Celestial Pearl Danio (Danio margaritatus)

Danio margaritatus, the celestial pearl danio, a small cyprinid from Burma. (Image Credit: TropicalFiskKeeping.com)

Danio margaritatus, the celestial pearl danio, a small cyprinid from Burma. (Image Credit: TropicalFiskKeeping.com)

Sometimes, a fish can simply leave you speechless.  Leaving you to simply mutter, “Wow.”

That was my reaction when I saw the photo above.

While I was writing the recent post on hitch (Lavinia exilicauda), I searched Google to look up the smallest members of the Family Cyprinidae. This photo and the words “galaxy rasbora” popped up in one of my search returns.

I had been out of the aquarium fish hobby for quite a few years, and apparently, I have been missing out on some incredible new species. I was stunned to see this luxurious combination of colors — gold spots upon dark teal, fins trimmed  with bright strawberry-red. And this bombastic name — galaxy rasbora — seemed so audacious for a tiny fish that could barely stretch across a U.S. nickel coin (0.8 inches/2.1 cm).

It was an unbelievably beautiful fish. And as it turns out, many people did not believe it was a real fish either, at first.

The stunning colors of Danio margaritatus, whose specific name translates as "adorned with pearls". (Image Credit: unknown; sourced from www.myfishtank.net)

The stunning colors of Danio margaritatus, whose specific name translates as “adorned with pearls”. (Image Credit: unknown; sourced from http://www.myfishtank.net)

Practical Fishkeeping article from 2010 and a Tropical Fish Magazine article from 2007 recount that when an eminent Thai fish exporter first shared photos of this fish on the internet in 2006, some aquarists were skeptical and thought the photos to be Photoshopped jokes. The beauty of this so-called “galaxy rasbora” seemed too good to be true.

But the joke was on the skeptics when within weeks, live specimens became available for sale. Eventually, a shipment of specimens was sent to Tyson Roberts, a research associate of the Smithsonian Tropical Research Institute.

A 21.2 mm mature male (ZRC 50706) that served as the holotype specimen used to describe the new species Celestichthys margaritatus, later renamed Danio margaritatus. (Image Credit: Kamphol Udomritthiruj, published in Roberts 2007)

A 21.2 mm mature male (ZRC 50706) that served as the holotype specimen used to describe the new species Celestichthys margaritatus, later renamed Danio margaritatus. (Image Credit: Kamphol Udomritthiruj, published in Roberts 2007)

A 20.5 mm mature female (ZRC 50707) used as the paratype specimen used to describe Celesichthys margaritatus, later renamed Danio margaritatus. (Image Credit: Kamphol Udomritthiruj, published in Roberts 2007)

A 20.5 mm mature female (ZRC 50707) used as the paratype specimen used to describe Celesichthys margaritatus, later renamed Danio margaritatus. (Image Credit: Kamphol Udomritthiruj, published in Roberts 2007)

The specimens came from small pools near the town of Hopong, in the Shan State of Myanmar (Burma), about 3,420 feet (1,040 m) in elevation.

Roberts would describe the fish as a new genus and species, Celestichthys margaritatus — which means “a heavenly fish adorned with pearls” (Roberts 2007). Roberts also suggested that “celestial pearl danio” be used as the English name, owing to his analysis that the new fish was more closely related to danios, a known group of cyprinid species, rather than rasboras, another group of cyprinid species.

The locale near Hopong, Myanmar, where the type specimen of Danio margaritatus was collected. (Image Credit: Kamphol Udomrittthiruj, published in Roberts 2007)

The locale near Hopong, Myanmar, where the type specimen of Danio margaritatus was collected. (Image Credit: Kamphol Udomrittthiruj, published in Roberts 2007)

Roberts’ danio diagnosis proved to be more accurate than he thought. In 2008, researchers at St. Louis University in Missouri, United States, would conduct additional analysis on the body structure and genetics of the celestial pearl danio. They found it to be similar enough to known fish species in the genus Danio and not different enough to warrant its own, unique genus, so they revised its name and classification to Danio margaritatus (Conway et al. 2008).

This name-change trivia finally gives me an example with which to explain a little detail from the world of zoological taxonomy…

In each Better Know a Fish profile, I list the scientific name of the species at the end. But you may have wondered why there is always a person’s name and year attached to that name. For example, in this post you will find:

Danio margaritatus (Roberts, 2007)

Here, Roberts’ name is in parentheses. But compare that to this:

Acanthurus achilles Shaw, 1803

No parentheses around Shaw’s name — which isn’t a typing error.

So what do these names and parentheses mean?

When researchers come across a potentially new animal species, some measure of research has to be done to declare it to be new. The new animal has to be examined and compared against specimens of similar, known species, in order to determine where this species fits into human classifications of known living things.

It is difficult work — imagine comparing the jaw bone shapes of these tiny danios. Once the analysis is complete, the researchers will present the evidence in an article for publication in a scientific journal. In the article, the researchers also have the privilege of proposing a two-part scientific name (like Celestichthys margaritatus), and optionally, an English common name.

With that article, the species becomes officially “described” to the world of professional science.

The authors of that article also receive credit for describing and naming the new species, and by taxonomic etiquette, whenever that species is mentioned in any future research articles for the first time, the describing author and the year of description is written alongside its scientific name.

But of course, science is not static — it is a process through which evidence can always reexamined and new findings determined. With any species, additional research may reveal evidence to suggest changes to the original classification.

Here, researchers Kevin Conway, Wei-Jen Chen and Richard Mayden reexamined Celestichthys margaritatus and determined that it really doesn’t warrant a new genus, and reclassified the species as Danio margaritatus — and this has since become widely accepted as the appropriate designation.

But under zoological taxonomy rules, Roberts’ name will always be attached to the celestial pearl danio, even if the species is reclassified yet again by another team. And to signify that the currently accepted scientific name was the work of researchers after Roberts, Roberts’ name is now put in parentheses.

Keeping the original authors with each species helps future researchers look up the original description research, should they ever need to. Of course, the continued recognition of the original authors isn’t so bad — describing a new species is a big deal, and a handsome feather in any biologist’s cap.

Now compare this to Acanthurus achilles Shaw, 1803. No parentheses. This means that no one has challenged (at least successfully) Shaw’s original assignment that the Achilles tang belongs in the genus Acanthurus, and that the name has never been changed since Shaw’s original mention.

I should note that I have greatly simplified the species description process here. The official code of conduct — there is one — has far more regalia and almost court-like procedures, steered by the International Commission on Zoological Nomenclature (ICZN) and the International Union of Biological Sciences (IUBS).

One last tidbit: There are no such etiquette or procedures for establishing English common names. An aquarium store can choose to advertise Danio margaritatus as the “galaxy rasbora” or “fireworks rasbora” or “celestial pearl danio” — which ever one sells better, I suppose, although eventually, a name will stick in the public mindset or among professional enthusiasts.

Which name do I like? For me, I’ll probably just stick with “Wow” and keep on admiring….

Danio margaritatus (Roberts, 2007)
Celestial Pearl Danio
Click for name etymology (ETYFish Project)
Click for names in other languages (FishBase)

Class Actinopterygii (Ray-finned Fishes)
Order Cypriniformes (Carp-like Fishes)
Family Cyprinidae (Carps and Minnows)

FishBase Page: http://www.fishbase.org/summary/63298

Citations

Conway, KW, WJ Chen, RL Mayden. 2008. The “Celestial Pearl Danio” is a miniature Danio (s.s)(Ostariophysi: Cyprinidae): evidence from morphology and molecules. Zootaxa 1686: 1-28.

Roberts, TR. 2007. The “celestial pearl danio”, a new genus and species of colourful minute cyprinid fish from Myanmar (Pisces: Cypriniformes). The Raffles Bulletin of Zoology 55(1): 131-140.

– Ben Young Landis

Talk About This Fish

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s