The chrysopterus group includes a handful of distinct populations scattered throughout the Central Pacific, conforming perfectly to our understanding of ecoregional speciation in this area and absent only from isolated Polynesian islands like Hawaii and Rapanui. These large anemonefishes (capable of reaching nearly 7 inches) are typically associated with the outer habitats of oceanic reefs and utilize a variety of anemone hosts.
Traditionally, these fishes have been classified as a single species, A. chrysopterus, but it takes little effort to see that there are some obvious differences across their range. Those from Melanesia have black ventral fins. Those from Micronesia and Vanuatu have a white caudal fin, while those from the Mariana Arc and the Fijian plate have it yellow. And the population in Polynesia is notable for tending to only darken to a light brown along the back and in having reduced stripes.
These have usually been treated as belonging to the clarkii group, based on broad similarities in their size, shape and appearance, but these similarities likely reflect the ancient condition of the “anemonefish clade” rather than an indication of a more direct relatedness. Genetic data also points towards a unique origin for these fishes, and the broad area of sympatry in Melanesia shared by the clarkii and chrysopterus groups adds biogeographical support to this argument.
Another distinctive trait of this group is the curious tendency for a “dark morph” to develop. There doesn’t seem to be any obvious explanation for this phenomenon, as little correlation is seen with variables such as sex, size or host selection. Such individuals have been reported from every major ecoregion, and groups comprised entirely of these dark individuals have been reported (some regions, such as the Cook Islands, seem to show a higher concentration of these individuals relative to the normal phenotype). Mixed-morph pairs are often seen, which can easily lead to confusion. The similarity between the dark morph of A. chrysopterus and A. akindynos has resulted in erroneous reports of this latter species from outside its subtropical Australian range.
In areas where this group overlaps with the Orange Skunk Anemonefish (A. sandaracinos), the two hybridize to form the “A. leucokranos” phenotype, which has inappropriately been recognized as a species.
Obviously, a great deal of work remains to be done with this group. At least five new species await description here, none of which have previously been recognized, despite the ease with which they can be visually diagnosed. The relationship with A. akindynos is also in need of study. These two groups may have independently arrived upon their similar appearances, as their geographical and ecological differences hint at discrete evolutionary histories.