Rasboras, danios & minnows · Trigonostigma heteromorpha

Harlequin rasbora care guide

Also called: Harlequin, Het rasbora, Harlequin fish, Blue harlequin rasbora, Black harlequin rasbora

The harlequin rasbora is a calm, copper-pink schooling fish with a black triangle near the tail. It's hardy, easy to feed and a great fit for planted community tanks, as long as you keep a group of 8 or more.

Harlequin rasboras need a tank of at least 15 gallons (57 L), a group of 8 or more, and water at 22–27°C (72–81°F) with a pH of 6–7.5. They grow to about 4.5 cm (1.8 in) and are peaceful.

Plan a tank with harlequin rasborasSee all tank mates

Harlequin rasbora quick facts

Scientific nameTrigonostigma heteromorpha
FamilyDanionidae
OriginSouthern Thailand, Peninsular Malaysia, Singapore and Sumatra (most sold today are farm-bred)
Adult size4.5 cm (1.8 in)
Minimum tank15 gallons (57 L), at least 60 cm (24 in) long
Temperature22–27°C (72–81°F)
pH6–7.5
Hardness (GH)2–12 dGH
Group size8 or more (schooling fish)
TemperamentPeaceful
Swims atMiddle
DietOmnivore
Care levelEasy
Lifespan5–8 years
Safe with shrimp?Mostly (eats baby shrimp)
Safe with plants?Yes

Tank setup

Keep a group in at least 15 gallons (57 L), ideally in a tank 24 in (60 cm) long or more. Plant the back and sides densely and leave open water in the middle for schooling. A dark substrate, floating plants and some driftwood bring out their best color. Gentle to moderate filter flow suits them.

How many harlequin rasboras in a tank?

The smallest common tank that suits harlequin rasboras is a 15 gallon. Here is roughly how many fit in each size when they are the only fish, based on adult size and waste output. Leave room if you want tank mates.

TankHarlequin rasboras (alone)
3 gallonToo small
5 gallonToo small
10 gallonToo small
15 gallon8–17
20 gallon8–22
20 gallon long8–22
29 gallon8–33
40 gallon8–45
55 gallon8–62
75 gallon8–85
125 gallon8–142

What you need for harlequin rasboras

Sized for a 15 gallon tank, the smallest common size that suits a group of 8 harlequin rasboras. For a different tank or a mix of fish, use the stocking calculator for a list sized to your plan.

Tank and equipment

Food and extras for harlequin rasboras

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Water parameters

Aim for 22–27°C (72–81°F), pH 6.0–7.5 and soft to moderately hard water (about 2–12 dGH). Farm-bred fish settle well in most treated tap water. Wild fish come from soft, tea-stained forest streams and need softer, more acidic water. Change part of the water weekly to keep nitrate low.

Best tank mates for harlequin rasboras

These popular species share harlequin rasboras' water needs and temperament. See the full list of 100 good matches.

Avoid keeping harlequin rasboras with

  • Oscar: Oscar can eat harlequin rasboras: they're small enough to fit in its mouth once it's grown.
  • Bala shark: Bala shark can eat harlequin rasboras: they're small enough to fit in its mouth once it's grown.
  • Chinese algae eater: Chinese algae eater is aggressive and will bully or injure peaceful harlequin rasboras.
  • Convict cichlid: Convict cichlid is aggressive and will bully or injure peaceful harlequin rasboras.
  • Discus: They need different temperatures: Harlequin rasbora 22–27°C (72–81°F), discus 28–30°C (82–86°F).
  • Electric blue acara: Electric blue acara can eat harlequin rasboras: they're small enough to fit in its mouth once it's grown.

Feeding

In nature they pick tiny insects, worms and small crustaceans out of the water. Feed a good micro pellet or crushed flake every day. Add frozen or live daphnia, brine shrimp or bloodworm a few times a week for the best color. Small meals once or twice a day are plenty.

Behavior

Harlequins are gentle mid-water fish that never bother tank mates. In groups of 8–10 or more they swim together confidently and males show off with brighter color. Kept in small numbers they hide and look pale. Good companions include small tetras, other rasboras, pygmy corydoras, small gouramis, bettas and dwarf shrimp.

Breeding

Unlike most rasboras, they stick their eggs to the underside of broad leaves such as cryptocoryne or anubias. For best results use a separate dim tank with soft, acidic water (pH 5.0–6.0) at the warm end of the range. Remove the adults after spawning, as they eat eggs. Fry hatch in 1–2 days and need infusoria first, then baby brine shrimp.

Tips from experienced keepers

  • Buy at least 8 at once. A bigger school is calmer and shows much better color.
  • A dark substrate and floating plants make their copper body and black patch stand out.
  • Adult dwarf shrimp are safe with harlequins, but expect some baby shrimp to be eaten.
  • Blue, black and gold harlequins are color forms of the same fish and need the same care.
  • Males are slimmer with a sharp-edged black patch. Females are rounder and slightly larger.

Frequently asked questions

How many harlequin rasboras should be kept together?

Keep at least 8, and 10 or more if your tank allows it. Larger groups school better, feel safer and show stronger color.

Can harlequin rasboras live in a 10-gallon tank?

A 10-gallon (38 L) tank is tight for a proper school of these active fish. A tank of 15–20 gallons (57–76 L) that is at least 24 in (60 cm) long is a better minimum.

Are harlequin rasboras good with shrimp and bettas?

Yes. They are too small to harm adult dwarf shrimp, though they will eat newborn shrimplets. Their calm nature and short fins also make them one of the better tank mates for a betta in a planted tank.

Sources

We checked these references when writing this page. Values are for healthy long-term keeping, not survival limits. Last reviewed 2026-10-13. See our editorial policy.