Japanese Swallow Angelfish

Lore & Background

Genicanthus semifasciatus was first formally described in 1934 as Holocanthus semifasciatus by Japanese ichthyologist Toshiji Kamohara, with the type locality given as Kashiwajima in the Kochi Prefecture of Japan. The specific name is a compound of semi meaning 'half' and fasciatus meaning 'banded', referring to the banding on the males' backs which does not extend onto the abdomen.

The species is sexually dichromatic: the male has a yellow head and anterior flanks with a darker yellow dorsal area marked with dusky vertical bars, while the female has a greyish brown dorsal area and white ventrally, with a yellow margin to the dorsal fin and black on the head and tail. Both sexes have a forked tail that narrows at the base, creating a 'swallow tail'. The dorsal fin contains 15 spines and 15–16 soft rays, and the anal fin has 3 spines and 17 soft rays.

This species is protogynously hermaphroditic and is normally encountered in harems consisting of a male and several females. It feeds on plankton in the water column and occurs at depths between 15 and 200 metres on the seaward sides of rocky and coral reefs.

Reader's Guide

Genicanthus semifasciatus is a marine angelfish of the family Pomacanthidae, found in the Western Pacific from southern Japan, including the Ogasawara Islands, the Izu Islands, and the Ryukyu Islands, to the northern Philippines. It inhabits depths of 15 to 200 metres on the seaward sides of rocky and coral reefs. The species is protogynously hermaphroditic, typically forming harems of one male and several females, and feeds on plankton in the water column. Its maximum total length is 21 centimetres. The Japanese swallow is rather infrequently found in the aquarium trade, with specimens usually coming from the Philippines. Its scientific name, Genicanthus semifasciatus, was originally described as Holocanthus semifasciatus by Toshiji Kamohara in 1934, with the specific name referring to the half-banded pattern on the male's back. The species is notable for its sexual dichromatism and swallow-like tail, which narrows at the base.

Did You Know?

• The Japanese swallow angelfish is sexually dichromatic, with males and females having different color patterns.
• It is protogynously hermaphroditic and typically lives in harems of one male and several females.