The Frenatus Group

by | Aug 25, 2020 | 0 comments

The final group left to examine are the Tomato Clownfishes,  so named for the reddish coloration shared by several of the species in this lineage. These have a tall, robust body profile and a single white bar behind the head, while juveniles briefly have a second bar that disappears at an early age. These occur only in the broader West Pacific (inclusive of peripheral areas like the Andaman Sea and Micronesia) and are specialists in the small, clonal variety of Entacmaea quadricolor that occurs in great abundance along shallow lagoons. It’s not uncommon for hundreds of these highly territorial clownfishes to occur in close proximity, though how they keep from constantly bickering with one another is far from clear.

The true Tomato Clownfish is Amphiprion frenatus, a species restricted to the Northern Coral Triangle, including the Philippines north to the Ryukyu Islands and west to the Gulf of Thailand. Sexual dichromatism is an important feature to note in this population. The black sides seen in females are markedly different from the bright red coloration of the males. The pelvic fins are also dichromatic across the sexes, with females having the leading edge colored black, sometimes expanding further to darken most of the fin. When comparing different populations of this group, the relative color and saturation of the dorsal and caudal fins can be a useful trait, along with the extent and curvature of the black patterning along the back. In frenatus, mature females almost always have the black back continuing onto the caudal peduncle. 

Elsewhere in the Pacific, a familiar pattern of regional endemism is observable; however, despite the phenotypic differences of these populations, most remain lumped under the catchall taxon Amphiprion melanopus, known commonly under a number of different names: the Red and Black Clownfish, the Cinnamon Clownfish, the Fire Clownfish. The diagnostic traits that unite these geographically disparate forms are the solidly black pelvic fins of females and the general lack of sexual color differences. With the type locality for A. melanopus being at Ambon, Indonesia, this species name should likely only be applied for those fishes found in Indonesia, but, in contrast with other widespread Amphiprion lineages, there are no obvious differences in the populations found at Melanesia and Micronesia. Should A. melanopus eventually be split, specimens from Milne Bay, Papua New Guinea have been described as Amphiprion monofasciatus Thiollière 1857, while the Micronesian population has no name associated with it.

The variety of A. melanopus found on the Great Barrier Reef is more easily recognized thanks to the beautiful saffron coloration of the dorsal fin, which tends to extend into caudal peduncle and onto the posterior portion of the anal fin. This gives the black sides a smooth arc that is pleasing to the eye. Occasional specimens buck this trend and instead develop a black caudal peduncle, but the dorsal and caudal fins of such individuals are still a much brighter yellow than what’s found in the comparatively muddy colors of the Indonesia A. melanopus. Rarely, the white bar will be completely missing, a trait that becomes more common in the Indian Ocean species.

The population at New Caledonia and Vanuatu is in most respects similar to its Aussie counterpart, but these are arguably even more vibrant, having the black coloration reduced to just a small smudge along the back, which never extends onto the caudal peduncle. This also results in a much brighter anal fin, having only a touch of black present along the margins. Additionally, the pelvic fins of males are not fully darkened, leaving an orange basal portion quite unlike the true Indonesian A. melanopus. A strong case could be made that this is the most beautiful member of the group.

The Fijian Plate is home to A. barberi, a fish that is somehow both lighter and duller in color than its neighbor to the west. It is distinguished by the relative lack of black pigmentation along the back, with males appearing mostly orange and females taking on an increasingly sooty appearance. In both sexes, the pelvic fins are fully orange, save for a thin black line along the anterior edge.The white bar of A. barberi appears slightly thinner when compared to the various populations of A. melanopus, but this gets even more attenuated further east, at Tonga, where yet another distinct phenotype resides. This Tongan fish has seemingly regained much of the dark pigmentation that A. barberi lost, but is otherwise fairly similar. And in the peripheral reefs of Samoa and Wallis & Futuna, the resident tomato clownfish is once again of the typical A. melanopus phenotype, with dull colors and black pelvic fins, presumably representing another cryptic species. Within Melanesia, this pattern of speciation is noted in some other groups of reef fishes, most notably in fangblennies (e.g. the Meiacanthus atrodorsalis group) and foxfaces (e.g. the Siganus vulpinus group).

The reefs of Northwest Australia are home to one of the most uncommonly seen of the tomato clownfishes, A. rubrocinctus. This ugly sombre fish is heavily blackened along the sides, including the caudal peduncle, and has the curious tendency of partially or completely losing its white bar with age, leaving behind only a ghostly remnant. It differs from the nearby A. melanopus of Indonesia in having mostly orange-red anal and pelvic fins, thus appearing somewhat similar to the geographically distant A. barberi. Prior to the description of that species in 2008, their resemblance caused confusion within the aquarium trade, with the commonly exported Fijian fish passing as the much rarer (and more expensive) A. rubrocinctus.

And the last species to discuss in our journey through Amphiprion biodiversity is the confusingly named Red Saddleback Clownfish A. ephippium. Despite the name, this species lacks any obvious saddle-like markings and is of no direct relation to the true saddleback clownfishes of the polymnus Group. Instead, the counterintuitive nomenclature derives from the scientific name, ephippium, which translates from Latin as “saddlecloth”, given to this fish in reference to the dark blotch along the sides, which in some specimens can expand to darken much of the fish—this is reportedly a common occurrence in captive specimens. A. ephippium is restricted to the Andaman Sea and south to Java, making it the only Amphiprion currently recognized as being endemic to this region, though both the Maroon Clownfish and Ocellaris Clownfish likely follow the same trajectory, as does the true A. akallopisos. Juveniles start out life with white bars, but these are lost relatively early on in their development, such that the adults are a mostly red fish, aside from the black edge of the pelvic fins.


As it currently stands, there are 29 officially recognized species of Amphiprion, plus the Maroon Clownfish, unnecessarily classified in the monospecific Premnas. Two of these taxa are known to be hybrids and will need to be synonymized, and at some point Premnas biaculeatus will need to officially be renamed as Amphiprion biaculeatus. The true diversity of the genus is, however, much greater than what has been reported. Unfortunately, determining what does and does not count as a “species” is an issue wrought with challenges. By my estimation, there are ~60 distinct populations that show some indication of evolutionary novelty, be it phenotypic or biogeographic in nature. The question then becomes, are these ALL “species”, and, if not, which of these populations is unworthy of the designation. To give just one example of the taxonomic inconsistencies that plague this genus, why does A. tricinctus deserve to be treated as a unique species when it only represents one of the ~15 different geographical variants of A. clarkii, many of which are every bit as distinctive?

Answers to these intractable problems will require considerable genetic study, piecing together the population dynamics within and between regions and comparing these across lineages. As a model organism for examining the process of speciation on Indo-Pacific reefs, there are few organisms that offer quite so much potential as Amphiprion, thanks to this group’s enormous diversity and a lifecycle that fosters endemism. While aquarists justifiably delight in the color and personality clownfishes bring to an aquarium, their unique propensity to speciate and hybridize makes these fishes some of the most singularly fascinating for the evolutionary biologist. For such a seemingly well-known group of fishes, there is still much left to learn.


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