Halfbanded angelfish

Lore & Background

Genicanthus semicinctus was first formally described as Holocanthus semicinctus in 1900 by the British-born Australian ichthyologist Edgar Ravenswood Waite, with the type locality given as Lord Howe Island. The specific name is a compound of semi meaning 'half' and cinctus meaning 'bands'. Males are marked with thin close-set wavy black vertical bars running from the back to two-thirds down the flanks, with the lower third of the body being yellowish-orange. They have a yellow dorsal fin and yellow lobes with long filaments on the caudal fin which has black spots; the chest also has black spots. Females are plain dark grey on the back with a whitish abdomen and have dark lobes to the caudal fin; their fins have thin blue margins and there is a black blotch above the eye with a vivid blue margin. The dorsal fin contains 15 spines and 15-16 soft rays while the anal fin has 3 spines and 17 soft rays. This species attains a maximum total length of 21 centimetres (8.3 in).

Reader's Guide

The halfbanded angelfish is found at depths between 10 and 100 metres on the deep outer slopes of coral and rocky reefs. It normally occurs in small groups, harems of a male and as many as 4 females. This species is a protogynous hermaphrodite: if the male in a group disappears, the dominant female will change into a male, a process that takes a few weeks. In the aquarium trade, Genicanthus semicinctus is very rare. Its restricted distribution—only around Lord Howe Island and the Kermadec Islands—and its striking sexual dimorphism make it a notable species among marine angelfish. The species' scientific name reflects its half-banded pattern, and its description by Edgar Ravenswood Waite in 1900 adds historical context to its study.

Did You Know?

• Males have thin close-set wavy black vertical bars on the upper two-thirds of the body, with a yellowish-orange lower third.
• This species is a protogynous hermaphrodite; if the male disappears, the dominant female changes into a male over a few weeks.
• It is found only around Lord Howe Island and the Kermadec Islands in the southwestern Pacific Ocean.