Celestichthys margaritatus
Encyclopedia
The Celestial Pearl Danio, Danio margaritatus - often referred to in the aquarium trade as galaxy rasbora or "Microrasbora sp. 'Galaxy'" - is a small cyprinid
from Myanmar
. It has so far been found only in a very small area near Hopong
east of Inle Lake
, at an altitude of over 1,000 m (3,400 ft). Its habitat
is part of the Salween basin, namely the Nam Lang and Nam Pawn rivers. Discovered in 2006, the species
quickly appeared in the aquarium trade
, where its small size and bright colours made it an instant hit.
with a markedly blunt snout, measuring just 1.5–2 cm standard length. The body is about three times as long as it is high. In general shape, it resembles Danio erythromicron
more than any other known species.
This species shows some sexual dimorphism
: males have a bright blue background color (dull blue-green in females), and their 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
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
s shine through.
The males' fins (except the pectoral fins), which they will prominently display to conspecifics, show two parallel black lines with a bright red area in between; on the tailfin 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.
Courting males develop 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. Females 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. Males have 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.
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 that the Celestial Pearl Danio was a member of the genus Danio, with Danio erythromicron and Danio choprae as its closest relatives.
similar to Elodea
(water weed).
The Celestial Pearl Danio shares its habitat with very few fish species. Namely, a Microrasbora
similar to M. rubescens, a rosy loach
(Yunnanilus
, possibly a new species) and the dwarf snakehead Channa harcourtbutleri
. The latter species presumably is the only known significant predator of D. margaritatus.
The species is locally fished for food to some extent; it is dried and bought as a protein
source by poor people. A can of some 500 D. margaritatus sold for food fetched about 25 kyat (about 2 UK pounds/3.9 US$/2.7 EUR) before the fish was discovered for the aquarium trade.
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 and follow the mating pair, either to try to fertilize the eggs with their own sperm
or eat them.
At 24-25°C, the larva
e hatch after 3–4 days. They are dark and cryptic
initially and for about three days after hatching, they hide away between substrate and detritus
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.
is currently asking that only aquarists prepared to breed the fish should buy any fishes 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 pools, it seems 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. On the other hand, if only part of a local subpopulation is removed, it seems likely that pools from which all Celestial Pearl Danios have been removed will be recolonized with a healthy population again after one year or so.
The government of Myanmar banned exports of the fish in February 2007; as the fish were still available in numbers in the aquarium trade since then, it is unclear to what degree the ban was enforced. Since then, new populations of this fish have been found around Hopong. In the long run, this fish seems a valuable source of income for locals; by early 2007, a single fisherman could make up to 750 kyat (about 60 UK pounds/116 US$/80 EUR) from a single day's work; in 2005 the average gross domestic product
per capita (PPP
) in Myanmar was just around 1,700 US$.
. 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 6 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
has been successfully used). A dense tangle of natural plants for spawning has the additional advantage of harboring protist
s on which the fry feed initially. The Celestial Pearl Danio seems overall quite peaceful, though some fin-nipping occurs. Consequently, it cannot be accompanied 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. Note than many danionins prefer slightly acidic water however, and that maintaining the rather high pH
found across the Inle basin seems a necessary condition to keep fish from there successfully.
Cyprinid
The family Cyprinidae, from the Ancient Greek kyprînos , consists of the carps, the true minnows, and their relatives . Commonly called the carp family or the minnow family, its members are also known as cyprinids...
from Myanmar
Myanmar
Burma , officially the Republic of the Union of Myanmar , is a country in Southeast Asia. Burma is bordered by China on the northeast, Laos on the east, Thailand on the southeast, Bangladesh on the west, India on the northwest, the Bay of Bengal to the southwest, and the Andaman Sea on the south....
. It has so far been found only in a very small area near Hopong
Hopong
Hopong is a town in the Shan State of eastern Burma. It is located in Hopong Township in Taunggyi District.-External links:*...
east of Inle Lake
Inle Lake
Inle Lake is a freshwater lake located in the Nyaungshwe Township of Taunggyi District of Shan State, part of Shan Hills in Myanmar . It is the second largest lake in Myanmar with an estimated surface area of , and one of the highest at an altitude of...
, at an altitude of over 1,000 m (3,400 ft). Its habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
is part of the Salween basin, namely the Nam Lang and Nam Pawn rivers. Discovered in 2006, the species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
quickly appeared in the aquarium trade
Fishkeeping
Fishkeeping is a popular hobby concerned with keeping fish in a home aquarium or garden pond. There is also a fishkeeping industry, as a branch of agriculture.-Types of fishkeeping systems:...
, where its small size and bright colours made it an instant hit.
Description
This is a small plump danioninDanionin
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 and Devario. They are native to the fresh waters of southeast Asia. Many species are brightly coloured and are available as aquarium fish worldwide...
with a markedly blunt snout, measuring just 1.5–2 cm standard length. The body is about three times as long as it is high. In general shape, it resembles Danio erythromicron
Microrasbora erythromicron
Danio erythromicron 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 the genus Danio based on morphological data, but it was cautioned that more research would be necessary...
more than any other known species.
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
: males have a bright blue background color (dull blue-green in females), and their fin
Fin
A fin is a surface used for stability and/or to produce lift and thrust or to steer while traveling in water, air, or other fluid media, . The first use of the word was for the limbs of fish, but has been extended to include other animal limbs and man-made devices...
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
Pearl
A pearl is a hard object produced within the soft tissue of a living shelled mollusk. Just like the shell of a mollusk, a pearl is made up of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other...
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
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s shine through.
The males' fins (except the pectoral fins), which they will prominently display to conspecifics, show two parallel black lines with a bright red area in between; on the tailfin 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.
Courting males develop 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. Females in reproductive age can be recognized by a black anal
Anus
The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...
spot which separates the belly color from the uniformly reddish base of the anal fin. Males have 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.
Systematics and taxonomy
Initially the Celestial Pearl Danio was assumed to be a member of the genusGenus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Microrasbora
Microrasbora
Microrasbora is a genus of small fishes. The generic name means "small Rasbora", however these are more closely related to the danios than rasboras. They inhabit mainly Thailand and Myanmar, with one putative species in China.-Current Taxonomy:...
, 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 that the Celestial Pearl Danio was a member of the genus Danio, with Danio erythromicron and Danio choprae 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 and thus D. margaritatus is probably tolerant of temperatures in the low to mid 20s. Like most waterbodies in the Inle drainage, the water is slightly alkaline. The habitat is heavily vegetated with HydrocharitaceaeHydrocharitaceae
Hydrocharitaceae is a flowering plant family that includes a number of species of aquatic plant, broadly called the Tape-grasses, and includes the well known Canadian Waterweed and Frog's Bit.The family includes both fresh and marine aquatics...
similar to Elodea
Elodea
Elodea is a genus of aquatic plants often called the waterweeds. Elodea is native to North America and is also widely used as aquarium vegetation. The introduction of some species of Elodea into waterways in parts of Europe, Australia, Africa, Asia, and New Zealand has created a significant problem...
(water weed).
The Celestial Pearl Danio shares its habitat with very few fish species. Namely, a Microrasbora
Microrasbora
Microrasbora is a genus of small fishes. The generic name means "small Rasbora", however these are more closely related to the danios than rasboras. They inhabit mainly Thailand and Myanmar, with one putative species in China.-Current Taxonomy:...
similar to M. rubescens, a rosy loach
Loach
Loach may refer to:* Loaches, fish families in the Cypriniformes:** Cobitidae, the "true" loaches – formerly all loaches were united in this family** Balitoridae, the hillstream loaches – the largest family, closely related to Cobitidae...
(Yunnanilus
Yunnanilus
Yunnanilus is a genus of ray-finned fish in the hillstream loach family Balitoridae.- Species :It contains the following species:* Yunnanilus altus Kottelat & X. L. Chu, 1988* Yunnanilus analis J. X. Yang, 1990...
, possibly a new species) and the dwarf snakehead Channa harcourtbutleri
Channa harcourtbutleri
Channa harcourtbutleri is a species of snakehead endemic to Inle Lake and surroundings in Myanmar. Locally called nga ohn-ma, among aquarists it is known as one of the "dwarf snakeheads", but no significant import for aquarists is known. It is one of the smallest species of snakehead and has a...
. The latter species presumably is the only known significant predator of D. margaritatus.
The species is locally fished for food to some extent; it is dried and bought as a protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
source by poor people. A can of some 500 D. margaritatus sold for food fetched about 25 kyat (about 2 UK pounds/3.9 US$/2.7 EUR) before the fish was discovered for the aquarium trade.
Reproduction
The spawning behavior has significant consequences for captive breeding (see below). It appears as if the Celestial Pearl Danio is adapted to somewhat ephemeral habitat. It does not have a dedicated spawningSpawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called 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 and follow the mating pair, either to try to fertilize the eggs with their own sperm
Sperm competition
Sperm competition is a term used to refer to the competitive process between spermatozoa of two different males to fertilize an egg of a lone female. Competition occurs whenever females engage in promiscuous mating to increase their chances in producing more viable offspring...
or eat them.
At 24-25°C, the larva
Larva
A larva 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...
e hatch after 3–4 days. They are dark and cryptic
Crypsis
In ecology, crypsis is the ability of an organism to avoid observation or detection by other organisms. It may be either a predation strategy or an antipredator adaptation, and methods include camouflage, nocturnality, subterranean lifestyle, transparency, and mimicry...
initially and for about three days after hatching, they hide away between substrate and detritus
Detritus
Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
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 had become so rare that collectors were obtaining only a "few dozen fish per day". Whilst some aquarists have managed to breed the fish successfully, almost all the fishes currently offered for sale are wild-caught. British fishkeeping magazine Practical FishkeepingPractical Fishkeeping
Practical Fishkeeping is the United Kingdom's best-selling aquarium magazine. It is published every four weeks by Bauer...
is currently asking that only aquarists prepared to breed the fish should buy any fishes 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 pools, it seems 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. On the other hand, if only part of a local subpopulation is removed, it seems likely that pools from which all Celestial Pearl Danios have been removed will be recolonized with a healthy population again after one year or so.
The government of Myanmar banned exports of the fish in February 2007; as the fish were still available in numbers in the aquarium trade since then, it is unclear to what degree the ban was enforced. Since then, new populations of this fish have been found around Hopong. In the long run, this fish seems a valuable source of income for locals; by early 2007, a single fisherman could make up to 750 kyat (about 60 UK pounds/116 US$/80 EUR) from a single day's work; in 2005 the average gross domestic product
Gross domestic product
Gross domestic product refers to the market value of all final goods and services produced within a country in a given period. GDP per capita is often considered an indicator of a country's standard of living....
per capita (PPP
Purchasing power parity
In economics, purchasing power parity is a condition between countries where an amount of money has the same purchasing power in different countries. The prices of the goods between the countries would only reflect the exchange rates...
) in Myanmar was just around 1,700 US$.
In the aquarium
The Celestial Pearl Danio is a rather undemanding fish if its basic requirements are being taken care of. It seems quite hardy but obviously thrives best in fairly soft and slightly alkaline water at not too high a temperature - conditions that can often be met with pretreated tap waterTap water
Tap water is a principal component of "indoor plumbing", which became available in urban areas of the developed world during the last quarter of the 19th century, and common during the mid-20th century...
. It does not require much space, as it is not a very active swimmer, and is not a true shoaling
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
fish, meaning it does not require large numbers of conspecifics for its well-being. In a small tank, a group of 6 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
Java Moss is a moss belonging to the Hypnaceae family. Native to Southeast Asia, it is commonly used in freshwater aquariums. It attaches to rocks, roots, and driftwood...
has been successfully used). A dense tangle of natural plants for spawning has the additional advantage of harboring protist
Protist
Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy...
s on which the fry feed initially. The Celestial Pearl Danio seems overall quite peaceful, though some fin-nipping occurs. Consequently, it cannot be accompanied 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. Note than many danionins prefer slightly acidic water however, and that maintaining the rather high pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
found across the Inle basin seems a necessary condition to keep fish from there successfully.
External links
- Danio margaritatus
- Danio margaritatus on the Aquarium Wiki Encyclopaedia