Harlequin Rasbora
Trigonostigma heteromorpha
A highly popular, peaceful schooling fish recognizable by its metallic copper/orange body and the distinct black triangular 'porkchop' patch on its hindquarters. Originating from peat swamps and blackwater streams in Southeast Asia, they are active swimmers that thrive in heavily planted aquariums with gentle to moderate water flow.
Harlequin Rasbora At a Glance
Harlequin Rasbora Tank Requirements
Will Harlequin Rasbora fit in your tank?
Care guides tell you what Harlequin Rasbora needs, the next question is whether your tank can safely provide it. Test Harlequin Rasbora against your tank size, maintenance needs, and the fish you already keep before you buy.
Harlequin Rasbora Water Parameters
Harlequin Rasbora Temperament & Compatibility
Harlequin Rasbora Varieties
Each variety inherits the species defaults above. Only differences are highlighted.
Standard
The classic wild-type coloration featuring a bright orange-copper body and a sharp, dark black wedge starting from the mid-section and extending to the caudal fin.
Same care requirements as the base species
Also known as: Wild Type, Classic Harlequin
Black / Purple Morph
A selectively bred color morph featuring a dark blue, deep purple, or black wash over the entire body, obscuring the traditional triangular patch.
Same care requirements as the base species
Also known as: Black Harlequin, Purple Harlequin, Blue Harlequin
Gold / Albino
A leucistic or albino variation displaying a pale golden body with a translucent, silvery, or white triangular patch.
Same care requirements as the base species
Also known as: Gold Harlequin, Albino Harlequin
Harlequin Rasbora Care Guide Summary
The Harlequin Rasbora, scientifically known as Trigonostigma heteromorpha, belongs to the Cyprinids family group. Adults reach a maximum size of approximately 4.5 cm and have a fusiform body shape with a moderate growth rate. Classified as peaceful, this species primarily occupies the mid-level and surface zones of the aquarium and produces a low level of biological waste.
To thrive, the Harlequin Rasbora requires a freshwater only aquarium with a minimum volume of 60 litres and a tank length of at least 60 cm. Water temperature should be maintained between 22°C and 28°C, with a pH range of 5–7.5 and a general hardness of 2–12 dGH. A moderate water flow is preferred.
The Harlequin Rasbora is a rewarding species to keep, provided its core environmental needs are met. This species is available in 3 varieties: Standard, Black / Purple Morph, and Gold / Albino. Each may differ slightly in size, temperament, or care needs, so it is worth checking the specific requirements of the variety you plan to keep.
Harlequin Rasbora Habitat Setup
When setting up an aquarium for the Harlequin Rasbora, a moderate water flow best suits their natural preferences. Because this species occupies the mid-level and surface zones, the aquarium layout should prioritise adequate surface area with floating cover to make them feel secure near the waterline and open swimming space in the centre of the tank for free movement. Useful additions include leaf litter or blackwater tannins to replicate their natural soft-water habitat and dense planting to provide cover, break sightlines, and reduce stress.
Harlequin Rasbora Compatibility Notes
Classified as peaceful, the Harlequin Rasbora is a schooling species that feels most secure in a sizeable group, where natural shoaling behaviour reduces stress and brings out their best colours. When choosing tankmates, their energetic swimming style may stress more sedentary or timid species. Selecting tankmates that favour different water layers from the mid-level and surface zones can help reduce competition and territorial overlap.
Who Harlequin Rasbora Is Actually For
Harlequin Rasbora is best for a fishkeeper who wants a species that can settle into a calmer community setup and can provide a keeper who can commit to a proper group of at least 6. It makes the most sense for a hobbyist who will actually build around its needs, especially plants.
The most common mistake is buying Harlequin Rasbora for looks first and only later discovering how its adult size, behavior, or bioload changes the whole tank plan. Another frequent problem is underestimating its social needs. A token pair or trio often behaves very differently from a real group.
Harlequin Rasbora Recommended Tank Sizes
Standard aquarium sizes that meet the minimum volume and length requirements for Harlequin Rasbora.
20 Gallon High
20 Gallon Long
29 Gallon Standard
30 Gallon Breeder
36 Gallon Bowfront
40 Gallon Breeder
Show 19 more tank sizes
Frequently Asked Questions About Harlequin Rasbora
How big does Harlequin Rasbora get?
Harlequin Rasbora (Trigonostigma heteromorpha) typically reaches a maximum adult size of approximately 4.5 cm. They have a fusiform body shape and a moderate growth rate.
What tank size does Harlequin Rasbora need?
A minimum aquarium volume of 60 litres and a tank length of at least 60 cm are recommended for Harlequin Rasbora. This ensures enough swimming space and helps maintain stable water conditions.
What water parameters does Harlequin Rasbora need?
Harlequin Rasbora thrives in freshwater only conditions with a temperature range of 22–28°C, a pH between 5 and 7.5, and a general hardness of 2–12 dGH. A moderate water flow is preferred.
Is Harlequin Rasbora peaceful or aggressive?
Harlequin Rasbora is classified as peaceful with an aggression score of 1 out of 10. They are generally well-suited to peaceful community tanks.
How many Harlequin Rasbora should be kept together?
Harlequin Rasbora is a schooling species and should be kept in groups of at least 6. Larger groups help distribute aggression and encourage natural schooling behaviour.
Does Harlequin Rasbora have any special tank requirements?
Yes. Harlequin Rasbora benefits from plants - densely covered and leaf litter/blackwater in the aquarium. These features help replicate their natural habitat and promote overall health and well-being.
Useful setup supplies
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Guidarium Editorial Desk
Reviewed against Guidarium care, stocking, and compatibility standards. Read the editorial policy.
- Last reviewed
- April 28, 2026
- Last updated
- April 28, 2026
- Issues or corrections?
- Contact the editorial team
Top Tank Mates for Harlequin Rasbora
These fish are strong compatibility matches for Harlequin Rasbora based on water preferences, temperament, adult size, and tank behavior.
Spotted Hillstream Loach
Gastromyzon punctulatus
Ideal Tank MatesTrapdoor Snail
Cipangopaludina chinensis
Ideal Tank MatesSkunk Cory
Corydoras arcuatus
Ideal Tank MatesSan Juan Cory
Corydoras bilineatus
Ideal Tank MatesHillstream Loach
Beaufortia leveretti
Ideal Tank MatesSchwartz's Cory
Corydoras schwartzi
Ideal Tank MatesPlants That Suit Harlequin Rasbora
These plants pair well with Harlequin Rasbora based on shared water preferences, layout fit, and how likely they are to hold up in the same aquarium.
Afzel's Anubias
Anubias afzelii
Amazon Sword
Echinodorus amazonicus
Anacharis
Egeria densa
Anubias Barteri
Anubias barteri
Baby Tears
Lindernia rotundifolia
Balansae
Cryptocoryne crispatula
Fish Similar to Harlequin Rasbora
Copper Harlequin Rasbora
Trigonostigma hengeli
A small, peaceful, and highly active schooling fish known for the striking glowing orange or copper stroke above its thin black 'pork-chop' marking. Smaller and much more slender than the standard Harlequin Rasbora, they are perfect for planted nano aquariums. They must be kept in schools of at least 6 to feel secure and display their best colors.
Espei Rasbora (Lambchop Rasbora)
Trigonostigma espei
A small, peaceful schooling fish native to Southeast Asia. Closely related to the Harlequin Rasbora but distinguished by a more copper-orange coloration and a thinner, 'lambchop' shaped black marking on its flank. They thrive in heavily planted, mature aquariums with gentle water flow and slightly acidic water.
Blackline Rasbora
Rasbora borapetensis
The Blackline Rasbora, often sold as the Red-tailed Rasbora, is a hardy and highly active schooling fish native to Southeast Asia. Recognizable by a bold black lateral line topped with gold and a bright red caudal fin, they are peaceful but energetic. They require plenty of horizontal swimming space in the middle to upper levels of the aquarium and must be kept in schools to feel secure.
Redline Rasbora
Rasbora pauciperforata
A slender, elegant schooling fish native to the blackwater peat swamps of Southeast Asia. Distinguished by a brilliant, glowing neon-red stripe running from its mouth to its tail. They are true blackwater fish, requiring soft, acidic water and plenty of tannins from leaf litter or driftwood to thrive and show their best colors. Peaceful but can be skittish if not kept in appropriately large schools with overhead cover.
Brilliant Rasbora
Rasbora einthovenii
The Brilliant Rasbora is a peaceful, highly active schooling fish native to the forest streams and peat swamps of Southeast Asia. Known for its shimmering silver body and distinct dark lateral stripe, they thrive in gently flowing, heavily planted blackwater setups with subdued lighting. They are known jumpers, requiring a tight-fitting lid.
Emerald Eye Rasbora
Brevibora dorsiocellata
A small, active schooling fish native to Southeast Asia, famous for the striking black-and-white spot on its dorsal fin and its reflective 'emerald' eyes. They are highly peaceful and thrive in heavily planted or blackwater aquariums. As a strict schooling species, they must be kept in groups to feel secure, establish a natural hierarchy, and display their best colors.