Emerald Dwarf Danio (Danio erythromicron)

Emerald Dwarf Danio (Danio erythromicron) is a small striped danio from Myanmar's Lake Inle region, also sold in the UK as the Emerald Dwarf Rasbora. In a planted aquarium it shows blue-green body bars, orange-red fin detail and active but shy group behaviour. One quantity buys one fish, supplied unsexed and at the dispatch size shown in the size selector above — not at adult size. This is a shoaling species: buy a proper group rather than one or two, because a lone or near-lone fish stays hidden and colours down.

Quick facts

Not the same fish as the Celestial Pearl Danio

These two are constantly mixed up, and the reason is genuine rather than careless: both are miniature danios, both come from the same corner of Myanmar, and both spent years being shuffled between genus names. They are still different species. This fish is Danio erythromicron, patterned with vertical bars along the flank. The Celestial Pearl Danio is Danio margaritatus, and it is spotted with pearl-like flecks rather than barred. If a listing shows a spotted fish, it is not this species. We list and supply the two separately, and we do not sell hybrids of them. Seriously Fish records that there is limited evidence the two have been crossed in the hobby, with the offspring sold on as female Celestial Pearl Danios — fish that show the spotted body of D. margaritatus but the unmarked fins and dark caudal-peduncle spot of this species. That is also the reason the two should not share an aquarium, which is covered under Tank mates below.

Three names, one fish

Shoppers meet this species under three different genus names, which is worth knowing before you compare listings. It was described in 1918 as Microrasbora erythromicron — the species name simply joins the Greek words for "red" and "small". Work published in 2008 by Conway, Chen and Mayden, combining anatomy with molecular data, showed that this fish and the Celestial Pearl Danio belong among the true miniature danios, which is why FishBase and this listing use Danio erythromicron. Some specialist references still file it under Celestichthys erythromicron. All three names refer to the same fish, and the old rasbora name is still the one most UK keepers search for.

Care and setup

Keep a group in a mature planted aquarium with moss, fine-leaved plants and open swimming gaps. In the wild the species lives around the vegetated margins of Lake Inle, among grass and reed-like plants, which is a useful picture to copy: dense cover at the edges, clear water in the middle. They are small and easily intimidated, so avoid boisterous tank mates and very strong flow. Lake Inle is a hard, alkaline lake, so this is one of the few popular nano fish that suits harder UK tap water rather than fighting it — aim for the recommended ranges in the table above rather than chasing soft, acidic conditions. Keep the tank covered; small active cyprinids are capable jumpers.

Group size and behaviour

This is the point most keepers get wrong. Eight fish will work, but the species does far better in numbers, and specialist guidance is to buy as many as you can house — ideally 20 or more. The reason is not just confidence. Dominant males spar with each other, and in a large group that sparring is spread thinly across many individuals instead of being concentrated on one or two targets. Bigger groups are also bolder, spend more time in open water where you can actually see them, and hold better colour. A footprint of at least 60 x 30 cm gives sparring males the room to settle their differences without cornering anyone.

Feeding

Use tiny pellets, crushed flake, daphnia, cyclops, baby brine shrimp and other fine foods. The mouth is very small, so particle size matters more than quantity, and small frequent feeds work better than large portions. Regular small live and frozen foods such as daphnia and brine shrimp bring out the best colour and bring fish into breeding condition.

Telling males from females

Fish are supplied unsexed and we cannot select or guarantee sex, pairs or ratios. As they mature you can usually tell them apart yourself: males are the more colourful sex, with well-defined iridescent blue vertical bars and red colouring in the fins, while adult females tend to grow slightly larger and look plainer. Young fish arrive before this colour has fully developed, so expect the pattern to strengthen over the following weeks in settled, well-fed conditions.

Breeding

Like many small cyprinids it is an egg-scattering spawner and gives no parental care, so eggs and fry are not protected from the adults. A separate, densely planted or moss-filled tank is the usual approach if you want to raise any numbers.

Tank mates

Do not keep this fish with the Celestial Pearl Danio. The two are close relatives, and the specialist reference Seriously Fish is explicit about it: "The closely-related C. margaritatus is not recommended as these two are probably capable of hybridisation." The same profile adds that there is already limited evidence of hybrids being produced and sold on as female Celestial Pearl Danios. We stock both species because both are excellent aquarium fish, but they belong in separate tanks — the Celestial Pearl Danio link earlier on this page is there to help you tell the two apart, not to pair them up.

For actual companions, Seriously Fish names other small Myanmar cyprinids as suitable: members of the genus Microdevario, which is where the Neon Green Rasbora (Microdevario kubotai) belongs, and Danio choprai, which we sell as the Glowlight Danio. Both are peaceful, close enough in size not to intimidate a 2-3 cm danio, and will not outcompete it at feeding time. Beyond those two the deciding factor is water chemistry: this is a hard-water, alkaline fish, so choose species that genuinely want the same water rather than ones that merely tolerate it.

Two nano fish that often get suggested need a caveat. The Gold White Cloud Mountain Minnow does share this species' liking for harder water, but Seriously Fish puts Tanichthys albonubes most comfortable at 14-22°C and warns that permanent exposure to warmer conditions is likely to shorten its life — so the two overlap only at the cool end, roughly 20-22°C, and suit each other only in a tank deliberately run cool. The Glowlight Rasbora is a poorer match again: Trigonopoma pauciperforatum is a soft, acidic blackwater fish kept at pH 4.0-7.5 and 0-179 ppm hardness, which does not reach this danio's 215-357 ppm at all. You can browse the full range of danios, rasboras and Tanichthys to compare options.

On shrimp: an adult fish reaches only about 2-3 cm and feeds on small invertebrate foods, so adult Neocaridina such as cherry shrimp are far too large to be swallowed — but as with almost any small fish, newly hatched shrimplets may be eaten, so plan on cover if you want shrimp to breed in the same tank.

Arrival and guarantee

Order when the tank is mature, covered and stable, with gentle acclimation ready for a small danio. Young fish are the size shown in the selector above and will grow into the adult size given in the quick facts. Livestock is packed for dispatch across the UK and sent by a licensed live-animal courier where live-animal shipping applies. Livestock orders are covered by our Live Arrival Guarantee. The product photo is a representative image of the species rather than a photograph of the exact fish you will receive.

Sources & further reading

• FishBase species summary — Danio erythromicron (Annandale, 1918): valid name, 3.0 cm maximum size, Lake Inle endemism, temperature and hardness ranges. fishbase.se
• FishBase species summary — Danio margaritatus (Roberts, 2007): used to confirm the Celestial Pearl Danio is a separate species. fishbase.se
• Seriously Fish species profile — adult size, 60 x 30 cm minimum footprint, 20-24°C, pH 7.0-8.0, 215-357 ppm hardness, group-size and male-sparring guidance, suitable companions, the recommendation against keeping it with C. margaritatus and the evidence for hybrids in the trade, sexual differences, egg-scattering reproduction, habitat and etymology. seriouslyfish.com
• Seriously Fish species profile — Tanichthys albonubes: temperature 14-22°C and the warning that permanent exposure to warmer water shortens its life. seriouslyfish.com
• Seriously Fish species profile — Trigonopoma pauciperforatum (Glowlight Rasbora): pH 4.0-7.5 and 0-179 ppm hardness. seriouslyfish.com
• Conway, K. W., Chen, W.-J. & Mayden, R. L. (2008), "The 'Celestial Pearl danio' is a miniature Danio (s.s.) (Ostariophysi: Cyprinidae): evidence from morphology and molecules", Zootaxa — the basis for the move from Microrasbora to Danio.