Chagos anemonefish  (Amphiprion chagosensis)

The Chagos anemonefish has yet to be assessed by the IUCN.

The Chagos anemonefish (Amphiprion chagosensis) belongs to the family Pomacentridae, a group of 29 species of small reef fish which are often referred to as clownfish (3). A deep-bodied and brightly coloured species, the Chagos anemonefish is yellow-orange to light brown, with two dark-edged white bars. The dorsal, anal and pelvic fins are dusky brown, and the caudal fin is whitish (3) (4).

This species is very similar in appearance and morphology to Amphiprion akindynos from the Great Barrier Reef and Coral Sea Region, and the closely related Amphiprion nigripes from the Maldives and Sri Lanka, although A. nigripes only has a single white bar on the body (3) (4).

The Chagos anemonefish is endemic to the Chagos Archipelago in the western Indian Ocean (3) (4) (5).

Generally restricted to shallow coral reefs at depths of less than 15 metres (6), the Chagos anemonefish is primarily found on seaward reef slopes, but is occasionally observed on lagoon reefs and reef tops (2).

Along with the other species of the family Pomacentridae, the Chagos anemonefish has developed a complex symbiotic relationship with sea anemones (3) (7) (8). The small fish live within the tentacles of a ‘host’ anemone; however, there is currently very little information available about the specific anemone species with which the Chagos anemonefish associates.

Most species of anemonefish are adapted to live with only a single or few species of sea anemone (3). While the tentacles of sea anemones can deliver a nasty sting to other fish and potential predators, anemonefish are thought to be protected by a thick mucus coating which covers the skin, although the exact mechanism is unknown (3) (7) (9) (10). Individual anemonefish usually remain within a few metres of their host anemone and return quickly when threatened, being particularly vulnerable to predation without the protection of their host. In return for this protection, the anemonefish feeds on small invertebrates which would otherwise prey on the host anemone, hence providing mutual protection (7).

The genus Amphiprion has an unusual social structure. Generally, an adult female and an adult male form a pair and defend a small territory around their host anemone. Several sexually immature juveniles are also usually found close to the adult pair. These immature, non-breeding fish are prevented from developing into adults by the dominant adult male, and may only reach maturity if one of the adult pair dies. Juvenile fish always develop into males. If the adult male dies, one of the juveniles, usually the largest, will develop into an adult male. If the adult female dies, the adult male changes sex to become female, while one of the larger juveniles replaces the adult male (11).

There are currently no known direct threats to the Chagos anemonefish.

There are currently no conservation measures targeted directly at the Chagos anemonefish. Furthermore, the Chagos archipelago has suffered relatively little in terms of direct human impact due to its isolated position and limited access, making it one of the most important island and coral reef wilderness areas in the Indian Ocean (12).

In 2010, the Chagos Archipelago, also known as the British Indian Ocean Territory, was designated as the world’s largest Marine Protected Area (MPA). This near pristine ocean ecosystem now represents 16 percent of the world’s fully protected coral reef and 60 percent of the world’s no-take protected areas (5).

ARKive is supported by OTEP, a joint programme of funding from the UK FCO and DFID which provides support to address priority environmental issues in the Overseas Territories, and Defra

Find out more about conservation in the Chagos archipelago:

• Sheppard, C. and Spalding, M. (2003) Chagos Conservation Management Plan. British Indian Ocean Territory Administration, London. Available at:
  http://www.zianet.com/tedmorris/dg/chagos_conservation_management_plan_2003.pdf

Find out more about conservation in the UK Overseas Territories:

• United Kingdom Overseas Territories Conservation Forum:
  http://www.ukotcf.org/