Taxonomy & naming
Microdevario gatesi was first described by Albert William Herre in 1939 from material collected near Judson College, Yangon, and placed at that time in the genus Microrasbora — a catch-all for small, slender cyprinids of mainland South and Southeast Asia. The valid combination Microdevario gatesi (Herre, 1939) dates from 2009, when molecular and morphological work redistributed several Microrasbora species into the resurrected genus Microdevario. The parenthetical authority marks Herre's original epithet being retained under a different generic placement. GBIF and FishBase both record the transfer and carry the species under its current binomial.
The species epithet honours Gordon E. Gates, a lumbricologist (earthworm specialist) who worked at Judson College in Yangon — an unusual eponym for a fish, reflecting Herre's collegial acknowledgement of a fellow naturalist on the same campus where the type series was caught. The genus name Microdevario combines the Latin micro- ('small') with Devario, the genus for the large, deep-bodied danios, signalling that these are miniaturised relatives of that group.
Morphology
M. gatesi is an extremely small fish, reaching only about 1 in in standard length and rarely exceeding 1 in in total length. The body is slender and laterally compressed, with a slightly upturned mouth suited to surface and mid-water feeding. Overall colouration is a warm, semi-translucent golden-olive, with a faint lateral stripe that may appear as a pale iridescent band along the flank under good lighting — the feature that earns it the trade name 'Burmese golden rasbora'.
Sexual dimorphism is subtle but follows the pattern typical of the genus: females become noticeably deeper-bodied and more rounded in the abdomen when gravid, while males remain slimmer. There are no elaborate fin extensions or dramatic colour differences between the sexes outside of reproductive condition.
Habitat
The species is endemic to the lower Irrawaddy basin of Myanmar, with records from the Irrawaddy Delta and the Sittaung and Bago tributary drainages; the type locality is a pond near Judson College in Yangon. It inhabits sluggish and standing freshwater environments — rice paddies, swampy depressions, weedy ponds and drainage ditches — characterised by dense submerged vegetation, still or barely moving water, and soft substrates.
SeriouslyFish records water parameters for the natural habitat as 68–81 °F, pH 6.0–7.5, and hardness 18–215 ppm — a notably wide range reflecting the varied and often seasonally fluctuating conditions of lowland Myanmar. This is not a blackwater species; the chemistry spans near-neutral, moderately soft to moderately hard water rather than the strongly acidic peat-swamp conditions found in some Sundaland micro-cyprinids.
Feeding
In the wild M. gatesi feeds on small invertebrates, algae and zooplankton gleaned from vegetation and the water surface. Its diminutive mouth limits prey to very small items — mainly microcrustaceans, small insect larvae, diatoms and organic detritus of the kind abundant in the weedy, nutrient-rich paddy and pond habitats it occupies.
In the aquarium the species accepts small live and frozen foods readily: baby brine shrimp (Artemia nauplii), Daphnia, micro-worms and finely powdered dried foods. Its tiny mouth means standard community flake should be crushed or replaced with nano-specific pellets. Varied feeding maintains good condition and encourages spawning.
Mating
Like all Microdevario, M. gatesi is an egg-scattering, non-guarding spawner. There is no pair bond, no nest, and no parental investment beyond the act of spawning itself. Courtship consists of driving behaviour: a ripe male pursues a gravid female through dense vegetation, positioning alongside her until eggs and milt are released together among the plants.
Spawning typically occurs in the early morning. The adults show no interest in the eggs after releasing them and will readily consume any they encounter, making separation of parents from eggs the standard approach for hobbyists wishing to raise fry.
Breeding
Breeding M. gatesi in the aquarium follows the standard small-danio protocol. A separate, densely planted spawning tank — fine-leaved plants such as Java moss or spawning mops work well — is set up with the same water parameters as the display tank (pH 6.0–7.5, 75–79 °F). A well-conditioned group of adults is introduced and spawning generally follows within a day or two.
Eggs scattered among the vegetation hatch in approximately 72 hours. The larvae become free-swimming three to four days after hatching, at which point they accept infusoria, paramecia and powdered first foods before graduating to Artemia nauplii. Adults should be removed promptly after spawning to prevent egg predation. The species is not bred commercially in significant numbers, contributing to its scarcity in the hobby.
In the aquarium
M. gatesi is rarely seen in the aquarium trade but makes an excellent nano fish where it can be found. SeriouslyFish recommends a minimum footprint of 45 × 12 in and groups of at least eight to ten individuals; as with all shoaling micro-cyprinids, larger groups reduce skittishness and allow the fish to display natural behaviour. It is entirely peaceful and unsuitable for housing with anything large enough to eat it.
The aquarium should be densely planted with fine-leaved vegetation, with gentle filtration to replicate the still or sluggish waters of its native habitat. Water conditions should be maintained between 68–81 °F, pH 6.0–7.5, and soft-to-moderate hardness. The species is reported as uncommon in the hobby (FishBase), so sourcing may require specialist retailers or aquarium society networks.
Conservation
M. gatesi is assessed as Least Concern (LC) on the IUCN Red List (2022 assessment). It has a distribution centred on the lower Irrawaddy basin — a substantial river system — and occupies a broad range of lowland freshwater habitats including rice paddies and drainage channels, which arguably buffers it against localised habitat loss.
Nevertheless, the lower Irrawaddy Delta is a heavily farmed, densely populated landscape subject to increasing agricultural intensification, pesticide use, water extraction and wetland conversion. These pressures affect the small, weedy waterbodies that M. gatesi depends on, and the species' overall obscurity in both science and the trade means monitoring data are thin. Its current LC listing reflects the absence of quantified decline rather than demonstrated security.