Taxonomy & naming
Danio erythromicron was first described by Nelson Annandale in 1918, originally placed in the genus Microrasbora as Microrasbora erythromicron — a combination that reflects the ichthyological consensus at the time that these tiny barb-like fishes sat within or near Rasbora. A subsequent re-examination placed the species in Celestichthys, a genus erected specifically for the miniature, ornamented danionins of the Inlé basin, and the Seriously Fish literature and many hobby sources still use the combination Celestichthys erythromicron.
The Catalog of Fishes (Eschmeyer, the authority for valid names) and GBIF currently record the valid name as Danio erythromicron (Annandale, 1918), placing it within the broadened genus Danio. That broader circumscription, which absorbed Celestichthys and related miniature genera, is followed here. Hobbyists searching by the trade name will find references under all three genus combinations — Microrasbora, Celestichthys and Danio — and the species is sometimes sold as the "crossbanded dwarf rasbora" despite not being a true Rasbora at all.
Morphology
This is one of the smallest danios in the genus, with mature fish typically reaching only 1 in (1 in) standard length; FishBase records a maximum of around 1 in, though aquarium specimens seldom approach that. The body is slightly deeper than those of slender danios such as Danio rerio, with a rounded snout, large eyes and the small upturned mouth typical of a micro-predator that picks from the water column.
Males are strikingly patterned: a series of 10–14 iridescent blue-green vertical bars cross the flanks from behind the head to the caudal peduncle, alternating with warm orange-red ground colour, and the fins — particularly the dorsal, anal and caudal — carry red to orange pigment. The overall effect under good light is strongly reminiscent of an ember tetra or a neon, but in a danio body plan. Females are plainer, with subdued colouration and a deeper, more rounded abdomen when gravid — a reliable sexing cue once fish are adult.
Habitat
Danio erythromicron is endemic to the Lake Inlé basin in Shan State, central-eastern Myanmar, with the IUCN noting its occurrence also near Loi Kaw township — an extent of occurrence under 31 mi². Inlé lies at roughly 2953 ft elevation and is an unusually clear, shallow lake (typically 7–10 ft deep over its broad central area) with karstic geology and dense submerged and emergent vegetation along its margins. Water temperatures in this highland setting are notably cool for a tropical fish: the species is recorded in ranges of roughly 68–75 °F, and pH is recorded as 7.0–8.0 — moderately alkaline by the standards of lowland Southeast Asian cyprinids, reflecting the carbonate-rich Shan plateau geology.
Within the lake the fish inhabits shallow vegetated margins, channels among floating garden rafts and beds of aquatic plants, where dense cover provides protection from predators and a supply of the tiny invertebrates that make up its diet. It is typically found in groups among vegetation rather than in open water.
Feeding
Danio erythromicron is an omnivorous micro-predator, taking small invertebrates, zooplankton and algae in the wild. Its tiny mouth limits it to correspondingly small prey items, and in nature the dense vegetation of Inlé's margins provides a rich supply of micro-crustaceans, insect larvae and other minute organisms.
In the aquarium the species accepts a range of prepared foods but does best on a diet that includes live or frozen items appropriate to its size: newly hatched brine shrimp, micro-worms, daphnia and similar invertebrates. Its small mouth means that standard flake is often too large unless crumbled finely, and micro-pellets or powdered food suit it better for dry meals. Frequent small feedings better match its natural foraging mode than a single large daily feed.
Mating
Like other danios, Danio erythromicron is an egg-scattering, non-guarding spawner. There is no pair bond, no nest and no parental care of any kind. Courtship consists of a male pursuing a gravid female through vegetation, the two coming briefly together as eggs and milt are released among fine-leaved plants or over the substrate.
The species spawns readily when in good condition and at suitable temperatures — around 72–73 °F is often cited as ideal. Because the adhesive eggs are small and scattered among plant stems, and because adults readily consume their own eggs and fry, successful breeding in the aquarium requires either removing the adults after spawning or providing a spawning medium — dense moss or fine plants — from which the eggs fall or adhere out of the adults' reach.
Breeding
Breeding Danio erythromicron follows the standard danio pattern. A conditioning period on live and frozen foods brings females into obvious spawning condition. A separate, shallow spawning tank furnished with fine-leaved plants such as Java moss or spawning mops, with gentle filtration and temperature set around 72–73 °F, encourages a pair or trio to spawn at first light. The adults scatter small adhesive eggs among the plants, after which they should be removed to prevent egg predation.
Eggs hatch in approximately two to three days at spawning temperature. The tiny larvae are initially difficult to feed — infusoria or commercial fry foods of appropriate size are needed for the first days before newly hatched brine shrimp can be accepted. Growth is relatively slow compared with larger danios, reflecting the species' very small adult size. Fry are sensitive to water quality, making regular small water changes and clean conditions important through the early weeks. The species has been bred successfully in captivity and a limited supply of aquarium-raised stock reduces pressure on the wild population.
In the aquarium
Danio erythromicron is well established in the specialist nano-fish hobby and is regularly available from breeders, though wild-caught fish are sometimes encountered. Its very small size — under 1 in in most aquarium specimens — means it suits tanks of 10 US gal upward, planted with fine-leaved vegetation and furnished with driftwood or smooth stones that echo the dense margins of Inlé. The species is a shoaler and should be kept in groups of at least six to eight; solitary or paired fish are shy and may not thrive.
Water parameters should reflect the Inlé plateau: moderately alkaline (pH 7.0–8.0), cool (68–75 °F), and well-filtered but not strongly turbid — the lake is clear, not a soft blackwater environment. Its small size makes tankmate selection critical; it must not be housed with anything large enough to treat it as a food item, and it can itself be out-competed for food by faster or more aggressive nano-fish. It is best kept as a species tank or with similarly sized, placid companions. Dedicated hobbyists keeping this species are participating, in a small way, in a conservation buffer for a genuinely threatened fish.
Conservation
Danio erythromicron is listed as Endangered (EN) on the IUCN Red List. The assessment reflects the species' extreme endemism — its entire known range consists of Lake Inlé and the area near Loi Kaw township in central-eastern Myanmar, with an extent of occurrence estimated at under 31 mi² — combined with documented and ongoing degradation of that range.
Lake Inlé, despite its fame as a tourist destination and protected area, faces sustained pressure: agricultural expansion and the conversion of surrounding land to cultivation have increased nutrient runoff and sediment load; introduced non-native fish species compete with and prey upon native fauna; water extraction for irrigation reduces lake depth; and uncontrolled aquaculture operations disturb habitat quality. Invasive species introductions are considered a particular threat. The combination of tiny range, declining habitat quality and absence of confirmed populations elsewhere makes Danio erythromicron one of the most conservation-sensitive members of the genus.