A celestial pearl danio is about the length of your thumbnail, navy blue, and covered in spots that look like someone flicked a paintbrush at it. When the first photos circulated in 2006, plenty of people assumed they had been edited.

The fish is real, and easier to keep than the price tag suggests. What catches people out is that these danios behave nothing like the hardy starter fish most of us begin with. They hide, they refuse dry food, and they sit in a corner until the tank gives them a reason to come out.

Celestial Pearl Danio at a Glance

Detail	Specification
Scientific name	Danio margaritatus, also listed as Celestichthys margaritatus
Other names	Galaxy rasbora, CPD
Adult size	About 0.8 inches (21 mm)
Lifespan	3 to 5 years
Minimum tank	10 gallons with a footprint of at least 18 x 12 inches
Temperature	68 to 79°F (20 to 26°C)
pH	6.5 to 7.5
Hardness	5 to 15 dGH
Temperament	Peaceful toward other species, sparring among males
Group size	10 minimum, 20 or more for the best display
Diet	Micropredator, small live and frozen foods preferred
Care level	Easy once established, tricky during the first few weeks

Where Celestial Pearl Danios Come From

The species turned up in August 2006 in a shallow pool near the town of Hopong in Shan State, eastern Myanmar, at around 1,040 metres above sea level. Photos spread through the hobby so fast that some people assumed they had been edited. Within months the fish was being exported by the thousand under the name galaxy rasbora, and by early 2007 reports of over-collection led Myanmar to ban exports.

Surveys later found five additional populations near Hopong, and the species is no longer considered at immediate risk from collection. Almost every celestial pearl danio sold today is commercially bred, which also means the fish you buy has never seen its wild habitat and is used to aquarium conditions.

That original habitat still tells you how to set the tank up. The water sits about 30 cm deep, runs clear rather than tea-stained, and is packed with aquatic plants. Temperature at that altitude stays moderate rather than tropical.

Tank Setup for Celestial Pearl Danios

The setup does more for these fish than any other part of their care. A bare tank turns them into ghosts that hide behind the filter all day.

Minimum Tank Size and Footprint

Because they stay under an inch, these fish get sold for tiny desktop tanks. That misses how they use space, since males claim patches of floor and chase each other across them all day. Surface area matters more than volume.

Look for a footprint of at least 18 x 12 inches, which usually means a 10 gallon tank. A 20 gallon long is the better buy if room and budget allow, since the extra length spreads territories out and holds twenty fish.

Substrate Colour and Lighting Levels

Dark substrate does more for their colour than any food or supplement on the market. Over pale gravel the blue flattens and the pearl spots lose contrast, which is why yours can look duller than the ones in the shop. Fine dark gravel or black sand fixes that.

Keep the lighting moderate. Bright open water reads as dangerous to a small fish, and floating plants breaking up the light relax a group faster than dimming the fixture.

Planting for Cover

Dense planting is the single biggest factor in whether you actually see these fish. Broken sight lines let them move around without feeling exposed.

• Java moss and other fine-leaved mosses, which also collect the microorganisms fry feed on
• Anubias and Java fern tied to rocks, both undemanding and slow growing
• Cryptocoryne species for midground cover in low light
• Floating plants such as salvinia or frogbit to soften the light
• Hornwort or another fast grower to soak up nitrate in a small volume

New to live plants? Anubias and Java fern are the forgiving place to start. Both grow from a horizontal stem called a rhizome, which should be attached to hardscape rather than buried. 

Filtration and Flow

An air-powered sponge filter suits this species better than anything else. It runs off a small air pump, moves water gently, houses the bacteria that keep your water safe, and cannot pull in a fry. These danios come from still water, so with a hang-on-back filter, point the outflow at the glass to break the stream up. 

Heater Settings and Target Temperature 

Set the heater between 73 and 75°F and leave it there. This is a cooler-water fish than most tropical stock sold alongside it, and months above 78°F speed up their metabolism and burn through their lifespan. A 25 to 50 watt adjustable heater covers 10 gallons in a room around 68°F.

Check it with a separate thermometer, since the dial on the heater body drifts. Steady beats exact, so a tank holding 74°F all year beats one swinging between 70 and 78°F.

Decor to Leave Out of the Tank 

Driftwood and almond leaves are so standard in nano tanks that skipping them feels odd, and they belong with blackwater species. These danios came from clear, slightly alkaline water, so leaf litter pulls the pH the wrong way for them.

Water Parameters and Maintenance

Stability counts more than hitting an exact number. Celestial pearl danios handle a range of conditions and react badly to swings.

Parameter	Target	Notes
Temperature	73 to 75°F	Avoid sustained readings above 78°F
pH	6.5 to 7.5	A value of 7.3 was recorded at the type locality
Hardness	5 to 15 dGH	Mid-range tap water usually works untreated
Ammonia and nitrite	0 ppm	Any reading at all is a problem in a tank this small
Nitrate	Under 20 ppm	Water changes and fast-growing plants keep this down
Temperature	73 to 75°F	Avoid sustained readings above 78°F

Cycle the Tank Before They Arrive

Fish produce ammonia, ammonia is toxic, and a tank only becomes safe once it grows a bacterial colony big enough to convert that ammonia into nitrate. That takes four to six weeks, and it is the step beginners most often skip.

Doing it without fish is simple. Set the tank up fully, dose pure household ammonia to around 2 ppm, and test every couple of days. Once the tank clears a dose to zero ammonia and zero nitrite within 24 hours, you can stock. A bottled starter or a used filter sponge from an established tank shortens the wait.

Weekly Maintenance Routine

Change 15 to 20% of the water once a week, matching the temperature by hand and treating it with dechlorinator. Trim plants before they choke the flow, and squeeze the sponge filter out in a bucket of old tank water once a month. Rinsing a sponge under the tap kills the bacteria in it and sends a cycled tank back to square one.

Diet and Feeding for Celestial Pearl Danios 

In the wild, celestial pearl danios hunt tiny invertebrates and zooplankton. They are micropredators with mouths barely wider than a pinhead, and food size matters as much as food type.

What to Feed

Live and frozen foods produce the best colour and bring fish into breeding condition. Rotate through what you can get.

• Frozen or live daphnia, which they chase enthusiastically
• Baby brine shrimp, the closest match to their natural prey
• Microworms and grindal worms for variety
• Cyclops and copepods, sized right for adults
• Crushed micro pellets or finely ground flake as a base

Dry food alone leaves them thin over time. Newly imported fish in particular often arrive underweight and refuse dry food entirely, so start a new group on small live foods and introduce prepared foods once they are eating confidently.

How Often and How Much

Feed small amounts twice a day. These fish rarely rise to the surface, so floating flake sits untouched and then rots. Use sinking or slow-sinking food, or crush flake between your fingers and let it drift down through the plants where they hunt.

A well-fed adult has a gently rounded belly. A sunken stomach behind the gills means the fish is losing condition, usually from food that is too large or from competition with faster tank mates.

Behaviour, Shoaling, and How Many to Keep 

Celestial pearl danios shoal loosely instead of holding tight formation like tetras. Males spend much of the day sparring, flaring their fins and circling with their red colouration lit up. It looks far more serious than it is, and the worst it produces is a split fin that heals in a week.

Group size keeps that behaviour healthy. Six is the number most shops quote, and six gives you a nervous group where one or two dominant males have nobody to spread their attention across. At twenty or more, no individual gets singled out and the males hold their best colour.

Tank Mates for Celestial Pearl Danios

Their size and timidity narrow the field. Plenty of fish that would never eat a celestial pearl danio will still beat it to every meal, which amounts to the same problem over a few months. 

A species-only tank is a good choice, and if you want company, start here. 

Compatible Tank Mates 

• Chili rasbora (Boraras brigittae) matches them on size, temperament, and water parameters, and the red bodies set off the blue nicely.
• Glowlight danio (Celestichthys choprae) is a close relative from the same part of Myanmar, so temperature and hardness line up without compromise.
• Kubotai rasbora (Microdevario kubotai) holds the upper water where celestial pearl danios rarely venture, and an active fish up top gives shy ones confidence.
• Rosy loach (Petruichthys sp.) shares the natural habitat, stays under an inch, and works the substrate for leftovers.
• Pygmy corydoras shoal along the bottom and never compete for the same feeding space.
• Nerite snails and adult Neocaridina shrimp clear algae and leftovers at a level the danios ignore, though baby shrimp are small enough to be eaten.

Tank Mates to Avoid

• Bettas, gouramis, and angelfish are large enough to treat an inch-long fish as a meal, whatever their peaceful reputation.
• Barbs, guppies, and endlers beat them to every feeding, which slowly starves a timid group even without any aggression.
• Larger danios such as zebra danios swim at a pace that keeps shy fish behind plants permanently.
• Emerald dwarf rasbora (Celestichthys erythromicron) is close enough genetically to hybridise, which muddies both lines.

Breeding Celestial Pearl Danios 

Well-conditioned adults spawn almost daily in a planted tank. The challenge is keeping the eggs away from the parents, who eat them without hesitation.

Telling Males From Females

Males are steel blue to deep navy, with strong red and black striping through the fins, and a male in spawning condition flushes red along the belly.

Females are greener and softer, with weaker orange in the fins and no striping in the ventrals. They grow slightly larger and rounder, and one carrying eggs shows a small dark mark near the vent.

Conditioning Adults for Spawning

Feed live and frozen food twice a day for one to two weeks beforehand, with daphnia and baby brine shrimp doing the most good. A female cannot produce eggs every day, so a rested, well-fed one gives a far better clutch.

Setting Up a Spawning Container

Use a small container of 10 to 15 litres filled with aged water from the main tank. Fill most of the space with fine wool mops or Java moss. Lighting and filtration are optional, though a small air-driven sponge filter helps.

Add one pair, or one male with two or three females. More fish means more eggs eaten and more distraction between competing males.

Egg Laying and Incubation Time

A typical spawn is around 30 mildly adhesive eggs, which fall into the moss out of sight. Take the adults out as soon as spawning finishes, since they will hunt the eggs down otherwise. Incubation runs roughly 72 hours.

Raising the Fry

The fry are microscopic at hatching and stay stuck to surfaces for three or four days before swimming freely. For that first week they are too small for baby brine shrimp, which catches out most first-time breeders.

• Start with infusoria, a Paramecium culture, or dry fry food graded between 5 and 50 microns
• Feed several times a day, since fry this size run out of reserves quickly
• Move to baby brine shrimp and microworms once they thicken, usually in week two
• Siphon with airline tubing during water changes so you are not vacuuming up fry
• Expect first colour at three months and full adult patterning by six

About Tropicflow

Tropicflow breeds and hand-selects freshwater fish and plants at our facility in Lakeside, California, shipping nationwide with a 100% Live Arrival Guarantee and flat rate shipping from $25. Browse the full range and if you are hunting for a species we do not currently list, our fish request service will track it down.

Plant the tank heavily, let it mature for a month, then add your danios in a group large enough to relax. That decision changes the fish more than any piece of equipment.