Lamarck's Angelfish

Lamarck's angelfish is the most commonly sold species of the genus Genicanthus, the "swallowtail angelfish." Unlike other angelfish, members of this genus hunt plankton in open water instead of eating corals and sponges; this makes them some of the few large angelfish that can safely go into a reef aquarium. Its silver–white body carries several thick black horizontal stripes; the dorsal fin is black and the tail is deeply forked and lyre-shaped.

Males and females look very much alike, but the male has a small yellow spot on the forehead and black pelvic fins. Individuals are collected from the wild. It is a hardy species that quickly adapts to prepared foods.

It lives in the western Pacific at 10–50 meters, from shallow reef crests next to steep reef slopes down to deep reefs. In harems of one male and 3–7 fish, it picks plankton a few meters above the bottom.

• Volume: at least 500 liters for a single fish; 800 liters or more for a harem. Plenty of open swimming space.
• Water: salinity 1.023–1.026 specific gravity, pH 8.1–8.4, temperature 24–27°C. Good oxygenation and moderate flow.
• Light: because it lives in deep water, a newly arrived fish may be frightened by very strong light; dim the lights for the first few days.
• Reef compatibility: reef safe. It generally leaves corals, tridacna clams and shrimp alone; very rarely an individual fish may do some nipping.

An omnivore with a plankton-based diet. Use frozen mysis, enriched brine shrimp, copepods and small marine fish granules as the staple; supplement with spirulina foods and dried seaweed. It should be fed small amounts 2–3 times a day.

A peaceful, calm angelfish; it gets along with most reef fish. Males are aggressive toward each other. Fish that arrive timid open up within a few days and swim in the middle and upper parts of the water column.

Good companions: tangs, anthias, fairy and flasher wrasses, dwarf angelfish (in a large aquarium), clownfish, cardinalfish.

Avoid: a second male Genicanthus, large aggressive angelfish, triggerfish, lionfish.

In the wild it lives in a harem: one male and several females. All individuals start out female; if the male of a harem is lost, the dominant female changes into a male. A single fish can also be kept in the aquarium; if a harem is planned, one male and 2–3 females should be added at the same time.

It is a protogynous species (female first). Pairs release pelagic eggs in the water column in the late afternoon. Fry are not raised in home aquariums.

• Marine white spot and velvet: quarantine is recommended.
• Pressure and shipping stress: fish collected from deep water may swim unsteadily for the first few days; a calm, dim quarantine tank speeds recovery.
• Poor nutrition: fish fed only one meal a day lose weight.

The male has a small yellow spot on the forehead, black pelvic fins and is usually larger. Females have whitish pelvic fins and no yellow spot on the forehead.