Brilliant Rasbora Care Guide

'Brilliant' is a shop label, not a description — the real signature of Rasbora einthovenii is the bold dark 'long band' that runs nose to tail and straight through the eye on a pinkish, red-tailed body. What the cheerful name hides is size and pace: at around 9 cm this is one of the larger true rasboras, a fast open-water sprinter that wants a four-foot swimming lane, not the planted nano box its shelf-mates get. Give it soft acidic blackwater, a tight lid against a determined jumper and a big shoal to run with — and respect that 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 29-gallon tank comfortably suits about 6 Brilliant Rasbora as a single-species display, leaving room for tankmates.

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 and snatches the lion's share, so make sure slower bottom feeders like Corydoras still get their portion.

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 a name for its care guide, or use + to load the pairing in the planner.

• Amano Shrimp+Peaceful temperament, similar adult size
• Bamboo Shrimp (Wood/Fan Shrimp)+Peaceful temperament, similar adult size
• Bleeding Heart Tetra+Peaceful temperament, similar adult size
• 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
• Bronze Corydoras+Uses the bottom zone, peaceful temperament, similar adult size
• Celebes Rainbowfish+Peaceful temperament, similar adult size

A note on the shrimp and snails here: Brilliant 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 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 house it with a shrimp colony or with nano fish like the chili rasbora you'd hate to lose.
• 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. If a four-foot tank is out of reach, a smaller schooler from the freshwater fish list will serve you better than cramping this one.

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

Sources & confidence

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 →