How to Care for Celestial Pearl Danio (Galaxy Rasbora): A Complete Fact Sheet, Breeding, Behavior, and Care Guide

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Celestial Pearl Danios, often referred to as Galaxy Rasboras, are a fairly new freshwater fish in the aquarium trade. Overall, they pack a lot of color and personality into a small size.

They are well suited for community tanks and species specific tanks.

2 celestial pearl danio fish swimming in planted tank
Lindy de Bruyn | Flickr

Quick Intro To Celestial Pearl Danios

General AppearanceSlender, small fish with pearls or “dots” on their body. Their eyes tend to be much larger proportionally than you would see on other fish. They also have very small gills when compared to their body size.
How They Move in the TankSleek fish that swim quickly. Since they are somewhat skittish, you can expect them to dart quickly for cover and stay hidden.
Care LevelMid-level
Family NameCyprinidae
Scientific NameDanio margaritatus or celestichthys margaritatus
Other NamesCelestial Pearl Danio (equally common name), Fireworks Rasbora
Region of OriginMyanmar
Distant RelativesSpotted Danio, Pearl Danio, Zebra Danio, Harlequin Rasbora
Habitat TypeShallow ponds

Males vs. Females

Males tend to have more colorful bodies that range from bluish to copper colored.  Males also have striking red and black markings on their tails and fins, while females range more towards orange and black. 

The male’s coloring also changes in response to the reproductive cycle that occurs within female Galaxy Rasboras in the tank.  When females are ready to lay eggs, males will develop bright red or orange bellies as spawning time approaches.    

Overall, females have more of a grey colored body, however their spots are still very easy to see.  Their colors do not change the way a male fish’s does, however their bellies do get rounder as they get closer to spawning.

Optimal Water Conditions For Galaxy Rasboras

In their natural habitat, Galaxy Rasboaras live in the bottom region of fairly still ponds.  As such, they are not accustomed to the kinds of rapid water chemistry fluctuations that come with water changes.

After the tank is cycled, I recommend limiting water changes and using chemical means to adjust the water chemistry whenever possible.

Water Temperature73 – 79 degrees fahrenheit
Water Flow RateSlow
pH6.5 to 7.5
HardnessSoft to medium
Aquarium Salt (Y/N)No
Tannins (Y/N)No

Since these fish do not tolerate water chemistry changes well, this is one of the few places where I recommend starting off by matching the pH, hardness, and salinity to what you find in the bag they arrive in. 

If these parameters vary significantly from the optimal ranges listed above, then you can try shifting them in the direction recommended for the species.

Galaxy Rasboras can get accustomed to water parameters outside of their optimal, as long as they have plenty of time to do it.

Tank Setup

Minimum Tank Size5 gallon
Optimal Tank Size10 gallon
Optimal Tank ShapeLong, wide, and low small tanks

Extra Air and How To Provide It

Airstones set to low. Air curtains are likely to provide too much air. You can also bury airstones under the gravel so that just a few bubbles come up at a time.

Since Celestial Pearl Danios can be inquisitive creatures, this may provide a bit of a diversion for them.

First Year Testing Schedule

Test for pH, hardness, nitrites, nitrates, and ammonia every 2 – 3 days. The faster you catch even minor swings in these parameters, the less it will stress the fish when you make changes.

Testing Schedule After 1 Year

Test for pH, hardness, nitrites, nitrates, and ammonia weekly. If you see rapid swings, test every 2- 3 days until the tank stabilizes again. 

Best Filter Type

Your best option will be to use live aquatic plants with plenty of lighting and nutrients.

Your second best option is to use a bubble up filter. Use an airstone in filter help diffuse the water flow. 

If you use other filter types, you may need to use nylon stockings on the inlets to keep adult fish from getting stuck on the filter. Likewise, you can use floating aquarium plants and mesh screens to diffuse the force of water moving back into the tank from overhead filters.

As a rule, I don’t like under gravel filters unless the fish in question are very fragile and easily pushed around by water current from other filters. If you find Galaxy Rasboras have problems with bubble up filters, I’d recommend an under gravel filter.  

Just make sure that you can control the water chemistry with chemicals because cleaning these filters can be extremely disruptive!

You will also need to use nylon stockings for activated carbon, zeolites, and nitrite/nitrite pads since they won’t fit in an undergravel filter. Even though there will be very little water flow through them, it can still mitigate problems.

celestial pearl danio from behind web

Creating the Landscape

Rocky substrate or gravelGravel works well.
Sandy substrateAdd some sand in terraced areas to make it easier to keep the sand clean.
Overhangs and cavesSome
Open waterSome
Densely plantedYes
Best PlantsCelestial Pearl Danios enjoy densely planted aquariums. Use low growing, sprawling plants for them to hide in at the bottom of the tank, as well as taller growing ones that will offer safety if they decide to swim in the mid to upper levels of the tank.
Best LightingBright
Best DecorationsCaves, rocks, and mossy overhangs
Decorations to AvoidAvoid plastic toys and plants that they can scratch on or injure themselves. If you use driftwood, make sure all the tannins have been leached out.

Physiological Considerations

Maximum SizeLess than 1 inch
Rate of GrowthReaches full size in about 6 months to 1 year.
Life Span3 – 5 years. 
TemperamentNervous and skittish 
Preferred Tank RegionBottom
Scale ThicknessNormal scales that can withstand most antibiotics used in a freshwater setting. 
Gill ConsiderationsThese fish have very small gills that will show red easily. I don’t recommend keeping them in water deeper than 1 foot. In their natural habitat, the ponds are also very shallow.
Swimbladder ConsiderationsRelease food under water to avoid some swim bladder bloating issues. Keep water shallow as these fish aren’t adapted to deep water.
Fin Shape ConsiderationsCompact, powerful fins and tail that give them a lot of propulsion and ease of navigation. From a fin perspective, were it not for their swim bladder and gill challenges, these fish would do well in tanks of all depths.

Society

Females are peaceful and will swim together with each other. They will also swim with other peaceful fish living in the same community tank. 

Males, by contrast,  are extremely aggressive to each other. The dominant male will chase and attack other males in the tank until he succeeds in killing them. Male Celestial Pearl Danios may swim together with female fish of their own species.

  • Male to Female Ratio – 1 male per tank. The remainder of Celestial Pearl Danios in the tank should be females.
  • Schooling Behaviors – These fish will group together to eat, and may swim together in somewhat loose school formations.
  • Suitable Tankmates – Neon tetras and other small, peaceful fish. They will also do fine with snails and freshwater shrimp. Since Galaxy Rasboras are small and colorful, larger or more aggressive fish will see them as a snack.
  • Species to Avoid – Larger fish such as Cichlids, tiger barbs, buenos aires tetras, or just about any other fish that is bigger than them and interested in eating smaller fish.

Common Behaviors You May See in Aggressive Celestial pearl Danios

Changes in Eye ColorNot observed
ChasingYes
Circling with Fins SplayedYes
Fins Splayed as Other Fish Approach or When Approaching other FishYes
Intensified ColorsMales may increase coloration 
Mouth to Mouth BitingYes
NippingYes

Anti-Bullying Solutions That Work Best With Galaxy Rasboras

Add More Fish of the Same SpeciesYes
Add More Males or Females Remove all but 1 male, add more females.
Change Feeding Methods, Quantity, or Number of FeedingsYou can try smaller meals 3 – 4 times per day.
Increase Number of Hiding PlacesYes
Isolate the Bully Yes
Move Decorations to Shake Up Territorial BoundariesYes
Move to a Bigger TankYes
Water Chemistry or Temperature ChangesNo

Gender, Breeding, and Reproductive Considerations

At the current time, researchers aren’t sure whether or not Celestial Pearl Danios are in danger of going extinct. There is some observation from aquarium fish traders that population numbers are declining.

If you are interested in breeding Celestial Pearl Danios, it may be difficult to determine if the fish you purchase are wild caught or captive bred. Usually, the latter are more tolerant of water chemistry variance and have sufficient behavior modification to permit captive breeding. The tradeoff, however, is captive fish are more likely to be inbred, and therefore produce weaker offpsring. 

Rather than  hope you get fish with good genes, it is best to purchase fish sold specifically for breeding purposes. Since this fish may also be endangered in its native habitat, you may also want to see if there are any programs available that will help you get set up with breeding and disbursing them. 

Possible rarity in nature aside, Galaxy Rasboras are readily available in pet stores.  As such, you may have a hard time providing adequate tank space if you wind up having to keep all the offspring, since most stores may have contracts with professional breeders.

How to Recognize Breeding PairsFemales will spawn with any male that gets close to them when they are laying eggs. Males develop more intense colors and will spend more time around a female that is about to lay eggs.
How Many Babies?12 – 30 per spawning cycle
Separate Hatchery?Yes. Adult fish will consume eggs almost as soon as they are fertilized. You will need a separate breeding tank that is well planted. Carpet plants, mosses, and other plants that produce dense surfaces will also help hide the eggs until you can remove the parents from the tank.
Managing the BabiesIf you don’t have room for a nursery tank and large numbers of Galaxy Rasboras, simply leave the parent fish in the community tank during spawning. The parents and other fish in the tank will consume the eggs.

Special Needs for the Fry

As with adults, fry are very sensitive to water chemistry fluctuations. Try to keep these parameters and the temperature as stable as possible.

Once the fry have consumed their yolk sack and are free swimming, you can feed them commercial fry food for egg layers or infusoran rich water.

Never feed young fry live baby brine shrimp. Make sure the brine shrimp are dead so they cannot harm the fry. As the fry mature, continue to give them live or frozen food and gradually add in crushed flakes or micro pellets.

Galaxy Rasboras are notorious for having a hard time adapting to staple foods, so wait until the fry are older to work on this process. Fry also need very slow, gentle filtration. 

Once the fry are free swimming, you may want to gently herd them into screened pens so that there is less chance of them getting caught up in the filter system. 

You can also try putting a nylon stocking over the filter, however the fry can still get trapped by the current flow into the filter. Since these fish do tend to be very fragile, it is best to keep the fry in pens.

celestial pearl danio profile view

Nutritional Needs

Wild FoodsGalaxy Rasboras are omnivorous. In a natural setting, they will eat algae, zooplankon and small worms. They may also consume insect larvae or anything else that reaches the bottom of the pond.
How ObtainedThese fish will hunt animal based food, or simply nibble on algae and plants.
How to ReplicateLeave some caves and rocks at the bottom of the tank filled with algae. You can also introduce live daphnia, or juvenile brine shrimp (in my opinion, adult brine shrimp are too big for these little fish to handle) into the tank.
Additional Foods for Optimal HealthAlgae wafers
Special Foods for Color and GrowthFrozen krill
When and How Often To Feed based on Place in Life CycleFeed juveniles 2 – 3 times per day. Cut back to 2 times per day for adults.

Best Sustenance Food

Live or frozen foods such as daphnia, tubifex worm cubes, micro sinking pellets.  As with several other fish in the Cyprinidae family, Celestial Pearl Danios have some teeth in their throat, which can make it hard for them to manage some foods.

Since their mouths are very small, these fish are very prone to choking. I don’t recommend using flakes, crushed or otherwise.

Finicky Fish Management Troubleshooting Checklist

Check (and get rid of) Ammonia and NitritesYes
Lower Nitrates to Level Suitable for Galaxy RasborasYes
Test (and Adjust if Needed) Other Water Chemistry ParametersYes
Check for IllnessYes
Look for Signs of Bullying Such as Missing Scales, Nipped Fins or other DamageIf you have more than one male in the tank, bullying related issues and injuries are likely to cause non-dominant males to stop eating.
Try These Frozen/Thawed or Live FoodsLive daphnia, finely chopped blood worms, live brine shrimp, live insect larvae

Observe for Possible Environmental Stresses

  • Too Much/Too Little Light  – Yes. 
  • Sounds  and vibrations – Unknown, however these fish do live at the bottom of ponds, so they might be very sensitive to sound and vibrations.
  • Odors From Air Sprays, Cooking, Construction, etc – Yes.

Common Diseases and How to Avoid and Treat Them

Celestial Pearl Danios are most susceptible to swimbladder disease, body fungus, fin rot, and tail rot.  Fungal and bacterial body infections usually occur when the fish are injured in a fight. In particular, non-dominant males are very inclined to wind up with infected injuries. 

Other than that, these fish are fairly hearty, but will still develop immune system collapses because of environmental and water chemistry-related stress.

  • How to avoid species-specific diseases: Keep only one male in the tank to avoid nipping, stress, and harassment. Make sure water chemistry and temperature remain stable and within optimal parameters.
  • Best antibiotics: I’ve often noticed that members of the Cyprinidae family do better with antibiotics that contain Malachite Blue as opposed to Victoria Green. They will also do Ok with aquarium salt and formulas that contain it. Erythromycin will work well.
  • Treatments to avoid: I don’t recommend formulas for these fish that contain formaldehyde.  This antibiotic does work well for some other ornamental fish, but I have not had success using it with this particular family. 
  • Food recommendations: Continue with live foods unless the fish are already adapted to pellets and flakes.  If they are consuming commercial foods, switch temporarily to medicated sinking pellets.
  • Isolation or Hospital Tank? No.

3 Interesting Facts About Celestial Pearl Danios

  1. Even though they look very different from Tiger Barbs, male Galaxy Rasboras remind me a lot of them in terms of temperament, mating, and bullying styles.  
  2. These fish do need a good bit of mental stimulation. Once they get used to their new home, they will lose a good bit of their shyness. Unlike other fish, however, they usually won’t become comfortable enough to nibble on your fingers or explore if you put your hand in the tank.
  3. Many aquarium keepers claim these fish are peaceful, however I have often found they are happiest when hunting for live animal based food and exploring as many hiding places as possible at the bottom of the tank.

Final Thoughts About Galaxy Rasboras

When Galaxy Rasboras first arrived on the market, many home aquarium hobbyists were stunned by their beauty.  They are, indeed, gorgeous fish that will also display a good bit of personality once they get to know you. Just bear in mind, however, that it is not advisable to keep more than one male to a tank.

Where to buy Galaxy Rasboras

While you can find Galaxy Rasboras at most pet stores that sell aquatic pets, our preference is Amazon for convenience. Unfortunately Amazon doesn’t usually have any sellers. You can try another option we found below.

Here’s our top recommendation:

galaxy rasbora

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