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''Danio margaritatus'', the celestial pearl danio, often referred to in the aquarium trade as galaxy rasbora or ''Microrasbora'' sp. 'Galaxy',Clarke (2007b) is a small
cyprinid Cyprinidae is a family of freshwater fish commonly called the carp or minnow family. It includes the carps, the true minnows, and relatives like the barbs and barbels. Cyprinidae is the largest and most diverse fish family and the largest verte ...
from
Myanmar Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John C. Wells, Joh ...
. It has so far been found only in a very small area near Hopong east of Inle Lake, at an elevation of over 1,000 m (3,400 ft). Its
habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
is part of the
Salween , ''Mae Nam Salawin'' ( , name_etymology = , image = Sweet_View_of_Salween_River_in_Tang_Yan_Township,_Shan_State,_Myanmar.jpg , image_size = , image_caption = Salween River in Shan State, Myanmar , map ...
basin, namely the Nam Lang and
Nam Pawn This is a list of rivers in Myanmar (also known as Burma). This list is arranged by drainage basin from east to west, with respective tributaries indented under each larger stream's name. Indian Ocean * Nāf River * Kaladan River * Lemro Riv ...
Rivers. Discovered in 2006, the
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
quickly appeared in the aquarium trade, where its small size and bright colours made it an instant hit.Clarke (2006)


Description

This is a small, plump
danionin The danionins are a group of small, minnow-type fish belonging to the family Cyprinidae. Members of this group are mostly in the genera ''Danio'', ''Devario'', and ''Rasbora''._They_are_primarily_native_to_the_s_...''._They_are_primarily_native_t ...
with a markedly blunt snout, measuring just 2–2.5 cm
standard length Fish measurement is the measuring of individual fish and various parts of their anatomies. These data are used in many areas of ichthyology, including taxonomy and fisheries biology. Overall length * Standard length (SL) is the length of a fish m ...
. The body is about three times as long as it is high. In general shape, it resembles ''
Danio erythromicron ''Danio erythromicron'', often known as emerald dwarf danio and emerald dwarf rasbora, is a species of cyprinid fish which is endemic to Inle Lake in Myanmar. Taxonomy and systematics In 1999, it was suggested that the species be transferred to t ...
'' more than any other known species. This species shows some
sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
: males have a bright-blue background color (dull blue-green in females), and their
fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...
s are more brightly colored. The tail end of their bodies (the caudal peduncle) is also higher than in females. The body is sprinkled with small,
pearl A pearl is a hard, glistening object produced within the soft tissue (specifically the mantle) of a living shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pearl is composed of calcium carb ...
y dots. The back is bronzy green, and the belly in females is yellowish-white. The gill covers are transparent, letting the blood-red
gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
s shine through. The males will prominently display their unpaired fins to conspecifics. All fins, save the
pectoral fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...
s, show two parallel black lines with a bright red area in between; on the tail fin, this pattern is present twice (once on each lobe) and the outer black band is vestigial. Females have a weaker version of the pattern in the tail and dorsal fins only, sometimes in the anal fin, too. A courting male develops a red belly and the flanks brighten and darken, making the pearly spots stand out even more, with the back appearing paler than the flanks and also standing out. A female in reproductive age can be recognized by a black anal spot which separates the belly color from the uniformly reddish base of the
anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...
. The male has a small black pad at the edges of the lower jaw, which is absent or reduced in females. Immature fish show some indication of a striped pattern, which eventually decomposes into the pearly dots. File:danio_männchen_2.jpg, Male File:Danio_männchen_3.jpg, Male File:danio_weibchen_2.jpg, Female


Systematics and taxonomy

Initially, the celestial pearl danio was assumed to be a member of the
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
'' Microrasbora'', due to its similarity to '' "Microrasbora" erythromicron''. Less than a year after the discovery of the celestial pearl danio, it was scientifically described and given the genus name ''Celestichthys''. In 2008, a more comprehensive study showed the celestial pearl danio was a member of the genus ''Danio'', with ''
Danio erythromicron ''Danio erythromicron'', often known as emerald dwarf danio and emerald dwarf rasbora, is a species of cyprinid fish which is endemic to Inle Lake in Myanmar. Taxonomy and systematics In 1999, it was suggested that the species be transferred to t ...
'' and ''
Danio choprae The glowlight danio (''Danio choprae'') is a small, schooling fish closely related to the popular zebrafish ''Danio rerio''. This should not be confused with the GloFishbr> a trademarked brand of fluorescent zebrafish that appear to glow in the d ...
'' as its closest relatives.


Ecology

The fish lives in small ponds created by seeping groundwater or overflow from small brooks or springs. Water temperature in January was rather low (22–24 °C), but as the habitat is very shallow, it would heat up quickly during hot spells, thus ''D. margaritatus'' is probably tolerant of temperatures above the low 20s. As in most water bodies in the Inle drainage, the water is slightly
alkaline In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...
. The habitat is heavily vegetated with Hydrocharitaceae similar to '' Elodea'' (water weed). The celestial pearl danio shares its habitat with a very few fish species: a '' Microrasbora'' similar to '' M. rubescens'', a rosy loach (''
Yunnanilus ''Yunnanilus'' is a genus of small stone loaches that are endemic to southeastern China, especially Guangxi and Yunnan. They are found in rivers, streams and lakes; some species are restricted to caves. Species There are currently 35 recogniz ...
'', possibly a new species, and the dwarf snakehead ''
Channa harcourtbutleri ''Channa harcourtbutleri'', the Burmese snakehead, is a species of snakehead endemic to Inle Lake and surroundings in Myanmar. Locally called ''nga ohn-ma'', among aquarists it is considered one of the dwarf snakeheads, but no significant impor ...
''. The latter species presumably is the only known significant
predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
of ''D. margaritatus''. The species is locally fished for food to some extent; it is dried and bought as a
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
source by poor people. A can of some 500 ''D. margaritatus'' sold for food fetched about 25
kyat The kyat (, or ; my, ကျပ် ; ISO 4217 code MMK) is the currency of Myanmar (Burma). The typical notation for the kyat is "K" (singular) and "Ks." (plural), placed before the numerals followed by " /-" The term ''kyat'' derives from th ...
(about 2 UK pounds/3.9 US$/2.7 EUROfficial exchange rate of January 21, 2008, as pe
XE.com Universal Currency Converter
) before the fish was discovered for the aquarium trade.Clarke (2007a)


Reproduction

The spawning behavior has significant consequences for captive breeding (see
below Below may refer to: *Earth *Ground (disambiguation) *Soil *Floor *Bottom (disambiguation) Bottom may refer to: Anatomy and sex * Bottom (BDSM), the partner in a BDSM who takes the passive, receiving, or obedient role, to that of the top or ...
). The celestial pearl danio appears to be
adapted In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
to somewhat ephemeral habitats. It does not have a dedicated spawning season, nor do the females lay continuously. Rather, they produce small batches of around 30 eggs per spawning episode. The time between spawnings is unknown at present. Eggs are not strewn freely into the water, but they are not deposited in clutches to a prepared surface either; rather, it seems, that they are hidden away in vegetation as a loose batch. Courting males will seek out and try to defend a patch of dense vegetation. While pursuit swimming has been observed, it does not seem to be connected directly to the actual act of reproduction in which the male displays to a passing female, and tests her readiness with a brief chase. The pair then moves into the substrate and deposits the eggs. Other males noticing reproduction will try to follow the mating pair, either to try to fertilize the eggs with their own sperm or eat them. At 24–25 °C, the
larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...
e hatch after 3–4 days. They are dark and
cryptic Cryptic may refer to: In science: * Cryptic species complex, a group of species that are very difficult to distinguish from one another * Crypsis, the ability of animals to blend in to avoid observation * Cryptic era, earliest period of the Earth ...
initially and for about three days after hatching, they hide away between substrate and
detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...
and are very hard to see. They subsequently become lighter in color and start swimming freely and feeding on their own. At some 8–10 weeks after hatching, they undergo metamorphosis to adult form, and the color pattern starts to appear from week 12 onwards.


Status and conservation

Within six months of its appearance in the aquarium trade, the species was falsely reported as having become so rare, collectors were obtaining only a "few dozen fish per day". Initially, only a small number of aquarists managed to breed the fish successfully, while nearly all the fish offered for sale were wild-caught. The (unfounded) concern over the wild populations led British fishkeeping magazine '' Practical Fishkeeping'' to request that only aquarists prepared to breed the fish should buy any fish they see for sale, to reduce pressure on the wild stocks by diminishing the demand for them in the UK. As the species seems adapted to living in and colonizing small, possibly
ephemeral pool Vernal pools, also called vernal ponds or ephemeral pools, are seasonal pools of water that provide habitat for distinctive plants and animals. They are considered to be a distinctive type of wetland usually devoid of fish, and thus allow the safe ...
s, it seemed not very well able to withstand prolonged and intense exploitation—if the stock in all pools at one location is entirely fished off, it is unclear in how far the fish would be able to recolonize them. Conversely, if only part of a local subpopulation is removed, pools from which all celestial pearl danios have been removed likely will be recolonized with a healthy population again after one year or so. The dire warnings reported by Clarke, later in 2007 were found to be unfounded. The celestial pearl danio is prolific, spawning "almost every day", causing ponds that were thought to be empty to be fully restocked a few months later as fry hatched, grew, and reproduced quickly. The government of Myanmar banned exports of the fish in February 2007. However, an inquest into the species by Myanmar officials discovered populations of the fish in at least "five locations around Hopong". Currently, the fish is captive-bred worldwide commercially and by hobbyists,celestialpearldanio.com (forum) pushing the price down from its initial high of $20 or more per fish to around $4 each.


In the aquarium

The celestial pearl danio is a rather undemanding fish if its basic requirements are being met. It does not require much space, as it is not a very active swimmer, and is not a true shoaling fish, meaning it does not require large numbers of conspecifics for its well-being. In a small tank, a group of six individuals—half males, half females—will do well and exhibit natural behavior. They tend to be rather stationary, hovering in a peculiar position in favorite spots; males and females tend to keep separate when at rest. Altogether, their behavior again resembles ''Danio erythromicron'' more than other fish. Tanks for the celestial pearl danio should be well-planted and direct daylight may be favorable (the natural habitat is so shallow as to be well lit throughout). Water weed and similar plants should be abundant, and stones and wood to create hiding spots should be provided. It is advisable to supply the fish with a spawning mop or a dense growth of suitable plants (
java moss Java moss is a common name for several plants and may refer to: *''Taxiphyllum barbieri'' *''Vesicularia dubyana ''Vesicularia dubyana'', known as Java moss or Singapore moss, is a species of moss native to Asia. It is common in the aquarium tra ...
has been successfully used). A dense tangle of natural plants for spawning has the additional advantage of harboring
protist A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exc ...
s on which the fry feed initially. The celestial pearl danio seems overall quite peaceful, though some fin-nipping occurs. Consequently, it cannot be kept with large or "bully" fish. Small, swarming danionins which require similar water conditions would be a natural choice for company, as such more active species provide nice contrast behaviorally and, being available in a wide range of colors and patterns, also make it possible to choose fish that complement the brilliant colors of ''D. margaritatus''. Many danionins prefer slightly acidic water, however, and maintaining the rather high pH found across the Inle basin seems a necessary condition to keep fish from there successfully.


References

* * (2006)
The next big thing: ''Microrasbora'' sp. Galaxy
'' Pract. Fishkeeping'' Version of September 9, 2006. Retrieved August 12, 2012. * (2007a)
Galaxy rasbora under threat
'' Pract. Fishkeeping'' Version of February 5, 2007. Retrieved August 12, 2012. * (2007b)
Galaxy rasbora placed in new genus
'' Pract. Fishkeeping'' Version of February 28, 2007. Retrieved August 12, 2012. * (2007c)
New populations of ''Celestichthys'' discovered
'' Pract. Fishkeeping'' Version of June 5, 2007. Retrieved August 12, 2012. * * * (2007)
The Celestial Pearl Danio: A Cautionary Tale
''Tropical Fish Magazine'' Published July 2007. Retrieved August 12, 2012. *

Retrieved August 12, 2012. * (forum)
Celestial Pearl Danio Information and Breeding forum.
Retrieved August 12, 2012.


External links

*
Danio margaritatus
' * ''Danio margaritatus'' on the Aquarium Wiki Encyclopaedia {{DEFAULTSORT:Danio Margaritatus Endangered fish Fishkeeping Danio Fish described in 2007 Taxa named by Tyson R. Roberts