Celestial Pearl Danio

Celestichthys margaritatus

Also known as: Galaxy rasbora, CPD

Water Parameters

• Temperature: 20–25°C
• pH: 6.5–7.5
• Hardness (GH): 89–268 ppm (5–15 dGH)

Values above are general hardness (GH). For carbonate hardness (KH), the buffer that keeps pH stable, see the water parameters guide.

Care Summary

Discovered in Myanmar in 2006 and immediately became one of the most popular nano fish in the hobby. Males display extraordinary patterning: pearl-spotted blue-green body with red-orange fins, like miniature aquatic peacocks. Genuinely beginner-friendly when kept in proper groups in stable water. Prefers densely planted tanks with subdued lighting and plenty of cover. Will breed readily in well-planted tanks, producing small clutches of eggs deposited among plants. A genuine recommendation for keepers wanting a striking small species without the dietary fussiness of scarlet badis. Note: original wild populations were nearly fished out by aquarium demand within a year of discovery; today's specimens are nearly all captive-bred.

Behaviour and Temperament

Celestial pearl danios do not behave the way their reputation suggests. They are usually sold as a schooling nano fish, but in a settled tank they do not school tightly. They spread out and hold small individual territories among the plants, coming together loosely rather than moving as one body. A keeper expecting the coordinated shoaling of a rasbora will think something is wrong when nothing is.

The group size of eight is not negotiable, and the reason is male behaviour rather than shoaling instinct. Males display constantly at each other, flaring fins and running side by side in short sparring bouts that settle dominance without injury. In a group of eight or more this display is spread across enough individuals to stay harmless. In a group of four or five it concentrates on one or two fish, which are then chased persistently, lose colour, and stop feeding. Buying six to save money is the most common way this species fails in a home tank.

They also spend far more time in the lower half of the tank than most nano fish. The bottom and middle are where they feed and display, and they rarely come to the surface. This is worth knowing before stocking, because a tank whose other occupants are corydoras and loaches will feel crowded at the bottom while the top sits empty.

Colour is a direct readout of how settled they are. Males in a densely planted tank with subdued light develop the pearl-spotted blue-green body and red-orange fins the species is known for. The same fish in a bright, open tank turns washed out and grey within days. If your celestial pearl danios look nothing like the photographs, the tank is usually the reason rather than the stock.

Tank and Water Setup

Dense planting and broken sightlines matter more here than tank volume. The 38 litre (10 gallon) minimum is adequate for a group of eight, but only if it is heavily planted. Give them stem plants, moss, and floating cover to diffuse the light, with clear swimming lanes between the thickets. An open, brightly lit aquascape produces permanently stressed, colourless fish regardless of how good the water is.

The temperature range is the detail Australian keepers most often miss. Celestial pearl danios want 20 to 25°C, which is cooler than most tropical community fish and, critically, has a low ceiling. In Brisbane and Perth an unheated or lightly heated tank routinely exceeds 25°C through summer, and sustained heat above the range shortens their lifespan and suppresses breeding. This is a species where summer cooling is the real problem and winter heating is the easy one. The guide to cooling an aquarium covers the practical options.

On hardness, they need a general hardness of at least 89 ppm (about 5 dGH), which puts two capital cities out of range straight from the tap. Melbourne runs roughly 8 to 31 ppm and Sydney around 51 ppm, so both need remineralising with a GH booster before this species goes in. Adelaide at 108 ppm and Brisbane at roughly 121 ppm sit comfortably inside the range as supplied. Perth varies by suburb across almost the whole scale, so check your locality rather than assuming. The water parameters guide holds the full city profiles.

Filtration should be gentle. These are small fish from slow, weedy habitat, and strong flow from an oversized hang-on-back filter will pin them into corners. A sponge filter or a baffled outflow suits them better, and has the additional advantage of not drawing fry into the intake if they spawn.

Feeding

The limiting factor is mouth size. An adult celestial pearl danio is about 2 cm long with a mouth to match, and standard community flake is often simply too large to swallow. Fish that appear to be feeding will pick up a flake, fail to break it down, and spit it out repeatedly. Over weeks this reads as fussiness when it is really a mechanical problem.

Crush dry food finely, or use micro pellets and nano-specific granules sized for small mouths. They take live and frozen foods enthusiastically: baby brine shrimp, daphnia, cyclops, and microworms all suit them, and a few feeds of live food a week noticeably improves male colour. Feed small amounts twice a day rather than one large feed.

Watch what happens in a mixed tank. Celestial pearl danios are deliberate, unhurried feeders that will not compete with fast midwater fish for a sinking cloud of food. Housed with anything that feeds aggressively they quietly lose out, which is another argument for keeping them in a species tank or with equally measured tankmates.

Tankmates

An exceptionally peaceful nano species: a small mouth and gentle temperament make them shrimp-safe even with juvenile shrimp. Best kept in groups of 8+ for proper schooling and reduced shyness. Males are more vividly coloured and display to each other; females are slightly larger with rounder bellies. Compatible with most peaceful nano species. Cooler-water tolerance than many tropical nano fish makes them suitable for unheated tanks at room temperature in warmer Australian regions.

Compatible with

• Ember Tetra
• Chili Rasbora
• Pygmy Corydoras
• Scarlet Badis
• Cherry Shrimp
• Amano Shrimp
• Honey Gourami
• Peacock Gudgeon
• Dwarf Emerald Rasbora

Avoid keeping with

• Betta
• Angelfish
• Large Cichlids
• Tiger Barb
• Fin Nippers
• Tropical Warm Water Species

Breeding

This is one of the easier egg-scattering species to breed accidentally. A mature, well-planted tank with a group of eight will produce eggs continuously, usually in java moss or among fine-leaved plants where females deposit small clutches over several days rather than in a single spawning event.

The obstacle is not spawning but survival. Adults eat both the eggs and the fry, so in a normally stocked tank almost nothing reaches maturity, and keepers conclude the fish are not breeding when in fact they are breeding constantly. If you want fry, the practical approach is a dense mat of moss or a spawning mop that eggs fall into and adults cannot reach, removed to a separate container after a few days.

Fry are very small and need infusoria or commercially prepared liquid fry food for the first week before they can manage baby brine shrimp. Keep the water shallow and stable, and expect growth to be slow. Reaching full adult colour takes several months, and juvenile fish are drab enough that a first-time breeder often assumes the spawn failed.

Common Problems

• shyness in groups smaller than 8
• stress in bright open tanks
• pale colour in unsuitable water
• occasional ich

Common Mistakes

• Buying six rather than eight or more, which concentrates male sparring onto one or two fish and slowly kills them.
• Keeping them in a bright, open tank. Cover and diffused light are what produce the colouration the species is bought for.
• Letting the tank exceed 25°C through a Brisbane or Perth summer, which shortens lifespan and stops breeding.
• Using Melbourne or Sydney tap water untreated, both of which fall below the 89 ppm hardness minimum.
• Feeding standard flake without crushing it, so fish that look like they are eating are not actually swallowing anything.
• Expecting a tight-schooling display fish. They spread out and hold loose territories, and that is normal.
• Housing them with fast or aggressive feeders that outcompete them at every meal.

Sources: seriouslyfish.com, fishbase.org · Last updated: 2026-08-01