The galaxy rasbora, also sold as the celestial pearl danio, caused a stir when it appeared in the hobby in 2006, and it is easy to see why. Barely 2.5 cm long, it has a dark blue-grey body scattered with pearly spots and fins striped in orange and black, like a tiny trout. It is ideal for nano tanks and planted aquascapes, and it gets on well with shrimp. It is also shy and needs the right setup to show its best. This guide covers how to keep it well.
Galaxy Rasbora at a Glance
| Scientific name | Danio margaritatus |
| Other names | Celestial pearl danio, CPD |
| Adult size | 2 to 2.5 cm |
| Lifespan | 3 to 5 years |
| Minimum tank | 30 to 40 litres (45 cm long) |
| Temperature | 20 to 26°C, ideally 22 to 25°C |
| pH | 6.5 to 7.5 |
| Group size | At least 8, ideally 10 or more |
| Temperament | Peaceful, shy |
| Diet | Omnivore, small foods |
Rasbora or Danio?
Despite the common name, this little fish is not a true rasbora. Scientists placed it in the genus Danio, which is why it is also called the celestial pearl danio. You will see both names used for the same fish. It comes from small, heavily vegetated ponds and spring-fed pools on the Shan Plateau in Myanmar, where the water is shallow, clear and fairly cool, with lots of plant growth. Today most in the trade are captive bred.
Tank Size and Setup
Galaxy rasboras are small enough for a nano tank, but they need it to be well planted. A tank of 30 to 40 litres and at least 45 cm long suits a group of eight to ten. In a 60 litre tank, a larger group will spread out and behave more naturally.
- Dense planting. This is the most important factor. Without cover, galaxy rasboras hide and lose colour. Mosses, stem plants, cryptocorynes and floating plants all work well.
- Dark substrate. A dark sand or soil brings out the pearly spots.
- Gentle flow. A sponge filter or a small filter with a soft outflow is ideal.
- Moderate lighting. Floating plants help diffuse bright light.
- A lid. Like most danios, they can jump.
Water Parameters
- Temperature: 22 to 25°C is ideal. They tolerate cooler water than many tropicals, but still need a heater in a UK home.
- pH: 6.5 to 7.5.
- Hardness: Soft to moderately hard.
- Ammonia and nitrite: Always zero.
- Nitrate: Below 20 ppm. In a small tank, weekly water changes of 20 to 30 percent are essential, as water quality can change quickly.
Only add them to a mature, cycled tank. Nano tanks in particular should be given time to settle before fish go in.
Behaviour
Galaxy rasboras are not tight shoalers like neon tetras. They form a loose group, spread out through the plants, and often spend time near the bottom and lower half of the tank. Expect them to be shy for the first few weeks; they become bolder once they feel secure.
Males spar with each other, circling and flaring their fins to show off their colour. This is normal display behaviour and rarely causes harm, especially when there are enough plants to break up lines of sight.
Males and Females
Males are slimmer with deeper blue bodies and bright red-orange bellies and fins. Females are rounder, with paler, more olive bodies and duller orange in the fins. A ratio of one male to two females, or a larger mixed group, spreads out the males’ attention.
Best Tank Mates for Galaxy Rasboras
Because they are small and timid, tank mates need to be equally peaceful and not too boisterous:
- Cherry shrimp and other dwarf shrimp
- Chili rasboras and other nano rasboras
- Ember tetras
- Pygmy corydoras
- Otocinclus
- Nerite snails and small snails
- Endler livebearers
Adult galaxy rasboras are generally safe with adult shrimp, which makes them a favourite for planted shrimp tanks. They may pick off very small shrimplets, so heavy moss gives the babies somewhere to hide. If you are setting up a shared tank, our cherry shrimp care guide covers what the shrimp need. Avoid larger, fast or aggressive fish, which will stress them and outcompete them for food.
What to Feed Galaxy Rasboras
Galaxy rasboras have very small mouths and can be slow to take dried food at first:
- Staple: micro pellets or crushed, fine flake.
- Frozen foods: baby brine shrimp, cyclops and daphnia. These are excellent for colour and condition.
- Live foods: baby brine shrimp, microworms or daphnia, especially for newly arrived fish.
Feed small amounts once or twice a day. New arrivals sometimes refuse dried food for a few days; frozen or live foods usually tempt them. You will find suitable small foods in our aquarium fish food range.
Breeding Galaxy Rasboras
Galaxy rasboras breed readily in a mature, well-planted tank. They scatter small numbers of eggs into moss and fine-leaved plants on most days, rather than spawning in one large batch. The catch is that adults eat eggs and fry.
- Set up a small breeding tank with a sponge filter and plenty of java moss or a spawning mop.
- Add a conditioned group, or move the moss from your main tank every few days to a separate container.
- Eggs hatch in about three days. The fry are tiny and hide near the bottom.
- Feed infusoria or liquid fry food at first, then baby brine shrimp after a week or so.
- Keep water clean with small, frequent water changes.
Common Health Problems
Galaxy rasboras are hardy once settled, but they are often stressed during transport and in their first few weeks. Most losses happen at this stage and are linked to stress, poor water quality or not eating. Keep the lights low, offer live or frozen food, and maintain stable water. Watch for white spot and for fish that are consistently hiding with clamped fins.
Buying and Acclimatising Galaxy Rasboras
Look for fish with clear pearly spots, good orange in the fins and full bellies. Avoid thin or listless fish. Acclimatise slowly, ideally with the drip method, and keep the tank dim for the first day. Buy a group at once so they settle together.
Our galaxy rasboras are delivered by tracked courier in insulated packaging.
Frequently Asked Questions
How many galaxy rasboras should I keep?
At least eight, ideally ten or more. Larger groups are bolder and more colourful.
Are galaxy rasboras shrimp safe?
Mostly. They leave adult shrimp alone but may eat very small shrimplets. Plenty of moss helps.
Can galaxy rasboras live in a 20 litre tank?
A heavily planted 20 litre tank can hold a small group, but 30 litres or more is far more stable and gives better results.
Why are my galaxy rasboras hiding?
Usually because they are new, the tank is not planted enough, or the tank mates are too lively. Add cover and give them time.
Is a galaxy rasbora the same as a celestial pearl danio?
Yes. Both names refer to Danio margaritatus.
For other small schooling species that suit nano tanks, see our guide to types of rasbora, or read up on the chili rasbora, which makes a great companion.