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In 2006, a photograph surfaced on tropical fish forums all over the Internet. It depicted a brightly colored nano fish, the likes of which were previously unseen. This newly discovered fish was the celestial pearl danio. With a dark blue coloring that is speckled over with iridescent spots, these quirky little swimmers blew the minds of everyone who came across the photo.
15 years later, and the celestial pearl danio is one of the most highly sought-after freshwater nano fish. Not only are they gorgeous, caring for them is relatively easy. Yes, they’re expensive, and their shy behavior can take some time to overcome, but they make a highly enviable addition to freshwater community tanks.
Whether you’ve already gotten a hold of some celestial pearl danios (CPDs) or are looking to introduce them to your aquarium in the near future, our comprehensive guide below is all you need to get on the right track.
A Brief Overview of the Celestial Pearl Danio
|Scientific Name||Danio margaritatus|
|Common Names||Celestial Pearl Danio, Fireworks Rasbora, Galaxy Rasbora, Microrasbora sp. galaxy|
|Origin||Myanmar / South East Asia|
|Lifespan||3 to 5 Years|
|Minimum Tank Size||10 gallons|
|Temperature Range||72°F – 76°F|
|Water Hardness||2 – 10 dKH|
|pH Range||6.5 to 7.5|
|Difficulty to Breed||Easy to breed; lays eggs|
|Compatibility||Species tank or community nano tank|
|OK, for Planted Tanks?||Yes – plants recommended|
Origins and Habitat
The world first came to know of the celestial pearl danio in 2006, when a man called Kamphol Udomritthiruj discovered the fish in a plant-filled pond in a mountainous area near Hopong, east of Inle Lake, in Myanmar. He shared a photo of the fish on a Singaporean fishkeeping forum, and the rest is history1.
The ponds, which are the natural habitat of the galaxy rasbora, are heavily vegetated. They are located in a place consisting mainly of rice paddies and grasslands, which receive a lot of sun exposure. This is what leads to the fast growth of aquatic plants in the ponds, which make the celestial pearl danios’ home.
Since that time, this species of fish has not been found in any other area. But unsurprisingly, this species has proliferated in the aquarium trade despite that—one look at it, and you’ll understand the reason behind their popularity.
Now, when the fish was first found, the genus they belonged to was contested. But aquarium traders needed to market the beautiful new celestial pearl danio, and doing this meant guessing their place in the world of cyprinidae. That’s how they came to acquire the common name of galaxy rasbora.
In 2007, a new genus was created solely for the celestial pearl danio by Tyson R. Roberts, a scientist with the Smithsonian Tropical Research Institute.
So, even though the name “galaxy rasbora” is still widely used to refer to this fish, it’s something of a misnomer, as it was discovered by Roberts that these little guys are more closely related to the danios than to the rasboras.
What Does Celestial Pearl Danio Look Like?
Before they were Danio margaritatus, these vibrant little nano fish were given the scientific name of Celestichthys margaritatus. “Celestichthys,” from the Greek and Latin, is “heavenly fish” translated. Meanwhile, “margaritatus” translates to “adorned with pearls.”
Heavenly fish adorned with pearls—that’s a pretty good place to start if you want to guess at the appearance of the Danio margaritatus.
These are some of the smallest fish in the aquarium trade, not measuring more than 1.5 inches. They are vividly colored fish, with a base coloration of deep midnight blue.
They are covered all over with bright yellow/white spots responsible for the galaxy-like pattern that gives them their name. Their bellies tend to take on an orange coloration.
The fins of the celestial pearl danio, meanwhile, have a prominent shape and size. A tall dorsal fin protrudes from the lower third of the body of the fish. The anal and pelvic fins are wide.
The fins tend to have a red or deep orange color which contrast gorgeously with the rest of their body. You’ll also see dual black lines and a few transparent parts on all the fins of the fish.
The sexual dimorphism of the celestial pearl danio means that it’s possible to identify their sex. Males tend to have a thinner shape and a brighter coloring than females. Meanwhile, the coloring of females can be more accurately categorized as golden blue than dark blue.
How Big are They?
When it is fully developed and sexually matured—which takes about 3 months—the celestial pearl danio has an adult size of 1 inch in length. They can get as large as 1.5 inches.
This small body is why they are classified as a nano fish. They do best in large groups. Females and males differ slightly in size, with females being slightly larger.
How Long Do They Live?
In captivity, with appropriate conditions ensured, the average celestial pearl danio can be expected to live at least 3 years, and a maximum of 5 years. Like many other freshwater fish, celestial pearls respond poorly to stress and inadequate or unstable water conditions. Proper care, diet, and a low stress environment will contribute to a longer lifespan.
Temperament and Activity Level
Galaxy rasboras are mostly quiet, peaceful fish who love to swim together in groups, and they are curious explorers as well. Although they are not schooling fish as many wrongly think of them, celestial pearl danios are certainly very social, and you should aim to have at least 6-7 of these beauties in one tank.
When they all swim together, it creates a wavering, textured effect inside the aquarium that is truly awesome to behold. However, once they start getting used to their tank, they like spending time apart from the group as well.
The only concern when it comes to the behavior or temperament of the galaxy rasbora is related to their sex. It’s important to tell male and female pearl danios apart because a large number of males might cause a problem.
This is because males constantly battle over females, which unfortunately results in injury or, in the worst cases, even death. As such, you should keep fewer male CPDs in your aquarium than females.
What Are Good Tank Mates?
The best tank mates for a CPD are others of their kind. You should aim to keep at least 5-7 of these fish in the tank as they are a social species that love swimming together.
We stress once again that it’s very important to keep the number of female fishes higher than males, as having too many of the latter may lead to infighting for dominance.
Owing to their size, the celestial pearl danio also does well in nano tanks with other peaceful fish of the same size, such as guppies and neon tetras.
In fact, if you feel that your CPDs are much too shy or timid, introducing other fish might help them to feel more confident. In that way, suitable tank mates are a crucial part of celestial pearl danio care.
Given that galaxy rasboras like to occupy the middle of the tank, we recommend filling the tank with other species who stay near the top.
Good Tank Mates
With the above conditions in mind, the following make great tank mates for these danios:
- Tetras (regular, ember or green)
- Cory Catfish
- Molly Fish
- Endler’s livebearer
- Amano Shrimp
- Cherry Shrimp
You will notice that all of these species are small, just like the galaxy rasbora. Remember, if you decide to place so many small fish together, you have to make adjustments to the aquarium size accordingly. Small fish like this also lend well to planted tanks and aquascapes as the small size makes them a part of the scape versus the showcase. Most aquascapes are all about the design. The fish are a part of the piece so smaller fish work well with this style of aquarium keeping.
Fish Species to Avoid
It’s very important to choose only tank mates who are of the same size as your pearl danios. Even if they are generally peaceful, any fish significantly larger than celestial pearl danios might eat them. Not to mention, there will be competition for food.
You should absolutely avoid putting your galaxy rasboras in with any aggressive fish, such as oscars, cichlids, or Jack dempseys. These fish will happily snack on and eat your prized Danios.
Other fish who may not eat them, may be bothered by the dithering nature of these fish. Slow moving fish like Betta Fish often clash with Danios due to their nature. they also don’t compete well for food.
What Do They Eat?
As they are omnivores, celestial pearls will eat almost anything in the wild. They usually love plants and algae as well as zooplankton and might consume small invertebraes for protein.
In captivity, they take well to diets of pellets and flakes, but these should be of high quality. Not to mention, the pellets/flakes should be small enough that they can fit easily in the tiny mouths of your pearl danios.
Xtreme Aquatics Nano formula is specially designed for smaller fish and contained a well balance mix of raw ingredients. It is a great staple food for your nano fish.
They like eating at mid-tank levels, so try to choose pellets and flakes that won’t sink so easily.
What About Live Foods?
Celestial pearl danios will eat live food you give them, such as live baby brine shrimp, krill, daphnia, moina, white worms, and grindal worms. Frozen cyclops and frozen baby brine also make great snacks for them and help you to provide a balanced diet.
How Much and How Often to Feed?
CPDs should be fed 3 to 4 times a day, but you should make it a point to give them small amounts of food every time. This prevents overfeeding or food wastage and keeps the water quality clean.
It’s also important to cycle the food you give to your galaxy rasboras. This will ensure that they live longer and retain their vibrant coloring throughout their lives.
Something else you need to know about these little guys is that they are prone to stress. And when this happens, it will affect their eating habits.
So not only should you strive to ensure stress-free living conditions for your galaxy rasboras, you should also watch them closely when it’s feeding time. This will allow you to identify the picky or shy eaters as well as the more active ones and cater to their needs accordingly.
Tank Requirements (How to Set Up Your Fish Tank)
CPDs are relatively easy to care of, given that you ensure the best tank conditions for them. These little guys thrive in cold water and love to have plants to play around in. Here’s all you need to know about setting up a tank for your CPDs.
As we’ve already mentioned above, the minimum tank size for 5-7 celestial pearl danios is 10 gallons (so about 2 gallons per fish). This gives them the space they need to play or hide as they wish.
You’ll need to increase the aquarium size by an extra 10 gallons for every 5 of these fish you add. So if you have 30 CPDs, you’ll need a tank of at least 30 gallons.
Here are the particulars of the CPD fish tank setup:
When you’re setting up a tank for these little fish, it’s of utmost importance that you include plants to mimic the heavy vegetation of their natural habitat. These not only give the fish plenty of playing and hiding places, they also make for good snacks and provide ample space for breeding (if that’s one of your aims).
In fact, the more variety you can create in your aquascaping endeavors, the better for these fish. CPDs absolutely love these environments. So don’t hold back— include any and all plants you wish to or think would go well with your aquarium or your fish. Keeping healthy, stress-free CPDs is not possible without plants. If you want to make these easier for you consider low energy or beginner level plants.
As with plants, you have a wide variety of options when it comes to the aquarium substrate. Although they like swimming about in the middle of the aquarium, they also frequently stay towards the tank’s bottom half. Since they don’t dig, however, you don’t have to worry about substrate size.
That said, your chosen substrate should complement the plants you choose to place in the tank. Dark fine sand is a good option here as it will allow your plants to thrive and flourish, which is a requirement for keeping your danio fish happy. Sandy substrate is also easy to clean, an added benefit.
You have free reign when it comes to choosing decor for these fish as well. CPDs love having adequate spaces to hide and play in, so make it a point to include natural decor like rocks and driftwood where your fish can relax and play.
As with any other freshwater fish, it’s of crucial importance to maintain good water quality for the health of your danio fish. Here’s what you should know:
CPDs require strong filtration in their tanks. The biology of this fish is not able to handle too many pollutants in the water. Canister or power filters should work fine, although you should remember to block inlet tubes with sponges to prevent these tiny fish from getting sucked into them. They are very active fish and enjoy moving around the tank. A moderate flow will be healthy for them.
The rich vegetation found in the shallow ponds which these little fish inhabit give the water a clean and pure quality with low mineral and salt levels . These are the conditions you should aim to recreate for your CPDs if you want them to be happy and stress-free.
These are the basic recommended water parameters for CPDs:
- Water Temperature: 72°F to 76°F
- pH: 6.5 to 7.5
- Water Hardness: 2 – 10 dKH
As you know by now, taking care of these aquarium fish is pretty easy, given that you ensure clean water for them. Try to also keep levels of nitrates and dissolved organics low. Make regular water changes.
Test Water Conditions
In order to ensure proper water conditions for your aquatic pets, no matter if they’re CPDs or other fish, we recommend investing in a quality water testing kit. If you want a well-kept aquarium with healthy fish, accurate readings should be your first priority.
If you want to breed your CPDs, you’re in luck because they’re one of the easiest aquarium fish to breed.
In fact, males of this fish species spend a good chunk of their time just courting the females (which, as we mentioned above, can lead to fighting and injury/death), which makes this a species that is constantly spawning — pretty much daily.
So, triggering the breeding process of this fish shouldn’t require much input from you; just make sure you give your fish a steady and nourishing amount of live food.
Are Your They Male or Female?
As we discussed above, identifying the sex of this danio species is easy due to the species’ sexual dimorphism. Although they are similarly sized, your female CPDs will have a rounder shape and a duller body color in comparison to the males.
When a female is ready to spawn, she should develop a darkly colored, swollen spot near her anal fin. If you need a visual aid on determined if your danio is male or female, check out this video by The Secret History Living In Your Aquarium.
The Mating Process
How do you know when your CPDs are ready to spawn? Well, aside from the fact that both males and females try to breed almost daily after reaching maturity (which takes 3-4 months at most), there are some markers in behavior.
Males will typically hover near a spawning mop or Java moss (whatever you provide for spawning), and when a female is nearby, males will shake and flare their fins to attract her.
Once a male has caught her attention, a female CPD will swim down to where he is in the aquarium and nudge his anal fin with her head. Then they will shake together, releasing the eggs and milt.
The Breeding Process
CPDs are egg layers. To lay her eggs, a female CPD will find a spot in the tank where there is low water flow. She will usually also choose a large plant leaf to lay the tiny eggs—more than 30 at a time—so you should provide that once again.
You have to be alert and present during this process because male CPDs do eat their mate’s eggs. So as soon as you see that the eggs have been laid, gently take them out and put them into a designated spawning tank.
This also means that if you don’t want too many CPDs just leave the eggs as they are. They will be eaten by their dads and disappear from the aquarium.
Once they’re in the spawning tank, the eggs will take up to 2-4 days to incubate, after which you will see tiny fry beginning to hatch.
During this time, you should feed them micro foods. As they grow older and you move them into the main CPD tank, you can introduce them to live foods such as small worms and baby brine shrimp as well as flakes and pellets.
Health and Disease
CPDs are not as prone to disease as other freshwater fish who are harder to care for. Nor have any diseases been discovered which are exclusive to CPDs.
That said, they are still prone to being afflicted by common freshwater diseases.
Signs of Health
A healthy CPD, although shy and fond of hiding at times, is a pretty social fish. He or she will spend a lot of time swimming in groups and playing a little bit. As eager breeders, CPDs also spawn almost every day.
Common Health Issues and Treatment
Fin rot, in particular, is noticeable in these fish. As with any other fish, this freshwater disease can be identified by visual markers on the edges of the fish’s fins. If the edges of the fins look discolored or frail, as if it’s disintegrating, you can assume fin rot has taken a hold.
Fin rot can be caused by a number of factors, the most common being poor water quality. However, it can be easily avoided if you constantly monitor pH levels with a good water testing kit.
Fighting is another cause of fin rot. You can prevent your CPDs by fighting by ensuring a low male-to-female ratio in the aquarium. The more males there are, the higher the level of aggression and competition will be, leading to injurious fighting.
If you do suspect fin rot, try to restore optimal water conditions as soon as possible. Then you can use antibacterial medications to treat the condition. The fins should begin to grow back.
Where to Buy?
Compared to other freshwater aquarium fish, CPDs do tend to be more expensive, sometimes going up to $15 to $20 for just one fish. However, since they are active breeders, they’re not too hard to find in a well-stocked aquarium shop. You can also find them being sold online, but be careful and do your research.
Frequently Asked Questions
How many should be kept together?
You should keep no less than 6-7 CPDs together, as they like to group together (even though they are not shoaling fish). Remember to include a lower number of males than females.
Do they need a heater?
No—they actually have an affinity for cool water, so their fish tank should ideally be unheated.
Are they hardy?
They are indeed quite hardy and easy to take care of in any freshwater aquarium.
How many should I have?
In one 10-gallon tank, you can put 6 to 7 of these fish. If you wish to add more, you must increase the aquarium size as well.
Can they live with bettas?
No, because they have contrasting temperature requirements. Bettas require warmer water to live in (75 to 80 degrees C), while CPDs do well in cold water (below 74 degrees).
The breathtaking beauty and shy nature of CPDs make them a popular choice for aquarists interested in nano fish and dither fish. A group of CPDs makes a great addition to any large, well-planted freshwater community tank, given they don’t have any aggressive tank mates.
They’re easy to take care of and easy to breed if you ensure proper water conditions. Celestial pearl danios are definitely a rewarding fish to keep!
Mark is the founder of Aquarium Store Depot. He started in the aquarium hobby at the age of 11 and along the way worked at local fish stores. He has kept freshwater tanks, ponds, and reef tanks for over 25 years. His site was created to share his knowledge and unique teaching style on a larger scale. He has worked on making aquarium and pond keeping approachable. Mark has been featured in two books about aquarium keeping – both best sellers on Amazon. Each year, he continues to help his readers and clients with knowledge, professional builds, and troubleshooting.