow and live rock for grazing. Juveniles and smaller adults appreciate caves, overhangs, and shaded areas for refuge. This species thrives in mature aquariums with stable water chemistry and high oxygenation.
Diet and Feeding
The Masked Swallowtail Angelfish is omnivorous, feeding mainly on plankton, small invertebrates, and algae in the wild.
Recommended Foods:
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Frozen or prepared angelfish formulas enriched with sponge and algae
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Mysis shrimp, brine shrimp, finely chopped seafood (clam, scallop, squid)
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Spirulina- or algae-based flakes or pellets
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Occasional live rock grazing to promote natural feeding behaviors
Feed 2–3 times daily, offering multiple small portions to encourage natural grazing behavior. Adequate nutrition helps maintain vibrant coloration and overall health.
Temperament and Compatibility
The Masked Swallowtail Angelfish is peaceful and mid-water oriented, making it suitable for most community reef tanks.
Suitable Tankmates:
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Peaceful species like tangs, butterflyfish, clownfish, and wrasses
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Other Genicanthus species in sufficiently large aquariums (>400 litres)
Avoid:
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Aggressive or highly territorial angelfish
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Overly dominant fish that may stress this mid-water grazer
This species is shy when first introduced but gradually becomes confident and active in the tank environment.
Reef Compatibility
✅ Reef Safe
Masked Swallowtail Angelfish are generally reef safe, rarely disturbing corals or sessile invertebrates. They are suitable for mature reef aquariums and contribute to natural algae and micro-invertebrate grazing.
Best Practices:
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Provide abundant live rock and algal surfaces for grazing
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Ensure adequate supplemental feeding to reduce potential coral nipping as the fish matures
Additional Information
Maximum Size: 20–25 cm (8–10 inches)
Lifespan: 10–15 years in captivity with proper care
Difficulty Level: Intermediate
Natural Behavior: Peaceful, mid-water grazer, often schooling; gradually becomes bolder with acclimation
Origin: Western Pacific – Japan, Taiwan, northern Indonesia
Sexual Dimorphism: Pronounced; males typically display more vibrant tail coloration and larger dorsal fins, while females are paler and smaller.
Summary
The Masked Swallowtail Angelfish (Genicanthus semifasciatus) is a peaceful, reef-compatible species that thrives in mature aquariums with ample swimming space, live rock for grazing, and a nutritionally complete diet. Its striking masked pattern and mid-water schooling behavior make it an attractive centerpiece for intermediate and advanced aquarists. With proper care, this species can live over a decade, maintaining vibrant colors and natural behaviors.
| SKU | Masked Swallowtail Angel |
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