Emerald Dwarf Rasbora Care Guide (Microrasbora erythromicron)

April 27, 2025

The Emerald Dwarf Rasbora is one of the most overlooked nano fish in the freshwater hobby — a 3/4-inch schooling fish from a single shallow lake in Myanmar, with an iridescent emerald-green body, dark vertical bars, and bright orange-red fins that flicker like sparks under planted-tank lighting. At Tropical Treasures Wyo in Cheyenne, Wyoming, Emeralds are our quiet favorite among aquascapers — less famous than Celestial Pearl Danios or Chili Rasboras, but every bit as stunning, and they bring a different color profile (green and red) that complements both species in mixed nano communities.

They're also one of the most commonly mis-stocked nano fish, mostly because they're confused with Galaxy/CPD lookalikes and stocked too thinly. Most "my Emeralds are colorless and hiding" complaints trace back to the same three causes: too few fish, harsh lighting, and tank mates too aggressive at feeding time. This guide walks you through how to actually keep them thriving, based on how we keep and ship them.

Ready to add some to your tank? Browse our Emerald Dwarf Rasbora and the rest of our Rasbora collection — every fish quarantined before shipping.

Quick Facts

Scientific name: Microrasbora erythromicron (also Celestichthys erythromicron, sometimes Danio erythromicron)
Common names: Emerald Dwarf Rasbora, Dwarf Emerald Rasbora, Emerald Microrasbora
Origin: Lake Inle, Myanmar (and surrounding shallow streams)
Adult size: 0.75–1 inch (2–2.5 cm)
Lifespan: 3–5 years with good care
Temperament: Peaceful, loosely schooling, sometimes mildly territorial males
Care level: Easy to moderate
Minimum tank size: 10 gallons; 20 gallons preferred for a proper school

Are Emerald Dwarf Rasboras Hard to Keep?

No — they're one of the hardier nano fish once established, and they tolerate a wider range of water parameters than Chili Rasboras or many wild-type species. They were once thought to need cool, hard, alkaline water like Lake Inle, but tank-bred stock now adapts to typical neutral, moderately soft tap water without issue.

The two areas where new keepers go wrong are school size (anything under 8 fish hides constantly) and lighting (harsh top-down LEDs without floating plant cover wash them out). Get those right and Emeralds are a beginner-friendly nano fish that rewards good husbandry with sparking color.

Tank Size & Setup

Minimum tank size

Small school (8–10 fish): 10 gallons
Display school (12–20 fish): 20 gallons
Mixed nano community with Emeralds as feature fish: 20–29 gallons

Footprint matters more than height. Emeralds spend most of their time in the lower-middle water column drifting through plants and hardscape.

Substrate

Dark substrate (black sand, dark gravel, or planted-tank soil) makes their emerald-green body and orange-red fins pop dramatically. Light or pale substrate washes them out.

Aquascape

Heavy planting is essential. Java moss, Anubias, cryptocoryne, mosses, and stem plants like rotala all work well. Heavy planting is what makes Emeralds feel safe enough to display.
Driftwood and rocks. Spider wood, Malaysian driftwood, and seiryu stone create natural break-up and territory zones. Tannins also gently soften the water.
Floating plants. Amazon frogbit, red root floaters, or salvinia diffuse top-down lighting and make Emeralds far more confident.
Tight-fitting lid. They can jump when startled — cover any gaps in your hood.

Filtration & flow

A sponge filter or low-flow HOB is ideal. Like most Lake Inle and stream fish, Emeralds prefer gentle flow and will hide in corners with strong current. Baffle any HOB output. For more help, see our aquarium filtration guide.

Heating

Yes, they need a heater. Emeralds prefer cooler tropical temps in the mid-70s — they don't tolerate heat as well as most community fish. A 25–50 watt heater handles a 10–20 gallon tank.

Water Parameters

Parameter	Ideal Range	Notes
Temperature	72–78°F (22–26°C)	74–76°F is the sweet spot — they prefer cooler water
pH	6.5–7.5	Neutral to slightly alkaline
GH	3–10 dGH	Soft to moderately hard
KH	2–8 dKH	Stable carbonate hardness
Ammonia	0 ppm	Non-negotiable
Nitrite	0 ppm	Non-negotiable
Nitrate	Under 20 ppm	Sensitive — keep low

Stability matters more than perfect numbers. Use a quality dechlorinator like Seachem Prime on every water change. We offer free water testing at our Cheyenne store — bring in a sample.

Diet & Feeding

Emeralds are micro-predators with small mouths. Like CPDs and Chilis, they need food sized appropriately to their tiny gape.

Staple: high-quality micro-pellets and crushed nano flakes (Hikari Micro Wafers, Bug Bites Micro Granules, Xtreme Nano)
Frozen / live (essential for color): baby brine shrimp, microworms, daphnia, cyclops 2–3× per week
Powdered fry food like Hikari First Bites also works well between meals

Feed small amounts 1–2× per day. Crush flakes between your fingers — Emeralds will completely ignore food too large to swallow. For more, see our how often to feed your fish guide.

Tank Mates

Emeralds are peaceful and pair beautifully with other nano fish, shrimp, and snails. Avoid anything fast or large enough to out-compete them at feeding.

Great tank mates

Other nano fish — Celestial Pearl Danios, Chili Rasboras, ember tetras, sparkling gouramis
Pygmy corydoras and Otocinclus catfish
Neocaridina shrimp (Cherry, Blue Dream, Yellow) — adults are safe
Ghost Shrimp and Caridina shrimp in stable, well-cycled tanks
Mystery and Nerite snails

Avoid

Larger or fast-feeding fish — guppies, larger tetras, danios (out-compete them at meals)
Bettas in small tanks (mixed results — sometimes nipping)
Any cichlids, even dwarf species
Fin nippers — serpae tetras, tiger barbs
Goldfish, larger gouramis, or any predator

Risky but possible

Caridina shrimplets and Emerald fry. Adults may eat very small shrimplets and their own fry. Heavy moss and floating plants give shrimp and fry hiding spots. See our Neocaridina shrimp care guide.

Male vs. Female: How to Sex Emerald Dwarf Rasboras

Sexing tiny Emeralds takes a careful look but is doable on adult fish:

Males are slimmer with brighter orange-red fins and bolder vertical barring. They display by flaring fins and sparring with rival males in a non-aggressive courtship dance.
Females are slightly larger and rounder, with paler fin coloration and softer barring. Mature females show a visibly fuller belly when conditioned.

For breeding, target a 1:1 to 1:2 male-to-female ratio in a school of 10+.

Breeding Emerald Dwarf Rasboras

Emeralds are egg-scatterers and breed readily in a heavily planted, stable tank. As with most nano fish, the challenge is saving eggs and fry from being eaten by adults.

Setup: A 10–20 gallon species tank with thick Java moss, Christmas moss, or spawning mops. Cooler temperatures (74°F) and live food trigger spawning.
Conditioning: Feed live baby brine shrimp daily for 1–2 weeks to bring fish into spawning condition.
Spawning: Pairs scatter small clear eggs over moss and plants. Most spawning happens in early morning. Healthy pairs spawn over multiple days.
Egg care: Adults eat eggs. Move moss/spawning mops to a separate hatching container, or breed in a dedicated species tank.
Hatching: Eggs hatch in 3–4 days. Fry are tiny and need infusoria, vinegar eels, or the smallest fry foods (Hikari First Bites, Sera Micron) for the first 7–10 days before they can eat baby brine shrimp.
Growth: Slow — fry take 3–4 months to reach adult coloration.

Common Problems & Diseases

Constant hiding / dull color: almost always too small a school, lack of plant cover, or harsh lighting. Add more Emeralds (8+ minimum), heavy moss and floating plants.
Loss of color: stress from heat, bright top-down lighting without floating plants, or wrong tank mates. Drop the temperature, add floating plants.
Ich (white spot): common after shipping. Treat with heat (raise to 82°F briefly) and a half-dose ich medication safe for nano fish (Hikari Ich-X at half dose). See our Common Fish Diseases guide.
Skinny disease (mycobacteriosis): Emeralds eat normally but waste away. Often genetic in farm-raised stock. Cull affected fish; buy from quality sources.
Sudden deaths in new fish: usually shipping shock or uncycled tank. Drip-acclimate over 1–2 hours and only add Emeralds to a fully cycled tank.

Tips for Long-Term Success

Keep at least 8, ideally 12+. Confidence and color come from numbers — small groups hide constantly.
Heavily planted tank with floating plants. Plants are not optional for Emeralds.
Cooler temps. 74–76°F is the sweet spot. Don't put Emeralds with warm-water fish like discus or rams.
Drip-acclimate slowly. Emeralds are sensitive to parameter swings during transfer.
Live or frozen foods. Color comes from food. A pellet-only Emerald looks dull next to one fed live baby brine.
Buy from a quarantining source. Every Emerald we sell at Tropical Treasures Wyo is quarantined in-house.

Frequently Asked Questions

How many Emerald Dwarf Rasboras should I keep?

At least 8, ideally 10–12 or more. They're loosely schooling fish that hide constantly in small groups.

Are Emerald Dwarf Rasboras beginner-friendly?

Yes — once established in a stable, planted tank they're hardy and forgiving. Just keep a school of 8+, crush their food, and avoid aggressive tank mates.

Can Emerald Dwarf Rasboras live with shrimp?

Yes — adult Cherry, Blue Dream, and other Neocaridina coexist beautifully. Very small shrimplets may get eaten but heavy moss usually shelters them.

Can I keep Emerald Dwarf Rasboras with Celestial Pearl Danios or Chili Rasboras?

Yes — they're an excellent pairing. Same water needs, similar size, and they share the lower-mid water column without competition. The combined color profile (emerald green, sparkly silver-blue CPDs, fiery red Chilis) is one of the most striking nano-aquascape combinations possible.

What size tank do I need for Emerald Dwarf Rasboras?

10 gallons minimum for a small school of 8–10. A 20 gallon is much better and lets you keep 12+ with room for shrimp and other nano fish.

What temperature do Emeralds need?

72–78°F, with 74–76°F as the sweet spot. They prefer cooler water than most tropicals — avoid keeping them with warm-water species.

Do Emerald Dwarf Rasboras breed in captivity?

Yes — they spawn readily in a planted tank with cool temperatures and live foods. Eggs and fry need protection from the adults.

How long do Emerald Dwarf Rasboras live?

3–5 years in a stable, planted nano tank.

Why are my Emerald Dwarf Rasboras hiding all the time?

Three common causes: school is too small (add more), not enough plant cover (add Java moss and floating plants), or tank mates are intimidating them (remove larger or faster fish).

Shop Emerald Dwarf Rasboras at Tropical Treasures Wyo

Visit us in Cheyenne at 190 S College Dr, or order online — we ship healthy, quarantined nano fish and aquarium supplies nationwide to all 48 states with our 7-day live arrival guarantee.

Shop Emerald Dwarf Rasbora →
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Visit us in person at 190 S College Drive, Suite D, Cheyenne, WY 82007 or call 307-369-1118. We offer free water testing for Cheyenne locals, expert advice for every tank size, and nationwide shipping to all 48 states with a 7-day live arrival guarantee.

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