RSS Awesome Fish Spotlight: Who took a tuka and made it pascalus?

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  1. MASA Admin

    MASA Admin Moderator

    8 May 2007
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    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 emergence of various insular variations.

    [​IMG]Pseudanthias tuka, female. In P. pascalus, the females completely lack any yellow coloration and are uniform steely purple. Photo by Vincent Chalias.

    Pseudanthias pascalus and P. tuka form a two species complex within the subgenus Mirolabrichthys, and are both superficially similar. The females can be readily identified by colour, being purple overall but possessing a yellow dorsal stripe which extends into both caudal lobes in P. tuka. P. pascalus has uniformly purple females, and are sometimes steely in appearance.

    [​IMG]Pseudanthias tuka, male. Note fine orange spots along the body, and a uniformly red dorsal fin. Two traits that P. tuka “should not” possess, the former being thought to be diagnostic of P. pascalus. Photo by Vincent Chalias.

    The males can be tricky to separate, 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 separation 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. In no papers does it mention any other characteristic ID keys such as tail or dorsal fin coloration. We also went on to to find out that this “orange or dark spots” is not true to some forms of P. pascalus, and this begs the question. Is that not a reliable feature for identification, and are there other cryptic species nestled within the pascalus and tuka complexes?

    [​IMG]A stunning male Pseudanthias pascalus, photographed at the Suzanne and Walter Scott Aquarium in Omaha’s Henry Doorly Zoo.

    Within a few friends, 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, purple overall but with a solid yellow caudal fin. Without much thought I initially went on to reply Tim with Pseudanthias pascalus as the identity of that anthias.

    [​IMG]Another male Pseudanthias pascalus, photographed at the Suzanne and Walter Scott Aquarium in Omaha’s Henry Doorly Zoo. Here it is displaying with another male in the background. Take note of the yellow tails.

    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. Remember, at this time we completely thought that the proper identification of Pseudanthias pascalus was through the possession of “orange and dark spots” in males, while being completely purple. Seeing as these specimens at the zoo were lacking said spots, and instead having a yellow caudal fin, I reevaluated and thought Pseudanthias tuka would be a better fit.

    A new set of questions surfaced. Are there any known forms or regional variations where Pseudanthias tuka can possess a yellow tail? Also, 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 quite clearly defined yellow dorsal fins. We also asked Joe Rowlett, and he initially suggested that the yellow tails could be a remnant female characteristic brought on during sex change. This also isn’t a completely farfetched idea, seeing as many species often change incompletely, or develop strange unnatural coloration in captivity.

    [​IMG]Regional forms of Pseudanthias pascalus. Photos by Dr. J. E. Randall, fish base. Take special note of P. pascalus from the Ryukyu peninsular with yellow caudal fins.

    Unsatisfied with the answers, 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 marked 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 as well as the placement of the red blotch is another highly variable characteristic, and it ranges from absent to very distinctive as seen above as well. *Note that in P. tuka and P. pascalus, the dorsal fin blotch is different. In P. tuka, it sits as a rather distinctive spot at the base of the soft dorsal fin, and sometimes also present along the spinous portion. This is another key that was never mentioned in any of the description papers.

    Another variable factor 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 be totally lacking in the spots, which again leads to that being an inconclusive definitive ID key.

    [​IMG]Pseudanthias pascalus from Moorea. Photo by Jeffrey Williams.

    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 again, this time with a more conscience search criteria. We started with the red coloration on the dorsal filament, and exactly how intensive it gets. In some specimens like this individual above from Moorea, dorsal fin rays could be totally devoid of red markings. This particular specimen does however, have the orange spots when examined closely.

    [​IMG]P. pascalus with varying shades of red on the dorsal fin. Photos by Moguring and S2club.

    This set of image above however, shows a complete opposite of the Moorea specimen. In these individuals, the red coloration appears to be highly extensive. The individual on the left from Iriomote as well as the inset photo of a specimen from Saipan shows a large portion of the dorsal fin coloured in red. The tail lobes in the Iriomote specimen appears to be slightly red washed as well. The right photo of an individual from Ishigaki shows a completely red dorsal fin, way more extensive than any of the rest.

    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 intensity of the red dorsal fin being restricted to these locales so far.

    [​IMG]Pseudanthias tuka, male specimen in aquaria. Note uniformly purple dorsal fin, lack of orange spots and dorsal fin blotch placed at the bottom portion of the soft rays.

    In Pseudanthias tuka, the red appears to more be often than not extended throughout the dorsal fin, sometimes up to the spinous portion as well. The photo of P. tuka at the beginning of the post and immediately below show specimens with very extensive red wash on the dorsal fin. However like P. pascalus, this this not always true and is rather variable as well. Immediately above is an aquarium specimen of P. tuka with a uniformly purple dorsal fin.

    [​IMG]P. tuka male with extensive red in dorsal fin. Photo by Florent Charpin.

    As mentioned before, P. tuka has a blotch that is present on the base of the soft dorsal fin, and sometimes an additional one on the spinous portion as well. P. pascalus totally lacks this blotch, and instead has it suffused messily high above the soft dorsal base, and never touches the body.

    Also, as previously mentioned, the orange and dark spotting is not entirely reserved for P. pascalus. We’ve seen specimens in this post which completely lacks it, and we’ve also seen this present in P. tuka as well. Take a look at the same red dorsal finned P. tuka above, and notice that the body is plagued with fine orange and dark spots too. This should make more sense now than when it was mentioned at the beginning.

    [​IMG]Examples of P. tuka with variations in their characteristics.

    This small collage of Pseudanthias tuka males show the great diversity and variations within this species as well, with difference in dorsal fin coloration. The ones on the lower left have the red so extreme that it strays onto the upper lip and lower jaw, forming a saddle. Also note some of these individuals with the presence of the orange spots as well, and that in all these individuals, the dorsal blotch regardless of size, appears to be restricted to only the base of the soft dorsal fin. This is at least pretty consistent for P. tuka.

    Throat coloration for P. tuka appears to be rather variable as well. In P. tuka, it is usually yellow but sometimes white throated individuals are seen as well. P. pascalus however appears to have no yellow throated forms.

    [​IMG]Pseudanthias pascalus from Fiji. Male with yellow submarginal ray, females with red tipped caudal lobes. Photo by Ryan Photographic.

    Back to Pseudanthias pascalus again, and this time with more variations of the fins. Here is a male from Fiji showing very unusual traits for both sexes, and this is as far as we know, the only variation of the female sex for this species so far. In the males here, the fish is uniformly purple with spotting on the body, as expected. However, both caudal lobes possess a single submarginal yellow ray that bears a slight resemblance to the females of P. tuka.

    The females here are uniformly purple, but possess a red tip on each tail lobe, somewhat akin to the tails of female P. hypselesoma.

    [​IMG]Pseudanthias pascalus from Fiji, with red submarginal caudal rays and dorsal fin. Photo by Robert Fenner.

    Another male Fijian specimen here above shows instead, a red submarginal ray coming out of the tail lobes. What’s interesting is that in both male Fijian specimens, the spinous portion of the dorsal fin is coloured red, in some way or another. Fiji has a rather high rate of endemism, and it’s possible that these showing early signs of speciation from the P. pascalus type.

    [​IMG]P. pascalus, male. Clean spotless body, yellow tail and red blotched dorsal fin.

    Finally, as a last closure, above is Pseudanthias pascalus from Japan showing the yellow tail, clean spotless body and the red dorsal blotch. This is a live photo of a wild individual that matches the plate in Randall’s Ryukyus specimen, as well as the live ones at the Omaha Zoo. With such intensive digging and sleuthing, we’ve pretty much managed to get all the answers we are 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.

    [​IMG]A table summary of the variations (as far as we know) of P. tuka vs P. pascalus.

    Whatever it is, it appears that both Pseudanthias tuka and Pseudanthias pascalus are housing within their respective species, a lot 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 with their unique forms and appears to not overlap with the standard pascalus type.

    In the former, the females have red tipped tails while the males have a single red or yellow submarginal ray on each of both caudal fin lobes. In the French Polynesia, all male specimens appear to lack any of the red dorsal blotch on the soft dorsal fin portion. 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 at hand.
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