Harlequin Rasbora Care Guide: Lifespan, Size & Tank

The harlequin rasbora is a freshwater fish of the Cyprinidae family native to Singapore, Malaysia, Sumatra, and southern Thailand. Its orange to pink body and black wedge make it easy to recognize, and it looks similar to the lambchop rasbora and glowlight rasbora.

It is popular because of its schooling behavior and color. Harlequin rasboras suit a small community tank and are a good choice for beginners. With good care they live about 5 to 8 years.

Harlequin Rasbora Facts & Overview

Origin

The harlequin rasbora (Trigonostigma heteromorpha) is a tropical freshwater fish found in Southeast Asia, including peninsular Malaysia, southern Thailand, and Singapore, with records from Sumatra as well. In nature, it lives in forest streams and heavily vegetated peat swamps with slow water flow.

These waters have little dissolved mineral content and a lot of humic acid from decaying plant matter, which gives them a yellowish-brown tint. The IUCN lists the harlequin rasbora as Least Concern.

Related species are often sold under the same name, including T. espei (the lambchop rasbora) and T. hengeli (the glowlight rasbora). The true harlequin has a broader, more triangular black marking and a deeper body.

How big do harlequin rasboras get, and how long do they live?

Harlequin rasboras are small. Most reach about 1.75-2 inches (FishBase lists a maximum of 5 cm, Seriously Fish 4.5 cm standard length). Fish from Thailand are often smaller and slimmer than those from Singapore.

The lifespan of harlequin rasboras has not been studied systematically, but with good care they commonly live 5 to 8 years in an aquarium. Poor water quality, stress and a bad diet shorten that. Fish bought from stores that arrive underweight, thin or faded rarely reach that age.

Availability

Harlequin rasboras are among the most common schooling fish and are sold in most pet stores.

Currently, these online stores have stock of harlequin rasboras:

• LiveAquaria
• FlipAquatics
• AquaHuna

A single harlequin rasbora costs $3.50-$4.50 on average, while a school of six costs $19-$26.

Appearance

Harlequin rasboras are hardy and adapt to most aquarium conditions, and their color and calm behavior make them an easy choice.

Colors, Patterns, Fins, and Sex Differences

The body is elongated and laterally compressed, with a small mouth and a deeply forked tail. Compared with the lambchop and glowlight rasboras, the harlequin is deeper-bodied, with a convex belly.

The fins are tinted red. The inner part of the forked tail is clear, with the red concentrated at the outer edges.

Body color ranges from pale pink or bright red to copper-orange. A black triangular marking covers the back half of the body, starting below the dorsal fin and tapering to a point near the base of the tail.

How can you tell males from females? Males are slimmer and often a little more brightly colored, with a larger black wedge that is slightly rounded along its lower edge. Females are rounder and slightly larger, with a wedge that has a straight lower edge. The difference is subtle, so look at the shape while the fish are in good light.

There are several color forms. Copper or golden-bodied fish are sold as golden harlequin rasboras. Black harlequin rasboras have mostly black bodies. Some fish have a bluish tint and are sold as blue harlequins.

Typical Behavior

Harlequin rasboras are active, peaceful and fast. They do best in groups of at least 8-10, and larger schools are better. A school this size looks and behaves more naturally, and individuals are less likely to hide or become stressed.

They swim in the middle of the tank and rarely go to the bottom or surface. When stressed, or when they want to avoid bright light or larger tank mates, they hide among plants. Less active fish may not tolerate a lively school.

Harlequin Rasbora Care & Tank Requirements

Harlequin rasboras are easy to care for as long as you keep the water clean and the school large enough. Their natural habitat is soft, slightly acidic water with slow flow, dense vegetation, an open swimming area and dim light.

To copy that, use a planted tank with a gentle filter, a dark substrate and floating plants to diffuse the light.

Habitat and Tank Requirements

The fish spend most of their time in the middle and upper levels. They need room to swim, so a long tank of at least 24 inches (36 inches is better) works well.

A gentle filter is enough. Sponge filters or filters with a spray bar or baffled outlet keep the current slow, which suits fish from still blackwater streams.

Change 25% of the water weekly. A monthly change is not enough in a tank holding a school. Vacuum the substrate lightly during changes to remove waste.

Use soft sand or fine gravel, or a dark substrate, which brings out the orange color. Add dense plants, bogwood, dried leaves (such as Indian almond leaves), rocks and broad-leaved plants. Floating plants cast shadows that make the fish feel secure.

Tank Conditions

Harlequin rasboras need a tank of at least 15 gallons for a school of 8-10 (Seriously Fish gives a 24 x 12 inch base, about 14 US gallons). A 20-gallon tank is better, and a larger school needs a larger tank. Ten gallons is too small for a proper school.

Keep the temperature between about 72 and 81°F. The fish do best in soft, slightly acidic water, with a pH of 6.0-7.5 (ideally around 6.5) and hardness of 2-12 dGH. They tolerate harder water than their wild habitat, but their color is best in soft, slightly acidic water. They do not belong in brackish water.

A good filter keeps the tank clean, but it should not produce a strong current in the middle of the tank.

In short, give them a planted tank with open swimming room, a quiet filter and regular water changes.

Disease

Harlequin rasboras are fairly resilient, but they can catch the usual fish diseases in a freshwater tank. Stress, a poor diet and bad water quality raise the risk. Watch for clamped fins, hiding, faded color, white spots, bloating, or fish that stay near the surface.

Common problems include:

• Dropsy is swelling of the body, often with raised scales (a pinecone look), caused by a bacterial infection and organ problems. It is often fatal. Quarantine the fish and treat with antibiotics.
• Ich is a parasite that causes small white spots on the body and fins. Treat with an ich medication, or by gradually raising the temperature to around 86°F for several days with extra aeration, as many keepers do.
• Fin rot is a bacterial infection that frays fins and tail, sometimes with dark or white edges. Improve water quality first, then use an antibacterial treatment if it continues.

Tank Mates

Harlequin rasboras are peaceful and can live with most fish that aren’t large or predatory. Keep them with calm, similarly sized fish that like soft, slightly acidic water. Very slow or shy fish may find a fast school stressful. Large, predatory fish will eat them.

Good tank mates include:

• Neon tetra
• Rummy nose tetra
• Danios
• Dwarf gourami
• Cherry barbs
• Cory catfish
• Apistogramma
• Honey gourami
• Bolivian ram
• Mollies
• Kuhli loach
• Guppies
• Hatchetfish
• Platies

Mollies, guppies and platies prefer harder, more alkaline water than harlequins. They can work in a tank where the water falls in the middle (around pH 7 and moderate hardness), but the rasboras’ colors will be less intense. Snails and small shrimp are also fine, although adult shrimp are safer than baby shrimp.

Diet and Feeding

In the wild, harlequin rasboras eat small insects, worms, crustaceans and zooplankton. In an aquarium, feed a good-quality flake or small pellet food, plus small live or frozen foods such as brine shrimp, daphnia and bloodworms a few times a week.

Their mouths are small, so crush large flakes and choose small pellets. Feed once or twice a day, giving only what they finish in about two to three minutes, and remove leftovers.

Breeding

Harlequin rasboras are tricky to breed. They need the right water, and spawning can take days of courtship. They are egg-layers that stick their eggs to the underside of broad leaves.

To prepare, pick young, healthy fish and feed them small live foods several times a day for about four weeks. This should fill out the females and bring up the males’ color.

How to Prepare

Set up a dim breeding tank with 6-8 inches of water. Keep the water very soft (about 1.5-2.5 dGH), slightly acidic (pH 5.3-6.0) and warm (77-82°F), close to their natural water.

Add broad-leaved plants such as Cryptocoryne or Microsorum, and a spawning mop to catch eggs that fall.

The Breeding Process

Add the breeding fish in the evening. For a group of young fish, use more males than females (about two males per female).

Spawning usually happens in the morning. The male leads the female under a leaf and courts her by nudging her sides. The pair lays a few eggs at a time on the underside of the leaf, up to 80-100 eggs over an hour or two.

Remove the adults when spawning ends, because they eat eggs and fry. Eggs hatch in about 24-48 hours, and the fry swim freely after about a week. Feed infusoria or similar fine food at first, and move to baby brine shrimp after around a week or two.

Should You Get a Harlequin Rasbora for Your Aquarium?

The harlequin rasbora is a peaceful, hardy schooling fish that adds color to a community tank. Buy at least 8-10, give them a planted tank with open swimming space, and keep the water clean.