At the moment, there are many unrecognized species in this diverse and widespread group, with only A. clarkii of the Indo-Pacific and A. tricinctus of the Marshall Islands currently recognized by most resources. This discrepancy can largely be chalked up to the variable phenotypic nature of these fishes, which is heavily influenced by such factors as geography, age, sex, ecology, and intraspecific variation.
Of particular note is the tendency for this group to turn black when hosting in Stichodactyla carpet anemones. This is perhaps the single greatest reason for the current confusion, as these black forms often look quite similar. Even so, there are often subtle traits which have gone unnoticed. In many regions, the caudal fin can be highly diagnostic, even in melanistic individuals. The distinctive population from Ogasawara is noted for being permanently darkened, while those from Chagos seem immune to this anemone-induced phenomenon.
An unusual phenomenon of phenotypic homogenization through hybridization seems to have taken place in two separate locations. Populations at the Chagos Archipelago and the Great Barrier Reef are both nearly identical to more distantly related species that occur sympatrically here. This implies a long period of interbreeding that has merged their phenotypes towards one another. Not surprisingly, these species have long been confused and misidentified.
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