Harlequin rasboras with shrimp

By the Shrimp Tank Hub editorsUpdated Oct 26, 2026Research-based

The harlequin rasbora (Trigonostigma heteromorpha) is a small schooling cyprinid from southern Thailand, Peninsular Malaysia, Singapore and Sumatra (Seriously Fish). It has been in the hobby for more than a hundred years and is now mass-produced, which Seriously Fish says has left farmed fish with less color than wild ones. For shrimp keepers it is one of the easier fish to recommend: it is peaceful, small and not built to tackle adult shrimp.

Harlequins at a glance

The tank sizes differ even between two The Shrimp Farm pages, so we show all three. A 20-gallon long is the comfortable choice if you want a proper school plus a shrimp colony; a 24-inch, 15-gallon tank is the practical minimum.

Will harlequin rasboras eat shrimp?

• Adults: no. The Shrimp Farm's harlequin care guide says they get along with shrimp and are much too small to take on an adult, even a tiny Neocaridina, and its tankmates guide rates them "does not eat adult shrimp".
• Shrimplets: some. The Shrimp Farm says only newly hatched babies are at risk and that dense planting protects them. Practical Fishkeeping lists rasboras in a group of fish that will almost certainly eat the young, and says plants, hiding places and well-fed fish reduce losses. Seriously Fish describes wild harlequins as micropredators of small insects, worms, crustaceans and zooplankton.
• Which shrimp: The Shrimp Farm says cherries, crystal reds, Amanos and similar shrimp should work well, but is less sure about fancy bee shrimp ("maybe not"). See crystal red shrimp before mixing soft-water Caridina with fish.

In practice a cherry colony can keep growing alongside harlequins if there is plenty of moss, but more slowly than on its own. For the fewest shrimplet losses, otocinclus are the safer fish. Compare chili rasboras, a much smaller rasbora for nano tanks, and see cherry shrimp tank mates.

Matching the water

The shared zone is our comparison of the published ranges, not a tested target. The Shrimp Farm says wild harlequins come from soft, lightly acidic water and probably won't do well in more alkaline conditions, but tank-bred fish are very flexible as long as the tank is cycled and stable. That flexibility is what lets them share a tank with cherry shrimp, which want enough minerals to molt; see shrimp GH and KH explained.

Tank size and setup

• Size: Seriously Fish treats a 24 × 12 in base as the smallest tank because harlequins should be kept in numbers. The Shrimp Farm suggests a 15-gallon long for a small to medium group. See how many shrimp per gallon.
• Dim light and plants: Seriously Fish says they do best under fairly dim lighting with shade-tolerant plants such as java fern, mosses, Cryptocoryne and Anubias, plus some floating plants. The Shrimp Farm says they don't like overly bright light or a bare tank. See shrimp tank lighting. Mosses are also where shrimplets hide; see java moss and best plants for a shrimp tank.
• Leaf litter: both sources suggest dried leaves for a natural look; Seriously Fish says the microbe colonies that grow on them are a secondary food source for fry. For using leaves in a shrimp tank, see driftwood and botanicals for shrimp.
• Filter: use a sponge filter or a sponge over the intake so shrimplets aren't pulled in; see shrimp-safe filters.

Feeding both

• Small foods for the fish: Seriously Fish suggests good-quality dried flakes and granules plus small live and frozen foods such as bloodworm, Daphnia and Artemia. The Shrimp Farm feeds a quality microfood as a staple and mixes in frozen or live foods.
• Feed the shrimp on the bottom: drop sinking shrimp food into the plants after the fish have eaten. See best shrimp food.
• Well-fed fish hunt less. Practical Fishkeeping lists keeping fish well fed as one way to reduce shrimp losses.

Fry and eggs

Unlike most small cyprinids, harlequins stick their eggs to the undersides of broad leaves rather than scattering them, and give no parental care (Seriously Fish). In a mature, densely planted tank a few young may appear with no help, but Seriously Fish says adults eat any eggs they find after spawning, which is why breeders use a separate tank. In a shrimp tank, expect the occasional surprise fish rather than a population boom.

Buying healthy harlequins

The Shrimp Farm says harlequins are bred on a massive scale and, because they are cheap, aren't always given the care they need: avoid fish that look lethargic or emaciated, and expect color to improve after a few weeks in your tank. Long-finned, purple, gold and "blond" forms are sold (The Shrimp Farm). The lambchop rasbora (T. espei) looks similar but is slightly smaller with a thinner black marking; The Shrimp Farm says its care is the same and the two will school together. Seriously Fish also separates harlequins from T. espei and T. hengeli by the shape of the dark triangle.

A centerpiece option

Aquarium Co-Op suggests a honey gourami as a centerpiece with a school of harlequin rasboras in a nano community. Gouramis are a closer call with shrimp; see honey gouramis with shrimp before adding one.

How to add harlequins to a shrimp tank

• Shrimp first. Practical Fishkeeping suggests letting the colony build up before adding fish.
• Mature tank: fully cycled and stable; see how to cycle a shrimp tank.
• Quarantine the fish separately. Practical Fishkeeping says many fish medications are not safe for invertebrates. If fish get sick, ask a fish veterinarian or an experienced store about treatment that won't harm the shrimp. See how to quarantine and is copper toxic to shrimp.

Common mistakes

• Buying three or four harlequins instead of a proper school.
• Using a short 10-gallon tank for an active schooling fish.
• Bright lights over a bare tank.
• Expecting a fast-growing shrimp colony with fish present.
• Medicating fish in the shrimp tank.

Track it

Log temperature, pH, GH and TDS on the free Water Parameter Log printable so you can keep the tank in the range both species share.

Frequently asked questions

Do harlequin rasboras eat shrimp?

Not adult shrimp. The Shrimp Farm says harlequins are much too small to take on an adult shrimp, even a tiny Neocaridina. Newly hatched shrimplets are at risk, so plant the tank densely.

Can harlequin rasboras live with cherry shrimp?

Usually, yes. The Shrimp Farm lists cherries, crystal reds and Amanos as shrimp that should work. Expect the colony to grow more slowly than in a shrimp-only tank.

How many harlequin rasboras should I keep?

At least 8 to 10 according to Seriously Fish. The Shrimp Farm says 6 to 8 is okay but 20 to 30 is better, and small groups become skittish.

What size tank do harlequins and shrimp need?

Seriously Fish treats a 24 by 12 inch base (about 14 gallons) as the smallest. The Shrimp Farm suggests a 15-gallon long for a small to medium group and 20 to 30 gallons for 20 or more.

Are harlequin and lambchop rasboras the same?

No. The lambchop rasbora (T. espei) is a similar, slightly smaller species with a thinner black marking. The Shrimp Farm says care is the same and they school together.

Sources: Seriously Fish, Trigonostigma heteromorpha (harlequin) (Trigonostigma heteromorpha; southern Thailand, Peninsular Malaysia, Singapore, Sumatra; mass-produced, farmed fish lack wild color; 45 mm SL; 60 × 30 cm base, about 54 litres, the smallest considered; 21–28 °C, pH 5.0–7.5, 1–12 dGH; forest streams, soft weakly acidic water, dim; dim lighting, Microsorum, Taxiphyllum, Cryptocoryne, Anubias, floating plants, dark substrate, leaf litter; micropredator of small insects, worms, crustaceans, zooplankton; flakes, granules, live and frozen foods; very peaceful; groups of at least 8–10; eggs on the underside of broad leaves, no parental care; adults eat eggs; told apart from T. espei and T. hengeli by the marking); The Shrimp Farm, Harlequin rasbora care (up to about 1.8 in; 15-gallon long for a small to medium group, 20–30 gallons for 20+; dislikes bright light and bare tanks; tank-bred fish flexible; pH 5.0–7.5, 70–82.5 °F, TDS 20–200; groups of 6–8 okay, 20–30 better, skittish alone; too small for adult shrimp, even tiny Neocaridina, only newly hatched babies at risk, plant densely; bee shrimp maybe not, cherries, crystal reds, Amanos should work; microfood staple plus frozen or live; bred on a massive scale, avoid lethargic or emaciated fish; long-fin, purple, gold, blond morphs; lambchop rasbora T. espei look-alike, same care); The Shrimp Farm, Shrimp tankmates and compatibility (harlequin up to 1.8 in, 20+ gallons, beginner-proof, does not eat adult shrimp); Practical Fishkeeping, What can I keep with shrimp? (rasboras in the 'maybe' group that will almost certainly eat young; plants, hiding places and well-fed fish reduce losses; build the colony first; many medications not invertebrate-safe); Aquarium Co-Op, 5 best fish stocking ideas for small aquariums (honey gourami centerpiece with a school of harlequin rasboras); The Shrimp Farm, Red rili shrimp tank set-up and care (Neocaridina range used for comparison: pH 6.2–8.0, 65–85 °F, GH 4–8).