Chili rasbora

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Typically wild-caught; acclimate slowly.

Feeding

Mouth is genuinely tiny, so food size matters. Standard flake and pellet products are usually too coarse and most of the food goes uneaten. Use micro pellets, finely crushed flake, frozen baby brine shrimp, frozen cyclops, and live food (microworms, vinegar eels, baby brine shrimp) in small frequent portions. Live food in particular triggers the strongest feeding response and the most intense colour. The fish picks food out of the upper and middle water column and rarely feeds off the substrate. In a mature planted tank, the school supplements its diet by grazing on biofilm and microorganisms growing on moss, leaves, and hardscape. Feed two or three small times daily; underfeeding is a more common problem than overfeeding because the fish is easy to overlook.

Compatibility

• A nano species at the small end of the small end: 1 to 2 cm adult body, occasionally up to 3 cm. Anything in the tank with a mouth wider than the fish's body is a potential predator
• Best with other nano species: ember tetras, celestial pearl danios, pygmy corys, otocinclus, dwarf shrimp, scarlet badis, sparkling gourami. Cherry shrimp pair particularly well and the two species ignore each other
• Groups of 12 or more produce a real schooling display; smaller groups (under 8) tend to hide in corners and stay washed out. The fish disperses through the tank with dominant males flashing red as they spar
• Heavily planted, dimly lit, blackwater-leaning setup brings out the natural colour. Hard alkaline water with bright lighting works for survival but the fish never looks like its photos under those conditions
• Mixed Boraras setups (B. brigittae with B. urophthalmoides, B. maculatus, or B. merah) form natural multi-species shoals that share the same water requirements and don't compete or fight

Origin and habitat

A miniature cyprinid endemic to the peat-swamp landscapes of southwestern Borneo, Indonesia, across the Indonesian provinces of West, Central, and South Kalimantan. The type locality is Bandjarmasin (now spelled Banjarmasin), a port city in South Kalimantan from which Dieter Vogt collected specimens for his 1978 description in the German aquarium magazine Aquarien und Terrarien-Zeitschrift (DATZ 31(5):154-157), where he introduced the fish as Rasbora uropthalma brigittae and named the new subspecies after his wife Brigitte. The taxon was later elevated to full species rank as Rasbora brigittae, and then transferred to the new genus Boraras when Kottelat and Vidthayanon erected it in 1993 (Ichthyological Exploration of Freshwaters 4(2):161-176) to separate a group of miniature cyprinids from the larger Rasbora assemblage based on a different morphology and reproductive pattern. The genus name is a deliberate anagram of Rasbora, referencing a reversed ratio of abdominal to caudal vertebrae in these small species. Conway's 2005 paper in Ichthyological Exploration of Freshwaters (16(3):249-264) confirmed monophyly of the genus. Wild habitat is shallow, slow-flowing blackwater streams and pools inside ancient peat-swamp forests, where the water is stained tea-coloured by tannin and humic compounds from decaying leaf litter, extremely soft (negligible measurable hardness), and acidic with pH that can drop below 4.0. The fish lives among submerged branches, root systems, fallen leaves, and aquatic vegetation, in heavily shaded conditions under overhanging forest. The range covers the Jelai and Barito river basins and the intervening drainages, with an estimated extent of occurrence of 87,117 km2 per the 2020 IUCN assessment (Lumbantobing 2020). Adults reach 10 to 20 mm, with the largest known specimen recorded at 3.1 cm total length. Males are smaller, slimmer, and more intensely red, with the strongest crimson on the dorsal edge of the dark lateral stripe and on the dorsal and anal fins, and the colour peaks in breeding condition; dominant males show the deepest red. Females are slightly larger, plumper, and lighter in tone. Striped male individuals exist and there is some unresolved taxonomic discussion (Korner 2010, Kottelat 2013) about whether B. brigittae and the closely related B. merah may be the same species or two species with different colour-pattern ontogenies. IUCN lists the species as Data Deficient; peat-swamp forests across Southeast Asia have already declined by more than 60 percent, and oil-palm conversion and urbanisation continue to pressure the habitat. Trade fish are usually wild-caught.

Breeding

A continuous spawner that scatters a small number of eggs at intervals rather than producing one large clutch. Adults eat the eggs they find, so dense moss (Java moss, Christmas moss, Fissidens) or fine-leaved plants are essential cover. In a species-only nano tank with thick moss carpets and no predators, fry appear on their own without any direct intervention from the keeper. For higher yield, place a conditioned pair or trio in a small breeding container with mature soft acidic water and a clump of moss, leave the adults in for two or three days, then remove them and let the eggs hatch in place. The fish does not have a specific spawning trigger like cool water changes; conditioning on live and frozen food and consistently soft, slightly acidic water seems to be enough. Eggs are tiny and transparent and the fry are nearly microscopic at hatch; first food needs to be smaller than baby brine shrimp (infusoria, paramecium, green water, vinegar eels are all standard, with vinegar eels the most practical because they stay suspended in the water column). Growth is slow, with juveniles reaching adult body size in three to four months and full colour later. Sexing is reliable in mature fish: males show deep red on the dorsal stripe and fins, females are paler and rounder.

Common problems

Washed-out colour is the most common cosmetic complaint. Chili rasboras kept in hard, alkaline water with bright open lighting often appear pale orange-pink instead of the deep crimson the species is famous for. The fix is environmental rather than dietary: soft water, light tannin staining (Indian almond leaves, alder cones, or pre-cycled blackwater extract), dim or shaded lighting, dark substrate, and dense planting. Internal parasites are reasonably common in wild-caught stock, presenting as slow wasting with otherwise normal behaviour; levamisole is the standard treatment. The fish's tiny body makes it more vulnerable to parameter swings than larger species, and small tank volumes (under about 20 litres) are harder to keep stable than the 5-gallon recommendation in many care guides suggests; a 30 to 40 litre tank with mature filtration is far more forgiving. Mycobacterial infections occasionally appear in farm-bred or stressed wild stock and are essentially untreatable. With reasonable husbandry the species lives 3 to 5 years, longer than most keepers expect from a fish this small.

Bioload

Further reading

• Why your angelfish ate your neons
• Keeping shrimp with fish: what actually works