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.
At a Glance
Tank Requirements
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Water Parameters
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Temperament & Compatibility
Available 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
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🟢Ideal Tank MatesHarlequin 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. An aquarium test kit can help you monitor these values.
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.
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
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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.
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