Quick answer: The galaxy rasbora, also sold as the celestial pearl danio (Danio margaritatus), is a tiny nano fish from Myanmar that grows to about 1 inch, lives 3 to 5 years and does well in a planted 10 gallon or larger tank at 72 to 76 F. Keep at least 6, and 8 to 12 is better, with more females than males. They’re peaceful, shrimp-safe with adult shrimp, and hardy once settled. What most people get wrong is expecting a tight school. Galaxy rasboras are shy, loose shoalers that spend a lot of time in plants, and males spar constantly. A bare tank or a small group makes them hide and lose color. Give them dense plants and a bigger group, and they come out and show off.
Galaxy rasbora at a glance
| Detail | Galaxy rasbora (celestial pearl danio) |
|---|---|
| Scientific name | Danio margaritatus |
| Other names | Celestial pearl danio (CPD), galaxy danio, fireworks rasbora, galaxy microrasbora |
| Origin | Small spring-fed ponds on the Shan Plateau, Myanmar. Described in 2007 |
| Adult size | 0.75 to 1 in (2 to 2.5 cm) |
| Lifespan | 3 to 5 years |
| Temperature | 72 to 76 F (22 to 24 C) ideal, handles about 68 to 78 F (20 to 26 C) |
| pH | 6.5 to 7.5 |
| Hardness | Soft to moderately hard, about 2 to 12 dGH. Stability matters more than an exact number |
| Minimum tank | 10 gal (38 L) for a group of 6 to 8. 15 to 20 gal is better for 10 or more |
| Group size | 6 minimum, 8 to 12 or more is best |
| Temperament | Peaceful and shy with other fish. Males spar with each other |
| Diet | Micropredator. Tiny foods like crushed flakes, micro pellets, baby brine shrimp and daphnia |
| Care level | Easy to moderate. Hardy once settled, but sensitive in a new tank |
| Swimming level | Middle and lower levels, around plants |
Galaxy rasbora vs celestial pearl danio: is it a rasbora or a danio?
It’s a danio. When this fish appeared in the hobby in 2006, it was sold as the “galaxy rasbora” because of its tiny size and spotted look. Scientists described it the next year and placed it in a new genus, Celestichthys, but it was later moved to Danio. So “galaxy rasbora” and “celestial pearl danio” are exactly the same fish, sold under different names. It isn’t a tetra either, even though some stores label it “galaxy tetra”.
| Name you see | Is it the same fish? |
|---|---|
| Galaxy rasbora | Yes, the most common trade name |
| Celestial pearl danio, CPD | Yes, the more accurate common name |
| Galaxy danio, galaxy microrasbora, fireworks rasbora | Yes, older or regional store names |
| Galaxy tetra | Usually a mislabel for the same fish |
| Emerald dwarf rasbora | No, a different but closely related fish, Danio erythromicron |
Galaxy rasbora vs other nano schooling fish
| Fish | Size | Minimum tank | Behavior | Best for |
|---|---|---|---|---|
| Galaxy rasbora | 1 in (2.5 cm) | 10 gal | Loose shoal, shy, males spar | Dense planted nano tanks |
| Emerald dwarf rasbora | 1 in (2.5 cm) | 10 gal | Even shyer, stays low | Heavily planted, very calm tanks |
| Chili rasbora | 0.75 in (2 cm) | 5 to 10 gal | Tight little groups, mid water | Very small tanks, soft water |
| Ember tetra | 0.8 in (2 cm) | 10 gal | Active, more visible | Beginners who want easy color |
Here’s the honest part most galaxy rasbora guides leave out. These fish look incredible in photos, but photos are usually taken in mature, heavily planted tanks with a big group. In a new or bare tank, most galaxy rasboras hide, pale out and look nothing like the pictures. That’s not a sign you bought bad fish. It’s a sign they don’t feel safe yet. If you want a nano fish that’s on show from day one, ember tetras are easier. If you’re patient and have plants, galaxy rasboras are worth it.
Appearance and how to tell males from females
Galaxy rasboras have a steel blue to dark gray body covered in pearly gold spots, like a night sky. Their fins have black and red-orange stripes. Colors deepen as they settle in, and males get brighter when they’re displaying.
| Feature | Male | Female |
|---|---|---|
| Body color | Darker blue body | Paler, more greenish gray body |
| Fins | Bright red-orange with bold black stripes | Paler orange to clear, softer stripes |
| Belly | Red to orange underside, especially when breeding | Off-white belly, rounder when full of eggs |
| Shape | Slimmer | Rounder and slightly larger |
| Behavior | Flares and spars with other males | Calmer |
Galaxy rasbora tank setup
Tank size. A 10 gallon tank works for 6 to 8. For a group of 10 or more, or if you want to add other fish, a 15 or 20 gallon tank is easier and more stable.
Plants and cover. This is the most important part. Galaxy rasboras need lots of plants to feel safe. Mosses like java moss and flame moss, stem plants, hornwort and floating plants all help. Our low light aquarium plants list has easy options.
Substrate and lighting. A dark substrate and moderate light make their colors pop. Floating plants soften bright light.
Filter and flow. Gentle flow. A sponge filter or a small hang-on-back filter with the flow turned down works well.
Cycling. Cycle the tank before adding them. These fish are hardy once settled, but they struggle in brand new tanks. Our how to cycle a fish tank guide shows how.
Lid. Small fish can jump, especially when males chase each other. A lid or a lowered water level helps.
Water parameters
| Parameter | Ideal range |
|---|---|
| Temperature | 72 to 76 F (22 to 24 C) |
| pH | 6.5 to 7.5 |
| Hardness | 2 to 12 dGH |
| Ammonia and nitrite | 0 ppm |
| Nitrate | Under 20 ppm |
Galaxy rasboras come from cool, clear highland ponds, so they prefer the cooler side of tropical. Avoid keeping them above about 78 F long term. Small tanks change fast, so keep up a steady 20 to 30 percent weekly water change. Our aquarium water change calculator shows exactly how much to change.
What to feed galaxy rasboras
Their mouths are tiny, so food size matters more than brand.
Daily food. Crushed high quality flakes or micro pellets, around 0.2 to 0.5 mm.
Treats. Baby brine shrimp, daphnia, cyclops and frozen bloodworms chopped small, 2 or 3 times a week. Live and frozen foods bring out the best colors.
How much. A small pinch they finish in about 1 to 2 minutes, once or twice a day.
Shy eaters. They often won’t come to the surface to feed, especially with faster tank mates. Use slow-sinking food and feed near their hiding spots.
Group size and behavior
How many to keep together. At least 6, but 8 to 12 or more is best. Larger groups are bolder and more visible.
Male to female ratio. Aim for more females than males, around 1 male to 2 females. This spreads out the males’ attention so no single fish gets chased all day.
Do they school? Not really. They shoal loosely, spreading out through plants and gathering when startled. Don’t expect the tight school you’d see with harlequin rasboras.
Male sparring. Males circle and flare at each other with fins spread. It looks dramatic but is normal and rarely causes injury, as long as there are plants to break line of sight.
Are galaxy rasboras hardy? Once they’re settled in a mature, stable tank, yes. The first few weeks are the risky part, since fish are often stressed from shipping. Quarantine or acclimate slowly, and add them to an established tank.
Best galaxy rasbora tank mates
| Good tank mates | Why they work |
|---|---|
| Ember tetras and chili rasboras | Same size, peaceful, similar water |
| Pygmy corydoras | Tiny, peaceful bottom dwellers |
| Otocinclus | Gentle algae eaters for planted tanks |
| Kuhli loaches | Shy, stay on the bottom |
| Neocaridina and Amano shrimp | Adult shrimp are safe. Some baby shrimp may get eaten |
| Nerite snails | Peaceful cleanup crew |
| Honey gourami | One calm centerpiece in a 15 to 20 gallon tank |
Fish to avoid with galaxy rasboras
| Avoid | Why |
|---|---|
| Bettas | Some ignore them, many hunt them. Risky in small tanks |
| Tiger barbs and other boisterous barbs | Too fast and pushy. They outcompete and stress galaxies |
| Angelfish and larger cichlids | Will eat them |
| Fast, large danios and rainbowfish | Take all the food and scare them into hiding |
| Goldfish | Different temperature needs and big appetites |
Sample galaxy rasbora stocking ideas
| Tank | Stocking idea |
|---|---|
| 10 gallon | 8 galaxy rasboras, a few Amano or cherry shrimp, 1 nerite snail |
| 15 gallon | 10 galaxy rasboras, 6 pygmy corydoras, shrimp |
| 20 gallon long | 12 galaxy rasboras, 8 ember tetras, 6 pygmy corydoras, 2 otocinclus |
Before you buy, check your list with our aquarium stocking calculator. It includes galaxy rasboras and checks tank size, group size and temperature for you.
Breeding galaxy rasboras
Galaxy rasboras breed often in planted tanks, but the adults eat their eggs and fry. To raise babies, you need to separate them.
Breeding tank. A 5 to 10 gallon tank with a sponge filter, a heater set to about 74 to 76 F, and a thick clump of moss or a spawning mop.
Conditioning. Feed the group live or frozen foods for a week. Females will look noticeably round.
Spawning. Males chase females into the moss, where they scatter a few eggs at a time. Move the moss with eggs to the breeding tank every day or two, or move a few adults in and remove them after a couple of days.
Eggs. Eggs hatch in about 3 to 5 days depending on temperature. Fry hang on the glass for a couple more days before swimming freely.
Raising fry. The fry are extremely small. Start with infusoria or green water, then move to vinegar eels and baby brine shrimp after about a week. Keep the water very clean with small daily water changes. Fry show adult colors at around 2 to 3 months.
Common galaxy rasbora problems
Always hiding. Too few fish, not enough plants, a new tank or bully tank mates. Add plants and increase the group.
Faded colors. Stress, bright bare tanks or poor diet. Add floating plants and live or frozen foods.
Not eating. Food is too big or faster fish are getting there first. Crush flakes and feed near the plants.
Males chasing nonstop. Too many males. Add more females and break up sight lines with plants.
Deaths in the first two weeks. Usually shipping stress or a tank that isn’t fully cycled. Acclimate slowly, test the water and avoid buying fish that look thin.
Thin or “sunken belly” fish. Often internal parasites in imported fish, or simply not getting enough food. Feed small amounts more often and watch which fish are eating.
Cloudy water in a small tank. Usually overfeeding. Our cloudy fish tank water guide explains how to fix it.
FAQ
How big do galaxy rasboras get?
About 0.75 to 1 inch (2 to 2.5 cm) as adults.
How many galaxy rasboras should be kept together?
At least 6, but a group of 8 to 12 or more with more females than males is best.
What size tank do galaxy rasboras need?
A 10 gallon tank is the minimum for a small group. A 15 to 20 gallon tank is better for larger groups or community tanks.
What temperature do galaxy rasboras need?
Around 72 to 76 F (22 to 24 C) is ideal. They handle roughly 68 to 78 F but don’t like long-term heat.
Are galaxy rasboras hardy?
They’re hardy once settled in a mature tank, but can be delicate for the first few weeks after shipping.
Is a galaxy rasbora the same as a celestial pearl danio?
Yes. They’re the same fish, Danio margaritatus. It’s actually a danio, not a rasbora.
Can galaxy rasboras live with shrimp?
Yes. They’re safe with adult shrimp, though they may eat some baby shrimp. Dense moss gives shrimplets places to hide.
