The chili rasbora — also called the mosquito rasbora — is one of the most visually striking nano fish in the freshwater hobby. Despite reaching barely ¾ of an inch, a school of 15–20 chili rasboras moving through a blackwater planted tank is a genuinely breathtaking sight: vivid red bodies flickering in synchronized movement through amber-tinted water and dense moss. They are peaceful, long-lived, and uniquely suited to the blackwater planted aquarium aesthetic.
Taxonomy & Classification
The chili rasbora belongs to the genus Boraras — a group of micro-rasboras separated from the larger Rasbora genus in 1993. The genus name is a reverse anagram of Rasbora. Boraras brigittae is one of the smallest aquarium fish available and one of the most strikingly colored nano fish in the freshwater hobby.
| Rank | Classification |
|---|---|
| Kingdom | Animalia |
| Phylum | Chordata |
| Class | Actinopterygii |
| Order | Cypriniformes |
| Family | Cyprinidae |
| Genus | Boraras |
| Species | B. brigittae |
Natural Habitat
Chili rasboras are native to the blackwater peat swamp forests of southwestern Borneo. Their natural habitat is among the most extreme freshwater environments on earth:
- Blackwater: water stained dark amber-brown by tannins from decomposing peat and leaf litter
- Extremely acidic: pH as low as 3.5–4.5 in wild habitats
- Very soft water: near-zero mineral content (GH under 2 dGH)
- Warm but variable temperature: 75–82°F in the rainy season, cooler in dry season
- Dense shade: forest canopy blocks most light; fish are adapted to low light
Water Requirements
| Parameter | Wild Preference | Aquarium Range |
|---|---|---|
| Temperature | 75–82°F (24–28°C) | 68–82°F (20–28°C) |
| pH | 3.5–5.0 (wild) | 4.0–7.0 (captive-bred tolerate up to 7) |
| Hardness (GH) | <1 dGH | 1–6 dGH |
| Ammonia | 0 ppm | 0 ppm |
| Nitrite | 0 ppm | 0 ppm |
| Nitrate | Near zero | <10 ppm |
Tank Setup
A 5-gallon nano tank can house a school of 8–10 chili rasboras, though a 10-gallon allows a more impressive group of 15–20. Ideal setup:
- Blackwater aesthetics: dark substrate (black sand), Indian almond leaves, spider wood, and tannin-releasing botanicals
- Dense planting: Java moss, Anubias nana petite, mini Bucephalandra — low-light plants suited to soft water
- Floating plants: Salvinia, Frogbit, or duckweed to diffuse light and mimic the dense Bornean canopy
- Gentle flow: sponge filter only; chili rasboras are easily overwhelmed by strong current
- Dark background: black or natural dark background; enhances coloration and reduces skittishness
Schooling & Behavior
Chili rasboras are schooling fish that feel insecure in small numbers. A minimum of 8–10 fish is recommended; larger schools of 15–20 produce much bolder behavior and more vivid group swimming displays. In small groups they become shy and tend to hide.
In a well-planted blackwater tank with a large school, chili rasboras display remarkable color — the red body intensifies and the black lateral stripe becomes sharply defined. Males in breeding condition show the most vivid coloration and will display to females by flaring their fins.
Diet & Feeding
Chili rasboras are micro-predators in the wild, eating tiny zooplankton, small insects, and insect larvae. Their small mouths require appropriately sized food:
- Staple: micro-pellets specifically formulated for nano fish (Hikari Micro Pellets, Sera Micron), or very finely crushed flake
- Best condition food: micro worms, baby brine shrimp (newly hatched), Walter worms, infusoria
- Frozen: cyclops (small enough), daphnia (small), baby brine shrimp
- Avoid: standard-size pellets or flake — chili rasboras cannot eat food larger than about 0.5mm
Compatible Tank Mates
Chili rasboras are peaceful and fragile — tank mates must be chosen carefully to avoid predation or competition. Good companions include:
- Other micro-rasboras (Boraras species)
- Pygmy corydoras (Corydoras pygmaeus, C. habrosus)
- Ember tetras (similar size and temperament)
- Small shrimp — Neocaridina (cherry shrimp), caridina; juvenile shrimp may occasionally be eaten
- Otocinclus (peaceful algae cleaners)
- Betta fish (only in larger tanks with careful observation; individual temperaments vary)
Avoid: Any fish large enough to swallow them (most tetras over 1.5 inches, gouramis, cichlids), aggressive species, or fast feeders that will outcompete them for food.
Common Health Issues
- Velvet (Oodinium) — extremely common in chili rasboras; appears as golden-dust coating; treat with copper-based medication in a hospital tank; remove invertebrates first
- Ich — white spots; temperature increase to 82°F plus medication
- Bacterial infection — usually from water quality issues; maintain pristine soft-water conditions
- Wasting / failure to thrive — often caused by feeding adult-size food they cannot eat; ensure food is appropriately micro-sized
This species profile was reviewed for biological accuracy and practical aquarium care guidance by the FishCare AI editorial team.