Photo: Tucsouffle (CC BY 2.5) — via Wikimedia Commons
Harlequin Rasbora (Trigonostigma heteromorpha)
A copper-bodied classic with a bold black triangle: the shoaling fish that defines the soft-water community tank.
Will it live with a Harlequin Rasbora?
We compare each fish against your harlequin rasbora on temperament, size, water parameters and swimming zone. Set your tank size and filter the results.
- Adolf's Cory✅ CompatiblePeaceful · 5.5 cm · Medium care · 22–26 °C (72–79 °F)
- Both are peaceful, and their water overlaps around 23–26 °C — no size, zone or temperament conflicts.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Adolf's Cory in a shoal of 6+ or it gets stressed and nippy.
- Axelrod's Cory✅ CompatiblePeaceful · 5 cm · Easy care · 23–28 °C (73–82 °F)
- Both are peaceful, and their water overlaps around 23–28 °C — no size, zone or temperament conflicts.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Axelrod's Cory in a shoal of 6+ or it gets stressed and nippy.
- Bandit Corydoras✅ CompatiblePeaceful · 5 cm · Easy care · 22–27 °C (72–81 °F)
- Compatible on the things that matter: shared water near 23–27 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Bandit Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Bloodfin Tetra✅ CompatiblePeaceful · 5.5 cm · Easy care · 18–28 °C (64–82 °F)
- Compatible on the things that matter: shared water near 23–28 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Bloodfin Tetra in a shoal of 6+ or it gets stressed and nippy.
- Checkered Barb✅ CompatiblePeaceful · 5 cm · Easy care · 20–25 °C (68–77 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Checkered Barb in a shoal of 6+ or it gets stressed and nippy.
- Cherry Barb✅ CompatiblePeaceful · 5 cm · Easy care · 23–27 °C (73–81 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Cherry Barb in a shoal of 6+ or it gets stressed and nippy.
- Chocolate Gourami✅ CompatiblePeaceful · 5 cm · Hard care · 25–30 °C (77–86 °F)
- Both are peaceful, and their water overlaps around 25–28 °C — no size, zone or temperament conflicts.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Chocolate Gourami in a shoal of 6+ or it gets stressed and nippy.
- Cochu's Blue Tetra✅ CompatiblePeaceful · 5 cm · Medium care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 23–28 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Cochu's Blue Tetra in a shoal of 8+ or it gets stressed and nippy.
- Firehead Tetra✅ CompatiblePeaceful · 5 cm · Medium care · 24–28 °C (75–82 °F)
- Compatible on the things that matter: shared water near 24–28 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Firehead Tetra in a shoal of 8+ or it gets stressed and nippy.
- Five-banded Barb✅ CompatiblePeaceful · 5 cm · Easy care · 23–27 °C (73–81 °F)
- Compatible on the things that matter: shared water near 23–27 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Five-banded Barb in a shoal of 6+ or it gets stressed and nippy.
- Forktail Blue-eye✅ CompatiblePeaceful · 5 cm · Easy care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 23–28 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Forktail Blue-eye in a shoal of 6+ or it gets stressed and nippy.
- Half-striped Penguin Tetra✅ CompatiblePeaceful · 5 cm · Medium care · 23–28 °C (73–82 °F)
- Both are peaceful, and their water overlaps around 23–28 °C — no size, zone or temperament conflicts.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Half-striped Penguin Tetra in a shoal of 6+ or it gets stressed and nippy.
- Honey Gourami✅ CompatiblePeaceful · 5 cm · Easy care · 22–28 °C (72–82 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Horseman Cory✅ CompatiblePeaceful · 5 cm · Medium care · 22–26 °C (72–79 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Horseman Cory in a shoal of 6+ or it gets stressed and nippy.
- Japanese Trapdoor Snail✅ CompatiblePeaceful · 5 cm · Easy care · 10–28 °C (50–82 °F)
- Compatible on the things that matter: shared water near 23–28 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Julii Corydoras✅ CompatiblePeaceful · 5 cm · Easy care · 23–26 °C (73–79 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Julii Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Masked Corydoras✅ CompatiblePeaceful · 5 cm · Easy care · 22–28 °C (72–82 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Masked Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Mystery Snail✅ CompatiblePeaceful · 5 cm · Easy care · 20–28 °C (68–82 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Panda Corydoras✅ CompatiblePeaceful · 5 cm · Medium care · 20–26 °C (68–79 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Panda Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Rummy-nose Tetra✅ CompatiblePeaceful · 5 cm · Medium care · 23–29 °C (73–84 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Rummy-nose Tetra in a shoal of 6+ or it gets stressed and nippy.
- Skunk Corydoras✅ CompatiblePeaceful · 5 cm · Easy care · 22–26 °C (72–79 °F)
- Both are peaceful, and their water overlaps around 23–26 °C — no size, zone or temperament conflicts.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Skunk Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Stoliczka's Barb✅ CompatiblePeaceful · 5 cm · Easy care · 20–26 °C (68–79 °F)
- Both are peaceful, and their water overlaps around 23–26 °C — no size, zone or temperament conflicts.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Stoliczka's Barb in a shoal of 6+ or it gets stressed and nippy.
- Xingu Black Neon Tetra✅ CompatiblePeaceful · 5 cm · Medium care · 24–28 °C (75–82 °F)
- Compatible on the things that matter: shared water near 24–28 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Xingu Black Neon Tetra in a shoal of 8+ or it gets stressed and nippy.
- Zebra Danio✅ CompatiblePeaceful · 5 cm · Easy care · 18–25 °C (64–77 °F)
- Both are peaceful, and their water overlaps around 23–25 °C — no size, zone or temperament conflicts.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Zebra Danio in a shoal of 6+ or it gets stressed and nippy.
- Amano Shrimp⚠️ With cautionPeaceful · 5 cm · Easy care · 18–28 °C (64–82 °F)
- Adult Amano Shrimp might survive with Harlequin Rasbora, but expect the young to be eaten — plant heavily.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Black Ruby Barb⚠️ With cautionSemi-aggressive · 6 cm · Easy care · 22–26 °C (72–79 °F)
- Black Ruby Barb is semi-aggressive and may chase or nip the smaller Harlequin Rasbora — plant heavily and break up sight lines.
- Your 75 L tank is below the ~100 L this pairing really wants — crowding raises aggression.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Black Ruby Barb in a shoal of 6+ or it gets stressed and nippy.
- Black Skirt Tetra⚠️ With cautionSemi-aggressive · 6 cm · Easy care · 20–26 °C (68–79 °F)
- Expect Black Skirt Tetra to harass Harlequin Rasbora at times; give dense cover and watch them at feeding.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Black Skirt Tetra in a shoal of 6+ or it gets stressed and nippy.
- Blue Turbo Snail⚠️ With cautionPeaceful · 5 cm · Medium care · 25–30 °C (77–86 °F)
- pH preferences only just meet (Harlequin Rasbora 5.5–7 vs Blue Turbo Snail 7.5–8.5) — target the overlap and acclimate slowly.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Desert Goby⚠️ With cautionSemi-aggressive · 6 cm · Easy care · 18–28 °C (64–82 °F)
- Desert Goby and Harlequin Rasbora are close in size, but the semi-aggressive one tends to dominate — add harlequin rasbora in a group to spread the pressure.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Dwarf Chain Loach⚠️ With cautionPeaceful · 6 cm · Medium care · 24–29 °C (75–84 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Dwarf Chain Loach in a shoal of 6+ or it gets stressed and nippy.
- Eastern Betta⚠️ With cautionSemi-aggressive · 6 cm · Medium care · 24–28 °C (75–82 °F)
- Eastern Betta and Harlequin Rasbora are close in size, but the semi-aggressive one tends to dominate — add harlequin rasbora in a group to spread the pressure.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- GloFish Tetra⚠️ With cautionSemi-aggressive · 6 cm · Easy care · 21–28 °C (70–82 °F)
- Expect GloFish Tetra to harass Harlequin Rasbora at times; give dense cover and watch them at feeding.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep GloFish Tetra in a shoal of 6+ or it gets stressed and nippy.
- Humpbacked Tetra⚠️ With cautionSemi-aggressive · 5 cm · Hard care · 24–28 °C (75–82 °F)
- Humpbacked Tetra is semi-aggressive and may chase or nip the smaller Harlequin Rasbora — plant heavily and break up sight lines.
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Humpbacked Tetra in a shoal of 8+ or it gets stressed and nippy.
- Morse Code Corydoras⚠️ With cautionPeaceful · 5 cm · Medium care · 23–26 °C (73–79 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Morse Code Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Odessa Barb⚠️ With cautionSemi-aggressive · 6 cm · Easy care · 20–26 °C (68–79 °F)
- Odessa Barb is semi-aggressive and may chase or nip the smaller Harlequin Rasbora — plant heavily and break up sight lines.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Odessa Barb in a shoal of 6+ or it gets stressed and nippy.
- Panda Loach⚠️ With cautionPeaceful · 6 cm · Hard care · 18–23 °C (64–73 °F)
- Different pH ranges (5.5–7 vs 7.2–8.2); doable if you sit in the shared band, but not ideal long-term.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Silvertip Tetra⚠️ With cautionSemi-aggressive · 5 cm · Easy care · 22–28 °C (72–82 °F)
- Expect Silvertip Tetra to harass Harlequin Rasbora at times; give dense cover and watch them at feeding.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Keep Silvertip Tetra in a shoal of 6+ or it gets stressed and nippy.
- Spotfin Betta⚠️ With cautionSemi-aggressive · 5 cm · Medium care · 23–28 °C (73–82 °F)
- Spotfin Betta is semi-aggressive and may chase or nip the smaller Harlequin Rasbora — plant heavily and break up sight lines.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Striped Red-Eye Puffer⚠️ With cautionAggressive · 5 cm · Hard care · 24–28 °C (75–82 °F)
- Striped Red-Eye Puffer and Harlequin Rasbora are close in size, but the aggressive one tends to dominate — add harlequin rasbora in a group to spread the pressure.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Wine Red Betta⚠️ With cautionAggressive · 5 cm · Medium care · 24–28 °C (75–82 °F)
- Wine Red Betta and Harlequin Rasbora are close in size, but the aggressive one tends to dominate — add harlequin rasbora in a group to spread the pressure.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Alligator Gar⛔ Not recommendedAggressive · 250 cm · Hard care · 24–28 °C (75–82 °F)
- Harlequin Rasbora is bite-sized to a 250 cm predatory alligator gar — it will be eaten.
- Alligator Gar is aggressive and may chase or nip the smaller Harlequin Rasbora — plant heavily and break up sight lines.
- Your 75 L tank is below the ~3785 L this pairing really wants — crowding raises aggression.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Clown Knifefish⛔ Not recommendedAggressive · 90 cm · Hard care · 24–28 °C (75–82 °F)
- Clown Knifefish (90 cm) is big enough to swallow the 5 cm Harlequin Rasbora whole.
- Expect Clown Knifefish to harass Harlequin Rasbora at times; give dense cover and watch them at feeding.
- Your 75 L tank is below the ~750 L this pairing really wants — crowding raises aggression.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Fire Eel⛔ Not recommendedSemi-aggressive · 100 cm · Medium care · 24–28 °C (75–82 °F)
- Harlequin Rasbora is bite-sized to a 100 cm predatory fire eel — it will be eaten.
- Fire Eel clearly outsizes Harlequin Rasbora and is semi-aggressive; risky unless the tank is big and well-planted.
- Your 75 L tank is below the ~380 L this pairing really wants — crowding raises aggression.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Koi⛔ Not recommendedPeaceful · 90 cm · Medium care · 4–28 °C (39–82 °F)
- Size gap is too large (90 vs 5 cm): Koi will treat Harlequin Rasbora as food.
- Your 75 L tank is below the ~3800 L this pairing really wants — crowding raises aggression.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Redtail Catfish⛔ Not recommendedAggressive · 120 cm · Hard care · 24–27 °C (75–81 °F)
- Harlequin Rasbora is bite-sized to a 120 cm predatory redtail catfish — it will be eaten.
- Redtail Catfish is aggressive and may chase or nip the smaller Harlequin Rasbora — plant heavily and break up sight lines.
- Your 75 L tank is below the ~5700 L this pairing really wants — crowding raises aggression.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Spotted Gar⛔ Not recommendedAggressive · 90 cm · Hard care · 18–26 °C (64–79 °F)
- Spotted Gar (90 cm) is big enough to swallow the 5 cm Harlequin Rasbora whole.
- Expect Spotted Gar to harass Harlequin Rasbora at times; give dense cover and watch them at feeding.
- Your 75 L tank is below the ~600 L this pairing really wants — crowding raises aggression.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Wels Catfish⛔ Not recommendedAggressive · 300 cm · Hard care · 15–25 °C (59–77 °F)
- Size gap is too large (300 vs 5 cm): Wels Catfish will treat Harlequin Rasbora as food.
- Wels Catfish clearly outsizes Harlequin Rasbora and is aggressive; risky unless the tank is big and well-planted.
- Your 75 L tank is below the ~20000 L this pairing really wants — crowding raises aggression.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Wolf Cichlid⛔ Not recommendedAggressive · 72 cm · Hard care · 24–30 °C (75–86 °F)
- Harlequin Rasbora is bite-sized to a 72 cm predatory wolf cichlid — it will be eaten.
- Wolf Cichlid is aggressive and may chase or nip the smaller Harlequin Rasbora — plant heavily and break up sight lines.
- Your 75 L tank is below the ~760 L this pairing really wants — crowding raises aggression.
- Keep Harlequin Rasbora in a shoal of 6+ or it gets stressed and nippy.
Compatibility is computed from each species' care data — a strong starting point, not a guarantee. Individual temperament varies, so always introduce new fish slowly and watch them.
Harlequin Rasbora care specs
- Care level
- Easy
- Breeding
- Hard
- Max size
- 5 cm (2 in)
- Min tank size
- 60 L (15.9 gal)
- Temperature
- 23–28 °C (73–82 °F)
- pH
- 5.5–7
- Hardness
- 1–10 dGH
- Lifespan
- 4–6 years
- Diet
- Omnivore
- Swim level
- Middle
- Group size
- 6+ (shoaling)
- Family
- Cyprinidae
- Origin
- Southeast Asia — Malay Peninsula, Sumatra, southern Thailand
What is a Harlequin Rasbora?
The harlequin rasbora (Trigonostigma heteromorpha) is one of the most enduring and recognisable freshwater aquarium fish in the hobby. Its warm copper-orange body, marked by a bold black triangular patch that sweeps from mid-body down toward the tail, is instantly distinctive. Few fish of this size — reaching just 5 cm (2 in) — deliver that much visual impact in a planted community tank.
Belonging to the family Cyprinidae, the harlequin has been a staple since the early twentieth century, long predating the explosion of exotic aquarium species. Its popularity is not nostalgia: it is genuinely easy to keep, completely peaceful, and delivers the kind of coordinated shoaling behaviour that makes a well-planted tank come alive. If you are setting up a soft-water community tank for the first time, this species belongs near the top of your shortlist.
Where do Harlequin Rasboras come from?
Harlequin rasboras are native to Southeast Asia — the Malay Peninsula, Sumatra, and southern Thailand. In the wild they inhabit the slow-moving, heavily shaded streams and peat swamps of lowland rainforest. This water is characteristically dark (stained brown by tannins from decomposing leaf litter), very soft, and quite acidic — conditions that sit at the extreme soft end of most community tank ranges.
Understanding that origin matters for water chemistry and tank decor. These fish evolved under a canopy that filtered most direct light, over a substrate of dark mud, root tangles, and fallen leaves. Replicating even a fraction of that environment — dark substrate, driftwood, Indian almond leaves, subdued lighting — not only keeps them healthier but dramatically improves the intensity of their copper colouration.
What size tank does a Harlequin Rasbora need?
The minimum practical tank size is 60 litres (about 16 gallons). That volume gives a shoal of six to eight fish adequate swimming space, allows you to maintain stable water parameters, and accommodates the planting that makes these fish comfortable.
Harlequin rasboras are active, open-water swimmers that occupy the middle layer of the tank. A tank that is longer than it is tall works better than a tall, narrow footprint — these fish shoal in horizontal runs rather than vertical dives. Aim for at least 60–75 cm (24–30 in) of tank length. Dense planting along the sides and back with an open central swimming lane is the ideal layout. A gentle filter current is fine; strong turbulence is not consistent with their blackwater origins. A secure lid is advisable — rasboras can jump when startled.
What water parameters do Harlequin Rasboras need?
- Temperature: 23–28 °C (73–82 °F). They tolerate the lower end of this range well, making them compatible with a wide range of tropical species.
- pH: 5.5–7.0. Captive-bred stock often tolerates up to 7.5, but acidic, soft water is the standard — and essential for breeding.
- Hardness: 1–10 dGH. Very soft water is ideal; hardness above 10 dGH begins to stress wild-type or closely bred specimens and makes spawning effectively impossible.
Stability is as important as hitting precise numbers. Weekly partial water changes of around 25–30% keep nitrates in check without creating sudden chemistry swings. If your tap water is hard and alkaline, an RO unit blended with tap, or the use of peat filtration and Indian almond leaves, can soften and acidify it naturally.
What do Harlequin Rasboras eat?
Harlequin rasboras are omnivores with a strong preference for small, protein-rich foods — which reflects their wild diet of tiny aquatic invertebrates and insects at or near the water surface. In the aquarium they are undemanding feeders that accept most standard fare.
A practical feeding rotation:
- Staple: quality micro-pellets or fine tropical flake, fed in small amounts once or twice daily.
- Enrichment: frozen or live daphnia, baby brine shrimp, micro-worms, or finely chopped bloodworm two to three times a week.
- Portion size: what the fish consume in two to three minutes. Rasboras are not particularly greedy, but uneaten food in a soft-water tank degrades water quality quickly.
Their small mouths mean food particle size matters — standard adult tropical pellets may be too large for juveniles. Crushed flake or specialist micro-pellets designed for nano and small fish are appropriate.
Are Harlequin Rasboras aggressive — and what fish can live with them?
Harlequin rasboras are entirely peaceful and represent a textbook community-tank species. They show no territorial behaviour, no fin-nipping, and no aggression toward tank-mates of any size. The only behavioural note worth making is that they are shoaling fish: a group that is too small (fewer than six) will look nervous and spend time hiding rather than swimming openly.
A proper shoal of eight to ten fish moves through the middle water in loose, coordinated formation — one of the most satisfying sights in the planted aquarium. Good tank-mates share the same soft, acidic water requirements and similarly peaceful temperament: small tetras (ember, neon, cardinal), dwarf gouramis, corydoras catfish, kuhli loaches, smaller apistogramma cichlids kept in peaceful pairs, and otocinclus all work well. Avoid large or predatory fish that could view the rasboras as a meal, and avoid fish with very different water chemistry needs.
For a full curated list of compatible and incompatible species, see Harlequin Rasbora tank mates.
How do you tell male and female Harlequin Rasboras apart?
Sexing harlequin rasboras is possible but requires a close look. Males are slightly smaller overall, display more intense copper-orange colouration, and have a distinctive feature in the black triangle: its lower rear edge curves inward (concave), giving the patch a rounded belly. Females are marginally larger and noticeably rounder-bellied, especially when carrying eggs, and the lower edge of their black triangle is comparatively straight or only slightly curved.
The difference is subtle in young fish and most obvious in mature, well-conditioned specimens viewed side by side. Colour intensity alone is not a reliable indicator in stressed or newly acquired fish — let them settle in for a few weeks before attempting to sex them.
How do Harlequin Rasboras breed?
Breeding harlequin rasboras is rated hard by aquarium standards — not because the fish themselves are delicate, but because triggering spawning requires closely replicating their native blackwater conditions, which many home aquariums cannot easily provide.
The species is an egg-scatterer with a twist: unlike many cyprinids that broadcast eggs randomly, harlequins deposit eggs on the undersides of broad leaves — Cryptocoryne species are the classic choice. The male courts the female beneath a leaf, and the pair roll upside-down together to deposit and fertilise a small batch of adhesive eggs on the leaf’s underside. This is repeated multiple times over a spawning session.
To trigger spawning, condition the pair separately on live and frozen foods, then move them to a dedicated breeding tank with very soft, acidic water (pH 5.5–6.5, hardness below 5 dGH, temperature around 26–28 °C / 79–82 °F), subdued lighting, and suitable broad-leafed plants. The eggs hatch in 24–36 hours under these conditions; the fry are tiny and need infusoria or commercial fry foods before graduating to baby brine shrimp. Remove the adults after spawning to prevent predation of eggs and fry.
What are common Harlequin Rasbora diseases?
Harlequin rasboras are robust fish when kept in appropriate water, and most disease problems trace back to poor water quality or inappropriate chemistry. The diseases most commonly encountered are:
- Ich (white spot): Fine white dots resembling salt grains on fins and body, caused by the parasite Ichthyophthirius multifiliis. Usually triggered by chilling or stress from sudden temperature drops.
- Fin rot: Ragged or receding fin edges, typically bacterial in origin and almost always secondary to poor water quality or injury from fin-nippers.
- Velvet (Oodinium): A dusty gold or rust-coloured sheen on the body — more common in soft-water fish kept in fluctuating conditions. Look for it under a torch in a darkened room.
- Neon tetra disease / microsporidiosis: A muscular wasting disease causing faded colouration and abnormal swimming. Rare but incurable; affected fish should be removed promptly.
Prevention covers the vast majority of health risks: a fully cycled tank, stable temperature, soft and acidic water within the correct range, regular water changes, and quarantining new fish for two to four weeks before introduction to the display tank.
Health note: disease diagnosis and medication dosing are beyond the scope of a care profile. Before medicating, confirm symptoms against a reputable veterinary or fish-health resource — many conditions look similar, and treating for the wrong disease can harm the fish further.
How long do Harlequin Rasboras live?
With good care, harlequin rasboras live 4–6 years. That lifespan puts them firmly in the mid-range for small community fish and means a well-maintained group will be a feature of your tank for a meaningful stretch of time.
The keys to reaching the upper end of that range are consistent water quality, an appropriately soft and acidic environment, a varied diet, and keeping the group large enough that the fish remain relaxed rather than stressed. Fish kept in hard, alkaline tap water, or in groups below six, tend to be shorter-lived. Give them the conditions their biology is adapted to and you can reasonably expect five or more years from a healthy shoal.
Frequently asked questions
What water conditions do harlequin rasboras need?
They come from soft, peaty blackwater streams, so aim for pH 5.5–7.0 and very soft water (1–10 dGH). Captive-bred fish are more forgiving — many do fine up to pH 7.5 in modest hardness — but spawning reliably requires replicating the soft, acidic conditions of their native habitat. Temperature 23–28°C suits them well.
How many harlequin rasboras should I keep together?
Keep a minimum of six, and eight to ten is better. A small group looks washed-out and stressed; a proper shoal of ten fills the middle of the tank with coordinated copper-and-black flashes. They are completely peaceful and mix well with small tetras, dwarf gouramis, corydoras and other soft-water community fish.
What you need to keep a harlequin rasbora
The baseline is a heated, filtered 60 L+ tank: a reliable heater to hold 23–28 °C (73–82 °F), a gentle filter that won't batter a harlequin rasbora in the current, and a tight-fitting lid. Cycle the tank fully before adding any fish.
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