Dwarf Emerald Rasbora Care Guide

The dwarf emerald rasbora is the odd one out of the nano crowd: a tiny (~2 cm) copper-and-turquoise gem from a single highland lake that wants cool, hard, alkaline water — the exact opposite of the blackwater recipe its 'rasbora' name implies. It is genuinely peaceful toward other fish but is bite-size prey itself, so it belongs in a calm, planted, cool-water nano tank kept among equally small tankmates, never in a general community.

Dwarf Emerald Rasbora at a glance

The sourced figures the welfare engine uses to judge Dwarf Emerald Rasbora — the parseable key facts.

Where it comes from

Despite the trade name, this is a danio, not a true rasbora, and it is endemic to one place on Earth: Inle Lake in Shan State, Myanmar, a shallow, clear highland lake sitting at roughly 880-900 m on the Shan plateau (with a small reported satellite near Loikaw, Kayah State). It lives in the densely-vegetated lake margins, among submerged plants and the roots of floating vegetation. That single biotope explains the whole care sheet. The altitude makes it a cool-water fish that wants the low end of the tropical range and often needs no heater. The lake water is mineral-rich, neutral-to-alkaline and hard — Seriously Fish gives the wild biotope as roughly 20-24 °C, pH 7.5-8.0 and 215-357 ppm hardness — so this fish wants hard, alkaline water and sources state plainly it 'will not do well in acidic water'. Forget the tannin-stained blackwater kit. And the weed-choked margins are why a shy fish needs dense planting and gentle flow to feel secure.

Did you know?

• It lives nowhere on Earth except Inle Lake, Myanmar (plus a tiny Kayah State satellite) — a shallow, mineral-rich highland lake at ~880-900 m.
• It is IUCN Endangered (assessed 2011) — markedly worse than the Data Deficient chili rasbora and celestial pearl danio, making 'buy captive-bred' a genuine welfare hook.
• It named a genus by mistake: when the celestial pearl danio was discovered in 2006 it so resembled this fish that it was first traded as 'Microrasbora sp. Galaxy', and both were later united in the genus Celestichthys — making the emerald the CPD's closest relative.
• A cool-water 'tropical' that often needs no heater: from a ~900 m mountain lake, it prefers ~20-24 °C, one of the few popular aquarium fish kept happily unheated.
• It is a hard-water nano gem — unusually for a tiny 'rasbora', it thrives in hard, alkaline water, the opposite of the blackwater nano crowd, and it is a danio rather than a true rasbora despite the trade name.

Tank size — and why

About 10 US gallons is a sound practical floor, and a longer ~10-15 gallon footprint is better — not for bioload (a 2 cm fish is near waste-free) but because the binding constraint is group size and the cover a timid fish needs. Seriously Fish recommends a 60 x 30 cm base, a bigger footprint than it asks for the chili rasbora or celestial pearl danio, precisely so the welfare-recommended group of 10-20+ has room and male sparring can spread out. Prioritise footprint over height for the mid-water swimming lane. The truest 'minimum', though, is maturity rather than litres: the species is notably intolerant of ammonia and nitrite, so it must go into an established, fully-cycled tank, never a brand-new one.

As a guide, a 20-gallon tank comfortably suits about 9–13 Dwarf Emerald Rasbora as a single-species display, leaving room for tankmates.

See it to scale

Adult Dwarf Emerald Rasbora reach only about 2 cm (0.8 in) long — close to the size they are sold at, so what you see is roughly what you get. The catch is the group: a proper shoal still needs about a 10-gallon tank, around 51 cm long.

Adult size is sourced; tank length is approximate for a standard 10-gallon aquarium.

Water parameters in practice

This is where it parts company with almost every other nano fish. Keep it cool — around 20-24 °C, and do not let it sit above ~25 °C, because the highland origin makes sustained warmth a chronic stressor; it is one of the few popular fish kept happily unheated in a normal room. And keep the water hard and neutral-to-alkaline, roughly pH 7-8, which is the direct opposite of the chili/cardinal blackwater brief. Do not soften or acidify for this fish; if anything, hard alkaline tap water suits it. (FishBase lists a low pH cap of ~7.0, but that is the outlier against the wild measurement of 7.5-8.0 and every care source.) Beyond the chart, the load-bearing rules are stability and maturity: it tolerates a fairly wide stable band but reacts badly to ammonia/nitrite spikes and unstable parameters, so the danger window is the first weeks in an immature tank.

Will it thrive in your water?

The comfortable range for Dwarf Emerald Rasbora is about 20–24 °C (68–75 °F) and pH 7–8. Test your own tap water against it below.

These are the sourced comfortable ranges. Stable water matters more than chasing an exact number — a steady reading inside the band beats a "perfect" one that drifts. Some fish also need a particular water hardness (GH); where that applies, the prose above covers it.

Diet & feeding

In the wild it is a micropredator taking small invertebrates, algae and zooplankton. Its mouth is tiny (a little larger than a chili's), so offer small foods: a micro-flake or micro-pellet sized for a small mouth as a base, leaning heavily on small live and frozen fare — baby brine shrimp, daphnia, moina, cyclops, microworms, grindal worms and finely chopped or frozen bloodworm and mosquito larvae. Many keepers find it does best on small live/frozen and won't thrive on dry food alone. Feed small amounts once or twice daily. It is a shy, slow feeder that hovers and picks among the plants and is easily out-competed by faster fish — another reason to keep it only with equally small, calm tankmates. A mature, microfauna-rich planted tank supplements its feeding and is effectively essential for raising fry.

Gear & setup

A mature, densely-planted, cool nano tank with a dark substrate is the natural fit. Dense rooted and fine-leaved planting plus floating plants for shade and cover give a timid fish the confidence to come out and colour up; rocks and bogwood add structure. Filtration should be gentle — a sponge filter suits this still-margin lake fish, and a powerhead torrent is wrong for it. A heater is often unnecessary given the cool target, but if the room runs cold a heater set low holds stability. A lid is sensible, though it is not a notorious jumper. Dark substrate deepens the copper-and-emerald contrast and settles the fish.

Temperament & behaviour

Peaceful toward other species and timid, it is a loose shoaler rather than a tight schooler. The only aggression is intraspecific: rival males set up small display areas and spar on a regular basis, nipping each other's fins, but this rarely extends to tankmates. The behaviour the buyer wants only appears in numbers and security — a big group in a dim, densely-planted, cool hard-water tank comes out, displays and colours up, while a small group or a bright, open tank leaves pale, skittish fish hiding in the plants.

Group & social needs

Keep a big group. Seriously Fish says to buy as many as possible, ideally 20 or more; care sites push 10-15+. Treat 8-10 as the bare floor and aim for 12-20 or more. This is not cosmetic: rival males spar daily, and in a large group the sparring is diffused across many rivals so no single fish is bullied, the males colour up competing for display, and the naturally timid fish feel secure. In small groups of three to six they stay pale and hidden and a dominant male harasses the rest.

Compatible tank mates (preview)

A short, engine-cleared shortlist — the species TankStocking's welfare engine clears with Dwarf Emerald Rasbora and that suit its size and temperament best. Tap a name for its care guide, or use + to load the pairing in the planner.

• Assassin Snail+Uses the bottom zone, peaceful temperament, similar adult size
• Black Neon Tetra+Peaceful temperament, similar adult size
• Black Phantom Tetra+Peaceful temperament, similar adult size
• Cardinal Tetra+Peaceful temperament, similar adult size
• Celestial Pearl Danio+Peaceful temperament, similar adult size
• Cherry Shrimp+Peaceful temperament, similar adult size
• Chili Rasbora+Peaceful temperament, similar adult size
• Clown Killifish+Uses the top/surface zone, peaceful temperament, similar adult size

A note on the shrimp and snails here: Dwarf Emerald Rasbora is peaceful and generally invertebrate-safe — but almost any fish will take very small shrimplets given the chance, so give shrimp dense cover (moss, leaf litter) if you want a colony to grow, rather than expecting every baby to survive.

This engine-cleared shortlist is Dwarf Emerald Rasbora's tankmate surface for now — a dedicated tank-mates guide can follow for high-demand species.

Breeding & sexing

Sexing is reasonably clear: males are smaller, slimmer and more vibrantly coloured, with intense red-orange fins and stronger emerald bars, while females grow slightly larger and are noticeably rounder in the belly with paler, more transparent fins. Breeding is moderate — it is an egg-scatterer with no parental care, and it is harder to raise the fry than to spawn the adults. Condition the adults on live and frozen food in a mature, densely-planted (fine-leaved plants, moss or a spawning mop) tank in the cool, hard, neutral-to-alkaline band; males display and scatter around 30 mildly adhesive eggs among the plants, which hatch in about 72 hours. Adults eat the eggs, so use dense cover or remove them. The tiny fry need infusoria or microscopic foods first, progressing to microworms and Artemia nauplii after a week or two — which is exactly why a microfauna-rich tank raises fry where a sterile one fails. Critically, do not breed or co-house with the celestial pearl danio: they are probably capable of hybridising.

Lifespan

Around three to five years with good care in a stable, cool, planted nano tank — consistent hobby reporting rather than a published scientific maximum. What shortens it is predation by any tankmate that can swallow a 2 cm fish, ammonia/nitrite spikes and immature or unstable water (its specific Achilles' heel), chronic overheating against its cool-water need, too-small a group, and starvation from being out-competed by faster fish.

Common mistakes

• Treating it as a soft, acidic blackwater fish. The 'rasbora' name misleads — it is an Inle Lake endemic that wants hard, neutral-to-alkaline water (pH ~7-8) and 'will not do well in acidic water'. Do not soften or acidify.
• Keeping it too warm. It is a cool-water highland fish — hold it at ~20-24 °C, never above ~25 °C, often unheated. Treating it like a 26-28 °C tropical shortens its life.
• Putting it in a general community tank. At ~2 cm it is prey, and bigger or faster 'peaceful' fish will eat, harass or out-compete it.
• Housing it with the celestial pearl danio. The two close cousins hybridise, yet many shops and blogs wrongly pair them — don't.
• Adding it to a brand-new, immature tank. It is acutely sensitive to ammonia and nitrite; wait until the tank is established and stable.
• Keeping too few. A group of three to six stays pale, hidden and stressed with a bullying dominant male — buy 12-20 or more.
• Feeding dry food only. It needs small live and frozen foods to thrive and colour up.

Signs of trouble

• Colour fading and a fish hanging away from the shoal — usually too small a group, an immature tank, or poor water.
• A thin, sunken belly despite food in the tank — starvation, often from being out-competed by faster tankmates or food too large for the mouth.
• Skittish, washed-out fish that never leave the plants — the group is too small or the tank too bright and open.
• Clamped fins, lethargy and loss of condition in the first weeks — settling stress in often wild-caught stock, worsened by unstable or warm water.
• Flicking, white spots or fungal patches — standard nano ailments; treat cautiously, and note any ich treatment that raises temperature must stay near the top of its cool range, not beyond ~25-26 °C.

Is this fish right for you?

Don't buy dwarf emerald rasboras for a general community tank with any fish big or fast enough to eat or out-compete a 2 cm fish; for a tank you keep warm (≥26 °C); for soft, acidic water you can't harden; for a brand-new, uncycled tank; or for a tank that already holds celestial pearl danios (they hybridise). And don't buy them if you can't commit to a group of 10 or more and to small live or frozen foods. On sourcing, this is the welfare standout: the species is an Inle Lake endemic listed by the IUCN as Endangered, with its single lake shrinking and degrading, and a meaningful share of trade stock is wild-caught — so favour captive-bred or tank-raised fish and quarantine new arrivals. There are no dyed or balloon morphs to avoid here.

Bringing one home

Add it only to a mature, cycled, cool, hard, neutral-to-alkaline, gently-filtered, densely-planted tank, and acclimate slowly — most stock is wild-caught and the first weeks are the danger window. Float to match temperature, add tank water gradually, then net the fish across and leave the transport water behind, and quarantine new arrivals.

Common questions

Does the dwarf emerald rasbora want soft or hard water?

Hard, neutral-to-alkaline water — pH ~7-8 — which is the opposite of most nano 'rasboras'. It is an Inle Lake highland endemic from mineral-rich water (wild pH 7.5-8.0, hardness 215-357 ppm) and 'will not do well in acidic water', so do not soften or acidify for it.

What temperature do dwarf emerald rasboras need?

Cool — around 20-24 °C, and never sustained above ~25 °C. The ~900 m highland origin makes it a cool-water fish, often kept happily unheated, so it pairs poorly with warm-water species like discus and many gouramis.

How many dwarf emerald rasboras should I keep?

Ten is the practical minimum; 12-20 or more is the real target. Big groups diffuse the daily male-versus-male sparring, bring the colour out and give a timid fish the confidence to come out of the plants. Small groups stay pale, hidden and stressed.

Can I keep dwarf emerald rasboras with celestial pearl danios?

No. They are close cousins in the same genus and are probably capable of hybridising, so Seriously Fish advises against keeping them together. Several care sites wrongly list the CPD as a tankmate — don't follow that advice if you want clean stock.

Are dwarf emerald rasboras good for a community tank or for beginners?

Only a small, calm, cool, hard-water nano community. At ~2 cm it is prey, so anything big or fast enough to swallow or out-compete it will. It stacks several non-beginner demands — a mature tank, cool water, a large group, small live foods and a CPD exclusion — so treat it as a cool-water nano-specialist, not a starter community fish.

Sources & confidence

Sources & confidence (9 species)

These back the Dwarf Emerald Rasbora figures and the previewed tank mates above. Each figure is read from the TankStocking species database (v2026.06); below is the care reference behind it and how confident we are in that data. Confidence reflects the source quality, not whether any pairing is safe. Full source list and the welfare model are on the methodology page.

• Dwarf Emerald Rasbora Celestichthys erythromicron — Seriously Fish (seriouslyfish.com/species/celestichthys-erythromicron) high confidence
• Assassin Snail Anentome helena (Clea helena) — The Shrimp Farm (theshrimpfarm.com/posts/assassin-snail-care) high confidence
• Black Neon Tetra Hyphessobrycon herbertaxelrodi — Seriously Fish / Aqua-Fish (Hyphessobrycon herbertaxelrodi) high confidence
• Black Phantom Tetra Hyphessobrycon megalopterus — Seriously Fish (Hyphessobrycon megalopterus) high confidence
• Cardinal Tetra Paracheirodon axelrodi — Seriously Fish (seriouslyfish.com/species/paracheirodon-axelrodi) high confidence
• Celestial Pearl Danio Celestichthys margaritatus — Seriously Fish (seriouslyfish.com/species/celestichthys-margaritatus) high confidence
• Cherry Shrimp Neocaridina davidi — Aquarium Co-Op cherry shrimp care; The Shrimp Farm high confidence
• Chili Rasbora Boraras brigittae — Seriously Fish (seriouslyfish.com/species/boraras-brigittae) high confidence
• Clown Killifish Epiplatys annulatus — Seriously Fish (Epiplatys annulatus); Aquarium Co-Op high confidence

Care-guide sources (5)

This guide synthesises the references below; where they disagree, the range and the disagreement are noted in the text above. The figures in the key-facts box are read from the TankStocking species database (v2026.06). Full welfare model on the methodology page.

• FishBase — Danio / Celestichthys erythromicron — authority (Annandale 1918), family Danionidae, valid combination Danio erythromicron, max 3.0 cm TL, aquarium temp 21-25 °C, pH cap ~7.0 (low outlier), dH 10-25, endemic to Lake Inle, Myanmar, trophic level 3.0, IUCN Endangered (assessed 24 Feb 2011)
• Seriously Fish — Celestichthys erythromicron — authority/etymology, family Cyprinidae, synonyms (Microrasbora / Danio erythromicron), Inle basin + Loikaw range, ~900 m karstic mountain lake biotope, wild temp 20-24 °C / pH 7.5-8.0 / hardness 215-357 ppm, 20 mm SL, 60x30 cm base, micropredator diet, group 'ideally 20 or more', 'timid', rival males sparring + fin-nipping that 'rarely extends to tankmates', sexing, egg-scatterer (~30 eggs, ~72 h hatch), hybridisation with C. margaritatus 'not recommended'
• Aquarium Source — Emerald Dwarf Rasbora 101: The Complete Care Guide — size 1-1.5 in, lifespan 'three to five years', temp 70-75 °F, pH 7.0-8.0, min 10 gal (20 better), shoaling/large groups, male sparring with 'nipped fins here and there', sexing, breeding (~72 h hatch), Inle 900 m, IUCN Endangered, 'does not do well in acidic water'
• AquariumStoreDepot — Emerald Dwarf Rasbora Care Guide — size ~3 cm max, lifespan 3-5 yr, temp 68-76 °F (20-24 °C), pH 7.0-8.0, GH 8-15 dGH / KH 4-10 dKH, min 10 gal, group 8-10, peaceful/shy, sexing, egg-scatterer (infusoria then brine fry), Endangered/Inle endemic, micropredator that 'won't thrive on dried foods alone'
• Maidenhead Aquatics (fishkeeper.co.uk) — Emerald Dwarf Rasbora — size 2.5 cm, temp 21-25 °C, pH 7.0-7.8, hardness up to 25 KH (neutral-to-moderately-hard alkaline), group 10+, shy, Inle endemic, diet (flake/micropellet/daphnia/baby brine/cyclops/mosquito larvae), 'plenty of cover... including floating species' with gentle filtration, sexing

More on Dwarf Emerald Rasbora

Related guides on TankStocking — each scored by the same welfare engine as the planner.

This care guide is a sourced planning reference, not veterinary advice — individual fish, filtration and maintenance all matter. Cycle the tank, test your water, and observe your fish. How TankStocking works →