Chilli Rasbora – Boraras spp.

Among the smallest aquarium fish in the hobby, the tiny chilli rasboras of the Boraras group have earned a special place in the hearts of aquarists. Their intense red colour, peaceful behaviour and interesting schooling habits make them perfect residents for planted nano aquariums. Although delicate in appearance, they are hardy if kept under the right conditions and bring life and movement even to the smallest tanks.

Meet the Chilli Rasbora – Boraras spp. and Their Relatives

The name “chilli rasbora” usually refers to Boraras brigittae, but aquarists often use it loosely for several tiny rasboras from the genus Boraras. All of them are diminutive cyprinids originating from Southeast Asia, inhabiting soft, acidic, slow-moving blackwater streams, peat swamps and flooded forest areas rich in leaf litter and decaying organic matter.

The most commonly seen species in aquariums include:

• Boraras brigittae – “true” chilli rasbora, intense red body with a dark lateral stripe and spots.
• Boraras merah – similar to brigittae, often a bit more orange-red, with subtle pattern differences.
• Boraras urophthalmoides – exclamation point rasbora, with a distinctive “!” mark along the side.
• Boraras maculatus – dwarf rasbora, with several dark spots on the body.
• Boraras naevus – strawberry rasbora, with a deep red tone and darker patches.

All Boraras share some key traits: a very small adult size (around 1.5–2 cm), slender bodies, large eyes relative to body size and a preference for calm water with subdued lighting. These fish are often labelled as “nano” species, ideal for carefully planned small aquariums. Despite their size, they display complex social behaviour and are best appreciated in groups of at least 10–20 individuals.

In their natural biotopes, Boraras live among roots, fallen branches, dense marginal plants and piles of leaves. The water tends to be stained brown by tannins, with low hardness and a pH often below 6.0. Regular exposure to such environments has shaped their evolution: they have adapted to low light, low mineral content and low conductivity, and they rely heavily on visual communication through body posture and colour intensity.

Ideal Aquarium Setup for Chilli Rasboras

Because of their tiny size, chilli rasboras are often associated with nano aquariums. While they can indeed thrive in small tanks, their active schooling behaviour and sensitivity to unstable water parameters mean that planning and equipment selection are crucial. A larger volume also provides a bigger safety margin for beginners.

At MB Store you will find a wide range of aquariums and aquarium equipment suitable for designing an optimal environment for Boraras. From compact nano tanks to larger planted layouts, and from reliable filters to controllable lighting systems, you can choose a setup tailored precisely to the needs of these delicate fish.

Tank size and layout

For a group of 10–15 chilli rasboras, a 25–30 litre tank is a reasonable minimum. If you want to keep a larger school or add compatible species, consider 40 litres or more. Although Boraras take up very little physical space, they benefit greatly from horizontal swimming room and numerous hiding spots.

• Choose a tank with a decent footprint (length and width) rather than only height.
• Use dark substrate to bring out their colours and make them feel secure.
• Provide dense planting with fine-leaved stems, mosses and floating plants.
• Add roots and branches to mimic forest stream environments.
• Include leaf litter or botanical elements if you like the blackwater look.

Aquascaping styles such as nature aquariums, jungle layouts and blackwater biotopes are especially appropriate. Floating plants like Salvinia, frogbit or water lettuce will soften the lighting, spread the fish’s confidence and encourage more natural behaviour.

Water parameters

Chilli rasboras are most comfortable in soft, slightly acidic water that mimics their natural habitat. However, most aquarium-bred individuals can adapt to a wider range, provided that stability is maintained.

• Temperature: 23–27 °C
• pH: 5.0–7.0 (ideally around 6.0–6.8 in community setups)
• General hardness (GH): 1–8 °dGH
• Carbonate hardness (KH): as low as possible, typically 0–4 °dKH

If your tap water is hard or alkaline, you might need to blend it with reverse osmosis (RO) water, use peat filtration or botanicals such as Indian almond leaves and alder cones to gently acidify and soften it. MB Store offers filters and media that help you shape and maintain such specific conditions with greater precision.

Regardless of the exact values, avoid rapid swings in temperature, pH and hardness. These small fish have a low body mass and can be easily stressed by abrupt changes, leading to weakened immune systems and susceptibility to disease.

Filtration and water flow

Boraras inhabit slow-flowing waters, therefore they prefer gentle currents. The filtration system must provide efficient biological filtration without creating a strong stream that pushes them around the tank.

• Use sponge filters, small hang-on-back filters or gentle internal filters.
• Direct the outflow towards the back glass or use spray bars to diffuse flow.
• Cover filter inlets with sponges to prevent tiny fish from being sucked in.

An oversized, high-quality filter run at reduced flow is often better than an underpowered unit. MB Store stocks a variety of filter models, sponges and accessories that can be combined to create a safe and quiet filtration system for nano fish.

Lighting and decor

Chilli rasboras display their richest red colour under moderate, diffused lighting. Very bright, unshielded light can make them shy and pale. Using adjustable LED lights, dimmer controls and floating plants allows you to find the perfect balance between plant growth and fish comfort.

Dark or natural-coloured backgrounds and substrates enhance the visual contrast of the fish. Fine-leaved plants like Myriophyllum, Rotala, Limnophila or various mosses provide excellent cover and resting spots. Hardscape elements should avoid sharp edges, since these fish may dart between branches when startled.

Water Quality, Maintenance and Care

Because chilli rasboras are small and lightly stocked in well-planted tanks, many aquarists assume that maintenance can be minimal. In reality, pristine water quality is vital. Their small size means that toxins like ammonia and nitrite affect them quickly, and chronic exposure to low-level nitrate or pollution can reduce lifespan and colour intensity.

Cycling the aquarium

Before adding any Boraras, ensure that the aquarium is fully cycled. Beneficial bacteria must be established in the filter and substrate to process fish waste efficiently. This biological filtration transforms toxic ammonia into nitrite and then into relatively safer nitrate.

• Run the aquarium with filter and plants for several weeks before adding fish.
• Use a liquid test kit to monitor ammonia, nitrite and nitrate levels.
• Introduce the fish slowly, in small groups, to avoid overloading the system.

MB Store can equip you with test kits, conditioners and bacterial supplements to make the cycling process safer and more predictable.

Regular maintenance

Once the tank is established, perform consistent, gentle maintenance instead of rare, drastic interventions. Boraras dislike abrupt changes; frequent small adjustments are better than infrequent large ones.

• Weekly water changes of 20–30% are ideal for stable conditions.
• Use a fine siphon to clean debris from open areas of the substrate.
• Avoid deep-cleaning planted areas where roots and beneficial bacteria reside.
• Rinse filter sponges in removed tank water, not under tap water.

Always match the temperature and approximate chemistry of new water to that of the aquarium. Pour it in slowly or use a drip method for very sensitive setups. Chilli rasboras will thank you with vibrant colours and confident behaviour.

Signs of stress and health issues

Monitoring behaviour and appearance is essential with such small fish. Because they cannot display obvious physical symptoms as clearly as larger species, subtle changes become important warning signs.

• Clamped fins, hiding constantly or swimming near the surface may indicate poor water quality or unsuitable parameters.
• Pale colours and lack of appetite can result from chronic stress or disease.
• White spots, frayed fins or unusual marks require immediate investigation.

Quarantine new fish whenever possible, especially if you plan to mix Boraras with other species. A small dedicated quarantine tank prevents the spread of external parasites, bacterial infections or internal worms. MB Store offers smaller aquariums and simple sponge filters that work perfectly as quarantine or hospital tanks.

Feeding Chilli Rasboras: Diet and Nutrition

The tiny mouth of a chilli rasbora strongly determines its diet. In nature, Boraras feed primarily on micro invertebrates, zooplankton, insect larvae and other small organisms floating in the water column or grazing on surfaces. In the aquarium they accept a variety of prepared foods, but they thrive when offered live and frozen items that match their feeding habits.

Dry food options

Choose high-quality micro pellets, nano granules or powdered foods designed for small fish. Regular flake food is usually too large unless finely crushed. When feeding dry food, pay attention to the following:

• Select foods rich in protein and carotenoids to enhance red coloration.
• Offer small quantities several times a day instead of one large feeding.
• Ensure that leftovers do not accumulate and decompose in the tank.

Live and frozen food

To fully display their natural colours and vitality, chilli rasboras should regularly receive live or frozen micro foods. These also stimulate natural hunting behaviours and help condition the fish for breeding.

• Newly hatched brine shrimp (Artemia nauplii) – excellent growth food for juveniles.
• Microworms and vinegar eels – suitable for very small individuals.
• Daphnia and Moina – provide variety and mild laxative effects.
• Frozen cyclops, rotifers and fine bloodworm – convenient and nutritious.

When using live food, make sure the source is clean and reliable, to avoid introducing parasites or pathogens. Frozen food should be thawed in a small amount of aquarium water and offered in moderation to prevent overfeeding.

Feeding routine and observation

Chilli rasboras are active feeders, but their stomachs are tiny. It is better to feed very small portions two to three times daily. Observe how much the school consumes within a minute or two; any food falling to the bottom untouched should be reduced next time.

Healthy Boraras respond quickly to food, darting about in short bursts and showing good colour. A fish that consistently ignores food or lags behind the group may be ill, bullied or suffering from unsuitable conditions.

Social Behaviour, Tank Mates and Community Setups

Despite their miniature size, chilli rasboras are very social. They are classic schooling fish and feel safest when surrounded by conspecifics. In small groups, individuals may hide more, display washed-out colours or show timid behaviour; in larger schools they become confident and dynamic.

Group size and behaviour

A minimum of 10 individuals is recommended, but groups of 20 or more look spectacular and help to disperse any aggression or competition. Boraras do not form strict hierarchies, yet males may occasionally display to one another, spreading their fins and intensifying colour in short, harmless confrontations.

Well-kept chilli rasboras spend their time exploring the mid and upper water layers, often forming loose shoals that tighten when they feel threatened. Under dim lighting and in heavily planted tanks they sometimes move more individually, weaving between stems and leaves with delicate, fluttering fin movements.

Suitable tank mates

Choosing compatible neighbours is crucial. Many larger or more boisterous fish see Boraras either as food or as targets of harassment. Ideal companions share similar parameter requirements, peaceful behaviour and small body size.

• Other tiny rasboras and microdanios (if fully peaceful and not overly fast).
• Small, peaceful shrimp like Neocaridina and Caridina, provided there are enough hiding places for shrimplets.
• Small, calm bottom dwellers such as pygmy Corydoras or small Otocinclus species.
• Snails like Neritina or small ramshorn snails for algae control and cleanup.

Keep in mind that even peaceful, larger species can cause stress simply by their size and speed. For truly natural behaviour, many aquarists prefer dedicated Boraras tanks or communities composed entirely of similarly sized nano fish.

Tank mates to avoid

Some species are clearly incompatible with chilli rasboras, including:

• Medium to large tetras, barbs, cichlids and gouramis that might see them as prey.
• Fin-nippers like some barbs or larger danios, which can damage delicate fins.
• Very active fish that create constant movement and stress.

Also use caution with predatory invertebrates. Certain larger shrimp species and crayfish may hunt or injure Boraras, especially at night. When in doubt, select the most peaceful species and provide dense plant cover so that the rasboras can retreat.

Breeding Chilli Rasboras in the Home Aquarium

Breeding Boraras in captivity is certainly possible, although they do not always reproduce spontaneously in community tanks due to egg predation. For dedicated breeders, setting up a separate spawning tank significantly increases success. Observing the entire process from courtship to free-swimming fry is very rewarding and provides insight into their delicate life cycle.

Sexing and conditioning

Adult males are usually slimmer and more intensely coloured, with deeper reds and more pronounced body markings. Females are slightly larger and rounder, especially when carrying eggs. To prepare the fish for breeding, feed them high-quality live and frozen foods several times a day, while maintaining impeccable water conditions.

Spawning tank setup

A small aquarium of 10–20 litres is sufficient for a breeding group. Use soft, acidic water with gentle filtration via a sponge filter. Add fine-leaved plants like Java moss, Najas or spawning mops where the eggs can fall and remain hidden. Many breeders prefer bare-bottom tanks for easier cleaning, with plants attached to small stones or mesh.

Introduce one or two well-conditioned pairs, or a small group with a male bias. Keep the lighting subdued to reduce stress. Some breeders place a mesh or grid above the bottom so that eggs can fall through and remain out of reach of hungry parents.

Spawning behaviour and egg care

Chilli rasboras are scatter spawners: they do not protect their eggs or provide parental care. During courtship, males intensify their colour and chase females, nudging them toward plants or spawning mops. Eggs and sperm are released almost simultaneously, and the tiny, transparent eggs fall among the vegetation or to the bottom.

To maximize survival, remove the adults soon after spawning is observed, or after a day or two in a breeding setup. The eggs typically hatch within 24–48 hours, depending on temperature. The fry are extremely small and sensitive, requiring gentle aeration and perfectly clean water free of harmful bacteria and pollutants.

Raising the fry

Newly hatched Boraras fry absorb their yolk sacs for a couple of days before becoming free-swimming. At that point they require microscopic food. Suitable first foods include:

• Infusoria cultures prepared from vegetable matter in aged water.
• Commercial liquid fry foods for egg-laying fish.
• Paramecium and other cultured protozoa.

After about a week, when fry have grown slightly, you can introduce vinegar eels and microworms, followed by newly hatched brine shrimp as their mouths enlarge. Keep water changes small yet frequent, using airline tubing to avoid sucking up fry. With patience and attention, many will grow into healthy juveniles ready to join the main group.

Why Chilli Rasboras Are Perfect for Planted and Nano Aquariums

Beyond their biological and behavioural traits, Boraras species hold a unique aesthetic value. Their tiny, bright bodies weaving through stems and over dark substrates create a vivid contrast in aquascapes. They are popular among aquascapers and planted tank enthusiasts seeking a subtle, naturalistic fish that does not dominate the scene but enhances it.

Visual impact in aquascapes

In heavily planted tanks, the deep red colour of chilli rasboras stands out against green foliage and mosses. They form soft, dynamic patterns as they move together, complementing rather than overshadowing the layout. Their small size allows aquascapers to maintain the illusion of a larger landscape: plants and hardscape appear more massive when compared to such tiny fish.

Because they do not uproot plants or disturb the substrate, Boraras are ideal residents for delicate layouts with fine carpeting plants like Hemianthus callitrichoides (HC) or Monte Carlo. They generate minimal waste compared to larger fish, which helps maintain water clarity and algae control if regular maintenance is performed.

Suitability for nano tanks

Not every aquarist has the space or desire for large aquariums. Chilli rasboras make the dream of an attractive, thriving nano aquarium realistic, as long as their environmental and social needs are respected. A carefully equipped 20–30 litre tank can host a stunning planted scape with a colourful Boraras school, shrimp and perhaps a few small snails.

MB Store supports such projects by offering a wide choice of compact aquariums, efficient nano filters, subtle lighting solutions and CO₂ systems appropriate even for smaller volumes. Combining the right hardware with thoughtful planning gives you a stable, healthy environment where Boraras can display their full potential.

Responsible fishkeeping and enjoyment

Although chilli rasboras are not particularly demanding once their basic requirements are understood, they should not be treated as decorative objects. Responsible fishkeeping means planning ahead, researching, and ensuring that the animals’ welfare is always the priority.

By providing soft, clean water, gentle filtration, varied nutrition and enough companions of their own kind, you will see these miniature fish in their most natural state: active, colourful, curious and completely at ease. Observing a thriving school of Boraras gliding through a lush underwater forest is one of the most rewarding experiences in the aquarium hobby.

FAQ – Chilli Rasbora (Boraras spp.)

How many chilli rasboras should I keep together?
Keep at least 10 chilli rasboras, but 15–20 is even better. They are schooling fish and feel secure in larger groups, which reduces stress and encourages natural behaviour. In bigger schools, colours intensify, and you will see more coordinated swimming and gentle social displays among males.

Can chilli rasboras live in a community tank?
Yes, they can, but tank mates must be peaceful and small. Avoid large or aggressive species that may see them as food or intimidate them. Ideal companions include dwarf shrimp, small peaceful bottom dwellers and other nano fish with similar water requirements, plus dense plant cover for shelter.

Are chilli rasboras suitable for beginners?
They can be suitable for careful beginners who are willing to learn. The key is providing a fully cycled aquarium, stable soft to moderately hard water, gentle filtration and regular maintenance. Their small size makes them vulnerable to mistakes, so patience and research are essential before purchase.

What should I feed my chilli rasboras?
Offer a mix of high-quality micro pellets or crushed flakes and small live or frozen foods. Newly hatched brine shrimp, daphnia, cyclops and microworms are excellent choices. Feed tiny portions two or three times daily, ensuring all food is eaten quickly to avoid polluting the water.

Do I need a heater and filter for a chilli rasbora tank?
A heater and filter are strongly recommended. Chilli rasboras prefer stable temperatures around 23–27 °C, which a heater provides. A gentle filter maintains water quality and oxygen levels. Choose a model with adjustable flow or use a sponge filter to avoid strong currents that might stress the fish.