Three-band anemonefish
Endemic to the Marshall Islands, a generalist host anemonefish.
The three-band anemonefish (Amphiprion tricinctus) is found only in the Marshall Islands, in the western Pacific. It lives in a symbiotic partnership with sea anemones, immune to their stinging tentacles. Socially, it operates under a strict size-based pecking order: the largest individual is the female, the next largest is the breeding male, and the rest are smaller non-breeding males. This fish is a protandrous sequential hermaphrodite—if the sole breeding female dies, the breeding male changes sex to replace her, and the largest non-breeder becomes the new breeding male. Its natural diet consists of zooplankton.
The body of *A. tricinctus* is yellow-orange on the snout, belly, and pelvic and anal fins, darkening to brown or black toward the tail. As an adult, it has three white bands, which give it its common name. It can reach about 13 cm (5.1 in) in length. Because it is endemic to the Marshall Islands, there is no geographic variation, but individuals can range from mostly orange to mostly black, with occasional odd color patterns. Fish living with the host anemone *Stichodactyla mertensii* (Mertens’ carpet sea anemone) are often black except for the snout and white bars.
Two other anemonefish species—*A. chrysogaster* and *A. fuscocaudatus*—also have three body bars and a dark tail, but they live in different regions. Three other anemonefish species occur in the Marshall Islands: *A. chrysopterus* (two body bars, whitish tail), *A. melanopus* (only a head bar), and *A. perideraion* (a white stripe along the back). These are easy to tell apart from *A. tricinctus*. Genetic work shows *A. tricinctus* is closely related to *A. clarkii*, and this pair is quite distinct from other species once grouped in the *A. clarkii* complex.
The fish lives in lagoons, pinnacle reefs, and seaward reefs. It is most common at depths of 3 to 40 m (9.8 to 131.2 ft), but occasionally appears deeper than 40 m (130 ft) hosted by solitary *Entacmaea quadricolor* anemones on seaward reef slopes.
Anemonefish and their hosts have a highly structured, non-random relationship. *A. tricinctus* is a generalist, using eight of the nine host anemone species found in the Marshall Islands.
Quick Facts
- Taxon
- Amphiprion tricinctus
Facts from the source article.
Lore & Background
The three-band anemonefish is a sequential hermaphrodite with a strict size-based dominance hierarchy: the female is largest, the breeding male is second largest, and nonbreeding males get progressively smaller. It exhibits protandry, meaning the breeding male changes to female if the sole breeding female dies, with the largest nonbreeder becoming the breeding male. Its natural diet includes zooplankton.
As an adult, the fish has three white bands or bars, with a body that is yellow-orange at the snout, belly, and pelvic and anal fins, tending to dark brown or black at the tail. It can grow to about 13 cm long. No geographic variation is seen due to its endemicity, but variations in the proportions of orange and black occur, from predominantly orange to predominantly black. Fish living with the host anemone Stichodactyla mertensii are frequently black except for the snout and bars.
Two other species have three body bars and a dark tail—A. chrysogaster and A. fuscocaudatus—but they are geographically separated. Three other anemonefish species found in the Marshall Islands are easily distinguished from A. tricinctus by bar patterns and coloration. Genetic analysis shows A. tricinctus is closely related to A. clarkii.
Reader's Guide
The three-band anemonefish is significant as an endemic species confined to the Marshall Islands, where it occupies lagoons and pinnacle and seaward reefs at depths of 3 to 40 m, occasionally deeper. Its ability to use a wide variety of host anemones—eight of the nine species found in the Marshall Islands—is thought to reduce its risk of extinction associated with habitat specialization. This generalist behavior contrasts with more specialized anemonefish and may buffer the species against environmental pressures such as coral reef degradation and anemone bleaching caused by increased water temperature or acidification. The species has been bred in captivity and specimens are occasionally sold for aquariums. Its conservation status is informed by its small geographic range and small local population, but its host flexibility is a mitigating factor. The fish's protandrous social structure and strict hierarchy are characteristic of anemonefish reproductive biology, and its close genetic relationship to A. clarkii places it within a distinct clade.
More in Clownfish and Damselfish 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced