Quick answer: The galaxy rasbora (Danio margaritatus), better known as the celestial pearl danio or CPD, is one of the most beautiful nano fish in the hobby. It has a dark blue-green body scattered with pearly “galaxy” spots and bright red-orange fins, it stays under an inch long, and it is peaceful and hardy once settled. Two things surprise new keepers. Despite the name, it is not a rasbora at all, it is a danio, and it likes cooler water and a well-planted, dimly lit tank, where it colors up and schools instead of hiding. Keep a group of at least 8 with more females than males, feed tiny foods, and buy captive-bred fish.
Galaxy rasbora at a glance
| Detail | Galaxy rasbora / celestial pearl danio |
|---|---|
| Scientific name | Danio margaritatus |
| Also called | Celestial pearl danio (CPD), fireworks rasbora |
| Adult size | 0.75 to 1 inch (2 cm) |
| Lifespan | 3 to 5 years |
| Temperature | 68 to 78 F, prefers 73 to 76 F |
| pH | 6.5 to 7.5, soft to neutral |
| Minimum tank | 10 gallons for a group |
| Group size | 6 minimum, 8 to 10 or more is better |
| Temperament | Peaceful and shy, but males spar |
| Care level | Easy once settled |
Galaxy rasbora or celestial pearl danio? The name confusion
This fish has a bit of an identity problem, and it is worth clearing up before anything else.
“Galaxy rasbora” is a trade name, but the fish is not a rasbora. It is a danio, with the scientific name Danio margaritatus. So the two most common names, galaxy rasbora and celestial pearl danio, point to the same fish, and the danio one is the accurate label. You may also see it sold as the fireworks rasbora.
There is a short, sobering history behind it too. The species was only discovered in 2006, in small ponds in Myanmar, and it became so instantly popular that wild populations were nearly wiped out within about a year. Collection limits followed, and today the fish you buy are almost all captive-bred. When you can, choose captive-bred stock. They are hardier, better adapted to aquarium life, and they take the pressure off the wild fish.
Appearance and how to sex them
Galaxy rasboras have a deep blue to blue-green body dusted with rows of iridescent, pearl-like spots, which is where the “galaxy” and “celestial” names come from, finished with bold red or orange fins. They are tiny, so the effect is like a scattering of stars in a moving jewel.
Telling males from females is fairly easy once they mature and color up.
| Male | Female | |
|---|---|---|
| Body | Deeper blue-green with brighter, more defined pearl spots | Duller, with paler and fewer spots |
| Fins | Vivid red-orange, with a black-lined red stripe through the dorsal, and a red belly | Softer orange, more translucent anal fin |
| Build | Slimmer | Rounder, plumper when full of eggs |
Males show their best colors when they are displaying to each other or to females, which is worth knowing for the temperament section below.
Setting up the tank
Galaxy rasboras come from shallow, clear, heavily planted ponds, and a tank that copies that is what turns a shy, washed-out fish into a bold, glowing one.
- Plant it heavily. Dense planting, fine-leaved stems, and mosses give them the cover they need to feel safe, and a secure CPD is a colorful, active CPD. Our low light aquarium plants and java moss guides are ideal here, and the fish tank decorations guide covers safe hardscape and cover.
- Keep the light subdued. Bright, open tanks make them nervous and washed out. Floating plants and shade help them relax and show their color.
- Leave open midwater. Balance the cover with some open space in the middle for the group to school.
- Gentle flow. Their natural water barely moves, so buffer the filter output and keep the current soft.
- Tank size. A group is happy in a 10 gallon, and a 20 gallon fish tank gives a bigger shoal room to shine.
- A lid. They are small and can be jumpy, so keep the tank covered.
Water parameters
Here is a care point most guides gloss over: galaxy rasboras like it cooler than typical tropical fish. Aim for 68 to 78 F, and honestly the sweet spot is around 73 to 76 F. They do not need or want a hot tank, and keeping them too warm shortens their lives and stresses them. Pair that with a pH of 6.5 to 7.5 and soft to moderately soft water. As always, keep ammonia and nitrite at zero in a cycled tank and control nitrate with weekly water changes, since these small fish feel poor water quickly.
Diet and feeding
Galaxy rasboras are micro-omnivores with tiny mouths, so the key is small food. Feed a good-quality micro-pellet or finely crushed flake as a staple, and supplement often with small frozen or live foods like baby brine shrimp, daphnia, cyclops, and micro worms, which really bring out their color. Because their mouths are so small, anything too big simply gets ignored, so match the food size to the fish.
Group size and temperament
Galaxy rasboras are shoaling fish and need to be kept in a group. Six is the minimum, and 8 to 10 or more is where they settle, school, and feel safe enough to color up and come out into the open.
Now the nuance the “totally peaceful” guides skip. Male galaxy rasboras display and spar with each other, flaring their fins and chasing rivals to show off to females. It rarely does real damage, but in a small group, or one with too many males and too few females, that constant chasing stresses everyone. The fix is simple: keep a decent-sized group with more females than males, so the males spread their attention and no single fish gets hounded. They stay peaceful toward other species throughout.
New fish are also shy and can hide for the first while as they settle in. Give them cover and time, and do not judge their color or behavior until they have relaxed.
Tank mates
Because they are so small and gentle, galaxy rasboras need equally small, calm companions, or they get intimidated and out-competed for food.
Good tank mates include other tiny peaceful nano fish like small rasboras and ember tetras, pygmy corydoras, and otocinclus, along with snails and shrimp. Amano shrimp work well, though very tiny dwarf shrimp fry may get eaten. For more calm options, see our best aquarium fish for beginners guide.
Avoid anything large, fast, or nippy. Bigger fish will bully them, out-eat them, or simply treat a one-inch CPD as a snack.
Breeding galaxy rasboras
Galaxy rasboras are easy and near-continuous breeders in a settled tank, which is one reason they are so widely captive-bred now.
They are egg scatterers. A conditioned female drops eggs among fine-leaved plants or moss, and the male fertilizes them. The parents will eat the eggs, though, so if you want fry, breed them in a separate tank with a thick moss carpet or spawning mops, then remove the adults, or use a mesh the eggs can fall through out of reach. Eggs hatch in a few days, and the fry are tiny, so they need very small first foods like infusoria before they can take baby brine shrimp. A well-planted main tank will often produce the odd surviving fry on its own.
Common galaxy rasbora problems
- Dull color and constant hiding. Almost always a setup issue, not a sick fish. Add planting, dim the light, and keep the group large enough, and the color comes back.
- Males chasing each other nonstop. A group that is too small or too male-heavy. Add more fish, weighted toward females.
- Fish staying skinny or nervous. Often they are being out-competed or intimidated by tankmates that are too big or too boisterous.
- Ich or fin rot. Usually follows stress or poor water. Keep parameters stable and the tank calm, and treat promptly if it appears.
FAQ
Is a galaxy rasbora a rasbora or a danio?
It is a danio. Its scientific name is Danio margaritatus, and “galaxy rasbora” is just a common trade name. Celestial pearl danio is the more accurate common name.
How many galaxy rasboras should I keep together?
At least 6, and ideally 8 to 10 or more, with more females than males. They are shoaling fish that only feel secure and show their best color in a group.
What size tank do galaxy rasboras need?
A group is fine in a 10 gallon, since they are true nano fish. A 20 gallon lets you keep a larger, more natural shoal.
What temperature do galaxy rasboras like?
Cooler than most tropical fish. Aim for 68 to 78 F, with the mid-70s being ideal. They do not need a hot tank, and too much heat stresses them.
What fish can live with galaxy rasboras?
Only small, peaceful tankmates like other nano fish, pygmy corydoras, otocinclus, snails, and larger shrimp. Avoid anything big, fast, or aggressive.
Are galaxy rasboras hard to keep?
No, they are easy once settled, as long as you give them a planted, calm, slightly cool tank and keep them in a proper group. Most problems come from a bare, bright tank or too few fish.
