Dogface pufferfishes are as common a marine fish as you’ll find in the aquarium hobby, but this is by no means true of all the species in this diverse group. The genus Arothron, as currently classified, contains fifteen species, several of which have never been collected for aquarists. These taxa are often poorly known, regionally endemic, or subtropical, and, in my continuing effort to shed light onto the hidden corners of the ichthyological world, they will be the focus of this article.
Before delving into the murky waters of Arothron, a word needs to be said regarding our tenuous understanding of its species. Being large and charismatic fishes, it should come as little surprise that most of these species were described early on in taxonomic history—all but two predate the twentieth century. But it might be surprising to learn that the genus as a whole has never received a proper taxonomic study.
Part of the difficulty in studying these species is the homogenous nature of their morphology. Specimens generally share identical counts of their fin rays and gill rakers, and there are of course no scales to count in pufferfishes. Even proportional measurements are made difficult by the protean nature of the pufferfish body when preserved in formalin. And so it is that coloration is the primary means for identifying species. Clearly, our understanding of the evolutionary history of Arothron and the geographic variation within species is still in a nascent state. Given the observable differences seen within some taxa, it would not be surprising if genetic study brings to light unexpected cryptic diversity.
Arothron caeruleopunctatus “Blue-spotted Pufferfish”
This large, widespread and easily identifiable species was only formally described in 1994, about a century later than every other species in the genus. A couple factors might explain this: 1) Judging by in situ photographs, this species is strictly solitary. 2) Likewise, this species is generally less common relative to its congeners. Even so, it is strange that this slipped past the radar for so long.
The body is black dorsally, with a white belly. There are many small spots of variable size, which can range in color from white to cornflower blue. The back is typically enveloped by an orange-brown, obfuscating the underlying black coloration. This last character is perhaps the easiest and most reliable for making identifications, but it may only be relevant for mature adults. The blue spots which give this species its common and scientific name appear to be particularly variable, with some specimens having only white spots and some having a complex blue reticulation.
The original description of this species only examined four specimens from Pacific collection localities, but it includes a photo indicating its presence at Reunion Island in the Indian Ocean. I have found images of at least two specimens from the Maldives which display an unusually reticulated patterning to the head which, to the best of my knowledge, has not been observed elsewhere. Whether this is just an individual aberration, a geographic variation, or potentially even a cryptic species is impossible to say without genetic study. Photos of sympatric specimens which show a more typical coloration suggest it may just be individual variation.
Arothron carduus “Thick-striped Pufferfish”
This is perhaps the most poorly understood species in the entire genus… so poorly known that I had to make up a common name. A. carduus is known from only four specimens, one of which was discovered as a lampshade in the curio trade. The documented range for these includes the Sea of Penang off Malaysia, the Ryukyu Islands between Taiwan and Japan, and the Izu Islands in Southeastern Japan, while the lampshade specimen may have been from the Philippines. This restricted range is unusual for an Arothron species, and the lack of photographs from the normally exhaustive catalog of Japanese diveblogs indicates it is genuinely rare in the wild.
This species can be diagnosed by the numerous dark stripes which run longitudinally along the body. The pattern is nearly identical to that seen in A. reticularis, with the exceptions that the white spots of that species have coalesced into stripes and the belly is unpatterned. It is also vaguely similar to A. manilensis, under which it was synonymized until recently, but the differences in the stripes are clear enough to avoid confusion.
So then, given that only four instances of carduus have been documented, is it more likely that this is a sister species endemic to Japanese waters or that it represents an uncommon aberration in reticularis? Only genetic study is likely to answer this question, but, given that reticularis is apparently sympatric in Japan, I’ll place my bet on the latter hypothesis.
Arothron firmamentum “Heavenly Pufferfish”
This is a fairly common species in its habitat, often being observed in immense schools. It ranges from surface waters to depths in excess of 1000 feet, with a range stretching across the subtropical waters of the Indo-Pacific. Populations are highly disjunct: Korea to Taiwan; South Australia to New Zealand; Southwestern South Africa; and possibly Argentina in the Atlantic. For obvious reasons, this species is unlikely to ever be available to aquarium hobbyists.
The shape and patterning of A. firmamentum are distinctive. The head is particularly blunt and round, while the coloration is black dorsally, with numerous white spots. Kuiter mentions specimens from Japan differing in color from those in the Southern Hemisphere. If confirmed with genetic study, this would result in the resurrection of A. gillbanksii for the Australian and New Zealand population, and presumably new names would be needed for the equally disjunct African and Argentine populations.
It occurs both pelagically and demersally over continental shelves, where it hunts an omnivorous diet heavy in crustaceans. Strong storms are known to wash specimens ashore in large numbers. Note that most references list the common name as “Starry Toadfish”, but this is only likely to cause confusion with the actual toadfishes of the Family Batrachoididae. “Starry Pufferfish” is already occupied by A. stellatus, so I suggest a common name of “Heavenly Pufferfish”, as a rough translation of the scientific name.
Arothron inconditus “Bellystriped Blaasop”
Thank the fine people of the Netherlands for the delightful common name of this species, as “blaasop” translates as “blow up” in Dutch. This is another endemic species, found only in South Africa, from Cape Town east to Durban, in surface waters down to twenty meters. It is known from a variety of habitats, including beaches, reefs, and even river mouths, but it is generally rare wherever it occurs and is listed as being vulnerable to extinction.
As the common name suggests, this species is striped along its belly, much like as in A. reticularis. The dark spot at the pectoral fin base suggests this species may be related to the widespread A. immaculatus. The main differences between the two are the belly stripes and dorsal blotches seen in inconditus.
Arothron leopardus “n/a”
I discuss this species only because it can be found in general references like fishbase.com and wikipedia, but in all likelihood this name is just a synonym for another species. Pufferfish authority Dr. Keiichi Matsuura has examined the only known specimen, which dates from the species’ description in 1878, and has suggested it is likely just a specimen of the widespread A. stellatus. A photograph alleging to be this species can be found on fishbase.com, but this is clearly just a misidentified A. hispidus.
The type specimen originates from near Madras, India and was described as follows: “Olive superiorly, extending two-thirds of the distance down the sides, with an interrupted black network surrounding white spots; three black cross bands, one over the head, with a V-shaped light interorbital band posterior to it; the second, above the pectoral fin; the posterior one from the base of the dorsal. Reticulated narrow black lines enclosing large white spots on the caudal and dorsal fins, the latter having likewise a narrow black basal band.”
If you see this fish, report it to the nearest ichthyologist immediately!
Arothron sp. “Red Sea”
Three photographs are all that exist of this potentially undescribed species. Two were taken near the city of Obhur, Saudi Arabia, which is located in the middle of the Red Sea. The photographer, Richard Field, mentions that these images have been seen by an authority in the group, who indicated this pufferfish cannot be identified as any known species (I concur). Unfortunately, they have been uploaded to fishbase.com as A. reticularis, despite the lack of an authoritative identification and reticularis being unknown west of India.
The pattern of thick grey stripes and thin white stripes running lengthwise along the body is unknown elsewhere in the genus. The caudal fin is filled with a dense convolution of wavy lines, which brings to mind the pattern seen in A. mappa. The parallel lines around the pectoral fins and head are analogous to what is seen in A. reticularis, but much about this fish’s coloration differs from that species.
So what do we have here? Is this an aberration from a known species, or is this truly an undocumented taxon? Or might this instead just be a hybrid? Given that the Red Sea is well-documented by recreational divers and scientists alike, why are there so few images of this fish? The ocean is full of mysteries.