Description
Few fish pack so much beauty into so little body. The celestial pearl danio is barely 2.5 cm, its dark blue flank scattered with golden spots and its fins edged in red and black. In a well-lit planted nano tank, a group of ten looks like a handful of stars moving through the moss.
Careful with the name: it is sold as galaxy rasbora, but it is not a rasbora. It was first described as Celestichthys margaritatus and is now classified as Danio margaritatus: it is a danio, a close relative of the zebra danio. The trade name stuck and there is no shifting it, but it is worth knowing if you are looking for serious information about it.
And it has a story worth telling. It was discovered in 2006, in a single wetland in Myanmar. Demand was so brutal that within two years the wild population was close to collapse and exports were restricted. What saved it was that it turned out to be easy to breed in captivity: today practically everything sold comes from farms, and the pressure on the original wetland disappeared. It is one of the few happy endings in the ornamental fish trade.
Behavior
Shy. That trait defines how you keep it and explains almost every disappointment: in a bare, brightly lit tank it spends the day hidden behind the filter, and whoever bought it for the colour ends up never seeing it.
The answer is not to wait for it to settle in, it is to give it cover: dense planting, moss, some floating vegetation. With that it comes out to swim and behaves normally within days.
It needs a group of eight or ten minimum. And it is worth keeping a balanced sex ratio, because the best thing about this species is the display between males: they face off, spread every fin and compete on colour intensity, never causing each other harm.
It lives well with Neocaridina shrimp — it is one of the best companions there is for a shrimp tank — otocinclus, dwarf corydoras and snails. It is so small it threatens practically nothing.
Avoid housing it with any medium or fast fish: not because of aggression, but because it hides and stops eating. A betta, a gourami or a shoal of danios shuts it down completely. This is a fish for a dedicated nano tank, not for a large community.
Habitat
Danio margaritatus lives in shallow, heavily vegetated pools and ponds in the mountains of Shan State, Myanmar, at some altitude. The water is clear, shallow, cool and practically still, with a plant-covered bottom.
Two practical consequences that get overlooked:
- It is not a warm-water fish. It is comfortable between 22 and 26 degrees. In a tropical community at 28 it gets stressed and lives less.
- It cannot cope with flow. It comes from still pools; a powerful filter in a nano tank exhausts it.
The ideal setup is exactly the one that shows it off: a planted nano tank with plenty of moss, some floating plants and minimal water movement. It is one of the few fish whose natural habitat matches precisely the kind of aquarium people want to keep.
El pez Rasbora galaxy es una especie de cardumen, lo que significa que, de forma natural, vive y se desplaza en grupos numerosos y coordinados.
Se recomienda mantener un mínimo de 8 individuos para que se sientan cómodos y reducir su nivel de estrés.
Details
🌊 Water parameters
🐠 Minimum tank size
Breeding
It spawns continuously, and that very ease is literally what saved the species from overexploitation.
In a mature, well-planted tank you need do nothing: the female releases a few eggs each day among the moss, and the adults neither tend them nor actively hunt them. With a good clump of Java moss some fry make it on their own, and one day you find a tiny fish you never put there.
If you want to breed seriously, simply move the moss with the spawn to a separate tank. The fry are minuscule and need infusoria or liquid food for the first week; brine shrimp nauplii are too big for them at first.
Diet
Omnivorous, but with one limitation that shapes everything: its mouth is tiny. It cannot manage a whole flake, and many people think their fish is not eating when in fact it cannot.
- Staple: micronised food or very finely crushed flake, fry-grade in size.
- Small live food: brine shrimp nauplii, microworms, small daphnia. This is what it most appreciates and what drives the males' colour.
- Fry: infusoria or liquid food during the first week.
A mature tank works in its favour: the microorganisms living in moss and biofilm are part of its natural diet and supplement whatever you provide. That is why it does so well in established shrimp tanks and so badly in a newly set up one.
Plan your next aquarium
Is this fish right for you? Plan a suitable aquarium before setting it up.