Over the years, this popular nano fish has gone by many names. At times considered a rasbora (introduced to the trade as galaxy rasbora in 2006), it is now considered a “danionin.” Hence the common name/abbreviation “Celestial Pearl Danio/CPD.” It is in a genus with the dwarf emerald rasbora (C. erythromicron) and distinct from the typical danio. To be sure, it belongs in the family Cyprinidae, which encompasses all minnow-like fish. This is an egg-scattering fish that presents few challenges to breed and raise.

Part of what makes the CPD so popular is its striking coloration. Both sexes have white spots on a blue-ish background with red in the fins. The male will have much more intense red coloration. This fish is often affectionately referred to as “tiny brook trout.” Tiny would be correct! These fish max out at about 0.75”. CPD’s are native to just a few small ponds in Southeast Asia (Myanmar) at an altitude of over 3,400 ft! Thankfully, despite their restricted habitat, these fish are readily available captive bred and almost none are harvested from the wild any more. 

Care Requirements

Due to their small size as adults, celestial pearl danios can be kept in tanks as small as 2.5 gallons. However, because they prefer to live in groups of six or more, a 5-10 gallon aquarium is much more suitable. Although they are not too fussy about pH, they do prefer cooler temperatures. They are really more of a subtropical fish, and should be kept no warmer than 76 degrees. Keeping them around 80 degrees will speed up their metabolism and cause them to waste away. They tend to be a bit shy and need lots of plant cover to thrive. It is advised to keep them only with similarly sized, peaceful fish. They can also be kept with small shrimp and snails.

You want to be careful that the CPD’s are getting enough food. Usually crushed flake food is not enough to sustain them; they do best with small live and frozen foods in their diet as they tend to feed mid-water. They are not high waste producers and do not need overpowered filtration; a small sponge filter or hang on the back will do just fine. With the right care, these fish can live 3-5 years in captivity. 

Breeding

Successfully breeding celestial pearl danios is really quite easy; it’s just a matter of separating the eggs from the adults. Like most egg-scattering fishes, CPDs will eat their eggs and offspring given the chance. They typically spawn amongst clumps of moss or other live plants. The male will chase around a female and they will release eggs and sperm, which will then sink into the plants or the substrate beneath.

To remove the eggs, one strategy is to keep the adult fish in a bare bottom tank and provide moss only above a cup that is weighed down with rock or a few marbles. CPD’s have such a strong preference for using plants to breed that they will seek out this moss and spawn only here. The eggs will fall into the bottom of the cup, where they can be removed. Spawning takes place almost daily, with each female laying about 10-30 eggs. To increase yield, it is recommended to have many females for each male.

Another strategy is to just keep your adults in a heavily planted tank and wait for fry to appear. This will not get you as many fry, but over time you may see a small recruitment in numbers. Yet another approach is to let the adults breed freely for a few days in a spawning tank and then move them and wait for fry to emerge. You may also try using coarse gravel and siphoning out eggs and wigglers periodically from the substrate. All eggs/wigglers removed from the breeding tank should be moved to a filtered (sponge) grow out tank.

Caring for Fry

Raising the fry can be a bit tricky if you’re not used to raising egg-scattering fishes. Unlike livebearers and most cichlids, CPD fry are unable to take crushed flakes or baby brine shrimp right away. Once the fry start swimming around, you will either have to go with paramecium/infusoria or you can try a fine powder like Sera Micron or 5-50 micron golden pearls. Once the fry are about a week into the free swimming stage, they can usually start taking live baby brine and microworms, at which point they will grow very quickly. (Read our blog about culturing microworms here).

CPD fry will be sexually mature at around 3-4 months of age. The survival rate is fairly high, with almost all fry hatched making it to adulthood when raised carefully. The fry tank should only have a sponge filter, set on a gentle flow. Water changes of 25-50% should be performed every few days. When replacing water, you want to make sure that the temperatures are closely matched. Starting the fry in a 2.5 gallon tank and then slowly bumping up to a 5.5 and then a 10 gallon over time is ideal. Keeping tiny fry in too big of a tank initially can make it harder for them to find food. 

Conclusion Celestial pearl danios are a very beautiful and rewarding fish to keep. They truly shine in densely planted, small aquariums and breed with very little prompting. They are also exceptionally peaceful with not a bad bone in their body. CPDs can cohabitate with other tiny cyprinids, tetras, small loaches (kuhli, rosy, sidthimunki), catfish (pygmy cories) and even small shrimp (Neocaridina/Caridina). This is a must-have fish for almost any nano aquarium.

Links of Interest:

https://en.wikipedia.org/wiki/Danio_margaritatus