Harlequin Rasbora fish by thevetscare.com

Harlequin Rasbora (Red Rasbora) Fish Breed Profile

This post include on query Harlequin Rasbora or Red Rasbora fish and everything you must know about Harlequin Rasbora by thevetscare.com

Characteristics, Origin, and Helpful Information for You

Harlequin Rasbora by thevetscare.com
Harlequin Rasbora by thevetscare.com

Fish hobbyists love the harlequin rasbora—it has a beautiful metallic color and it is easy to care for. A large school makes an aquarium vivid and vibrant with movement. This is a great fish for a smaller-sized community tank as it is peaceable with most other species. It is a smaller fish, so keep it with like-sized specimens; larger fish might be attracted by its shimmer and try to make a meal out of it.

The Harlequin Rasbora (Trigonostigma heteromorpha) makes an absolutely captivating addition to any aquarium. Its body is mostly a bright pinkish color, but it is known for the black or dark purple mark on its sides. The combination of these bold colors really makes this fish stand out from all others, especially when paired with dark-colored substrate. Males tend to be more colorful than females, and its “lambchop” markings are usually more pointed in appearance. Females are often rounder in shape. Its diminutive size makes this fish great for nano tanks! The Harlequin Rasbora is easy in care as long as it has stable water parameters with good water quality. Like all rasboras and danios, this fish is completely peaceful and totally safe to keep with other fish (as long as the other fish are peaceful as well), snails, shrimp, and live plants. While it is safe with adult shrimp, it might prey on shrimp fry. The Harlequin Rasbora is a schooling fish that can only thrive in groups of at least 6-8 specimens. Keeping this fish in a large school will ensure its most natural behavior, especially top coloration from males as they compete for the attention of females. When this fish is healthy and placed in a well-cycled and densely planted aquarium, it is fairly likely that it will spawn, and you may see fry start to appear.The Harlequin Rasbora is omnivorous and not too picky about eating. It will likely eat fish flakes or pellets, but also needs a varied diet of frozen meaty and/or live meaty foods (such as brine shrimp, bloodworms, daphnia, and insect larvae) in order to breed or even show its best coloration. It will also eat blanched vegetables such as lettuce, zucchini, kale, etc. The Harlequin Rasbora is a very undemanding, classic fish that is a prime candidate for the planted or nano aquarium!What We Like About This Fish:

  • Unique pattern and striking colors
  • Ideal schooling fish
  • Safe with plants
  • Completely peaceful


  • Temperature:  72° – 79° F (22° – 26° C)
  • pH:  6.0 – 7.0
  • KH:  2 – 10 dKH
  • Minimum tank size:  10 gallons


  • Diet:  Omnivorous.  Will readily accept most flake foods and algae wafers, as well as freeze-dried daphnia, bloodworms, tubifex, and brine shrimp.
  • Social behavior:  Peaceful, schooling/shoaling.
  • Origin:  Tank-bred, but indigenous to Thailand, Malaysia, Singapore, Borneo, Sumatra
  • Average adult size:  1.4 – 1.8 inches (3.5 – 4.5 cm)
  • Average purchase size:  .5-1 inch (1.3-2.5 cm) 

Quick Stats

Care LevelEasyTemperamentPeacefulColor FormOrangeDietOmnivoreWater Conditions72-77° F, KH 6-10, pH 6.0-6.5Max. Size2″OriginAsiaFamilyCyprinidaeMinimum Tank Size10 gallonsCompatibilityView Chart

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The Harlequin Rasbora is an extremely desirable aquarium addition thanks to its gorgeous metallic coloration and ease of care. It’s not difficult to see why so many hobbyists treasure it. A large school of Harlequin Rasboras fill the upper areas of the aquarium with movement and color so lively and vibrant that even non-hobbyists marvel at the display.

The Harlequin Rasbora is easily identified by its characteristic black “pork chop” shaped patch. Males will have a beautiful lustrous copper/orange body while females will be exhibit a more golden coloration . The distinguishing triangular patch begins near the dorsal fin and comes to a point near the base of the caudal fin. The patch on the female Harlequin Rasbora is slightly rounded at the bottom with an extended tip. In contrast, the patch on the male Harlequin Rasbora is straight. The female Harlequin Rasbora is also larger than the male. Juveniles will darken as they mature.

The Harlequin Rasbora does best in an established planted aquarium with open areas for swimming. The Harlequin Rasbora should be kept in schools of 8-10 individuals and housed with other small, peaceful fish. The mild nature of the Harlequin Rasbora makes it a great community fish.

Rasbora heteromorpha generally spawns on the undersides of broad-leaved plants. A breeding tank with shallow, warm, acidic, soft water with broad-leaved plants should be set up. To encourage spawning, pair a young (9-12 months old) female Harlequin Rasbora with a two-year old male and offer live food items. After spawning, remove the parents and keep the aquarium dark until the eggs hatch (after about 24 hours). Feed the fry infusoria.

An omnivore, the Harlequin Rasbora does well on a diet of prepared flake food, as well as freeze-dried bloodworms and tubifex.

Approximate Purchase Size: 1/2″ to 1″

Species Overview

COMMON NAME: Red rasbora

SCIENTIFIC NAME: Trigonostigma heteromorpha

ADULT SIZE: 1.75 inches (4.5 centimeters)


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OriginSoutheast Asia, Malaysia, Singapore, Sumatra, Thailand
SocialPeaceful, suitable for community tank
Tank LevelTop to mid-dwelling
Minimum Tank Size10 gallon
pH6.0 to 7.5
HardnessUp to 12 dGH
Temperature73 to 82 F (23 to 28 C)

Origin and Distribution

The harlequin rasbora is a native of Malaysia, Singapore, Sumatra, and southern Thailand. It inhabits streams and waters that are characterized principally by their low mineral content and high concentrations of dissolved humic acids, which is typical of water that flows through swamped forests. The waterlogged soils of these forests inhibit the complete decay of leaf litter, resulting in the formation of peat, which leaches humic acids. These conditions resemble those found in the blackwater habitats of South America.

Colors and Markings

Of the more than five dozen species of rasbora, the harlequin is arguably the most popular of them all. Often referred to as a red rasbora, the body is a reddish-copper color that is accented by a striking black wedge covering the rear half of the body. The distinguishing triangular patch begins near the dorsal fin and comes to a point near the base of the caudal fin. This species looks similar to Rasbora espei and R. hengeli.


The harlequin rasbora is a shoaling fish; it should be kept in schools of eight to 10 individuals. Schools of even larger numbers make for a beautiful display. You can keep harlequins with any fish as long it’s not large and predatory. It will not nip at or quarrel with any other species. Some potentially good tankmates may include cardinal tetras, bettas, neon tetras, small barbs, dwarf gouramis, danios, other small rasboras, and cory catfish.

Harlequin Rasbora Habitat and Care

Rasboras are a true freshwater family of fish and are never seen in brackish waters. They prefer the lowland waters of southeastern Asia, where the water is soft and acidic. Harlequins prefer an environment with areas of dense vegetation, an open area for swimming, a dark substrate, and subdued lighting.

An aquarium intended to house harlequin rasboras should be planted with live plants. Create open areas for swimming between stands of plants such as Cryptocoryne species, these being among the plants that inhabit the harlequin rasbora’s native waters.

Harlequin Rasbora Diet and Feeding

Harlequins readily accept all foods but prefer to eat live foods whenever possible. In nature, their diet consists primarily of insects. However, they will accept frozen foods and freeze-dried foods as well as flake foods. A varied diet will ensure that digestive problems or susceptibility to disease do not occur. Brine shrimp, daphnia, and any type of worm are excellent supplemental foods, particularly when conditioning before breeding.Feeding Your Fish Live Food

Gender Differences

Male harlequins are more slender than females and exhibit a rounded extension at the bottom edge of the distinctive black wedge covering the posterior of the fish. The black wedge on females is perfectly straight. The female harlequin rasbora is also larger than the male.

Breeding the Harlequin Rasbora

Harlequins are among the more difficult tropical freshwater species to breed, however, spawning may be achieved if you provide the proper conditions. Select young specimens and condition them with live foods such as daphnia and mosquito larvae before the spawning attempt. Harlequin rasbora differs from other popular rasboras in the aquarium when it comes to breeding. While other rasboras are egg-scattering spawners, harlequin rasboras are egg layers.

You can breed groups of young harlequins in a single aquarium. When spawned in groups, keep two males for every female. Hobbyists who are intent upon simulating natural conditions as closely as possible may choose to filter the aquarium water over peat, thus replicating the humic acid concentrations found in the fish’s native waters, although this is not necessary if the basic water chemistry parameters (no higher than 4 dGH of hardness, pH around 6.4) are correctly maintained. Optimum water temperatures for spawning are between 76 and 80 degrees Fahrenheit. Add Cryptocorynes or similar broad-leafed plants to the breeding tank.

Once you prepare the breeding tank, introduce the breeding stock late in the day. Spawning will usually begin in the morning and is initiated by the male dancing and trembling before the female. This spawning behavior is intended to direct the female beneath a suitable plant for depositing the eggs. You may see the male nudging the sides of the female and rubbing his belly against her back to move her to the spawning location.

When ready to spawn, the female will turn upside down and rub her belly against the underside of a leaf, signaling the male to join her. The male will approach her while continuing to tremble, then wrap himself around her body and fertilize the eggs as they are released. Six to 12 eggs are laid at a time. The fertilized eggs rise and adhere to the underside of the leaves. During one to two hours, as many as 300 eggs may be laid, although, 80 to 100 is more typical.

When spawning is complete, remove the breeding stock from the aquarium, as they will consume the fry once they hatch. In water temperatures of about 80 degrees Fahrenheit, the eggs will hatch in approximately 24 hours. The fry is translucent and remains attached to the leaf upon which the eggs were laid for another 12 to 24 hours, during which time the yolk sac is absorbed.

Once this process is completed, the fry become free-swimming, and at this stage, require very finely sized foods such as live infusoria for a period of seven to 14 days, after which the fry can feed upon newly hatched brine shrimp. If infusoria are unavailable, commercially prepared foods for an egglayer may also be used. Young harlequin rasboras then reach sexual maturity in approximately six to nine months.