Tetras & rasboras
Galaxy Rasbora
The galaxy rasbora (Danio margaritatus), also known in the aquarium trade as the celestial pearl danio, is a small cyprinid that became widely available to.
Species overview
The galaxy rasbora (Danio margaritatus), also known in the aquarium trade as the celestial pearl danio, is a small cyprinid that became widely available to hobbyists in the mid-2000s. It is prized for its striking pattern of pale spots over a dark blue-green body, accented by red-orange fins. Adults typically reach only 2-3 cm, making them suitable for well-maintained nano aquariums. The species is peaceful and best kept in a group of at least eight to ten individuals, where males display frequently and coloration deepens. Because it is small and relatively shy, it does best in a mature, planted tank with gentle filtration and stable water parameters. Galaxy rasboras are not demanding in terms of diet, but they require clean, oxygen-rich water and consistent maintenance. They are often recommended for aquarists who have some experience with nano fish and who can provide a quiet, species-appropriate environment. Their popularity has also raised concerns about wild collection, and captive-bred specimens are now common in the trade. Overall, this is an attractive, active shoaling fish for the smaller planted aquarium.
Natural habitat and origin
Danio margaritatus is native to Southeast Asia, specifically to the Salween River basin in Myanmar. It was first discovered in 2006 in a small, isolated area of upland habitat near Lake Inle. The natural environment consists of shallow, slow-moving or still water bodies, including small pools, marshy areas, and spring-fed streams with dense aquatic vegetation. These habitats are typically clear but often tea-colored from tannins, with a substrate of mud, leaf litter, and plant debris. Water temperatures in these shallow, exposed pools can fluctuate seasonally, and the water is generally soft to moderately hard with a slightly acidic to neutral pH. The species is adapted to heavily planted conditions, where it finds cover among fine-leaved plants and submerged grasses. Because its known range is very limited, habitat loss and collection pressure have been concerns. In the aquarium, replicating a planted, softly acidic environment with subdued lighting and plenty of hiding places helps replicate the natural conditions under which this fish thrives.
Appearance and color varieties
The galaxy rasbora is a small, laterally compressed fish with a maximum adult size of about 2-3 cm. Its base coloration is a deep blue-green to dark grey, overlaid with numerous small, pearly white or cream spots that give the species its common name. The dorsal, anal, and caudal fins are marked with red to orange-red highlights, and the belly of mature males may show a reddish tint. Males are generally slimmer and more intensely colored, with brighter red fin edges, while females tend to be slightly larger, rounder, and less vividly patterned. The fish is not known for a wide range of captive-bred color morphs; the wild-type pattern remains the standard in the hobby. Some variation in spot density and fin coloration occurs between individuals and populations. Juveniles are less colorful and may appear more silver or grey until they mature. Because of their small size and intricate pattern, they are best appreciated in a densely planted aquarium with a dark background and subdued lighting, which enhances their natural colors.
Tank setup and water conditions
A minimum aquarium volume of around 40 litres is commonly recommended for a small group of galaxy rasboras, though larger tanks provide more stable water conditions. The tank should be well planted, with fine-leaved plants, mosses, and floating vegetation to provide cover and diffuse light. A dark substrate and driftwood or leaf litter can help create a natural, tannin-stained look. Filtration should be gentle, as the species is small and not adapted to strong currents; a sponge filter or a low-flow canister filter works well. Water temperature should be maintained between 20-26 °C, and the pH should be kept in the range of 6.5-7.5. Soft to moderately hard water is suitable. Regular partial water changes and good maintenance are important, as the fish is sensitive to poor water quality. Because they are peaceful and somewhat shy, a quiet tank with plenty of hiding places and a stable environment will allow them to display natural shoaling behavior. Avoid sudden changes in temperature or chemistry.
Diet and feeding
Galaxy rasboras are omnivorous and accept a variety of small foods. In the aquarium, they do well on a staple diet of micro pellets or crushed flake food, supplemented with frozen or live foods such as daphnia, baby brine shrimp, and cyclops. Because their mouths are small, food items should be appropriately sized. Live and frozen foods are particularly useful for conditioning adults and encouraging spawning behavior. Feed two or three small meals per day, taking care not to overfeed, as uneaten food can degrade water quality. In a well-established planted tank, they will also graze on small microorganisms and algae. A varied diet helps maintain coloration and overall condition. As with all aquarium fish, a consistent feeding routine and removal of uneaten food are important. The species is not known to have any special dietary requirements beyond small, protein-rich foods and a balanced staple. Avoid offering large or hard food items that cannot be easily consumed.
Behavior and tank mates
The galaxy rasbora is a peaceful, shoaling species that should be kept in groups of at least eight to ten individuals. In a group, males perform frequent displays, sparring and flashing their fins, but aggression is rarely serious. They are active in the middle and lower levels of the aquarium, though they may retreat to cover if kept with larger or boisterous tank mates. Suitable tank mates include other small, peaceful species such as micro rasboras, small tetras, dwarf corydoras, and certain dwarf shrimp. Avoid large or predatory fish, as the galaxy rasbora is small enough to be eaten. Because of its timid nature, it is best not to house it with fast-swimming or aggressive species that may outcompete it for food. A species-only setup or a community of similarly sized, calm fish works well. In a well-planted tank with gentle water movement, they will spend much of their time foraging among plants and displaying to one another. They are not known to be territorial except during spawning.
Frequently asked questions
How many galaxy rasboras should be kept together? A group of at least eight to ten is recommended, as they are shoaling fish and display more natural behavior and better coloration in larger groups. What tank size do they need? A minimum of around 40 litres is commonly suggested for a small group, though a larger, well-planted aquarium provides more stable conditions. Are they suitable for beginners? They are generally considered intermediate in care level because they are small, sensitive to water quality, and somewhat shy, so they are best for aquarists with some experience in maintaining nano tanks. Can they live with other fish? Yes, they can be kept with other small, peaceful species in a community aquarium, but large or aggressive fish should be avoided.