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Celestial Pearl 'Danio' (Celestichthys margaritatus)

Celestichthys margaritatus
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Family: Cyprinidae

Type locality is ‘Pools at foot of mountain near Hopong town 30 kilometers east of Taunggyi, Myanmar, elevation 1040 meters’, thought restricted to a single locality around 1,040 m AMSL near the town of Hopong in Shan State, eastern Myanmar. It’s since been found in waters associated with the Salween (aka Thanlwin) River throughout southern Shan and even across the border in northern Thailand.

The type locality is an area of permanently-flooded grassland formed by the damming of a spring for agricultural purposes. The water is only around 30cm deep, transparent and supports dense growths of aquatic plants, mostly from the family Hydrocharitaceae which includes such genera as Elodea, Egeria and Blyxa. Sympatric species included Devario sondhii, a Microrasbora cf. rubescens, an undescribed Petruichthys species known to aquarists as the ‘rosy’ loach and Channa harcourtbutleri. From images most of the the other habitats look broadly similar, i.e., shallow areas of wetland surrounded by open grassland though at least one population was supposedly discovered in ‘deep forest’.

Maximum Standard Length:
The largest officially-recorded specimen measured just 21mm.

Aquarium Size:
Despite its small size we wouldn’t keep a group of these in anything with base dimensions measuring less than 45 x 30cm due to the sometimes combative behaviour of dominant males. It is advised to find a filter which has a water flow between 4-5 times the volume of your aquarium.

This timid species should ideally be kept in a heavily-planted set-up, preferably with a dark substrate. The broken lines of sight that exist in such a display allow it to display natural behaviour as well as helping to reduce skittishness. Floating plants are a useful addition but driftwood and oak/beech/almond leaf litter are best avoided as the tannins they release are not a feature of its natural waters. Use gentle filtration; an air-powered sponge-style unit should prove adequate.

Water Conditions:
20 – 26°C
pH: 6.5 – 7.5
Hardness: 90 – 268 ppm

In the aquarium it will accept dried foods of a suitable size but should not be fed these exclusively, and as it rarely rises to the surface there’s little point in offering floating products. Daily meals of small live and frozen fare such as Daphnia, Artemia and suchlike will not only result in the best colouration but encourage the fish to come into breeding condition.

Behaviour and Compatibility:
Likely to be intimidated or outcompeted for food by larger or more boisterous tankmates, although the presence of similarly-sized, surface-dwelling species seems to help reduce its shyness. Other small cyprinids from Myanmar such as Celestichthys choprae or members of the genus Microdevario are suitable companions, and we suspect it might also do well alongside Dario hysginon or D. sp. ‘Myanmar’. The closely-related C. erythromicron is not recommended as it’s probably capable of hybridising with C. margaritatus. Though gregarious by nature it’s a shoaling rather than schooling species with rival males sparring on a regular basis during daylight hours. It’s not uncommon to see nipped fins within a group though this behaviour does not normally extend to tankmates. Buy as many as possible, ideally 20 or more, as when larger numbers are present the aggression is spread between individuals plus the fish are bolder, more often-seen, and exhibit better colouration.

Sexual Dimorphism:
Males have a steel-to-deep blue body colouration extending over the majority of the flanks and intense red and black striping in all fins except the pectorals. The spots on the body are pearly white to cream-coloured and in nuptial individuals the abdomen turns reddish, overall body colour intensifies and as a result the pale stripe running lengthways over the top of the head becomes better-defined. Females have a blue-green base body colouration and less prominent, weakly red to orange colour patches in the fins with the ventrals patternless. The body spots are cream to golden and don’t extend into the anterior portion of the abdomen. They tend to grow a little larger than males and have a more rounded overall body shape, especially when gravid. When in spawning condition they display a small dark marking at the vent.

Like many small cyprinids this species is an egg-scattering spawner that shows no parental care. If the fish are in good condition they will spawn often and in a densely-planted, mature aquarium it’s possible that small numbers of fry may start to appear without intervention. However if you want to increase the yield of fry a slightly more controlled approach is required. The adult group can still be conditioned together but one or more smaller, perhaps 10-15ltr, containers should also be set up and filled with aged water. Fill much of the available space with fine wool mops, Taxiphyllum or other fine-leaved plant. Neither lighting nor filtration is necessary although you can install a small air-powered sponge filter if you prefer. When the adult fish are well-conditioned a single pair or group comprising one or two males and several females can then be introduced to each container, though it’s worth noting that the more individuals involved the greater the risk of egg predation, plus males may distract each other from females if there’s more than one in the tank. Spawning normally presents few problems with around 30 mildly adhesive eggs deposited in a typical event. At this point the adults are best removed as they will eat any they find, plus females need a recovery period before spawning again as they’re unable to produce eggs on a daily basis. In nature it apparently breeds year-round so you could always select another pair and work a rotation system if continuous production is the aim. Incubation is temperature-dependant to an extent but usually takes around 72 hours with the young free-swimming 3-4 days later. Initial food should be Paramecium or a proprietary dry food of sufficiently small (5-50 micron) grade, introducing Artemia nauplii, microworm, etc., once the fry are large enough to accept them.