Chili rasbora

Quick facts

Adult size

2 cm

Lifespan

can live up to 5 years; captive average is 2-3 in soft acidic conditions

Tank zone

mid

Temperament

peaceful

Difficulty

intermediate

Schooling

recommended 8+ (critical minimum 6, thrives at 12+)

Typically wild-caught

yes - acclimate slowly

Water parameters

Temperature

24–28°C

pH

4.5 to 7.0

Hardness

1 to 8 dGH

Tank requirements

Minimum volume

40 L

Minimum length

45 cm

Flow

low

Lighting

dim preferred

Substrate

any

Driftwood

preferred

Hiding spots

needed

Feeding

Diet: omnivore, feeds primarily at the mid.

Very small mouths. Standard fish food particles are too large. Micro pellets, crushed flake (crushed fine), frozen baby brine shrimp, frozen cyclops, live vinegar eels, live microworms, and live baby brine shrimp are the appropriate foods. They pick small food items from the water column; they rarely eat off the substrate. Feed two to three times daily in very small amounts. In established planted tanks, they supplement their diet by grazing on biofilm and microorganisms that grow on plant surfaces and hardscape. Live food brings out the most intense coloring.

Compatibility

• Nano fish that looks like a smaller, redder version of the celestial pearl danio's schooling partner. Tiny and timid. Any fish large enough to eat them is a threat, and that threshold is very low: anything with a mouth wider than 1 cm.
• Best with other nano species: ember tetras, pygmy corys, celestial pearl danios, otocinclus, and shrimp. Cherry shrimp are classic companions and the two species ignore each other completely.
• Groups of 15+ are ideal. In smaller groups they huddle in the corners and don't show their coloring. In large groups they disperse through the tank and the males display bright red constantly.
• A planted nano tank (20–40 L) with chili rasboras, moss, and shrimp is one of the most rewarding small setups in the hobby. Low cost, low maintenance, high visual impact.

Habitat

Native to blackwater peat swamp forests in Borneo (Kalimantan, Indonesia). The wild habitat is shallow, tannin-stained water with almost zero hardness, pH below 5.0, and dense accumulations of leaf litter and submerged roots. The water is the color of strong tea. This is an extreme soft-water specialist in the wild, though tank-bred specimens adapt to a broader range (pH 5.0-7.0). The species was described in 1903 as Rasbora brigittae, named after the collector Dieter Vogt's wife Brigitte (hence the other common name, Brigitte rasbora). It was moved to the genus Boraras when that genus was erected for the miniature members of the rasbora group. Adult size is only 1.5–2 cm, making it one of the smallest fish available to hobbyists. Males are bright crimson-red with a dark lateral stripe; females are duller orange-pink. The red coloring intensifies in soft, acidic water with tannins, and washes out in hard, alkaline water under bright lighting. Wild-caught specimens are still common in the trade, especially from Borneo, but tank-bred fish are increasingly available.

Breeding

Continuous spawner that drops a few eggs daily among moss and fine-leaved plants. The eggs are tiny and transparent. Adults eat eggs they find, so dense plant cover (moss mats, moss carpets, clumps of fissidens or Java moss) is essential for any fry to survive. In a species-only nano tank with thick moss, fry appear spontaneously without the keeper doing anything special. Dedicated breeding is more hands-on: place a conditioned pair in a small tank with a clump of moss, then remove the adults after 2-3 days and let the eggs hatch in place. Fry are nearly microscopic at hatching and need infusoria or paramecium for the first 5-7 days. Vinegar eels are the most practical first food because they stay suspended in the water column and survive long enough for the fry to find them. Growth is slow; 3-4 months to reach juvenile size. Sexing is reliable once the fish are mature: males are red, females are orange-pink.

Common problems

Washed-out coloring is the most common complaint. Chili rasboras kept in hard, alkaline water under bright LED lighting look pale orange instead of the crimson red shown in photos. The fix: soft water (GH below 8), tannins (Indian almond leaves or alder cones), subdued lighting, and dark substrate. This transforms the fish. Internal parasites are common in wild-caught specimens, causing wasting and thin body condition. Treat with levamisole. The tiny body size makes them vulnerable to parameter swings that larger fish would shrug off. Small water volume tanks (under 20 L) are harder to keep stable, which is ironic because that's the tank size most commonly used for nano fish. A 30–40 L tank is more forgiving. Lifespan is 4-6 years with proper care, which is longer than most keepers expect from such a small fish.

Bioload

Bioload coefficient: 0.3 (tiniest species so far; size formula compresses too aggressively, floor-lifted to 30% of a neon).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size