Freshwater Fish

Chili Rasbora

Boraras brigittae

Chilli-red speck from Borneo's peat swamps · Intermediate

Lifespan: 4-8 years
Adult size: 1.5-2 cm / 0.6-0.8 in
Min. habitat: Aquarium 20L+ / 5gal+ (mature, planted), heated and filtered; 40L / 10gal easier
Social needs: Shoaler; keep 10+ together
Diet: Micro-predator; micro pellets, live and frozen micro-foods
Time: Low-moderate; daily feeding, weekly water change
Cost: Low-Medium

Overview

The chili rasbora is a miniature 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 1.5 to 2 centimetres fully grown it is among the smallest fish in this guide, noticeably tinier than 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.

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.

Keep a shoal of ten or more in a mature, densely planted aquarium of at least 20 litres (5 gallons), with 40 litres (10 gallons) giving far more stable water and room for a larger group.
Heat the tank to 24-28C (75-82F) 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.

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 few litres 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.

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.

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 two-centimetre body leaves no margin once illness takes hold.

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.

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 3 centimetres, the chilis belong in a different tank.