🐠 Masked Swallowtail Angelfish (Genicanthus semifasciatus)
Marine Genuinely Reef-Safe Angelfish • Striking Sexual Dimorphism • Genuinely Rare Deep-Water Species • Intermediate to Advanced Marine Fish
 
📋 The Masked Swallowtail Angelfish (Genicanthus semifasciatus), also known as the Japanese Swallow Angelfish or Tosayakko, displays genuine sexual dimorphism — males show a bright yellow-orange face and frontal body with narrow black vertical bars running down the length, while females have a creamy white-to-yellow body with a dramatic black band over the eye and along the tail. Both sexes share the elegant crescent-shaped "swallowtail" that gives the genus its name.
Native to rocky reefs in the Northwest Pacific, from southern Japan to the Philippines, this species is genuinely rare — collected from meaningfully deep water and, in some areas, from protected zones where collection is restricted, which is exactly why it commands such a premium price.
Here's what makes this species genuinely special: like other Genicanthus, it's considered one of the few truly reef-safe angelfish in the hobby, feeding predominantly on zooplankton rather than corals — it won't nip at soft or stony corals or sessile invertebrates. That said, it may occasionally pick at smaller planktivorous tank mates like fairy wrasses, flasher wrasses, or firefish that compete for the same food, so watch behaviour carefully. Genuinely hardy and adaptable once settled, this species readily accepts aquarium fare and is best kept singly, as a mated pair, or in a small harem of one male with several females — never house two males together, as this leads to genuine, serious aggression.
 
💙💛 Highlights
🎨 Striking Sexual Dimorphism: Males and females look genuinely distinct
🌿 Genuinely Reef Safe: One of the few truly reef-compatible angelfish species
💎 Genuinely Rare: Collected from deep, sometimes protected waters
😌 Genuinely Peaceful: More docile than most angelfish, may occasionally chase small planktivores
👫 Naturally Forms Harems: One male with several females in the wild