Chili Rasbora

The chili rasbora, Boraras brigittae, is one of the smallest freshwater fish commonly kept in home aquariums, rarely exceeding three-quarters of an inch in total length. It belongs to the family Cyprinidae within the Boraras genus, a group of miniature rasboras that gained serious popularity as nano fishkeeping took off. Despite its size, the chili rasbora displays striking coloration - a deep ruby red body accented by a dark lateral stripe that intensifies under proper care. It is sometimes sold as the mosquito rasbora, though that name more accurately applies to its close relative Boraras merah.

The appeal is genuine visual impact in a small package. Where many colorful fish demand large tanks and complex setups, the chili rasbora delivers in as little as five gallons. A settled school moving through a densely planted nano tank is one of the more rewarding sights in freshwater fishkeeping. Their color deepens over time in good conditions, and a confident group becomes far more visible and active than the shy, pale fish you brought home from the store.

Care difficulty sits in the intermediate range, and that deserves honesty. They are not difficult in terms of exotic chemistry, but they are small and sensitive enough that beginners still learning to hold stable parameters may struggle. Temperature swings and ammonia spikes that barely register with hardier species can be dangerous for a fish this size. Keepers who have run a stable planted tank for a few months will find them manageable.

A proper setup starts with five gallons minimum, though ten gives more stability and room for a proper school. They prefer soft, acidic water between 74 and 82 degrees Fahrenheit with a pH of 4.0 to 7.0, doing best toward the lower end. These are obligate schooling fish - keep at least eight, with twelve being noticeably better for both comfort and the visual display they produce.

Expect an adjustment period after bringing them home. New chili rasboras typically hide for the first several days, show pale coloration, and may refuse food initially. This is normal stress behavior, not a sign that something is wrong with the fish. A well-planted tank with dim lighting and no aggressive tankmates gives them the security they need to settle in. Most groups start showing confident behavior and improved color within two to three weeks.

Before buying, understand these are not community fish in the traditional sense. Their size means most common community species are too large or boisterous to share space safely. Pet stores sell them alongside much larger fish with vague assurances about peaceful temperament, but peaceful and compatible are different things when size differences are significant. Plan the tank around them rather than fitting them into an existing community.

The chili rasbora is native to southwestern Borneo, specifically the Kalimantan province of Indonesian Borneo. Its range is limited, and wild populations face real pressure from habitat destruction driven by palm oil agriculture and logging. The blackwater streams and peat swamp forests where this species lives are among the most threatened ecosystems in Southeast Asia, making captive breeding increasingly important.

In the wild, these fish inhabit slow-moving or still blackwater environments that look nothing like a typical aquarium. The water is stained deep brown by tannins from decomposing leaves and wood, often so dark that visibility drops to inches. Chemistry is extreme - extremely soft with almost no measurable hardness and highly acidic with pH frequently below 4.0. The substrate is fallen leaves, submerged roots, and soft organic sediment. Dense vegetation along the banks creates a complex maze of cover extending into the shallows.

The chili rasbora fills the role of micro-predator here, feeding on tiny invertebrates, zooplankton, and insect larvae among the leaf litter. Their small size makes them prey for virtually every larger fish and many aquatic insects, which explains the strong schooling instinct and preference for dense cover. That constant predation pressure is why they are naturally cautious fish that need time and a sense of security to settle into new surroundings.

They entered the aquarium trade in the early 2000s and quickly gained a following among planted tank enthusiasts. Most specimens today are still wild-caught from Borneo, though captive breeding has become increasingly successful among hobbyists. Wild-caught fish arrive pale from shipping stress and can take weeks of good care before displaying full color. No selectively bred morphs exist because the natural coloration of a healthy, settled specimen needs no improvement.

Understanding this origin directly improves your fishkeeping. Blackwater conditions explain why they thrive in soft, acidic water and look best with tannin sources like Indian almond leaves or driftwood. The dense vegetation of their habitat explains why they hide in sparse tanks and come alive in heavily planted ones. Working with the biology rather than against it is the difference between a stressed, faded fish and one showing the deep red this species is known for.

Minimum tank size is five gallons, and that is a genuine minimum with very little margin for error at that volume. Ten gallons is a significantly better choice - more stable parameters, room for a larger school of fifteen or more, and space for proper planting. Longer tanks work better than taller ones since these fish use horizontal space far more than vertical.

Target 74 to 82 degrees Fahrenheit, with 76 to 78 as the sweet spot. Size your heater at three to five watts per gallon. pH should fall between 4.0 and 7.0, with 5.5 to 6.5 producing the best color and behavior. General hardness of 1 to 5 dGH and carbonate hardness of 0 to 4 dKH are ideal. If your tap water is hard and alkaline, you will need remineralized reverse osmosis water or a similar soft water source. Forcing these fish into hard conditions results in chronic stress, faded color, and shortened lifespans.

Filtration should be gentle. A small sponge filter is the classic choice - solid biological filtration, minimal current, and no risk of pulling in tiny fish. If you prefer a hang-on-back or canister, cover the intake with a fine sponge prefilter. Keep flow low to moderate, matching the nearly still waters they evolved in. Oversizing filtration to the point of creating strong current does more harm than good in a small tank.

A dark, fine-grained substrate like aquasoil brings out the best color through contrast and naturally softens water over time. Avoid bright or coarse substrates. Adding dried leaf litter on top mimics their wild habitat and supports the microfauna these fish graze on between meals. The leaf litter also releases tannins that contribute to the soft, acidic conditions they prefer.

Live plants are not optional. Dense plantings of fine-leaved species like java moss, Christmas moss, or Rotala provide the cover they need to feel secure enough to school in the open. Floating plants are especially valuable for dimming light and creating the shaded areas chili rasboras prefer. Leave some open swimming space in front for viewing, but err toward more plants rather than fewer. A tank that looks overgrown to you looks like home to these fish.

Keep lighting moderate and suited to your plants rather than maxed out. A tight-fitting lid matters because startled fish in shallow tanks can jump. Indian almond leaves or driftwood releasing tannins stain the water slightly amber, replicating natural conditions and visibly calming the fish. Some keepers resist the tinted water aesthetic, but for this species it is doing real work for their comfort.

In the wild, chili rasboras feed on tiny invertebrates, zooplankton, and insect larvae among leaf litter. They are micropredators that hunt small live prey rather than grazing on algae. This means protein-rich foods of appropriate size, and size is the key challenge - their mouths are remarkably small even by nano fish standards, and food that seems tiny to you may still be too large.

The staple diet should be high-quality micro pellets or crushed flake food small enough for them to actually eat. Many keepers find that crushing standard flakes between their fingers produces better-sized particles than the flakes themselves. Micro pellets that slowly sink through the water column work well since these fish feed most comfortably in mid-water rather than competing at the surface.

Supplemental foods make a real difference in color and vitality. Live baby brine shrimp are arguably the best food you can offer, and watching the school hunt them through the plants is genuinely entertaining. Frozen daphnia, cyclops, and micro worms provide excellent variety. Vinegar eels and microworms are easy to culture at home for a consistent live food source at the right size. Offer these supplements two or three times weekly alongside the staple diet.

Feed small amounts once or twice daily - only what the school finishes in about two minutes. Overfeeding is serious in small tanks because uneaten food decays fast in low-volume environments with very little buffer. Better to slightly underfeed than risk fouling the water. A slightly hungry chili rasbora is a healthy one, and microfauna in a mature planted tank provides constant grazing opportunities between scheduled meals.

New arrivals may refuse food for the first few days as they settle in. Do not panic and do not dump extra food trying to tempt them. Offer small amounts of live baby brine shrimp or frozen daphnia, which are usually the first foods a stressed chili rasbora will accept. Once they start eating, you can introduce dry staple foods gradually.

Diet connects directly to color intensity with this species. Fish fed exclusively on dry foods often look noticeably duller than those getting regular live or frozen supplementation. Carotenoids in brine shrimp and daphnia directly contribute to the deep ruby red that makes these fish appealing. If your fish look washed out despite good water quality, the diet is the first place to investigate.

Chili rasboras are peaceful schooling fish that spend most of their time in the middle water column, drifting through planted areas and darting after microscopic food. They are diurnal and most active during daylight, settling into quieter positions as lights dim. A settled school shows relaxed, fluid coordination that is markedly different from the skittish hiding you see in the first days after bringing them home. Give them a couple of weeks in a well-planted tank and the transformation in confidence is remarkable.

Schooling is not optional with this species. Keep a minimum of eight, with twelve or more producing significantly better natural behavior, confidence, and color intensity. Groups under eight hide constantly and rarely show the display that makes them worth keeping. A lone chili rasbora will be chronically stressed no matter how perfect everything else is. Within the school, males flash their fins and intensify color at each other, but these displays are entirely harmless sparring that never escalates to contact or injury.

Aggression is nonexistent in any practical sense. The real concern runs the other direction - these fish are so small and peaceful that they are easily intimidated, outcompeted for food, and stressed by larger or more active tankmates. That vulnerability defines their entire compatibility profile and is the single most important factor in choosing what else goes in the tank.

Ideal companions are other very small, peaceful species. Pygmy corydoras, especially Corydoras pygmaeus and Corydoras habrosus, are excellent - small, peaceful, and bottom-dwelling so they occupy a completely different zone without competing for space or food. Other Boraras species share similar needs and temperament. Small neocaridina shrimp coexist peacefully and contribute to tank maintenance. Otocinclus can also work well as gentle algae grazers that ignore the rasboras entirely.

The avoid list is longer than the compatible list, and this is where pet store advice fails. Any fish that can fit a chili rasbora in its mouth is a predation risk, including many species considered peaceful community fish. Standard tetras, most barbs, gouramis, and small cichlids like rams are all too large and active for safe cohabitation. Bettas are commonly suggested and commonly end badly - even a calm betta can stress or prey on fish this small in the confined space of a nano tank. When in doubt about a potential tankmate, keep the tank species-only.

Breeding happens readily in mature tanks. Males intensify color when courting, females scatter eggs among fine-leaved plants over several days. No parental care exists, and adults eat eggs they find, so fry survival depends on dense plant cover providing hiding spots. The breeding behavior creates zero disruption to tankmates.

A well-kept chili rasbora lives four to six years, surprisingly long for such a small fish. Reaching the upper end requires stable water, appropriate diet, and minimal chronic stress. Fish in unstable conditions or with incompatible tankmates rarely make it past two years. Their small body mass means very little reserve when things go wrong - problems a larger fish tolerates for weeks become critical in days.

Common health issues relate to water quality and stress rather than species-specific disease. Ich appears most often, usually following temperature drops or stressful events. Fin rot shows up when water quality slips. Internal parasites concern primarily wild-caught fish that skipped quarantine. Their small size makes medicating tricky because standard dosing can be too strong, so prevention through good husbandry always beats treatment after the fact.

Healthy fish show deep, consistent red coloration with a clearly defined lateral stripe. Body slightly rounded without bloating, fins intact and open rather than clamped. Active during the day, swimming with the school, interested in food at feeding time. Faded color, clamped fins, isolation from the group, appetite loss, or surface gasping all signal that something in the tank needs attention and should not be ignored.

Prevention starts with water quality. Weekly changes of twenty to thirty percent keep nitrates low. Match replacement water to tank temperature and chemistry to avoid shocking the fish during maintenance. Quarantine all new additions - fish, shrimp, or plants - for at least two weeks before they go into an established tank. Stress reduction is a genuine health strategy here, not a luxury. Dense plants, subdued lighting, appropriate tankmates, and consistent routines support an immune system that handles common pathogens effectively.

When something goes wrong, these fish decline fast. A fish that looked fine yesterday can be visibly ill today, and waiting to see if it improves is riskier than with larger species. If multiple fish show symptoms simultaneously, test water immediately - ammonia, nitrite, pH shifts, or temperature swings are the usual culprits. Fix the water first and many symptoms resolve without medication. Individual fish showing disease while the rest remain healthy may point to a pathogen introduced by a recent addition.