Freshwater Fish to Be On the Lookout For: Emerald Dwarf Rasbora

Though not one of the most well-known species of rasbora, the emerald dwarf rasbora (Celestichthys erythromicron) is one to keep an eye out for. This little fish has a unique appearance and their small size makes them an ideal choice for nano tanks.

Species Snapshot

  • Species Name: Celestichthys erythromicron
  • Common Names: Emerald dwarf rasbora, cross-banded dwarf rasbora, thick-band purple zebra danio
  • Size: 1 to 1.5 inches
  • Lifespan: 3 to 5 years
  • Native Distribution: Lake Inlé, Myanmar

Though commonly known as the emerald dwarf rasbora, this species has gone by several names. When first discovered, the fish was classified in the genus Microrasbora. Some have placed it in the Danio genus as Danio erythromicron, though it is now typically referred to with the scientific name Celestichthys erythromicron. Other common names for the emerald dwarf rasbora include the cross-banded dwarf rasbora and thick-band purple zebra danio.

The emerald dwarf rasbora is endemic to Lake Inlé in Myanmar which has clear, shallow water and loamy substrate. Wild specimens of emerald dwarf rasboras are typically collected from the margins of the lake which are lushly planted with grass and reed-like plants. Because they’re so quick and difficult to catch with a net, fishermen typically use special traps that are laid among the vegetation overnight.

If you’re looking for a colorful, active species to feature in a mature aquarium with plenty of live plants, the emerald dwarf rasbora might be an option to consider. Here’s what you need to know.

What Do They Look Like?

As the name suggests, emerald dwarf rasboras are small fish – they grow to a maximum length of just 1 to 1.5 inches (about 20mm). Females tend to grow slightly larger than males and have a more noticeably round belly. Males, by contrast, tend to be more colorful than females.

The emerald dwarf rasbora is similar in appearance to other danios. They have long, slender bodies and dark vertical striping. The scales around the gill plate are semi-transparent and there is a large spot on both sides of the body at the base of the tail.

Though the color of the stripes may vary from one fish to another, most emerald dwarf rasboras exhibit emerald green striping. In certain lighting, some may look more purple or blue. Males of the species tend toward the bluer tones and exhibit red coloration on the fins.

The beautiful emerald dwarf rasbora.

What Is the Ideal Tank Setup?

As long as tank conditions are kept consistent, emerald dwarf rasboras are fairly easy to care for. Their small size makes them an ideal choice for nano tanks, though larger tanks are typically easier to maintain in terms of water chemistry.
With strong filtration and frequent water changes, emerald dwarf rasboras can be kept in tanks as small as 10 gallons. A 20-gallon tank is more appropriate, however, and will accommodate larger groups.

The emerald dwarf rasbora is a shoaling not a schooling species, so they’re best kept in very large groups of 20 or more, when possible. These fish are generally peaceful, though fin nipping may occur among rival males if the group is too small. In a large enough tank, emerald dwarf rasboras can be kept with other small cyprinids, ideally surface-dwelling species.

In terms of tank setup, the emerald dwarf rasbora prefers a densely planted tank with plenty of places to hide. This species is likely to become shy or skittish in a barren tank setup, so use plants, rocks, and driftwood to create an interesting environment.

The ideal water parameters for emerald dwarf rasboras are:

  • Water Temperature: 68°F to 75°F
  • pH Level: 7.0 to 8.0
  • Water Hardness: 2 to 10 dKH

Emerald dwarf rasboras prefer very clean water with a neutral to slightly alkaline pH – they do not tend to do well in acidic water. These fish also prefer slightly cooler water temperatures.

To keep the water quality in your tank high, make sure you have strong filtration and perform regular water changes. Lighting requirements will vary depending on the number and type of plants you cultivate in the tank. Heating may or may not be necessary, depending on where you live, but it’s wise to keep the tank temperature as stable as possible.

What Do They Eat?

The emerald dwarf rasbora is an omnivore, typically feeding on algae, zooplankton, and small invertebrates in the wild. In the home aquarium, these fish are best fed a diet of live and frozen food like artemia and daphnia to encourage strong coloration.

Because emerald dwarf rasbora are mid- to bottom-dwellers, they don’t tend to feed from the surface of the water. When feeding dried foods, avoid floating products in favor of slow-sinking granules. Just make sure they are appropriately sized for the fish.

Do They Breed In Captivity?

Like other cyprinids, the emerald dwarf rasbora is an egg-scattering species. When kept in good condition in a mature aquarium, these fish will spawn often. The fish do not, however, exhibit any degree of parental care, so you are unlikely to see a high yield of fry unless you step in.

If you plan to breed emerald dwarf rasboras, it’s wise to set up a separate breeding tank. Condition the fish together as a group but move a pair or a small group consisting of one male and several females to the breeding tank when they are well-conditioned. Line the tank with fine-leaved plants so the eggs will have some protection from the adult fish.

Female emerald dwarf rasboras typically release about 30 eggs per spawn. Though breeding can occur year-round, the females will need a recovery period before spawning again.

In proper conditions, fertilized eggs should hatch after about 72 hours and the fry will become free-swimming 3 to 4 days later. The free-swimming fry should be fed very small foods – between 5 and 50 micron. Once they are large enough to accept them, you can progress to slightly larger foods like artemia and microworms.

Fun Facts About Emerald Dwarf Rasboras

These fish are incredibly active and, when kept in sufficiently large groups, can be very entertaining to watch as they swim around the tank.

The more fish you keep in your tank, the less shy your emerald dwarf rasbora will be. Keeping the fish in large groups will also help encourage healthy coloration.

The emerald dwarf rasbora is a very inquisitive fish and they enjoy exploring their environment, so provide plenty of live plants, rocks, and other decorations.
Though these fish may accept a variety of foods, they’ll be healthiest and the most colorful on a diet of live and frozen foods like microworms, daphnia, and brine shrimp.

These fish tend to prefer slow-moving waters similar to their native lake habitat, so avoid filtration systems that create too much flow.

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