Chili Rasbora Care Guide

The chili rasbora is a glowing red blackwater nano fish barely 1.5-2 cm long — one of the smallest fish in the hobby, and one of the most misunderstood. It is genuinely peaceful, but it is also bite-size prey, so it is not a starter community fish: it is a nano-specialist that wants a big group, a mature soft-water tank and food small enough for a tiny mouth, and it rewards all three with an electric red shoal.

Chili Rasbora at a glance

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

Where it comes from

Boraras brigittae is endemic to the peat-swamp forests of south-western Borneo — South and Central Kalimantan, with its type locality at Banjarmasin. Its home is slow, tea-coloured blackwater streams and pools over a bed of fallen leaves, branches and roots, deeply shaded and strongly acidic. That biotope explains the whole care sheet: the soft, acidic, tannin-stained, dim water is where it colours up and settles; the near-still swamp means a strong current physically exhausts it, so flow must be gentle; and the leaf litter teems with microfauna, which is why it does so much better in a mature, established tank than a brand-new sterile one. Replicate the swamp with dark substrate, dense and floating plants, driftwood and botanicals, and the washed-out shop fish turns deep red.

Did you know?

• It is one of the smallest fish in the trade — a typical adult is only about 1.5-2 cm, mostly translucent with a glowing red flank.
• 'Mosquito rasbora' is literal: in the wild it eats mosquito and insect larvae, and that micropredator diet is the origin of the trade name.
• The genus name Boraras is an anagram of Rasbora, coined for these dwarf forms that carry fewer abdominal vertebrae than true Rasbora.
• It was named after a wife — the epithet brigittae honours describer Dieter Vogt's wife, Brigitte (Vogt, 1978).
• It turns red on cue: the deep colour is driven by soft, acidic, tannin-stained water plus a big secure group and dim light, so the same fish looks washed-out in a bright, hard-water community tank.

Tank size — and why

A 5 US gallon tank is a defensible floor on bioload alone — this is a tiny, low-waste fish, and it has been kept in tanks as small as three gallons. But the binding constraint is not waste, it is group size: to house the ten to twenty-plus fish the species actually needs, about ten gallons or more (a 45-60 cm footprint) is the real-world target, footprint over height. And the truest 'minimum' here is maturity rather than litres — because the fish leans on microfauna and stable soft, acidic water, an established, cycled tank matters more than raw volume. Never add chilis to a brand-new tank. A lid is sensible, as they swim in the upper zone.

As a guide, a 20-gallon tank comfortably suits about 9–13 Chili Rasbora as a single-species display, leaving room for tankmates.

See it to scale

Adult Chili Rasbora reach only about 2 cm (0.8 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 5-gallon tank, around 41 cm long.

Adult size is sourced; tank length is approximate for a standard 5-gallon aquarium.

Water parameters in practice

Soft, warm, acidic blackwater is the brief. Aim for a stable mid-20s °C (roughly 24-27 °C, with 20-28 °C tolerated) and steer the pH towards the acidic end, around 5-6.5, in very soft water — that is where the red deepens and where they will breed. Store-acclimated or captive-bred stock copes with harder, more neutral water than wild fish, but most stock is wild-caught and arrives stressed from extremely soft acidic water, so it is vulnerable to mineral-rich or alkaline water and to unstable, immature tanks in its first weeks. The fish is reasonably hardy once settled; the danger window is the start. Acclimate slowly, prize stability over chasing an exact pH, and be cautious with medications — tiny soft-water fish can react badly to full doses.

Diet & feeding

In the wild it is a micropredator taking insect larvae (mosquito larvae among them, hence 'mosquito rasbora'), worms, microcrustaceans and zooplankton. The defining captive problem is the mouth: it is minuscule, and many standard flakes and pellets are simply too big to eat, so a tank that looks 'full of food' can slowly starve the fish. Crush dry food finely or use micro-granules, and lean heavily on small live and frozen foods — baby brine shrimp, microworm, daphnia, moina, cyclops, rotifers and finely chopped bloodworm, offered most days for colour and condition. They feed in mid-water and prefer slow-sinking or suspended food, often ignoring anything that drops too fast, and they are easily out-competed by faster fish — another reason to keep them only with equally tiny, slow tankmates. A mature, microfauna-rich tank supplements feeding and is effectively essential for raising fry.

Gear & setup

A mature, densely planted, dimly-lit blackwater nano tank is the natural fit. Use dark fine substrate, fine-leaved and floating plants for shade and security, plus driftwood and leaf litter or botanicals for tannins and the microfauna they graze. A heater holds the stable mid-20s. The single most important kit choice is the filter: these fish cannot tolerate much flow, so a gentle sponge or matten filter is ideal and a normal hang-on or canister current will exhaust them. A lid is sensible.

Temperament & behaviour

Very peaceful and timid — a loose mid-to-upper shoaler with essentially no aggression toward tankmates and only harmless competitive colour-displaying among the males. It is not a fin-nipper. The behaviour the buyer wants only appears in numbers and security: a big group in a dim, planted blackwater tank with no predators comes out, colours up and displays, while a small group or a bright, open tank leaves pale, skittish fish hiding in the plants. The colour the fish is bought for is, in effect, a confidence signal.

Group & social needs

Keep a big group. Seriously Fish sets a minimum of eight to ten; Aquarium Co-Op pushes eight to twelve with fifteen-plus best; AquaInfo says 'eight, but preferably much more'. Treat eight as the bare floor and aim for ten to fifteen or more. This is not cosmetic — in small groups they stay shy, washed-out and permanently hidden, and the colour only emerges in a secure large shoal. Bigger groups also dilute stress and individual targeting.

Compatible tank mates (preview)

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

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

A note on the shrimp and snails here: Chili 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 Chili Rasbora's tankmate surface for now — a dedicated tank-mates guide can follow for high-demand species.

Breeding & sexing

Sexing is reasonably clear in condition: males are smaller, slimmer and much redder, with dominant individuals intensely coloured; females are rounder, fuller-bodied and paler with clearer fins. Spawning the adults is easy-to-moderate in the right setup — a mature, densely planted, dimly-lit blackwater tank with soft acidic water, gentle flow and plant thickets, moss or spawning mops. They are continuous egg-scatterers that spawn a few eggs most days in good conditions and give no parental care, eating their own eggs and fry, so protect the spawn with dense planting or mesh. Expect few eggs at a time, up to roughly fifty, hatching in about one to two days. The bottleneck is the fry, not the spawning: the tiny larvae need infusoria or Paramecium first, then microworm and Artemia nauplii after a week or so, which is exactly why a mature, microfauna-rich tank raises fry where a sterile one fails.

Lifespan

Long-lived for such a tiny fish — commonly cited at four to eight years, though the realistic working figure is nearer four to six in a stable nano tank, with the eight-year top end resting on a single source. What actually shortens it is predation by tankmates that can swallow it, starvation from food too large for the mouth, an immature or sterile tank with no microfauna, mineral-rich water for wild stock, strong flow, and transport stress on wild imports added to unstable water.

Common mistakes

• Putting them in a general community tank. This is the single biggest error — they are bite-size prey, not a community staple, and tankmates that look peaceful but are bigger or faster will eat, harass or out-compete them.
• Adding them to a brand-new, immature tank. No microfauna and unstable parameters mean poor survival, especially for wild imports and any fry — wait until the tank is established.
• Keeping too few. A group of three to six stays pale, hidden and stressed and 'doesn't look like the photos' — buy ten to fifteen or more.
• Feeding food that is too big. Standard flakes and pellets can be physically un-eatable, so the fish slowly starve in a tank full of food — crush dry food finely and use micro and live foods.
• Too much flow. A normal hang-on or canister current exhausts them — use a gentle sponge filter.
• Buying a mixed bag unknowingly. Shipments often mix brigittae with B. merah and B. urophthalmoides; care is similar, but know what you actually have.

Signs of trouble

• Colour fading and fish hiding away from the shoal — usually too small a group, an immature tank, or poor water.
• A thin, sunken belly despite food in the tank — starvation, almost always because the food is too big for the mouth.
• Skittish, washed-out fish that never come out — a husbandry signal that the group is too small or the tank too bright and open.
• Clamped fins, lethargy and loss of condition in the first weeks after purchase — wild-import settling stress, worsened by mineral-rich or unstable water.
• Flicking, white spots or fungal patches — standard nano ailments; treat cautiously, as tiny soft-water fish can be sensitive to full-dose medications.

Is this fish right for you?

Don't buy chili rasboras for a general community tank with any fish big or fast enough to swallow or out-compete a 1.5 cm fish; for a brand-new, uncycled tank; for hard alkaline water you can't soften (for wild stock); or for a high-flow setup. And don't buy them if you can't commit to a group of ten or more and to tiny or live foods — those two demands, plus a mature soft-water tank and the fish's prey status, are what move this from a beginner fish to a nano-specialist one. Most stock is wild-caught and its restricted Borneo peat-swamp habitat is under pressure (the IUCN lists it as Data Deficient), so favour healthy, established-tank fish and quarantine new arrivals.

Bringing one home

Add chilis only to a mature, cycled, soft, acidic, gently-filtered tank, and acclimate slowly — most stock is wild-caught and arrives stressed from extremely soft blackwater, so a slow drip over a good twenty minutes to ease the chemistry change matters more than for tougher fish. Float to match temperature first, add tank water gradually, then net the fish across and leave the transport water behind. Quarantine new arrivals, since the first weeks are the danger window.

Common questions

Are chili rasboras good for a community tank?

Only a nano community. They are genuinely peaceful but they are bite-size prey at 1.5-2 cm, so anything that can fit them in its mouth — angelfish, gouramis, most full-size tetras, barbs and cichlids — will eventually eat or out-compete them. Keep them only with equally tiny, calm, shrimp-safe tankmates.

Are chili rasboras good for beginners?

Not really — they are a nano-specialist, not a starter fish. They stack four non-beginner demands: a mature, established tank with microfauna, food tiny enough for a tiny mouth, a large group of ten-plus, and a prey status that dictates a nano-only stocking plan. Add wild-caught fragility and a soft acidic blackwater preference and they are better as a second project than a first.

How many chili rasboras should I keep?

Eight is the bare minimum; ten to fifteen or more is the real target. In small groups they stay pale, shy and hidden, and the glowing red colour only emerges in a secure large shoal.

What do you feed chili rasboras?

Tiny food for a tiny mouth. Many standard flakes and pellets are physically too big, so crush dry food finely or use micro-granules, and offer regular small live and frozen foods — baby brine shrimp, microworm, daphnia, cyclops and rotifers. A 'full' tank of oversized food can starve them.

Are chili rasboras safe with shrimp?

With adult shrimp, yes — they won't bother adult cherry or Caridina shrimp and make classic shrimp-tank companions. They will opportunistically pick off newborn shrimp, though, so establish the shrimp colony first.

Sources & confidence

Sources & confidence (9 species)

These back the Chili 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.

• Chili Rasbora Boraras brigittae — Seriously Fish (seriouslyfish.com/species/boraras-brigittae) 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
• Cherry Shrimp Neocaridina davidi — Aquarium Co-Op cherry shrimp care; The Shrimp Farm high confidence
• Clown Killifish Epiplatys annulatus — Seriously Fish (Epiplatys annulatus); Aquarium Co-Op high confidence
• Dwarf Emerald Rasbora Celestichthys erythromicron — Seriously Fish (seriouslyfish.com/species/celestichthys-erythromicron) 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 — Boraras brigittae — authority (Vogt 1978), family Danionidae, common 1.8 cm SL / max 3.5 cm TL, temp 25-28 °C, pH 6.5-7.0, dH ≤10, trophic level 3.4, southern Borneo range, schooling, up to ~50 eggs on leaf undersides hatching ~48 h, IUCN Data Deficient (assessed 2019)
• Seriously Fish — Boraras brigittae — etymology (named for the author's wife), family Cyprinidae, synonym Rasbora urophthalma brigittae, Banjarmasin type locality and range, blackwater peat-swamp biotope, wild chemistry 20-28 °C / pH 4.0-7.0 / 18-179 ppm, 15-20 mm SL, 45×30 cm tank, gentle flow, micropredator diet with daily live/frozen, group 8-10, 'very peaceful', nano tankmate list, sexing, continuous egg-scatterer breeding, fry on Paramecium then Artemia
• Aquarium Co-Op — Care Guide for Chili Rasboras — ~2 cm, 72-82 °F, kept in tanks as small as 3 gal, school of 8-12 (15+ best), tiny-mouth food guidance (crushed flake, fry food, frozen cyclops/rotifers, microworm, baby brine), gentle-flow warning, shrimp-safe-with-adults, breeding in mature planted tanks
• Tropical Fish Hobbyist — The Genus Boraras: Miniature Jewels — six Boraras species, brigittae ~18 mm, male/female colour, distinctions from B. urophthalmoides (geography/clade) and B. merah (sterile-hybrid evidence), 15-20 gal long preferred, blackwater plus slow flow and oak-leaf breeding, micropredator diet
• AquaInfo — Boraras brigittae (Chili / Mosquito Rasbora) — max ~3 cm, lifespan 'up to four to eight years' (single-source top end), temp 20-28 °C, pH 4.0-7.0, GH 1-8, group 'eight but preferably much more', tiny-mouth feeding, egg-scatterer ('a few eggs every day', hatch 1-2 days), fry on infusoria then nematodes then brine, SW Borneo peat swamps, ID vs urophthalmoides
• The Shrimp Farm — Chili Rasbora care — ~1 in, 72-82 °F, acidic-to-neutral pH ~6.0-7.5, group 6+, gentle-flow sensitivity, micro/soft food for the tiny mouth, shrimp-safe-with-adults (hobby-consensus corroboration)

More on Chili 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 →