Brilliant Rasbora Care Guide

The brilliant rasbora is a four-foot-tank fish wearing a nano fish's name — an active, fast-moving, peaceful blackwater schooler that grows large for a rasbora, to around 9 cm, marked by a bold dark band running the full length of its body through the eye. It wants real swimming length, soft acidic water and a tight lid, and at 9 cm it is a micropredator, not the shrimp-safe nano many buyers expect.

Brilliant Rasbora at a glance

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

Where it comes from

Rasbora einthovenii comes from south-east Asia — the Malay Peninsula including southern Thailand, Peninsular Malaysia, Singapore, Borneo, Sumatra and Bangka Island. Its home is classic blackwater: shaded, tannin-stained peat-swamp streams and forest streams, where Seriously Fish records water that is very soft and acidic, with pH as low as 3.0 in the wild extreme. That biotope sets the care — reproduce it with driftwood, leaf litter and botanicals, dark substrate and floating cover for diffused light, and best colour and least stress follow; a bright bare tank washes it out. It is a forest-stream fish rather than a torrent fish, so an active swimmer that still prefers slow-moving water: give it length and open swimming lanes but keep the flow gentle.

Did you know?

• It is a blackwater extremophile by origin — its wild peat-swamp streams run acidic to pH as low as 3.0, far below most tap water, even though it tolerates near-neutral water in the aquarium.
• The 'long band' is its whole identity — the dark lateral stripe runs the full body and continues through the eye to the snout with distinctive crinkly edges, hence the alternative name Long-band Rasbora.
• It is one of the bigger true Rasbora — up to ~9 cm in tanks and 10.6 cm SL in the wild per FishBase, dwarfing the harlequin and the nano rasboras, a genuinely different stocking proposition.
• It was named by a giant of 19th-century ichthyology, Pieter Bleeker, in 1851, the patronym einthovenii honouring a person named Einthoven.
• It may never have been deliberately bred in the hobby — Seriously Fish is openly unsure, an unusually honest 'we don't know' for a traded fish.
• It is assessed by the IUCN as Least Concern, and is commercial in both food fisheries and the aquarium trade.

Tank size — and why

Sold like a small rasbora, this is an active ~9 cm fish that Seriously Fish keeps in a tank measuring at least 48 inches (120 cm), chosen specifically because it is an active species. The welfare driver is swimming length for a fast, fair-sized schooler, not bioload — the volume of a short tank can look adequate while the footprint is far too cramped. Treat a 48-inch, 4-foot tank as the proper target, with a 36-inch tank the realistic floor for a small group; a standard short tank is simply under-length. Prioritise horizontal length over height, because this fish spends its day cruising open water, not the vertical column.

As a guide, a 40-gallon tank comfortably suits about 6 Brilliant Rasbora as a single-species display, leaving room for tankmates.

How big does it really get?

Full-grown Brilliant Rasbora reach about 9 cm (3.5 in) long, but they are usually sold at only about 2.5 cm (1 in) — a typical shop size (estimate). At full size, Brilliant Rasbora needs roughly a 40-gallon tank, about 91 cm long; a common 10-gallon starter kit is only about 51 cm.

Adult size is sourced; the shop size is a typical-juvenile estimate; tank length is approximate for a standard 40-gallon aquarium.

Water parameters in practice

A soft-water blackwater fish at heart. FishBase pins the ideal narrow at pH 6.0 to 6.5 with hardness no higher than about 5 dH, while Seriously Fish gives a wider tolerated 5.0 to 7.5 and 2 to 10 °H for routine keeping; best colour and any hope of breeding need soft, acidic water, so hard alkaline tap reduces both. Temperature is a point of strong agreement: FishBase, Seriously Fish and the care guides all converge on 22 to 26 °C, so this is emphatically not a warm-water, discus-temperature fish — keep it at or below 26 °C. Like other peat-swamp fish it is more sensitive to unstable parameters and an uncycled or new tank than to a wide but steady range, so acclimatise it gradually and let the tank mature first.

Diet & feeding

A micropredator in the wild, feeding on small insects, worms, crustaceans and other zooplankton at a trophic level that leans carnivorous. In the tank it is an unfussy omnivore that accepts good-quality dried flake, micro-pellet or granules as a base, but Seriously Fish warns it should not be fed exclusively on dried food. Supplement with small live and frozen foods — daphnia, brine shrimp, bloodworm, cyclops — which Seriously Fish says give the best colouration and condition fish for breeding. Feed small amounts at least once a day and feed sparingly to protect water quality. It is a fast, active mid-to-upper-water feeder that darts for food, so make sure slower or shy tankmates also get fed.

Gear & setup

Build a blackwater layout: well-planted with open swimming room, dark substrate to deepen colour, and driftwood, leaf litter and botanicals to release the tannins that mimic its native water, with floating plants for diffused light. A tight-fitting lid is mandatory — this is an excellent jumper that will end up outside an open-top tank. A heater holds the stable low-to-mid-20s setpoint, and because it is a forest-stream rather than a torrent fish, keep filtration gentle and the flow modest rather than strong, while still giving the length an active swimmer needs.

Temperament & behaviour

Peaceful and gregarious — very peaceful indeed, in Seriously Fish's words, a gregarious species by nature with no territoriality, fin-nipping or same-species aggression reported. The caveat is size and speed, not temper. Activity level is high: this is a fast, constantly-swimming open-water fish, and that, combined with its ~9 cm size, is why tank length matters far more than for a typical small rasbora. As an active open-water schooler its confidence rises sharply with numbers — under-stocked fish hide and fade, a full group schools tightly and colours up, the tail turning a vivid red in mature, well-conditioned fish.

Group & social needs

Keep a real group. Seriously Fish gives a floor of at least six, but care sources recommend eight to ten or more for proper schooling, and Fish Laboratory notes a group of twenty-five or more is a mesmerising sight. Larger groups reduce skittishness, tighten the schooling and improve colour, while under-stocked fish hide and fade. Buy eight to ten or more as the real target and treat six as the bare minimum.

Compatible tank mates (preview)

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

• Boesemani Rainbowfish — Peaceful temperament, similar adult size.
• Bolivian Ram — Uses the bottom zone, peaceful temperament, similar adult size.
• Bristlenose Pleco — Uses the bottom zone, peaceful temperament, similar adult size.

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

Breeding & sexing

An egg-scatterer and continuous spawner with no parental care — not the leaf-underside spawner the harlequin is, and the adults eat their own eggs. Difficulty is advanced and genuinely uncertain: Seriously Fish is candidly unsure the fish has ever been deliberately bred in the hobby, though small numbers of fry may appear unbidden in a densely-planted, mature tank. Sexing is subtle, with mature females noticeably rounder-bellied and a little larger than males, and no reliable colour-based cue. To attempt it, use a separate shallow tank with a mesh grid or spawning mops to protect the scattered eggs, slightly acidic soft water at the upper end of the temperature range, and pairs conditioned on live food, expecting several spawning events before a female is spent. Eggs incubate roughly 18 to 48 hours with fry free-swimming 24 to 48 hours later; start them on infusoria, then newly-hatched brine shrimp.

Lifespan

Roughly four to six years is the honest central estimate, with about five a fair number and up to eight cited at the optimistic end; lighter-sourced pages give a lower 3 to 5. Be aware that captive longevity for this species is weakly documented — no primary figure was found, so these are hobby estimates. What shortens it is unstable or poor water, chronically warm keeping, a too-small tank or group for an active schooler, and stress from boisterous or oversized tankmates.

Common mistakes

• Putting it in too short a tank. The biggest trap: it is sold like a small rasbora but is an active ~9 cm fish that Seriously Fish keeps in a 48-inch tank. A short tank under-serves it however adequate the gallons look — plan for length.
• No lid. It is a noted jumper, and an open-top tank loses fish.
• Too small a group. One to five fish turn skittish, faded and hidden; buy eight to ten or more, with six the minimum.
• Expecting it to be shrimp-safe. A 9 cm micropredator hunts dwarf shrimp and tiny fish or fry — don't mix it with a shrimp colony or nano fish you value.
• Confusing the species at point of sale. 'Brilliant Rasbora' is loosely applied — one published care page under that exact name actually describes Rasbora borapetensis, and the fish must also be told apart from R. jacobsoni. Check for the crinkly full-length stripe running through the eye, a pinkish body and a red tail.
• Wrong water chemistry. It lives and colours best in soft, acidic water; hard alkaline tap dulls it and ends any chance of breeding.

Signs of trouble

• The dark lateral stripe and overall colour fading, with 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 usual stress and new-tank disease.
• Persistent skittishness in an active open-water fish — often a signal the group is too small or the tank too short rather than an illness.

Is this fish right for you?

Don't buy brilliant rasboras if you only have a short or small tank, can't fit a tight lid, want a shrimp- or nano-fish-safe schooler, can't keep a group of eight to ten, or run a hard-water or high-temperature community. The name oversells it as a nano fish; in reality it needs a 48-inch tank, soft acidic water and tankmates it can't swallow. Confirm you are buying true R. einthovenii — pinkish body, crinkly full-length band through the eye, red tail — rather than a mislabelled R. borapetensis, and pick active, well-coloured fish over any tank holding faded or curved specimens.

Bringing one home

Float the bag to equalise temperature, then drip or add tank water gradually over fifteen to twenty minutes before netting the fish into a mature, cycled, soft, stable tank and leaving the transport water behind. As a peat-swamp blackwater fish it resents sudden chemistry changes more than a hardy generalist would, so a slow acclimation and a settled, covered tank matter, and quarantining new arrivals protects the group.

Common questions

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

Aquarium adults usually reach about 5 to 7 cm and commonly ~9 cm, with FishBase documenting up to 10.6 cm SL in the wild — much bigger than a harlequin or a nano rasbora. Seriously Fish keeps them in a 48-inch (4-foot) tank because they are active swimmers; the driver is swimming length, not gallons, so a short tank under-serves them.

Are brilliant rasboras shrimp-safe?

No. At around 9 cm this is a micropredator — Fish Laboratory warns it will try to eat smaller species such as shrimp. Treat adult dwarf shrimp as at-risk and shrimplets and nano fish or fry as likely prey, even though the fish is peaceful toward appropriately-sized tankmates.

What water conditions do brilliant rasboras need?

Soft, slightly acidic water: pH around 6.0 to 6.5 ideal (tolerating 5.0 to 7.5), soft hardness, and 22 to 26 °C. It is a blackwater fish, so it colours best with tannins from driftwood and leaf litter, and it is not a warm-water or hard-water species.

Is the 'Brilliant Rasbora' I'm being sold the right fish?

Verify it. The name is loosely used — one published care page under it actually describes Rasbora borapetensis, and true R. einthovenii must also be distinguished from R. jacobsoni. Look for a pinkish body, a crinkly dark band that runs the full length through the eye, and a red tail.

Do brilliant rasboras jump, and how many should I keep?

Yes — they are excellent jumpers, so a tight-fitting lid is mandatory. Keep them in a group of eight to ten or more for proper schooling and colour, with six the bare minimum; under-stocked fish stay skittish and faded.

Sources & confidence

Sources & confidence (9 species)

These back the Brilliant 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.

• Brilliant Rasbora Rasbora einthovenii — Seriously Fish (seriouslyfish.com/species/rasbora-einthovenii) high confidence
• Boesemani Rainbowfish Melanotaenia boesemani — Seriously Fish; Aquarium Co-Op Boesemani guide high confidence
• Bolivian Ram Mikrogeophagus altispinosus — Seriously Fish (seriouslyfish.com/species/mikrogeophagus-altispinosus) high confidence
• Bristlenose Pleco Ancistrus sp. — Aquarium Source / aqua-fish.net Ancistrus care guides high confidence
• Bronze Corydoras Corydoras aeneus — Seriously Fish (seriouslyfish.com/species/corydoras-aeneus) 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
• Clown Pleco Panaqolus maccus — Fish Laboratory (fishlaboratory.com/fish/clown-pleco); AquariumStoreDepot high confidence
• Congo Tetra Phenacogrammus interruptus — Seriously Fish (seriouslyfish.com/species/phenacogrammus-interruptus) 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 — Rasbora einthovenii — authority (Bleeker 1851), family Danionidae, max 10.6 cm SL, temp 22-26 C, pH 6.0-6.5, dH to 5, range (Malay Peninsula and Indonesia), 'inhabits forest streams', diet (worms/crustaceans/insects), trophic level 3.3, spawns in thick vegetation, IUCN Least Concern, commercial
• Seriously Fish — Rasbora einthovenii (Brilliant Rasbora) — max ~9 cm, range (S Thailand, Pen. Malaysia, Singapore, Borneo, Sumatra), blackwater peat-swamp habitat (pH as low as 3.0), temp 22-26 C, pH 5.0-7.5, hardness 2-10 dH, tank 48x12x12 in / 113 L, 'active species', group of at least six, micropredator diet, 'very peaceful indeed', egg-scatterer / continuous spawner, 'not sure if it has been bred in the hobby', stripe 'extends through and beyond the eye' with crinkly edges, distinction vs R. jacobsoni
• Wikipedia — Brilliant rasbora — authority (Bleeker 1851), family Danionidae/Rasborinae, synonyms (Leuciscus einthovenii, Rasbora vegae, Rasbora labuana), range (Malay Peninsula, Borneo, Sumatra, Bangka), IUCN Least Concern (2020 Lumbantobing); gives size 'up to 5 cm', an outlier conflicting with FishBase/SF and excluded from size of record
• Fish Laboratory — Brilliant Rasbora (Rasbora einthovenii) Ultimate Care Guide — typical 2 in/5.1 cm, max 3.6 in/9 cm, lifespan 5 yr (up to 8), temp 22-26 C, pH 6-7.5, hardness 2-10 dH (KH 3-8), group 6 (10-12+ recommended, 25+ 'mesmerizing'), 'very peaceful', 'smaller species such as shrimp will try to eat them', gold stripe bordered in black, red tail, 'excellent jumpers' -> tight lid, omnivore diet, egg-scatterer (hatch 18-48 h)
• aqua-fish.net — Long-band (Brilliant) Rasbora Care — names 'Long-band (Brilliant) Rasbora', wild max ~9 cm TL / aquarium 5-7 cm, footprint 60-75 cm, lifespan 3-5 yr, temp 23-26 C, pH 6.3-7.0, hardness 4-10, group of 8, 'peaceful, active shoaler', tankmates (small calm species), omnivorous micropredator diet, egg-scattering breeding
• AquariumStoreDepot — 'Brilliant Rasbora' care guide (mislabelled) — data-quality flag: published under the name 'Brilliant Rasbora' but its content actually describes Rasbora borapetensis (blackline/redtail rasbora) — wrong species (~5 cm, pH 6.0-8.0, 3-5 yr). Cited only as evidence of trade-name confusion, never for any einthovenii parameter

More on Brilliant 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 →