Species Snapshot
- Species Name: Danio margaritatus
- Common Names: celestial pearl danio, galaxy rasbora
- Size: 0.75 to 1 inch
- Lifespan: 3 to 5 years
- Native Distribution: Myanmar, northern Thailand
With their dark blue bodies covered in bright white or yellow spots, these little fish are aptly named. The celestial pearl danio – also known as the galaxy rasbora – is a small species native to Myanmar and northern Thailand where they can be found in freshwater ponds surrounded by grassland and rice paddies. This little fish made a splash in the aquarium industry when they were first discovered in 2006 and they have been popular among hobbyists ever since.
Anatomy and Appearance
Like all danios, the celestial pearl danio is a small cyprinid – a member of the carp or minnow family. These fish typically grow no longer than 1 inch (2-2.5cm) in length and their bodies are about three times as long as they are high.
Their bodies are a little less elongated than pearl danios (Danio albolineatus). In fact, the celestial pearl danio most resembles the emerald dwarf danio (Danio erythromicron), another small cyprinid native to Inle Lake in Myanmar.
Celestial pearl danios exhibit some degree of sexual dimorphism. Males of the species are typically bright blue in color compared to a dull blue-green background seen in females. The fins of male fishes are more brightly colored as well, and the caudal peduncle is higher than a female’s. The bodies of both sexes are sprinkled with pearly white or light-yellow dots and the belly in females is yellowish white.
Male celestial pearl danios will display color changes during courtship and breeding. Their flanks brighten and darken while their belly turns red, causing their pearly spots to stand out. A mature female can be identified by the black anal spot that separates the reddish base of the anal fin from the yellow-white belly color.
Ideal Aquarium Setup
The celestial pearl danio appears to be a rather undemanding fish in terms of tank parameters as long as its base requirements are met. These fish aren’t particularly active swimmers, so they don’t need a great deal of space. They aren’t a true shoaling species either, so they don’t need to be kept with large numbers of their own kind to thrive.
Tank Size
Tank size is less important for celestial pearl danios than tank setup. A group of six individuals will do perfectly well in a tank as small as 10 gallons. These fish will exhibit some shoaling behavior, but they don’t tend to school in the traditional sense.
Male celestial pearl danios will spend most of their time sparring with rival males and courting females. If you plan to keep multiple males in one tank, it’s important to provide enough space for weaker males to escape. The more densely planted the tank, the better.
Water Parameters
Tank parameters appear to be unimportant for this species as long as they are kept relatively stable. The natural water parameters in which these fish are found are neutral pH or slightly above 7 with medium hardness. There’s no need to worry too much about the specific values but be sure to conduct large frequent water changes to keep the water quality in the tank high.
The ideal tank parameters for celestial pearl danios are:
- Temperature: 71°F to 78°F
- pH Level: 6.5 to 7.5
- Water Hardness: 1 to 5 dGH
While these fish can withstand fluctuations in water chemistry, they require high water quality. A slow bubbling sponge filter is the best option for filtration, though heavily planted tanks may need a small power head filter to promote water circulation.
Tank Décor
Because these fish are naturally found in ponds throughout the mountainous region of Myanmar, they prefer a richly planted tank. While they need space to swim, having places to hide among live plants is more important for celestial pearl danios – especially when they are kept in groups.
It’s best to include a variety of plants in your tank setup, both rooted and floating. Classics like java fern, bacopa, and elodea work well with floating plants like frogbit and water lettuce to provide cover. Adding rocks can provide hiding places but be sure to cure any driftwood so it doesn’t leech tannins into the water.
Diet and Feeding
In their natural habitat, celestial pearl danios are omnivores that feed on plants, algae, plankton, and small vertebrae. Captive fish should be fed a varied diet of finely crushed flakes, micro pellets, small worms, newly hatched brine shrimp, and daphnia.
Celestial pearl danio should be fed in small amounts two to three times per day. Because uneaten food can break down and affect water quality, remove any uneaten food after 5 minutes in the tank. This is especially important for larger foods like worms.
Temperament and Tank Mates
Celestial pearl danios are small, peaceful fish that generally get along well with likeminded species. It’s important to keep in mind, however, that males will fight for dominance. If there’s no place for the weaker males to swim away and hide, they could be killed.
The ideal tank mates for celestial pearl danios are similarly sized and do not occupy the same strata of the tank. These fish prefer the middle to lower strata of the tank, so a top-dwelling species like guppies or mid-dwelling species like neon tetras might work well. These fish may also get along with dwarf Corydoras, cherry shrimp, and snails.
Definitely avoid keeping celestial pearl danios with large, aggressive, or carnivorous fish. These little fish can easily become prey to larger species like Oscars, cichlids, and even larger barbs and betta fish.
Breeding Celestial Pearl Danios
Hobbyists around the world have experienced success in breeding celestial pearl danios. Once the fish are sexually mature and conditioned properly, they appear to breed easily.
To breed celestial pearl danios, it’s best to set up a breeding tank using aged water, a sponge filter, and a spawning mop or bed of java moss. Use one male and one female or one male and several females. You’ll know the female is ready to spawn when she develops a dark spot near the caudal fin.
Celestial pearl danios are egg scatterers and females usually lay less than a dozen eggs at a time. Because the adults will eat the eggs, they should be removed from the tank after spawning. The eggs will hatch after two to four days and the fry can be fed micro foods until they are large enough to accept newly hatched brine shrimp.
Other Interesting Facts
- Conditioning male and female celestial pearl danios separately may yield larger spawns – some hobbyists have reported up to 30 eggs from a single female in one spawn.
- Celestial danios do not form pair bonds and will spawn with multiple partners if suitable mates are available.
- Color variants for celestial pearl danios are becoming more common. Some fish exhibit orange rather than red coloration and others have long oval spots instead of small pearly dots.
- Because these fish are native to mountain ponds, they prefer cooler water – you may not need a heater if the ambient temperature in your home is between 71°F and 78°