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Harlequin Rasbora (Trigonostigma heteromorpha)

Harlequin Rasbora (Trigonostigma heteromorpha)

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Description
Freshwater Fish

Harlequin Rasbora

One of the most enduringly popular schooling fish in the hobby. A copper-red metallic body carrying a bold black triangular wedge, kept in aquariums worldwide for over a century.

Copper-Red Body with Black Triangle Trigonostigma heteromorpha Peaceful Schooling Fish pH 5.0–7.5 5 to 8 Year Lifespan Shrimp Compatible with Caution

Harlequin Rasboras (Trigonostigma heteromorpha) have been a cornerstone of the aquarium hobby since they were introduced in the early 1900s, and they have held that position for good reason. The body is a warm copper-red with a metallic sheen, carrying a bold black triangular wedge that begins at the dorsal fin and tapers to the base of the tail. The genus name derives from the Greek word for "differently shaped," referencing this distinctive body marking, and the common name comes from the resemblance of the black patch to the patterning on a harlequin's costume. Native to the blackwater streams and ponds of Thailand, Malaysia, Sumatra, and Singapore, they are hardy, adaptable, and long-lived at 5 to 8 years. In the wild they school in groups of over a hundred; in the aquarium a school of 8 to 10 is the practical minimum for natural behaviour. Note that the invoice designation Rasbora heteromorpha is an older name; the current accepted classification is Trigonostigma heteromorpha.

5.0–7.5pH
2–12GH (dGH)
72–80°FTemperature
2 inMax Size

The Black Triangle

Copper-red metallic body with a bold black triangular wedge from dorsal fin to tail base. The black marking is the species' signature and is larger and more sharply triangular than the similar markings on the related Lambchop Rasbora (Trigonostigma espei) and Hengel's Rasbora (T. hengeli). The copper-red base has a genuine metallic quality that catches light as the school moves. The fins carry subtle red lining that adds warmth to the overall colouration. Colour is most vivid in soft, acidic, tannin-stained water with dim lighting. Harlequin Rasboras come from blackwater environments and show their best colour in conditions that replicate them. Soft acidic water with Almond Leaves or driftwood tannins, dark substrate, and subdued or plant-diffused lighting produces noticeably richer copper-red colouration than bright, hard, alkaline conditions. School of 8 to 10 minimum, larger groups strongly preferred. In the wild this species moves in groups exceeding a hundred individuals. In the aquarium, groups below 8 result in nervous, scattered behaviour and faded colour. A school of 12 or more produces confident, cohesive schooling in the upper and middle water column and is where the species genuinely shines. Long-lived at 5 to 8 years with good care. Harlequin Rasboras are notably long-lived for a small schooling fish, with most individuals reaching about 6 years and well-cared-for specimens hitting the upper end of that range. This makes a school a genuine multi-year investment rather than a short-term addition. Requires a fully cycled, stable tank. Sensitive to water chemistry changes. While hardy once established, Harlequin Rasboras should only be added to tanks that have completed the nitrogen cycle. They are sensitive to ammonia, nitrite, and sudden parameter swings, and require adequate dissolved oxygen and consistent water quality.

Larger Than the Nano Species

Adult Neocaridina shrimp are generally safe. Shrimplets are at meaningful risk. At 2 inches, Harlequin Rasboras are noticeably larger than the nano species like Chili Rasboras and Blue-Eyes, with a correspondingly larger mouth. Adult shrimp at full size are safe, but shrimplets and small juveniles will be consumed opportunistically. Dense planting with Java Moss and Subwassertang is necessary to maintain a breeding shrimp colony alongside a Harlequin school, and colony growth will be slower than in a fish-free tank. Parameter overlap works well with soft-water Neocaridina and Caridina setups. At pH 5.0 to 7.5 and soft to moderately soft water, Harlequin Rasboras suit both soft Neocaridina tanks and Caridina blackwater setups. The blackwater aesthetic that brings out their best colour is the same aesthetic that suits Caridina shrimp. Upper and mid-water schooling reduces substrate-level interaction with shrimp. Harlequins occupy the top and middle of the water column, leaving the substrate and hardscape to the shrimp. The vertical separation reduces but does not eliminate predation pressure on shrimplets.
Keeper's Note

A school of 12 Harlequin Rasboras in a blackwater planted tank with Almond Leaves, dark substrate, and dim plant-diffused lighting is one of the most classically beautiful freshwater displays in the hobby, and it has been for a hundred years. The copper-red bodies with their black wedges moving in formation through tannin-stained water is the kind of tank that made people fall in love with the hobby in the first place. If you are keeping shrimp alongside them, plant heavily and expect a slower-growing colony in exchange for the display.

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Policies & Disclaimers
Before you order · Fish

Policies & Disclaimers

What to expect from your fish, overnight shipping requirements, and what to do when your order arrives.

Overnight shipping required for guarantee coverage

Choose overnight (next day air) shipping for fish. Our Live Arrival Guarantee does not cover fish shipped by 2-day, standard expedited or ground service. Overnight shipping is a condition of coverage; the claim deadline and documentation requirements below also apply.

Size & representative photos

Fish size and appearance vary by species, age and individual. Refer to the listing and selected option for any stated purchase size. Adult or maximum sizes in care information describe growth potential, not a guaranteed size on arrival. Photos represent the species or variety rather than the exact fish you will receive.

Color & settling in

Color and markings can vary between individuals and with age, sex, lighting and aquarium conditions. Fish may look paler after shipping. Follow the species-specific acclimation and care guidance and provide stable water conditions. If a fish arrives dead or visibly distressed, document its condition and contact us promptly rather than waiting beyond the claim window.

Species needs & compatibility

Check the specific listing for adult size, temperature, water requirements, diet and recommended group size. A small shipping size does not mean a fish will stay small. Choose suitable tankmates and allow for adult growth; a community-fish label is not a guarantee of compatibility with every fish or invertebrate.

Pack contents & selection

The selected quantity identifies the number of fish ordered. A group does not by itself promise a breeding pair or particular sex ratio. Any explicit sex or selection offered in the listing applies to that selected option.

Juvenile appearance, growth & sex differences

Young fish may have less intense coloration, different proportions or less-developed fins than mature examples in photographs. Species, age, sex and social conditions can affect their appearance. Adult-size figures describe growth potential, not the size guaranteed in the shipping bag.

Plan housing around adult needs. A small pleco, for example, still needs the space and diet appropriate to its identified species as it grows. Use the listing’s stated species and selected option rather than a photograph alone to judge what you are buying.

Unless a listing explicitly offers a sex-selected option, a quantity pack is not a specified sex ratio or breeding pair. Where an explicit selection is offered, that selected option applies.

Shipping appearance versus concerning distress

Paler colors, hiding and a reduced initial appetite can occur after transport. These observations alone do not establish a covered loss. They also should not be used to dismiss a fish that appears to be struggling.

Photograph or record visible concerns such as loss of balance, persistent labored breathing, an obvious wound or a fish that appears dead while it is still in the original packaging. Include the label and packaging and contact us promptly within the two-hour reporting window. Report observations rather than guessing a diagnosis.

Do not wait for color or activity to improve before reporting an arrival concern. Coverage and resolution follow the full guarantee; this guidance does not add a new health guarantee or extend the claim window.

Schools, tankmates & adult housing

Schooling fish should be housed with an appropriate group of their own species. The quantity options offered for purchase are not a statement that each option is a suitable permanent school size. Check the listing’s group-size guidance and the aquarium’s capacity.

Peaceful fish can still eat animals small enough to fit in their mouths, including shrimplets. Consider adult size, feeding behavior, water requirements and available shelter when choosing tankmates. No general community label guarantees compatibility in every aquarium.

Bottom-dwelling fish need food that reaches them; they should not be expected to live only on leftovers. Provide the species-appropriate diet and observe whether quieter fish are being outcompeted.

Acclimation & quarantine

Have a stable, cycled aquarium or suitable quarantine setup ready before the shipment arrives. Follow the acclimation instructions appropriate to shipped fish and the species; do not assume a single timed method is suitable for every shipment or bag condition.

Document arrival concerns before transfer under the guarantee’s instructions. Avoid adding shipping water to the established aquarium, and minimize unnecessary handling and disturbance during introduction.

Separate observation of new fish can help protect an established collection and make feeding and behavior easier to monitor. Quarantine is care advice here, not a newly added condition of claim eligibility. Do not medicate automatically without considering the species and the actual concern.

Bonus animals & your paid count

When inventory allows, our policy provides one bonus animal for every five ordered of the same species. Bonuses are discretionary and are not separately covered for refund or replacement. They count toward the total arriving alive when assessing whether your paid quantity was fulfilled.

For example, if you order 10 fish and receive 12, receiving 11 alive fulfills the paid count. If fewer than 10 arrive alive, the shortfall is assessed under the guarantee. Expected bonuses that were not included are not a paid-item shortage.

Checking quantities & reporting a short count

Check the actual animals received against your paid order quantity. For a suspected short count, the full policy calls for a clear counting photo showing all animals, the empty bag and the shipping label before they are introduced into an aquarium. Follow its counting instructions and contact us if you cannot document the count clearly.

Verified miscount claims are resolved with a refund for the missing paid animals under the current policy. A count made after release can be unreliable when animals hide among plants or hardscape.

Before opening: photographs & your first report

Use the email address on the original order and include all arrival concerns in the initial message to support@superiorshrimpaquatics.com within two hours of the carrier’s recorded delivery time. Photograph the sealed bag, visible and countable animals, shipping label, box and packing materials.

If the bag is leaking or damaged, photograph the leak or damage and wet packing before opening. Keep the original photographs and packaging. For cloudy water that prevents counting, take the original cloudy-water photo first and follow the full policy’s specific additional clear-container documentation instructions.

The guarantee contains restrictions on opening bags, acclimation and transfers. Review those instructions before taking action so the evidence needed to assess the claim is preserved.

Arrival problem? Document it promptly.

Email support@superiorshrimpaquatics.com within two hours of the carrier’s recorded delivery time, using the email address on your order.

  • Photograph the original sealed bag with the animals visible and countable.
  • Include the shipping label, outer box and packing materials.
  • Document any bag damage or leakage before opening.
  • Report all arrival losses in your initial message.

Read the full guarantee for photo requirements, cloudy-water documentation and claim eligibility before opening or transferring animals. Approved claims are resolved under the options and conditions stated there.

Shipping & coverage limits

Fish must ship by overnight (next day air) service to qualify for the Live Arrival Guarantee. Fish shipped by 2-day, standard expedited or ground service are not covered. Selecting a non-overnight method waives guarantee coverage for the fish in that order.

The guarantee applies to the first delivery attempt. Redirection, pickup holds and carrier delays can affect eligibility under the full policy. Any product-specific coverage restrictions stated in a listing also apply.

Hitchhikers & quarantine

Live aquatic products can carry tiny hitchhikers or eggs despite inspection. Pest-free arrival is not guaranteed. We recommend quarantining new arrivals before introducing them into an established aquarium.

Returns

Care guidance in this tab does not create additional guarantee requirements or exclusions. Please read the full policies for complete eligibility, documentation, resolution and return requirements.

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