Initially considered endemic to the northwestern slope of southern (peninsular) Thailand in the provinces of Ranong and Phang Nga but records now exist from Kanchanaburi and Tak provinces, north of the Isthmus of Kra. Type locality is ‘Khlong Phrae Sai at Ban Kreo Noi, kilometer 8 on road banching east, 32 kilometers north of Ranong on road from Ranong to Kra Buri (10°09’51″N, 98°41’11′E), Ranong Province, Thailand’.
In the Songgaria River, part of the Khwae Noi (River Kwai) drainage in Kanchanaburi an introduced population is apparently thriving, and it’s also been recorded in the Suriya ( known as Hanthayaw in Myanmar) River basin, a headwater tributary of the Salween system which flows from Thailand into Myanmar, so may yet prove more widely-distributed.
Apparently inhabits calmer stretches of well-oxygenated headwaters and minor tributaries. Such habitats tend to contain transparent water and substrates of sand, gravel, rocks, boulders and patches of leaf litter with submerged driftwood and the roots of riparian vegetation also typical features. The latter often grows thickly providing both shade and cover, plus patches of aquatic vegetation may exist in places.
In the Songgaria River the water is clear, substrate composed of fallen branches, leaf litter, gravel, rocks, and exposed bedrock forming submerged rocky outcrops around heavily-vegetated margins. Sympatric species include Rasbora rasbora, Batasio tigrinus, Badis khwae,Tetraodon leiurus, plus undescribed Rasbora and Schistura species.
In the Suriya the water is well-oxygenated, slightly turbid and aquatic plants such as Cryptocoryne crispatula var. balansae and Pogostemon helferi grow in stiller parts of the habitat. Other fishes include Parambassis pulcinella, Botia kubotai, Acanthocobitis pictilis, Schistura maepaiensis, Homaloptera modesta, Syncrossus berdmorei, Pangio fusca, Pethia stoliczkana, Crossocheilus burmanicus, Akysis vespa, Glyptothorax dorsalis, Amblyceps caecutiens, Batasio feruminatus, B. dayi, Caelatoglanis zonatus, Psilorhynchus robustus, and Tetraodon cutcutia.
Maximum Standard Length
15 – 20 mm.
Aquarium SizeTop ↑
Looks particularly effective in a heavily-planted arrangement with a darkish substrate, and can appear a little washed out in sparsely-decorated set-ups, or alternatively thrives in a set-up designed to resemble a flowing river or stream with a substrate of variably-sized rocks and gravel and some large water-worn boulders. This could be further furnished with driftwood branches and plants such as Microsorum, Bolbitis or Anubias spp. which can be grown attached to the décor.
Since it naturally inhabits running water this species should never be added to a biologically immature set-up as it requires stable water conditions, and weekly water changes of 30-50 % aquarium volume should be considered mandatory.
Temperature: 22 – 27 °C
pH: 6.0 – 7.0
Hardness: 18 – 179 ppm
Likely to feed on small invertebrates, algae and other zooplankton in nature. In the aquarium it will accept dried foods of a suitablly small size but should not be fed these exclusively. Daily meals of small live and frozen fare such as Daphnia, Artemia and suchlike will encourage optimal conditioning.
Behaviour and CompatibilityTop ↑
Very peaceful but doesn’t make an ideal choice for the general community aquarium due to its adult size and rather timid nature. It will do best when maintained alone or with comparably-sized species that enjoy similar conditions.
Other small fishes from Thailand such as Boraras micros, B. naevus, Trigonostigma heteromorpha, T. espei, Acanthocobitis zonalternans, Acanthopsoides and Pangio spp. make excellent companions, and we suspect it might also do well alongside some species normally recommended for non-community aquaria such as Dario or smaller Betta.
It’s a schooling species typically occurring in groups of 20-50 individuals in nature, so the purchase of at least 8-10 is recommended. Maintaining it in decent numbers will not only make the fish less nervous but will result in a more effective, natural-looking display. Males will also display their best colours as they compete with one other for female attention.
Mature females are usually rounder-bellied and noticeably larger than the more intensely-coloured males.
Has been bred successfully in aquaria. Like many small cyprinids Microdevario spp. scatter their eggs randomly, typically among aquatic vegetation, and do not exhibit 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 10-15 litre, 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 several males and 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. Spawning normally presents few problems when the adults are in condition, taking place on a daily basis.
The adults are best removed after 2-3 days as they will eat any eggs or fry they find. 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 and/or microworm once the fry are large enough to accept them.
This species is the most well-known member of the genus in the aquarium hobby. It can be distinguished from the congeners M. gatesi and M. nana by possession of hyaline dorsal and anal fins and 9-10 branched anal-fin rays, vs. a black blotch at tip of dorsal-fin and a greyish marking at tip of anal-fin in M. nana, and 13-14 branched anal-fin rays in M. kubotai.
The genus Microdevario was raised by Fang et al. (2009) after phylogenetic analyses revealed that some species formerly considered members of Microrasbora are more closely allied with Devario and required reclassification. It’s largely separated from Devario and the other closely related genera Chela and Laubuca by virtue of internal characters but also the following: small adult size; anal and dorsal fins with concave-shaped distal margin; absence of barbels; absence of perforated scales; 9-10 branched anal-fin rays; 7 branched dorsal-fin rays; less abdominal than caudal vertebrae.
Only two species remain in Microrasbora and according to Fang et al. (2009) ‘its status as a valid genus is contentious and the molecular data suggest inclusion or close relationship with Devario‘. The two were not synonymised because, unlike those species moved into Microdevario, Microrasbora does not share any derived morphological characters with Devario and in the tests performed the precise level of relatedness between the two could not be settled upon.
The results for Microdevario species were more consistent, distinguishing them markedly from M. rubescens and demonstrating that they possess enough unique characters to be classified separately from both Microrasbora and Devario.
The small adult size evolved via a process known as miniaturisation, characterised by sexually mature adults with a significantly reduced size of less than 20 mm SL. Among bony fishes cyprinids are one of the few groups in which this phenomenon occurs repeatedly with all Barboides, Danionella, Microdevario, Microrasbora, Horadandia, Boraras, Paedocypris, Sawbwa and Sundadanio species representing miniaturised taxa along with a few members of Danio, Laubuca and Rasbora. All show a preference for still or slow-moving waters, often in nutrient-poor habitats such as forest peat swamps.
The anatomical structure of miniaturised cyprinids can vary greatly, and there are two principle ‘groupings’ with some species possessing intermediate features to some degree. The first contains those fishes which though small are essentially proportionally dwarfed versions of their larger relatives, e.g., Barboides, Microdevario, Microrasbora, Horadandia, Boraras, Sawbwa, Sundadanio, Danio, Laubuca and Rasbora.
The other includes those in which anatomical development stops at a point where adult still resemble a larval form of their larger ancestor, i.e., Danionella and Paedocypris. The latter are usually referred to as ‘developmentally truncated’ or ‘paedomorphic‘ and are thought to have evolved via a process known as ‘progenetic paedomorphosis’, i.e., paedomorphosis brought about by accelerated maturation.
They typically exhibit a simplified skeletal structure along with species-specific morphological peculiarities such as the tooth-like projections in male Danionella dracula. Britz et al. (2009) consider that developmental truncation may have facilitated the development of such novelties ‘by freeing large parts of the skeleton from developmental constraints, dissociating developmentally linked pathways and creating a greater potential for more dramatic changes’.
- Kottelat, M. and K.-E. Witte, 1999 - Journal of South Asian Natural History 4(1): 49-56
Two new species of Microrasbora from Thailand and Myanmar, with two new generic names for small southeast Asian cyprinid fishes (Teleostei: Cyprinidae).
- Conway, K. W., W.-J. Chen and R. L. Mayden, 2008 - Zootaxa 1686: 1-28
The 'Celestial Pearl danio' is a miniature Danio (s.s) (Ostariophysi: Cyprinidae): evidence from morphology and molecules.
- Fang, F., M. Norén, T. Y. Liao, M. Källersjö and S. O. Kullander, 2009 - Zoologica Scripta 38(1): 1-20
Molecular phylogenetic interrelationships of the south Asian cyprinid genera Danio, Devario and Microrasbora (Teleostei, Cyprinidae, Danioninae).
- Mayden, R. L., K. L. Tang, K. W. Conway, J. Freyhof, S. Chamberlain, M. Haskins, L. Schneider, M. Sudkamp, R. M. Wood, M. Agnew, A. Bufalino, Z. Sulaiman, M. Miya, K. Saitoh, S. He, 2007 - Journal of Experimental Zoology, Molecular Development and Evolution 308B: 642-654
Phylogenetic relationships of Danio within the order Cypriniformes: a framework for comparative and evolutionary studies of a model species.
- Rüber, L. , M. Kottelat, H. H. Tan, P. K. L. Ng and R. Britz, 2007 - BMC Evolutionary Biology London 7: 1-10
Evolution of miniaturization and the phylogenetic position of Paedocypris, comprising the world's smallest vertebrate.