Taxonomy & naming
Microdevario kubotai was described by Maurice Kottelat and Jan-Dirk Witte in 1999 on the basis of material collected from Ranong Province, Peninsular Thailand. The same paper erected the genus Microdevario to accommodate a group of very small, large-eyed danionine cyprinids previously lumped with Devario or Microrasbora — genera to which kubotai had earlier been tentatively referred in aquarium literature. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) records the valid combination as Microdevario kubotai (Kottelat & Witte, 1999), with the parenthetical authority marking the transfer out of the authors' own genus construct from the same publication; in practice Kottelat & Witte described both genus and species together.
The genus Microdevario currently contains a small cluster of species centred on mainland Southeast Asia — Myanmar, Thailand and Indochina — distinguished from Devario by their very small adult size, large eyes relative to head size, and details of squamation and fin placement. GBIF places the family as Danionidae, consistent with the broader restructuring of the old Cyprinidae that has disaggregated it into several families. The name kubotai honours a Japanese aquarium importer who supplied the type material; no other combination or synonym is in current use.
Morphology
This is an exceptionally small fish: FishBase records a maximum standard length of 0.5 in, making it one of the tiniest cyprinids kept in the hobby. The body is slender and laterally compressed, with large eyes that take up a substantial fraction of the small head — a feature typical of Microdevario and useful for picking off tiny invertebrate prey in dim stream conditions. The mouth is small and slightly upturned, suited to surface and mid-water feeding.
Colouration shifts markedly between wild and captive conditions. In the field the body appears translucent yellowish; in the aquarium, once settled and in good health, the fish develops a shimmering greenish-yellow lateral stripe that runs from behind the eye to the caudal peduncle, with a golden lustre on the belly, opercle and eye. The fins are hyaline (glassy clear). This iridescence, produced by interference in the guanine-laden lateral stripe, is the basis of the trade name 'green neon rasbora', though the fish is unrelated to the neon tetras of South America.
Habitat
The type locality is Ranong Province in Peninsular Thailand, close to the Myanmar border; additional collection records exist from Phang Nga Province (also Peninsular Thailand) and the Ataran River basin in southern Myanmar. The Ataran is a short coastal drainage flowing to the Andaman Sea — a distinctly different catchment from the major Indochina river systems — and the species' range straddles the Thai–Myanmar border zone of the Malay Peninsula.
Within those drainages the species occupies headwaters and minor tributaries: FishBase describes calm to moderately flowing, well-oxygenated, transparent water over substrates of sand, gravel, rock and leaf litter, with driftwood and riparian roots providing structure. This is typical hill-stream and forest-stream habitat, not the turbid lowland rivers or rice paddies associated with many other danionines. Water chemistry recorded by Seriously Fish gives a pH range of 6.0–7.0 and a temperature window of 68–81 °F, reflecting the relatively cool, soft-to-moderately-hard waters of these forested upland catchments.
Feeding
In the wild Microdevario kubotai feeds on small invertebrates and zooplankton — the microcrustaceans, insect larvae and other tiny organisms drifting in or fallen onto the surface of clear forest streams. Its small mouth and large eyes both point to a visual, precision-feeding strategy rather than the opportunistic bulk feeding of larger cyprinids.
In the aquarium the species accepts a range of small prepared foods, but live and frozen items — Daphnia, baby brine shrimp (Artemia nauplii), micro-worms and similar — deliver the best colouration and condition. Dried foods should be small enough to fit the tiny mouth; crushed flakes or appropriately sized micro-pellets work well. Seriously Fish notes that the species will take both live and frozen small invertebrates alongside suitably sized dried foods, and variety appears important for long-term health.
Mating
Microdevario kubotai is a typical egg-scattering cyprinid with no parental care. Courtship follows the danionine pattern: a ready male pursues a gravid female persistently through the vegetation or moss of the breeding tank, pressing alongside her and driving her through plants until eggs and milt are released together in brief, close contact. There is no territory, no nest, no pair bond and no guarding behaviour — spawning is an act of simultaneous gamete release rather than a sustained partnership.
Females are presumably rounder-bellied when gravid, as in related species. In a group setting multiple males may compete for access to a female, producing the active, chasing school dynamic typical of danionines in breeding condition. Because adults will consume their own eggs immediately after scattering them, the aquarist must separate adults from eggs as quickly as possible.
Breeding
Breeding Microdevario kubotai in the aquarium requires attention to scale: a species less than 1 in long produces correspondingly tiny eggs and larvae. A small, dedicated breeding tank is standard — Seriously Fish recommends fine spawning mops or delicate plants such as Java moss to catch the adhesive eggs and shelter them from the parents. Water should be soft and slightly acidic (pH 6.0–7.0) and temperatures in the mid-twenties Celsius encourage spawning activity.
Eggs hatch in approximately 72 hours; the larvae become free-swimming after a further three to four days. Initial foods must be extremely small: Seriously Fish cites the 5–50 µm range, which means infusoria, commercial fry foods of equivalent particle size, or rotifers as first feeds, graduating to Artemia nauplii and micro-worms as the fry grow. There is no parental care at any stage — the adults are removed after spawning to protect the eggs. Growth to a saleable size is relatively slow given the minute adult dimensions.
In the aquarium
Microdevario kubotai is a popular nano-tank species, well suited to planted aquaria of 10–15 US gal or larger where its iridescent colouration can be appreciated and its schooling behaviour properly expressed. Seriously Fish recommends keeping a minimum group of 8–10 individuals; larger groups produce more confident, visually impressive schools and direct intraspecific chasing behaviour away from tankmates. Given its small adult size, it is best kept with other diminutive, peaceful species — small rasboras, tiny tetras or Otocinclus — rather than anything large enough to view it as food.
The aquarium setup should reflect the species' hill-stream origins: good water movement, high oxygenation, a darker substrate, smooth rocks and gravel, driftwood and robust fine-leaved plants such as Microsorum or Bolbitis. Seriously Fish gives a water chemistry window of pH 6.0–7.0 and temperatures of 68–81 °F, with hardness tolerance of 18–179 ppm (roughly very soft to moderately hard). Consistent water quality is important — weekly water changes of 30–50% are recommended. This is not a fish for a neglected or overstocked system; its native habitat is clean, well-oxygenated stream water, and it reflects deteriorating conditions quickly.
Conservation
Microdevario kubotai is assessed as Least Concern (LC) on the IUCN Red List. The species has an established presence in the aquarium trade and is commercially available from captive-bred stock, reducing pressure from wild collection. However, the IUCN notes that the population trend is likely declining, driven by habitat destruction for agricultural purposes in its naturally restricted Thai–Myanmar range.
The species occupies clear forest headwaters that are vulnerable to deforestation, agricultural encroachment and the associated increases in sedimentation and turbidity. The Peninsular Thailand and Ataran basin localities are subject to ongoing land-use change across southern Thailand and Myanmar. While the current Least Concern assessment reflects adequate range coverage and trade availability from captive sources, the restricted natural distribution means that localised habitat loss could have a disproportionate impact. Maintaining captive-breeding populations in the hobby is therefore more than a convenience — it is a meaningful buffer against wild population decline.