Freshwater Fish · Danios & Minnows

Celestial Pearl Danio

Danio margaritatus

Spotted nano fish from cool Burmese poolsIntermediate

Lifespan: 3-5 years
Size: 0.8-1 in
Social needs: Social; keep 12+ together
Time: Low-moderate; daily feeding, weekly water change
Cost: Low-Medium
Diet: Omnivore; micro pellets, crushed flakes, frozen foods

Overview

What is this animal?

The celestial pearl danio, also sold as the galaxy rasbora, is a tiny fish from cool, weedy spring-fed pools in Myanmar, discovered in 2006 and formally described in 2007.
Males show pearl spots over a deep blue body with orange-red fins, making it a popular nano species.

Wild populations were quickly over-collected after discovery, so seek captive-bred stock, which is now widely available and hardier.
It is not difficult to keep but is shy and small, needing a thoughtfully planted tank rather than a busy community.

Temperament

Peaceful but shy, celestials are not a true tight shoal; males display and spar gently among themselves while staying close to cover.
A group of twelve or more spreads out this sparring and encourages confident, colourful behaviour, and Seriously Fish suggests twenty or more where there is room.

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They suit calm nano setups with other small, gentle species and shrimp, but are easily bullied or outcompeted by larger, faster fish.
Keep them with equally peaceful tankmates so they feed and display without intimidation.

A good fit for

Planted biotope and species-only aquariums
Cooler, unheated or low-heat setups
Keepers seeking a captive-bred species
Peaceful shrimp-friendly community tanks

Common mistakes to avoid

Buying over-collected wild-caught stock
Keeping them too warm or in strong flow
Housing with larger, faster tankmates
Sparse tanks leaving shy fish no cover

Enclosure

Minimum 20 gallons, for a group of 12

Cannot be kept alone. The minimum is 12, and the space above is for that group.

A group of twelve or more needs a planted tank of at least 20 US gallons and 18 in long, the size Aquarium Co-op gives for a school of ten to fifteen, filtered and held at 68-75°F; they prefer cooler water than most tropicals and often need no heater in a warm room.
Dense planting, fine substrate and gentle flow recreate the still, vegetated pools they inhabit.

They are timid and need plenty of cover to feel secure and display.
Avoid strong current and overly warm water, and choose a well-cycled, stable tank, since such small fish are sensitive to swinging parameters in small volumes.

Check your enclosure

Supplies

Setup

Tank and stand
Filter
Thermometer, plus a heater only if the room runs below the species' range
Substrate, plants and decor
Liquid test kit
Dechlorinator and starter supplies

Ongoing

Quality tropical flake or micro-pellet
Frozen daphnia
Frozen brine shrimp
Frozen or freeze-dried bloodworm (chopped fine; whole bloodworm is too large for celestial pearl danios)
Frozen cyclops or baby brine shrimp (for celestial pearl danios)

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Spirulina or vegetable flake
Small feeding spoon for measured pinches
Fine net for removing leftovers

Safe substrate: Fine, smooth sand · Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras) · Bare bottom (quarantine and grow-out only)

Work out the cost

Care routine

Daily

Check temperature and equipment
Feed
Head-count and look everyone over

Every few days

Top up evaporationevery 3 days

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Weekly

Check the lid
Test the water
Water change and gravel vacuum
Wipe the front glass only

Every few weeks

Trim and thin the plantsevery 2 weeks

Monthly

Check supplies and reagent dates
Replace or recharge chemical media, if you use any (skip it in a blackwater tank)
Rinse the filter media

Health review: Quarterly temperature and stocking review, every 3 months

Tools

Is your enclosure big enough?Check your measurements against the recommended size What will it cost?Setup, monthly and over its whole life, itemised Is this ammonia reading dangerous?Works out the toxic part from your pH and temperature

Care in depth

Diet

Omnivore; micro pellets, crushed flakes, frozen foods

These are micro-predators that pick tiny invertebrates from plants and substrate.
Offer fine micro-pellets, crushed flake and powdered foods as the base, supplemented generously with frozen or live cyclops, baby brine shrimp, daphnia and microworms.

Feed small amounts once or twice daily, ensuring food is small enough for their minute mouths.
Live and frozen foods bring out their best colour and breeding condition, so rotate them in regularly alongside the dry staple.

Health

Signs of good health, and the common problems

Captive-bred celestials are reasonably hardy, but wild-caught fish arrive stressed and prone to parasites and rapid decline.
Ich and fin rot follow chilling or unstable water, and their tiny bodies show illness quickly.

Buy captive-bred stock, acclimatise slowly and quarantine new arrivals.
Keep water stable and on the cool side, perform weekly partial changes, and avoid crowding, as the small volumes of nano tanks punish overstocking and inconsistent maintenance.

Is this urgent?

6 warning signs and how fast to act, 3 of them right away

In a fish tank the patient is usually the water. Test before you treat: dosing a healthy tank for a disease it does not have makes things worse.

Go now

Any detectable ammonia or nitrite in a stocked tankLarge water change now with dechlorinated, temperature-matched water. Stop feeding. Test again in 12 hours. Both are directly toxic. How toxic the ammonia reading is depends on pH and temperature, so the same number can be harmless or lethal.

Now

Fish gasping at the surface with fast gill movement, or crowding the filter outflowIncrease surface movement now (gently in a betta or gourami tank, without creating a strong current), then test the water. Either the oxygen has crashed or the gills are being chemically burned. Both are hours-scale problems. Bettas, gouramis and corydoras rise to gulp air as part of normal breathing; the warning is constant gulping, fast gill movement, or the whole group hanging at the top.

Now

Sudden deaths, more than one fish in a dayTest ammonia, nitrite, nitrate and temperature before doing anything else. Do not add medication yet. Multiple simultaneous deaths usually point at the water or the equipment rather than a pathogen, so rule those out first.

Now

Today

Flashing: repeatedly scraping against decor or substrateTest the water, then look closely for parasites. Irritation is either chemical or parasitic; the test tells you which before you medicate.

Today

White salt-grain spots over the body and finsBegin the appropriate treatment today and check the temperature. The parasite's life cycle is temperature-driven, and it multiplies with every cycle you wait.

Today

Soon

Clamped fins, hiding, or refusing food for more than two daysTest the water and review recent changes. Usually the earliest visible sign of a parameter drifting.

A few days

Never add a new fish to a tank that is not fully cycled, and never treat blind. A test kit is cheaper than the fish.

This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it, and the time to find one is before you need one.

Bedding and substrate

3 safe, 4 with a caveat, 2 to avoid

Substrate in an aquarium is a filter as much as a floor. Most of the biology lives in and on it.

Safe

Fine, smooth sandCorrect for corydoras, kuhli loaches, eartheaters such as rams and acaras, and anything else that sifts or burrows. Barbels wear away on sharp gravel.

safe

Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras)Rinse thoroughly before use. Grain size should be too large to swallow and too small to trap food. Kuhli loaches need sand to burrow into and rams and acaras sift mouthfuls of it; bronze and panda corydoras manage on smooth fine gravel, but sterbai corydoras need sand.

safe

Bare bottom (quarantine and grow-out only)Legitimate for quarantine and grow-out tanks. Easy to clean, but it holds far less biological filtration, and it is no long-term home for burrowing loaches or sand-sifters.

safe

With a caveat

Crushed coral or aragoniteDeliberately raises hardness and pH. Correct for rift-lake cichlids, wrong for soft-water species.

with a caveat

Aquasoil for planted tanksExcellent for plants, but most active soils soften the water and pull pH and KH down for months, and many leach ammonia for the first weeks. Right for soft-water species; wrong for hard-water animals (livebearers, rainbowfish, goldfish, and snails, whose shells erode in soft, acidic water) unless you test GH and KH and remineralise. Cycle around it; do not stock into it.

with a caveat

Very deep sand bedsAnaerobic pockets form below about 2 inches in still sand. Either keep it shallow or keep it stirred.

with a caveat

Painted or coated gravelUsually fine, but coatings chip. Test a handful in a jar for a week first.

with a caveat

Never

Sharp or angular gravel with bottom-dwellersWears down barbels and leads to infection in corydoras and loaches.

never

Anything containing metal, limestone of unknown origin, or shells in a soft-water tankSlowly alters chemistry in ways that are hard to diagnose later.

never

This is our general list for freshwater fish. We have not built one specific to Danios & Minnows yet.

Top resources for more info

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