Lambchop Rasbora Care Guide

The lambchop rasbora is the harlequin's smaller, brighter sibling — a copper-bodied soft-water schooler barely 2.5 to 3 cm long, wearing a thin black blade where the harlequin wears a broad triangle. Kept as a real group in a shaded planted tank it is one of the easiest, most beginner-friendly centrepiece shoals you can buy, provided you buy the right fish on purpose, because shops mislabel it constantly.

Lambchop Rasbora at a glance

The sourced figures the welfare engine uses to judge Lambchop Rasbora — the parseable key facts.

Where it comes from

Trigonostigma espei comes from south-east Asia — south-west and south-east Thailand, the Prek Tuk Sap basin in Cambodia, and a population on Phú Quốc island, Vietnam. Its typical home is gently flowing, plant-choked forest streams, ponds and swamps: slow, shaded, soft and weakly acidic water. That heritage sets most of the care — best colour and least stress come in a planted, dimly-lit tank over dark substrate with floating plants for shade, driftwood and gentle flow, while a bright, bare tank washes the copper out. One detail breaks the usual blackwater story, though: a wild population in the Krabi region lives in karstic limestone sinkholes at pH 7.0 to 7.4, so the species is naturally exposed to a wider chemistry band than its reputation suggests and takes neutral, moderately hard tap water in its stride for everyday keeping.

Did you know?

• It is a leaf-spawner, not a scatterer — like its harlequin cousins it glues adhesive eggs to the underside of a broad leaf rather than scattering them, unusual egg-laying for a 'rasbora'.
• The name is a costume detail of its own: the thin black mark on the rear body is shaped like a lamb chop, narrower than the harlequin's broad triangle and the fastest way to tell the two apart.
• It lives in limestone sinkholes as well as soft streams — one wild population inhabits karstic sinkholes at pH 7.0 to 7.4, evidence the species is more chemistry-flexible than its blackwater reputation suggests.
• It is a 'false harlequin' named for a person — espei honours the collector Espe, and the fish was described by Hermann Meinken in 1967.
• Its solid copper-red body is generally regarded as more vivid than the harlequin's pinkish tone, which is exactly why hobbyists pick it as a smaller, brighter centrepiece shoal.
• It is assessed by the IUCN as Least Concern and is commercially traded for the aquarium hobby.

Tank size — and why

A 60 cm footprint, roughly a 15 to 20 US gallon long, is the right target for the group this fish wants, with a 10-gallon the tight floor for about six only. The driver is not waste — espei is tiny and low-waste — but swimming room and group size. A longer footprint gives a tighter, more confident shoal and steadier water; height matters far less than an open mid-water lane. There is no territorial or oxygen reason for a bigger tank here, only the welfare of the school, so prioritise length over height and treat 10 gallons as the minimum rather than the goal.

As a guide, a 20-gallon tank comfortably suits about 8–12 Lambchop Rasbora as a single-species display, leaving room for tankmates.

See it to scale

Adult Lambchop Rasbora reach only about 3 cm (1.2 in) long — close to the size they are sold at, so what you see is roughly what you get. The catch is the group: a proper shoal still needs about a 10-gallon tank, around 51 cm long.

Adult size is sourced; tank length is approximate for a standard 10-gallon aquarium.

Water parameters in practice

Soft, slightly acidic to neutral water suits it best — around pH 6 to 7 and low hardness — though it tolerates neutral, moderately hard tap water perfectly well thanks to that limestone-sinkhole population. Seriously Fish gives pH 5.5 to 7.5, FishBase a tighter 6.0 to 6.5, and care blogs stretch towards 7.9, so a stable middle is safe. Temperature wants a careful note: FishBase and Seriously Fish agree exactly on 23 to 28 °C, but aim for the middle, about 24 to 26 °C, and treat 28 °C as a tolerated ceiling and breeding temperature rather than the everyday ideal. Like most soft-water rasboras it is hardy once settled but more sensitive to unstable parameters and an uncycled tank than to a wide but steady range. Stability beats chasing perfect numbers.

Diet & feeding

An unfussy omnivore. In the wild it is a micropredator taking small insects, worms, crustaceans and other zooplankton; in the tank it readily accepts good-quality micro flake or a small pellet as the staple. Vary it with small live and frozen foods — bloodworm, daphnia, brine shrimp, mosquito larvae, white worms — to deepen the copper colour and condition for breeding. The mouths and stomachs are tiny, so feed small amounts and feed sparingly to protect water quality. As an active mid-water feeder that darts for food it can be out-paced by faster or surface fish, so make sure its share reaches it.

Gear & setup

A planted, dimly-lit setup over dark substrate is ideal — densely planted with Java fern, Anubias and broad-leaved plants, floating plants to diffuse the light (espei is sensitive to bright lighting), plus driftwood to tint the water. Broad leaves double as the spawning site. A gentle filter and modest flow match the slow forest streams and ponds it comes from; avoid strong current. It is a tropical fish, so a heater to hold a stable mid-20s temperature is wanted. A lid is sensible as with any active small fish, but espei is not a noted jumper.

Temperament & behaviour

Peaceful to a fault — very peaceful indeed, in Seriously Fish's words. This is a non-territorial, non-nipping mid-water shoaler with no same-species aggression, asking nothing of its tankmates and spending its day schooling in open water. The behaviour only appears properly in numbers: a confident, copper-bright shoal in a good-sized group, versus skittish, washed-out, hiding fish kept in ones and twos. It is a top choice for a small, peaceful planted community — a smaller, brighter alternative to the harlequin.

Group & social needs

Keep a real group. Six is the bare minimum cited across the care literature, but Seriously Fish recommends at least eight to ten, which is what to aim for. Bigger groups cut stress and timidity, tighten the schooling, brighten the colour and dilute any one fish being singled out. Under-stocked espei hide and fade, so treat six as the floor and buy eight to ten or more.

Compatible tank mates (preview)

A short, engine-cleared shortlist — the species TankStocking's welfare engine clears with Lambchop Rasbora and that suit its size and temperament best. Tap any to load the pairing in the planner.

• Amano Shrimp — Peaceful temperament, similar adult size.
• Assassin Snail — Uses the bottom zone, peaceful temperament, similar adult size.
• Black Neon Tetra — Peaceful temperament, similar adult size.

A note on the shrimp and snails here: Lambchop Rasbora is peaceful and generally invertebrate-safe — but almost any fish will take very small shrimplets given the chance, so give shrimp dense cover (moss, leaf litter) if you want a colony to grow, rather than expecting every baby to survive.

This engine-cleared shortlist is Lambchop Rasbora's tankmate surface for now — a dedicated tank-mates guide can follow for high-demand species.

Breeding & sexing

Like its harlequin relatives, the lambchop is a leaf-spawner rather than an egg-scatterer — it attaches adhesive eggs to the underside of broad plant leaves, the pair spawning beneath the leaf. (One care blog calls it an egg-scatterer, but the more authoritative Seriously Fish account of leaf-underside attachment is the one to trust.) Sexing is subtle: mature females are rounder-bellied and a little larger, and the black mark tends to show a sharper outline in males and a rounder one in females. Difficulty is moderate — some keepers find it freer-spawning than the harlequin, but it still needs a separate, dim, soft, acidic tank at pH 5.0 to 6.0 and 1 to 5 °H, with the pair conditioned heavily on live food first and older fish spawning better. Eggs hatch in roughly 24 to 48 hours and fry are free-swimming in about a week; remove the adults, which eat eggs and fry, and start the fry on infusoria or vinegar eels, then newly-hatched brine shrimp.

Lifespan

Three to five years is the consensus in a well-kept tank, with about five the realistic ceiling — shorter than the harlequin's five to eight, partly because espei is a smaller fish. What shortens it is unstable or poor water, an uncycled tank, chronically cold or unstable temperature, too small a group, and weak mass-bred stock.

Common mistakes

• Keeping too small a group. One to five fish become stressed, faded and hidden; buy eight to ten or more for a proper shoal.
• Adding them to a brand-new, uncycled tank. Hardy does not mean indestructible — new-tank instability drives most early losses.
• Confusing the species at point of sale. 'Lambchop', 'harlequin' and 'glowlight/hengeli' are sold interchangeably and mislabelled; confirm a true espei by its solid bright-copper body and thin hook-shaped blade, not the harlequin's deep-pink body and broad triangle, nor hengeli's grey body and orange glow stripe.
• Expecting fry in the wrong water. They live happily in neutral, moderately hard water but will not breed well outside soft, acidic conditions, so don't expect spawning in hard tap water.
• Over-bright, bare tanks. Espei is light-sensitive and shows its best colour in a shaded, planted setup; a bright bare tank produces washed-out, skittish fish.
• Housing them with predators or boisterous nippers. Adult angelfish, large cichlids and tiger barbs are wrong company for a ~3 cm peaceful shoaler.

Signs of trouble

• The copper colour going dull and a fish dropping out of the shoal — usually water quality, an immature tank, or too small a group.
• Clamped fins, hiding and loss of appetite — general stress cues worth investigating before they progress.
• Flicking and scratching against decor — early ich (white spot), the most common disease in this otherwise robust fish.
• Skittish, washed-out behaviour in a small group — a husbandry signal that the school is too small rather than an illness.

Is this fish right for you?

Don't buy lambchop rasboras if you can't keep a group of eight to ten, if your tank is only just set up and not yet cycled, or if your community contains predators their size or runs at hard-water rift-cichlid or discus-warm conditions. Be aware that what is sold as 'lambchop' is routinely mislabelled, so confirm you are buying a true espei — solid copper body, thin black blade — rather than a hengeli or harlequin, and pick the most colourful, active, well-shaped fish over any tank holding sick, curved or faded specimens.

Bringing one home

Float the bag to equalise temperature, then add tank water gradually over fifteen to twenty minutes before netting the fish into a mature, cycled tank and leaving the transport water behind. Soft-water rasboras resent sudden chemistry changes, so a slow drip and a settled tank matter more than for tougher species, and quarantining new arrivals protects the rest of the shoal.

Common questions

How many lambchop rasboras should I keep?

Six is the bare minimum; eight to ten or more is the real target. They are shoaling fish — small groups stay skittish and washed-out, while a larger school is confident, tightly-grouped and far more colourful.

What is the difference between a lambchop (espei) and a harlequin rasbora?

Look at the black mark and the body. The lambchop has a thin, hook- or blade-shaped mark on a solid bright-copper body and is smaller and slimmer; the true harlequin has a broad, full triangular wedge on a deeper-pink body. The glowlight/hengeli, the other look-alike, has a grey body with an orange glow stripe. Stores routinely mislabel all three.

How big do lambchop rasboras get and what tank do they need?

They are tiny — about 2.5 to 3 cm, smaller than the harlequin. A 10-gallon is a tight floor for around six; a 15 to 20 gallon, 60 cm footprint is the right target for the eight-to-ten school they want. The constraint is swimming room and group size, not waste.

Are lambchop rasboras safe with shrimp?

Adult dwarf shrimp are generally safe with this peaceful ~3 cm fish in a well-planted tank, though shrimplets may be picked off. Provide dense cover if you want shrimp to breed alongside them.

Are lambchop rasboras good for beginners?

Yes — they are hardy and easy once the water is stable, which makes them an excellent beginner schooler. The two things to get right are a proper group of eight to ten and a mature, cycled, gently-filtered planted tank; they fade and stress if kept as a few fish in a bright bare tank.

Sources & confidence

Sources & confidence (9 species)

These back the Lambchop Rasbora figures and the previewed tank mates above. Each figure is read from the TankStocking species database (v2026.06); below is the care reference behind it and how confident we are in that data. Confidence reflects the source quality, not whether any pairing is safe. Full source list and the welfare model are on the methodology page.

• Lambchop Rasbora Trigonostigma espei — Seriously Fish (seriouslyfish.com/species/trigonostigma-espei) high confidence
• Amano Shrimp Caridina multidentata — Aquarium Co-Op amano shrimp care; Aquadiction high confidence
• Assassin Snail Clea helena (Anentome helena) — The Shrimp Farm (theshrimpfarm.com/posts/assassin-snail-care) high confidence
• Black Neon Tetra Hyphessobrycon herbertaxelrodi — Seriously Fish / Aqua-Fish (Hyphessobrycon herbertaxelrodi) high confidence
• Black Phantom Tetra Hyphessobrycon megalopterus — Seriously Fish (Hyphessobrycon megalopterus) high confidence
• Cardinal Tetra Paracheirodon axelrodi — Seriously Fish (seriouslyfish.com/species/paracheirodon-axelrodi) high confidence
• Celestial Pearl Danio Celestichthys margaritatus — Seriously Fish (seriouslyfish.com/species/celestichthys-margaritatus) high confidence
• Checker Barb Oliotius oligolepis — Seriously Fish — Oliotius oligolepis (https://www.seriouslyfish.com/species/oliotius-oligolepis/) high confidence
• Cherry Barb Puntius titteya — Seriously Fish (Puntius titteya) seriouslyfish.com/species/puntius-titteya high confidence

Care-guide sources (6)

This guide synthesises the references below; where they disagree, the range and the disagreement are noted in the text above. The figures in the key-facts box are read from the TankStocking species database (v2026.06). Full welfare model on the methodology page.

• FishBase — Trigonostigma espei — authority (Meinken 1967), family Danionidae, max 2.5 cm SL, temp 23-28 C, pH 6.0-6.5, dH to 12, range (Thailand & Cambodia), pond/swamp habitat, 'lambchop-shaped black blotch on caudal peduncle', IUCN Least Concern, commercial
• Seriously Fish — Trigonostigma espei (Lambchop Rasbora) — synonym Rasbora espei, trade names (Lambchop, False Harlequin, Espe's), 25-30 mm SL, temp 23-28 C, pH 5.5-7.5, hardness 18-179 ppm, Krabi limestone-sinkhole population (pH 7.0-7.4), 60x30 cm tank, group 8-10, 'very peaceful', sexing, leaf-underside breeding (pH 5.0-6.0, 1-5 dH, 24-48 h hatch), bright copper body, distinctions vs heteromorpha and hengeli
• Wikipedia — Trigonostigma espei (Lambchop rasbora) — authority (Meinken 1967), synonym Rasbora espei, family Danionidae, etymology (mark 'like a lamb chop'), range (Thailand, Cambodia, Phú Quốc Vietnam), IUCN Least Concern
• Aquarium Co-Op — Harlequin & Espei (Lambchop) Rasboras — ~76 F, ~pH 7.2, soft water, 6 in a 10-gal floor, 'in smaller schools these fish will stress', omnivore diet, tankmates (bettas, neon/cardinal/black phantom tetras), espei brighter orange vs harlequin pinkish-brown, breeding needs warmer soft acidic water
• aqua-fish.net — Lambchop Rasbora care guide — lifespan 3-5 years, temp 22-26 C, pH 6.5-7.5, 10 gal floor for 6 / 20 gal preferred, group 6+, mid-level swimmer, light-sensitive (subdued light, floating plants), dark substrate, diet, breeding (soft acidic, dim, hatch 24-36 h, infusoria/vinegar eels for fry)
• Fish Laboratory — Lambchop Rasbora (Trigonostigma espei) care guide — lifespan 3-5 years, temp 23-28 C, pH 5.5-7.9, hardness 2-11 dH, 10 gal min for 6 / 8-10 recommended, peaceful, omnivore, several small meals/day, hatch 24-48 h + free-swimming ~7 days, tankmates; flagged internal conflicts (lists shrimp under 'avoid' vs Aquarium Co-Op; calls it 'egg-scattering' vs Seriously Fish leaf-attachment; gives inflated 3.8-5 cm TL size)

More on Lambchop Rasbora

Related guides on TankStocking — each scored by the same welfare engine as the planner.

This care guide is a sourced planning reference, not veterinary advice — individual fish, filtration and maintenance all matter. Cycle the tank, test your water, and observe your fish. How TankStocking works →