It’s been awhile since I’ve posted, but the hiatus ends today with another Awesome Fish Spotlight. This time we feature not one, but two species as we draw attention to Pseudanthias pascalus and Pseudanthias tuka. While looking superficially similar and rather uniformly unassuming, both species are deceptively complicated and difficult to identify. This problem is no less compounded by both species’ numerous forms and fickle diagnostics, especially with the presence of various insular variations.
Pseudanthias pascalus and P. tuka form a two species complex within the subgenus Mirolabrichthys, both of which are superficially similar in appearance. Both species however, differ greatly in morphometrics with P. pascalus attaining a greater length as well as having a greater number of lateral line scales and pectoral fin rays. The females of both species can be readily separated by colour, with P. tuka being purple overall but possessing a yellow dorsal stripe which extends into both caudal lobes. P. pascalus has uniformly purple females, and both species are steely in appearance.
The males however are trickier to separate, with both being purple overall. Or so it seems, at least. In the recent months we’ve been sleuthing and digging more into this and we’ve found out that the difference between P. pascalus and P. tuka isn’t as clear cut as it seems.
In literature, P. pascalus can be differentiated from P. tuka by possession of “orange or dark spots” that pepper the body haphazardly. Both species can also be separated by the presence of a dorsal fin spot, which is always present in P. tuka while absent in P. pascalus. With additional research, we found that the presence of these “orange or dark spots” is not true to some forms of P. pascalus, which begs the question. Is that not a reliable feature for identification, and are there other cryptic species nestled within the pascalus and tuka complexes?
There has been a long drawn on again off again discussion regarding the phenotypic ID keys for the two species at hand. It started about a year or two ago when Tim Morrissey (who by the way has done incredibly well maintaining this species) of the Henry Doorly Zoo in Omaha sent me a photo of a male Pseudanthias species. The fish in question was purple overall with a decidedly yellow caudal fin. Without much thought I initially went on to reply Tim with Pseudanthias pascalus as the identity of that anthias.
The yellow caudal fin however raised a couple of red flags, and this led to a series of long drawn questioning and badgering amongst various industry peers. At this time we were still influenced by the fact that Pseudanthias pascalus differed from P. tuka by having “orange or black spots”. Seeing as these specimens at the zoo were lacking said spots, I reevaluated and thought Pseudanthias tuka would be a better fit. We recently visited the Henry Doorly Zoo again and took a series of photos showing the unique coloration of this fish, all of which can be seen in the small gallery below.
A new set of questions then surfaced. Are there any known forms or regional variants where Pseudanthias tuka possesses a yellow tail? If not, what could possibly be the reason for these specimens in aquaria to have such a unique appearance? A few theories came up.
I initially thought that during courtship displays, the tail intensified from purple to yellow, and that the males here were just keeping their nuptial coloration permanently. Matt Wandell of Steinhart Aquarium thinks that these could be a regional geographic variation of P. tuka, where the tails are yellow instead of purple. This isn’t farfetched seeing as P. tuka from the Rowley Shoals possess a clearly defined yellow dorsal fin. We also spoke with Joe Rowlett, and he initially suggested that the yellow tails could be a remnant female characteristic that was left behind after sex change. This also wasn’t completely unbelievable, seeing as many hermaphroditic species often undergo incomplete colour change in captivity.
Unsatisfied with our theories, we continued digging around and came upon Dr. Randall’s collection of Pseudanthias pascalus photos on fish base. This collection shows various regional forms as depicted above, but look closely and pay special attention to each one. The colour is slightly faded and the specimens are dead, but P. pascalus from Tetiaroa shows red caudal lobes while P. pascalus from the Ryukyu peninsula show yellow caudal filaments (which corresponds almost perfectly with the Zoo specimens). A change in the identity once again occurred, and the Zoo specimens were now thought to be P. pascalus again; although this time we have corresponding evidence to suggest this change.
The dorsal fin’s extent of red suffusion is another variable characteristic, and it ranges from being absent to very distinct as seen above. On the topic of the dorsal fin, it is once again important to remember that both species differ in that P. tuka has a dorsal fin spot which P. pascalus lacks.
In P. tuka, the spot sits at the base of the soft dorsal fin, and sometimes an additional one is also present in the spinous portion. In P. pascalus, the dorsal fin is spotless but it occasionally bears varying degrees of red suffusion, sometimes deceptively “spot like”.
Another variable characteristic that is present within this species is the apparent density of the “orange and dark spots”. On close examination of the specimens above, most of them have it pretty densely spotted with the exception of the yellow-tailed Ryukus specimen. This form appears to lack any spotting, which again leads to that being an inconclusive definitive ID key.
With a solid lead on the ID being P. pascalus now and with new knowledge on the various forms, we once again consulted Joe Rowlett and begun digging around, this time with a more conscience search criteria. We started with the red spot on the dorsal fin and the variability of its intensity. In some specimens like this individual above from Moorea, the soft dorsal fin lacks any red suffusion. This particular specimen does however, have the orange spots on its body when examined closely.
This set of images above show a complete opposite of the Moorea specimen. In these individuals, the red coloration appears to be highly extensive and has spread throughout the dorsal fin. The individual on the left from Iriomote has another unusual trait, in that it has both caudal lobes washed in red. The specimen in the inset photo from Saipan as well as the specimen on the right from Ishigaki both have pretty extensive red dorsal fins, such that it encroaches into the spinous portion. The amount of red on the spinous portion of the dorsal fin is very limited to these Japanese and Marianas individuals.
In none of these Japanese and Mariana Island forms are the orange spots on the body evident. It seems that the area is prone to unusual diversity in this species, with the red dorsal fin varieties being restricted to these locales so far.
In Pseudanthias tuka, the red appears to more be often than not extended throughout the dorsal fin, often up to the spinous portion as well. The photos of P. tuka above and below show specimens with very extensive red wash on the dorsal fin. However like P. pascalus, this is not always true and the trait can be rather variable as well. Far above is an aquarium specimen of P. tuka with a uniformly purple dorsal fin.
As mentioned before, P. tuka has a spot that is present on the base of the soft dorsal fin, and sometimes an additional one on the spinous portion as well. While the spinous dorsal spot is variable, it is always present on the base of the soft dorsal in P. tuka.
Contrary to literature, the orange and dark spotting is not entirely reserved for P. pascalus. Some individuals as seen in the Japanese and Mariana forms lack much of the body spots. P. tuka, which was previously thought to lack this trait, can also appear to possess it. The specimens above and below show various individuals of P. tuka with this body spot patterning.
The dorsal fin coloration of P. tuka is also highly variable, as seen by the same image above. The ones on the lower left have the red so extreme that it strays onto the upper lip and lower jaw, forming a saddle. The traits that appear to be consistent in all examples of P. tuka is the placement of the dorsal fin spot, which irregardless of size, always sits at the base of the soft portion. The tails of P. tuka are also always purple, and so far we’ve not seen any examples where the tails are coloured differently.
Throat coloration for P. tuka appears to be another variable trait. In P. tuka, it is usually yellow but sometimes white throated individuals are seen. P. pascalus however appears to have no yellow throated forms.
Going back to Pseudanthias pascalus again, we explore more variations in the caudal as well as dorsal fin designs. Here is an example of P. pascalus from Fiji showing very unusual traits for both sexes, and this as far as we know, is the only variation of the female sex for the species. In the males here, the fish is uniformly purple with spotting on the body, as expected. However, both caudal lobes possess a single submarginal reddish ray that emerges from the caudal peduncle and ends as a filamentous tip.
The females here are uniformly purple, but possess a red tip on each tail lobe, somewhat akin to the tails of female P. hypselesoma. No other geographical form of P. pascalus appear to show variation in the female sex.
Interestingly the submarginal ray along the caudal lobes appears to be pretty consistent in Fijian males. What’s also interesting is that in both male Fijian specimens, the spinous portion of the dorsal fin is red washed, in some way or another. Fiji has a rather high rate of endemism, and it’s possible that these are showing early signs of speciation from the true P. pascalus type.
Finally, as a last closure, above is Pseudanthias pascalus from Japan showing the yellow tail, clean spotless body and the red dorsal suffision. This is a live photo of a wild individual that matches the plate in Randall’s Ryukyu specimen, as well as the live ones at the Omaha Zoo. With such intensive digging and sleuthing, we’ve pretty much managed to get most of the answers we were looking for. Or rather, at least now we can start looking in the right direction.
Where the zoo got their yellow tailed P. pascalus from however, is still a mystery. As far as I know, P. pascalus is not usually exported out from those locales in Japan. A quick search online reveals the presence of other yellow tailed specimens in aquaria, so perhaps another geographical zone within commercially collected areas harbour another population of this morph.
Whatever it is, it appears that both Pseudanthias tuka and Pseudanthias pascalus are housing within their respective species, a number of regional variants. It is highly possible that some of these may turn out to be cryptic species that could be separated in the future.
As far as Pseudanthias pascalus goes, most of the weirdly coloured specimens with red dorsal fins and yellow tails appear to overlap with standard forms, being sympatric in Japan as well as other parts of the Indo Pacific. These may very well just be local variations or unusual colour forms. The specimens from Fiji and the French Polynesia however are very consistent in their unique forms and do not appear to overlap with the standard pascalus type.
In Fiji, the females have red tipped tails while the males have a single red submarginal ray on each caudal fin lobes. In the French Polynesian chain, males appear to completely lack any red suffusion on their dorsal fin. Should speciation were to truly occur, these two regions and their corresponding forms could end up genetically distinct enough to warrant species recognition.
This topic would indeed serve as a wonderful thesis project. Special thanks to Joe Rowlett, Matt Wandell, Dr. Anthony Gill as well as Tim Morrissey for taking the time to delve into this matter with me.