Celestial Pearl Danio (Danio margaritatus)

Celestial Pearl Danio overview

The Celestial pearl danio is a “recent discovery” in the freshwater tropical fish world. The story of the fish’s introduction to the aquarium and scientific world is quite fascinating!

In 2006 Thai tropical fish exporter Kamphol Udomritthiruj took photographs of the tiny new fish and showed them to aquarists around the world. Kamphol called the fish Galaxy rasboras.

The fish was a small cyprinid about one-inch long. The bright red fins created a striking contrast to the bluish body sprinkled with pearly, iridescent spots. The translucent gill cover (operculum) allowed the reddish gill color through.

Everyone got excited and wanted to purchase these beautiful new jewels from Myanmar. But rumors soon spread that the fish was not real, just a photoshopped image created from two or more danios. Some thought he was playing a joke on the aquarium world. But Kamphol provided even more photographs to prove his fish was real and available to the hobby.

This “lit the fuse” for explosive demand for this new tropical fish. But within six months, it appeared that over-collecting would wipe out the native fish population. Collection rates in the wild were down to only a few dozen per day.

Myanmar’s Department of Fisheries stopped all exports while biologists investigated the native population and environmental impact. At the same time, some European fish shops were using the “Galaxy rasbora controversy” to promote sales to local breeders. The idea was to sell more fish at a premium price under the guise of saving the fish from extinction. Meanwhile, the Myanmar Department of Fisheries found that there was no shortage of fish or habitat.

The native population was reproducing quickly in many locations. Exporting of Galaxy rasboras resumed. In February 2007, Tyson Roberts, a research associate at the Smithsonian Tropical Research Institute, published an article describing a new genus and species called Celestichthys margaritatus. Margaritatus means ‘adorned with pearls’ in Latin.

Roberts determined that the Galaxy rasbora was actually a danio. Roberts gave the fish the common name of Celestial pearl danio. In 2008, three researchers from the University of Saint Louis reclassified the fish as genus danio under the name of Danio margaritatus, after confirming it was really a danio not a member of a new genus. And that is how the Celestial pearl danio entered the aquarium hobby! Here’s what you need to know about keeping Celestial pearl danios in your own aquarium.

Natural habitat

The wild Celestial pearl danios were discovered in shallow pools in Hopong, Myanmar. The fish was later found throughout the Salween basin. The common characteristics of this habitat are shallow pools with thick aquatic plant growth of Elodea, Egeria and Blyxa. The water is clear without tinting by natural tannins.

Water analysis of the Salween river shows that it is low in minerals and salts, compared to the Mekong and Yangtze rivers, but not as “soft” as South American rivers. The pH was about 8.4. As a comparison, the Celestial’s native water is similar to many rivers in the United States.

Aquarium requirements

Mature Celestial pearl danios are small, measuring only about 1 inch in length. Most of the fish sold in the hobby are captive bred and have a length of approximately ½ inch. Celestials are not strong swimmers and prefer quieter waters with low to medium flow patterns.

These danios are not true schooling fish and don’t require large numbers to thrive in an aquarium. They have a peaceful, non-aggressive nature and are happy in a group of six fish, half males and half females. Normal behavior includes hovering in the water or exploring plants, rocks and driftwood. You can keep this group in its own 10-gallon aquarium. A 20-gallon aquarium will provide room for more aquascaping and the addition of other compatible fish.

Water chemistry conditions

Celestial pearl danios do not require special water conditions. The fish can be kept in a wide pH range of 6.8 to 8.4. Some experts have had better long-term experience by keeping the pH slightly alkaline, in the 7.2-7.5 range. Soft water is not required to keep these fish in the aquarium but softer water is probably a good idea if the tank contains live plants.

Water hardness (GH) and alkalinity (KH) levels in a range of 5 to 10 degrees is acceptable. If your aquarium water has low alkalinity (<5°KH), the pH may drift to the acidic pH range over time. Alkalinity stabilizes pH. Natural acids produced by the break-down of fish waste and biological filtration neutralizes alkalinity. If the alkalinity drops to less than 3 degrees, the pH could suddenly drop below pH 6.0. Test pH and alkalinity every week or two to keep a close watch on these important water chemistry parameters.

Water changes, made every three to four weeks, will usually replenish alkalinity and stabilize the pH. Set the aquarium heater to maintain a water temperature of 73 to 79°F. An aquarium thermometer is helpful for making sure the heater is keeping the water temperature at the desired set point.

Ammonia and nitrite must always be zero. Even low levels of these pollutants will stress your fish. Chronic exposure to ammonia or nitrite will weaken the fish’s immune system, leading to many disease problems.

Water filtration

Being small fish, they won’t produce a lot of solid waste in the aquarium. This means a simple hang-on-back (HOB) power filter is all that is needed on a 10- to 20-gallon aquarium. A HOB power filter with a filter cartridge will provide adequate water flow that won’t disturb these gentle fish. Be sure the cartridge filter contains activated carbon to remove odors and adsorb dissolved organics.

If you have an aquarium larger than 20-gallons, consider a canister filter. A canister filter will provide more mechanical filter media like filter sponges, along with activated carbon and even biological filtration media. Mechanical filter media traps and hold solid particles, helping the water stay clear. The biological filter media provides a place for beneficial waste-degrading bacteria to live.

No matter what type of filter you choose, be sure to service it once a month. A dirty filter cartridge will still flow, even when clogged. Most aquarium filters are designed to allow water to bypass the filter media if it becomes clogged. This safety feature ensures the filter still pumps water, even if the media are clogged with sludge. The sludge will decompose inside the filter if not replaced frequently. Decomposing organic matter releases algae-promoting nutrients, like phosphate, into the water. This can stimulate green water blooms and algae growth on the glass, gravel and ornaments. Maintain the filter and your water will stay clean and clear.

Aquarium lighting for Celestial Pearl Danio

A well-lit aquarium is essential to show off the beauty of the fish along with your aquascaping skills. You can keep Celestial pearl danios in subdued or bright lighting. You’ll want a brighter light for if raising aquarium plants.

There are two choices in aquarium lighting. Fluorescent light fixtures have been the standard aquarium light for over 30 years. Modern LED lighting fixtures used to be reserved for high-end reef tanks but are now available for all types of aquariums. Here’s the benefits of both kinds of lighting. Most fluorescent aquarium light systems include a plastic lid and light fixture. It acts as an aquarium cover, lid and a light. Many fluorescent bulbs are designed to highlight the artificial “Day-Glo” colors of aquarium gravel, plastic plants and ornaments. This works if it’s the look you’re going for. Keep in mind that the natural colors of tropical fish appear muted in this type of lighting. Natural “daylight” fluorescent light bulbs are available as a retrofit, making it easier to grow live aquatic plants and bring out the subtle color patterns of freshwater fish. The downside is the light quality of fluorescent bulbs degrade over time. The bulbs will gradually dim during a period of 9-12 months. You’ll have to replace the bulbs to maintain the same level of illumination year after year.

LED lighting uses very little energy, produces less heat and lasts for many years. Most LED aquarium light fixtures are not incorporated into a hood system. The idea is to place the LED fixture above an open aquarium. This provides a clean look and recreates that “sunlight shimmer” as the light is refracted through moving water. The LED light will have adjustable mounting legs that straddle the ends of the aquarium frame. Some fixtures even have a built-in timer. The next level of LED light fixtures use more LEDS for better light coverage. This is helpful when you have a deeper tank or are growing live plants. Multi-color LED systems let you to adjust the light color and create a gradual sunrise and sunset lighting program.

Aquascaping the Celestial Pearl Danio aquarium

Celestial pearl danios are compatible with just about any style of aquascaping. You can use plastic plants, aquarium-safe ornaments and other typical aquarium decorations. Since the fish does not sift gravel or build a “nest,” any size aquarium gravel is OK to use. If you want to duplicate the shallow pools where wild Celestials are found, you’ll want a heavily planted aquarium. Add pebbles and branches of drift wood to duplicate their natural habitat. The shallow pool habitat is brightly lit, so don’t be afraid to use bright, full-spectrum lighting.

Feeding

Celestials have a tiny mouth. Don’t expect them to eat large amounts of food at each feeding. They’ll take a couple of bites and no more. Successful aquarists report the fish will eat a variety of ground flakes, micro pellets and powdered food. Frozen daphnia and blood worms are also favorites. Live brine shrimp and Grindal worms are readily eaten. Feed only what the fish will consume in a minute or two. Uneaten food collects in the filter, decays in the gravel and pollute the water.

Compatibility

Celestial pearl danios are gentle fish that prefer a peaceful aquarium. Fish that tend to chase and bully are not suitable with Celestials. Other danios will get along with Celestials. Angelfish, neon tetras, chili rasboras and small corydoras catfish are good tank-mates and will form a nice community aquarium.

Celestial Pearl Danio Breeding

Celestials are egg layers. If you happen to have a pair in a species or community tank, chances are they’re spawning. But the fry will have a difficult time reaching adulthood since other fish may eat them. For better breeding success you’ll need a spawning tank.

A popular method for egg-scattering danios is to use a small 5-gallon tank, lined with a single layer marbles.A spawning mop is placed inside the aquarium, mimicking aquatic moss. A biologically-active sponge filter will keep ammonia and nitrite under control. When the adult fish, in the main aquarium, have been conditioned with high-quality food, the female will look “plump” with eggs. The male, slightly larger and more streamlined, will develop intense coloration.

Place two females and one male into the spawning tank. The fish should remain in this aquarium for about five days. They’ll spawn continuously during this period.

The fish will lay eggs on the mop. Eggs will drop into the marbles and away from hungry fish. After about five days the fish are removed and the eggs begin to hatch. You’ll see wiggling fry on the glass and in the marbles after about 15 days. Feed the fry very fine flake or powdered food. They will also eat infusoria. Once the fish look like small adults, move them to another aquarium.

Final thoughts

Celestial pearl danios created a lot of excitement when they were first introduced to the hobby. Hobbyists and breeders struggled to find a pair for their own tanks. Aquarists worked for several years to figure out how to care for and breed these beautiful fish. Now they’re captive-bred and readily available from fish shops everywhere. If you’re looking for a tropical fish that’s gentle, easy to care for and beautiful, take a close look at Celestials. You won’t be disappointed!