Chili Rasbora

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.

Housing

• 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.

Diet

• 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

• 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.

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.

• 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.

Is your enclosure big enough?

Check your own enclosure against this

Is this urgent?

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

Today

Soon

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.

What it really costs

Setup, monthly, first year and across a whole life, itemised and with the electricity worked out from the actual wattage. Published figures for the same animal disagree by a factor of four, so the calculator shows ranges rather than picking one.

Work out the cost of a chili rasbora