Freshwater Fish · Rasboras

Chili Rasbora

Boraras brigittae

Chilli-red speck from Borneo's peat swampsIntermediate

Lifespan: 4-8 years
Size: 0.6-0.8 in
Social needs: Shoaler; keep 10+ together
Time: Low-moderate; daily feeding, weekly water change
Cost: Low-Medium
Diet: Micro-predator; micro pellets, live and frozen micro-foods

Overview

What is this animal?

The chili rasbora is a miniature danionid (a small carp relative long classed as a cyprinid) from the tannin-stained peat swamps and blackwater streams of southwestern Borneo, where males glow deep chilli red along a dark lateral stripe.
At 0.6 to 0.8 inches fully grown it is among the smallest fish in this guide, about the size of an ember tetra and a fraction the size of a harlequin rasbora.
Despite the common name it is not a true Rasbora but a Boraras, a genus of dwarfed species built for still, acidic water.

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Much stock is still wild-caught from habitat under pressure from peatland drainage, and those imports arrive small, thin and easily stressed, though captive-bred chilis are increasingly available and settle in far more readily.
It is an intermediate fish for a mature, planned tank, not a first fish for a new aquarium, and if your tank is younger than a few months the honest advice is not yet.
Ask your store whether stock is captive-bred, and favour it when offered.

Temperament

Chilis are peaceful and completely harmless, forming a loose shoal in which males claim tiny display territories and spar with flared fins, all bluff and no damage.
A group of ten or more spreads the sparring, builds confidence and produces the constant midwater activity and colour that a nervous group of six never shows.

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Tankmate choice is the hard part, because almost everything in the hobby can swallow or outcompete them, including peaceful staples like harlequin rasboras and bettas.
Adult dwarf shrimp are safe with them, so the best setups are a species-only shoal or a pairing with dwarf shrimp and at most one other Boraras-sized species, though the tiniest newborn shrimplets may occasionally be picked at.
If a planned community includes anything over about 1.2 inches, the chilis belong in a different tank.

A good fit for

Mature, planted blackwater aquariums
Species-only shoals with real presence
Dwarf-shrimp tanks needing a genuinely shrimp-safe fish
Aquascapers wanting a tiny, vivid centrepiece
Keepers ready to step beyond beginner fish

Common mistakes to avoid

Adding them to a new or immature tank
Hard, alkaline water dulling colour and shortening lives
Skipping slow drip acclimation for wild-caught arrivals
Tankmates big enough to swallow them, which is most fish
New fish refusing dry food without live micro-foods
Open-topped tanks, as they jump

Enclosure

Minimum 15 gallons, for a group of 10

Cannot be kept alone. The minimum is 10, and the space above is for that group.

Keep a shoal of ten or more in a mature, densely planted aquarium of at least 15 US gallons and 18 in long; a bigger tank holds steadier water and a larger shoal.
Heat the tank to 75-82°F and aim for blackwater styling: dark substrate, driftwood, leaf litter and tannins that echo the peat swamps and make the red glow.
Flow should be very gentle, and an air-driven sponge filter suits them better than a powerful internal filter.

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They want soft, acidic water, ideally pH 5.0-6.5 and low hardness, though stable slightly-acidic conditions are workable.
Stability matters more than chasing exact numbers, because a small volume of water buffers swings poorly and these tiny bodies absorb every mistake.
Never add them to a freshly cycled tank, and fit a tight lid, as they can jump through surprisingly small gaps.

Check your enclosure

Supplies

Setup

Tank and stand
Filter
Heater and thermometer
Substrate, plants and decor
Liquid test kit
Dechlorinator and starter supplies

Ongoing

Quality micro-pellet or fine flake
Frozen daphnia and cyclops
Frozen or live baby brine shrimp
Frozen bloodworm (to be chopped fine)
Small scissors or blade for chopping frozen food

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Fine net for removing leftovers
Small feeding spoon

Safe substrate: Fine, smooth sand · Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras) · Bare bottom (quarantine and grow-out only)

Work out the cost

Care routine

Daily

Check temperature and equipment
Feed a fine-grained food
Head-count and look everyone over

Every few days

Top up evaporationevery 3 days

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Weekly

Count the school
Test the water
Water change and gravel vacuum
Wipe the front glass only

Every few weeks

Trim and thin the plantsevery 2 weeks

Monthly

Check supplies and reagent dates
Replace or recharge chemical media, if you use any (skip it in a blackwater tank)
Rinse the filter media

Health review: Quarterly review with a new-stock check, every 3 months

Tools

Is your enclosure big enough?Check your measurements against the recommended size What will it cost?Setup, monthly and over its whole life, itemised Is this ammonia reading dangerous?Works out the toxic part from your pH and temperature

Care in depth

Diet

Micro-predator; micro pellets, live and frozen micro-foods

Chilis are micro-predators that pick zooplankton and tiny invertebrates from the water column, and their mouths are minute even by nano-fish standards.
Powdered food, finely crushed flake and the smallest micro-pellets form the dry staple, but freshly imported wild fish often refuse dry food entirely at first.
Live or frozen baby brine shrimp, microworms, cyclops and small daphnia are the reliable way to get new arrivals feeding and coloured up.

Feed small amounts once or twice a day, offering only what disappears within a minute or two.
Anything sized for ordinary community fish is too large, so check that every fish in the shoal is actually eating rather than mouthing and spitting food.

Health

Signs of good health, and the common problems

The risky period is the first month, because wild-caught chilis arrive stressed and may carry internal parasites that show as wasting despite eager feeding.
Drip-acclimatise them slowly over an hour or more, quarantine new arrivals, and expect washed-out brown fish to need weeks of quiet, tannin-stained water before the red returns.
Ich and fin rot follow chilling or unstable water, as with any small fish.

Once settled in a stable, soft, mature tank they are surprisingly durable and largely trouble-free.
Do gentle weekly partial changes with temperature-matched water rather than infrequent large ones, since big parameter swings shock a fish this size.
Daily observation is your early-warning system, because a 0.8-inch body leaves no margin once illness takes hold.

Is this urgent?

6 warning signs and how fast to act, 3 of them right away

In a fish tank the patient is usually the water. Test before you treat: dosing a healthy tank for a disease it does not have makes things worse.

Go now

Any detectable ammonia or nitrite in a stocked tankLarge water change now with dechlorinated, temperature-matched water. Stop feeding. Test again in 12 hours. Both are directly toxic. How toxic the ammonia reading is depends on pH and temperature, so the same number can be harmless or lethal.

Now

Fish gasping at the surface with fast gill movement, or crowding the filter outflowIncrease surface movement now (gently in a betta or gourami tank, without creating a strong current), then test the water. Either the oxygen has crashed or the gills are being chemically burned. Both are hours-scale problems. Bettas, gouramis and corydoras rise to gulp air as part of normal breathing; the warning is constant gulping, fast gill movement, or the whole group hanging at the top.

Now

Sudden deaths, more than one fish in a dayTest ammonia, nitrite, nitrate and temperature before doing anything else. Do not add medication yet. Multiple simultaneous deaths usually point at the water or the equipment rather than a pathogen, so rule those out first.

Now

Today

Flashing: repeatedly scraping against decor or substrateTest the water, then look closely for parasites. Irritation is either chemical or parasitic; the test tells you which before you medicate.

Today

White salt-grain spots over the body and finsBegin the appropriate treatment today and check the temperature. The parasite's life cycle is temperature-driven, and it multiplies with every cycle you wait.

Today

Soon

Clamped fins, hiding, or refusing food for more than two daysTest the water and review recent changes. Usually the earliest visible sign of a parameter drifting.

A few days

Never add a new fish to a tank that is not fully cycled, and never treat blind. A test kit is cheaper than the fish.

This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it, and the time to find one is before you need one.

Bedding and substrate

3 safe, 4 with a caveat, 2 to avoid

Substrate in an aquarium is a filter as much as a floor. Most of the biology lives in and on it.

Safe

Fine, smooth sandCorrect for corydoras, kuhli loaches, eartheaters such as rams and acaras, and anything else that sifts or burrows. Barbels wear away on sharp gravel.

safe

Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras)Rinse thoroughly before use. Grain size should be too large to swallow and too small to trap food. Kuhli loaches need sand to burrow into and rams and acaras sift mouthfuls of it; bronze and panda corydoras manage on smooth fine gravel, but sterbai corydoras need sand.

safe

Bare bottom (quarantine and grow-out only)Legitimate for quarantine and grow-out tanks. Easy to clean, but it holds far less biological filtration, and it is no long-term home for burrowing loaches or sand-sifters.

safe

With a caveat

Crushed coral or aragoniteDeliberately raises hardness and pH. Correct for rift-lake cichlids, wrong for soft-water species.

with a caveat

Aquasoil for planted tanksExcellent for plants, but most active soils soften the water and pull pH and KH down for months, and many leach ammonia for the first weeks. Right for soft-water species; wrong for hard-water animals (livebearers, rainbowfish, goldfish, and snails, whose shells erode in soft, acidic water) unless you test GH and KH and remineralise. Cycle around it; do not stock into it.

with a caveat

Very deep sand bedsAnaerobic pockets form below about 2 inches in still sand. Either keep it shallow or keep it stirred.

with a caveat

Painted or coated gravelUsually fine, but coatings chip. Test a handful in a jar for a week first.

with a caveat

Never

Sharp or angular gravel with bottom-dwellersWears down barbels and leads to infection in corydoras and loaches.

never

Anything containing metal, limestone of unknown origin, or shells in a soft-water tankSlowly alters chemistry in ways that are hard to diagnose later.

never

This is our general list for freshwater fish. We have not built one specific to Rasboras yet.

Top resources for more info

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