Glowlight Rasbora

Quick summary

The Glowlight Rasbora is an easy, peaceful nano fish that’s great for beginners and planted community tanks, as long as you can keep a shoal of at least eight in a 45+ litre tank with soft, slightly acidic water. Breeding is rated moderate difficulty, requiring specific soft-water conditions to succeed.

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In this guide:

• Introduction
• Quick Stats
• Appearance
• Natural Habitat
• Tank Size and Setup
• Water Parameters
• Filtration and Equipment
• Diet and Feeding
• Behaviour and Temperament
• Tank Mates
• Breeding
• Common Diseases
• FAQs

Introduction

The Glowlight Rasbora (Trigonostigma hengeli) is one of the most elegant and understated nano fish available to freshwater aquarists. Often overshadowed by its more famous cousin, the Harlequin Rasbora, this diminutive species from Southeast Asia has steadily gained a devoted following among planted tank enthusiasts and community aquarium keepers alike. Its subtle beauty, a slender, translucent body adorned with a glowing neon-orange stripe, becomes truly mesmerising when a shoal moves together through a well-planted aquarium.

First described by the Dutch ichthyologist Meinken in 1956, this species hails from the peat swamps and slow-flowing streams of Borneo and Sumatra. Its scientific name honours the Dutch aquarist and collector D. Hengel, who played a key role in bringing the species to the attention of European ichthyologists. Despite its delicate appearance, the Glowlight Rasbora is a surprisingly hardy fish once established in a mature aquarium, making it an excellent choice for both beginners and experienced hobbyists who appreciate subtlety over flash.

In the aquarium trade, this species is sometimes confused with other small rasboras, but its distinctive combination of a dark triangular patch and a luminous orange-copper line above it sets it apart immediately. This guide covers everything you need to know to keep Glowlight Rasboras healthy, vibrant, and thriving in a home aquarium.

Appearance

The Glowlight Rasbora is a compact, laterally compressed fish that typically reaches a maximum length of around 3 to 3.5 centimetres in aquarium conditions. Its body is slender and somewhat translucent, with a pale silvery or pinkish-copper base colour that allows light to pass through it, lending it an almost ethereal quality in a well-lit tank.

The most striking feature is the dark wedge-shaped marking on the posterior half of the body, which is noticeably narrower and shorter than the bold triangular patch seen on the closely related Harlequin Rasbora (Trigonostigma heteromorpha). Sitting directly above this dark marking is a vivid, luminous stripe that ranges in colour from bright orange to coppery gold, depending on the light and the fish’s condition. It is this glowing line that gives the species its common name and makes it so visually appealing when viewed in a group. The intensity of this stripe serves as an excellent indicator of overall health and contentment; well-kept specimens in soft, acidic water with a dark substrate display a remarkably intense glow.

The fins are largely transparent with a faint yellowish or amber tint, particularly on the caudal and dorsal fins. Males tend to be slightly slimmer and more intensely coloured than females, while females are marginally deeper-bodied, especially when carrying eggs. The eyes are relatively large in proportion to the head, a common trait among small cyprinids, and often have a subtle golden or reddish reflective quality. Overall, the Glowlight Rasbora is a species whose beauty reveals itself gradually, it is far more impressive in person than photographs tend to suggest, especially when kept in a large, well-conditioned shoal.

Natural Habitat

In the wild, Trigonostigma hengeli inhabits the peat swamp forests and slow-moving blackwater streams of Borneo and Sumatra in Indonesia. These are highly distinctive environments characterised by extremely soft, acidic water that is stained a deep amber or tea-brown colour by the decomposition of vast quantities of fallen leaves, branches, and other organic matter. The water chemistry in these habitats is remarkable, with pH values often dropping below 5.0 and general hardness measuring close to zero.

The substrate in these environments is typically composed of deep layers of waterlogged leaf litter, fallen wood, and peat, creating a dimly lit, tannin-rich environment with very little aquatic vegetation. Instead, the overhanging canopy of the tropical rainforest provides shade, and roots, submerged branches, and leaf litter offer shelter and foraging opportunities. The water flow in these habitats is sluggish to almost still, and dissolved mineral content is extremely low.

These peat swamp forests are among the most threatened ecosystems in Southeast Asia, facing ongoing destruction from palm oil plantations, logging, and drainage for agriculture. Although the Glowlight Rasbora has not been formally assessed by the IUCN, the rapid loss of its native habitat is a cause for concern. Most specimens available in the aquarium trade are wild-caught, though captive breeding does occur on a limited scale. Understanding this natural habitat is key to providing optimal care in the aquarium, as it explains the species’ strong preference for soft, acidic water and subdued lighting.

Tank Size and Setup

A minimum tank size of 45 litres is recommended for a small group of Glowlight Rasboras, though a tank of 60 litres or more is preferable and allows for a more natural shoaling display. These are active swimmers that utilise the middle and upper portions of the water column, so a tank with a reasonable horizontal footprint is more important than height. A standard 60-centimetre aquarium works very well for a dedicated species tank or a small community setup.

When it comes to aquascaping, the goal should be to replicate the dim, tannin-rich conditions of the species’ natural blackwater habitat as closely as practical. A dark substrate, whether fine gravel, sand, or aquatic soil, will bring out the best colouration in these fish and help them feel secure. Driftwood and bogwood are excellent additions, as they not only create a natural aesthetic but also slowly release tannins into the water, softening it and lowering the pH over time. Adding dried Indian almond leaves (Terminalia catappa) or other botanical material to the substrate further enhances the blackwater effect and provides a natural food source in the form of the microbial biofilm that develops on decomposing leaves.

Live plants are not strictly necessary to mimic the species’ natural environment, but they are highly beneficial in the aquarium setting. Java Fern, Cryptocoryne species, and various mosses are all excellent choices, as they thrive in the low-to-moderate lighting conditions that suit Glowlight Rasboras. Floating plants such as Amazon Frogbit or Salvinia are particularly valuable, as they diffuse overhead light and create the dappled, shaded conditions that make these fish feel most at home. When the lighting is subdued and the tank is well-planted with plenty of cover, the Glowlight Rasbora will reward the keeper by spending more time in the open and displaying its most vivid colours.

Avoid overly bright, exposed setups with pale substrates, as these conditions will cause the fish to appear washed out and may lead to chronic stress. A gentle current is preferred over strong water movement, reflecting the still or slow-flowing waters of their native streams.

Water Parameters

Maintaining appropriate water chemistry is one of the most important aspects of Glowlight Rasbora care. While these fish are more adaptable than their blackwater origins might suggest, they are at their healthiest and most colourful when kept in soft, slightly acidic water. The table below outlines the ideal ranges for long-term maintenance.

A temperature of around 25–26 °C represents a comfortable midpoint for everyday keeping. A pH in the range of 5.5 to 6.5 is ideal, and those keeping the fish in harder, more alkaline water may notice duller colours and reduced vigour, though the fish will generally survive in moderately hard water up to around 10 dGH. For breeding, however, very soft and acidic conditions are essential.

Regular partial water changes of 20–25% weekly are strongly recommended to maintain low nitrate levels and stable water chemistry. If you are using tap water that is harder or more alkaline than the species prefers, mixing it with reverse-osmosis (RO) water or using peat filtration can help achieve more suitable parameters. Consistency is more important than hitting an exact number, so avoid making large, sudden adjustments to pH or hardness, as these can be more stressful than slightly suboptimal but stable conditions.

Filtration and Equipment

Glowlight Rasboras do not require powerful filtration, and in fact, excessively strong flow can cause stress in this species, which naturally inhabits near-still waters. A sponge filter is an excellent choice for smaller tanks, providing gentle biological and mechanical filtration without creating a strong current. For larger or more heavily stocked setups, a small hang-on-back filter or a canister filter with an adjustable flow rate or spray bar works well. If using a more powerful filter, directing the output against the glass or using a lily pipe can effectively diffuse the flow.

A heater with a thermostat is essential unless the room in which the tank is kept is consistently warm, as these tropical fish require stable temperatures within their preferred range. A heater rated appropriately for the tank volume, typically around one watt per litre, is sufficient. It is good practice to use a separate thermometer to verify the heater’s accuracy, as built-in thermostats can sometimes drift.

Lighting should be moderate to low. If you are growing live plants, a standard LED aquarium light on a timer set for 8–10 hours per day will be adequate, especially if floating plants are used to diffuse the output. Overly intense lighting without adequate shade will cause the fish to retreat and may wash out their colouration. If you are aiming for a blackwater aesthetic, warm-toned LED lights or those with adjustable colour temperatures can beautifully complement the amber tones of the water and the fish.

An air pump is not strictly necessary if adequate surface agitation is provided by the filter, but it can be beneficial in warmer conditions when dissolved oxygen levels may drop. As with all aquariums, a tight-fitting lid or cover is advisable, as small rasboras can occasionally jump, particularly when startled.

Diet and Feeding

Glowlight Rasboras are omnivorous micropredators that feed primarily on tiny invertebrates, zooplankton, worms, and insect larvae in the wild, supplemented by algae and organic detritus. In the aquarium, they are not fussy eaters and will readily accept a wide range of commercially available foods, provided the particle size is appropriately small for their tiny mouths.

A high-quality micro-pellet or crushed flake food should form the staple of their diet. Look for products with a high proportion of whole fish meal, insect meal, or crustacean-based ingredients rather than those padded with fillers and cereals. Supplementing this staple with regular offerings of live or frozen foods will noticeably enhance their colour, vitality, and willingness to breed. Daphnia, baby brine shrimp (Artemia nauplii), micro-worms, grindal worms, and cyclops are all eagerly consumed and provide essential proteins and fats that dry foods alone cannot fully replicate.

Feed small amounts once or twice daily, offering only as much as the fish can consume within two to three minutes. Overfeeding is a common mistake with small fish and can rapidly degrade water quality in modestly sized tanks. It is good practice to fast the fish for one day per week, which aids digestion and helps prevent issues associated with overfeeding. Variety is key to a balanced diet, so aim to rotate between two or three different food types over the course of a week.

Behaviour and Temperament

The Glowlight Rasbora is a peaceful, sociable species that is best kept in groups of at least eight to ten individuals, though larger shoals of fifteen or more are strongly recommended where space permits. In smaller groups, these fish tend to be shy, scatter when approached, and spend much of their time hiding among plants and decorations. In a sufficiently large group, however, they exhibit confident, cohesive shoaling behaviour that is one of the great pleasures of keeping this species. A large shoal moving in unison through a well-planted aquarium, their glowing orange stripes catching the light, is a genuinely captivating sight.

Within the group, there is very little aggression. Males may occasionally display to one another with flared fins and intensified colours, particularly in the presence of receptive females, but these interactions are brief and harmless. There is no nipping, chasing, or territorial behaviour of any consequence. This gentle disposition makes the Glowlight Rasbora an ideal inhabitant for peaceful community aquariums and planted tanks.

They primarily occupy the middle water column but will explore all levels of the tank when feeling secure. In dimly lit setups with plenty of cover, they tend to be more active and spend more time in open water. Conversely, in bright, sparsely decorated tanks, they may become reclusive and pale. Their activity levels increase noticeably at feeding time, and they are generally diurnal, being most active during daylight hours and resting quietly among plants or near the substrate at night.

Tank Mates

The Glowlight Rasbora’s diminutive size and gentle nature mean that tank mate selection requires some care. The ideal companions are similarly sized, peaceful species that share a preference for soft, acidic water and will not compete aggressively for food or territory. Avoid any fish large enough to view the Glowlight Rasbora as prey, and steer clear of boisterous, fast-moving species that may outcompete these delicate fish at feeding time or cause chronic stress through constant activity.

Good tank mates

• Harlequin Rasbora (Trigonostigma heteromorpha), a close relative with identical care requirements that mixes beautifully in a shared aquarium.
• Ember Tetra (Hyphessobrycon amandae), another tiny, peaceful species that thrives in soft, acidic water and complements the Glowlight Rasbora’s warm colour palette.
• Chili Rasbora (Boraras brigittae), a fellow Southeast Asian micro-rasbora with very similar water requirements and a non-competitive temperament.
• Pygmy Corydoras (Corydoras pygmaeus), a tiny, peaceful bottom-dweller that adds activity to a different zone of the tank without causing any disturbance.
• Otocinclus (Otocinclus vittatus), a gentle algae-eating catfish that stays small and poses no threat to small rasboras.
• Kuhli Loach (Pangio kuhlii), a reclusive, nocturnal bottom-dweller from similar Southeast Asian habitats that coexists peacefully.
• Celestial Pearl Danio (Danio margaritatus), a stunning nano fish that occupies a similar niche and thrives in comparable conditions.
• Chocolate Gourami (Sphaerichthys osphromenoides), a delicate blackwater species from the same geographic region, ideal for a biotope-style setup.
• Amano Shrimp (Caridina multidentata), Excellent algae-eating invertebrates that are too large to be eaten and entirely peaceful.
• Cherry Shrimp (Neocaridina davidi), a colourful dwarf shrimp that coexists well, though very small shrimplets may occasionally be eaten.

Fish to avoid

• Oscar (Astronotus ocellatus), a large, predatory cichlid that would immediately consume Glowlight Rasboras.
• Angelfish (Pterophyllum scalare), Adults are large enough to eat small rasboras and may do so, particularly at night.
• Tiger Barb (Puntigrus tetrazona), a boisterous, nippy species that would harass and outcompete these delicate fish.
• Red-Tail Black Shark (Epalzeorhynchos bicolor), a territorial and aggressive bottom-dweller that can dominate a tank and stress smaller species.
• Convict Cichlid (Amatitlania nigrofasciata), an aggressive, territorial cichlid entirely unsuitable for peaceful community tanks with nano fish.
• Green Terror (Andinoacara rivulatus), a large, aggressive South American cichlid that poses a direct predation risk.
• African Cichlids (various Mbuna species), Require hard, alkaline water and are far too aggressive for cohabitation with small rasboras.
• Betta (Betta splendens), while sometimes suggested as tank mates, individual bettas can be unpredictable, and their territorial nature may lead to fin-flaring, chasing, or attacks on small shoaling fish.

Breeding

Breeding Glowlight Rasboras in captivity is achievable but requires some preparation and attention to water chemistry. Like other members of the genus Trigonostigma, this species is an egg-scatterer that deposits adhesive eggs on the undersides of broad-leaved plants, a behaviour that sets it apart from many other small cyprinids, which typically scatter eggs freely among vegetation or substrate.

To condition potential breeding pairs, provide a varied diet rich in live and frozen foods for several weeks prior to any spawning attempt. This high-protein diet encourages egg development in females and increases the likelihood of spawning behaviour. Females in breeding condition will appear noticeably plumper when viewed from above, while males will intensify in colour and may begin displaying more frequently to females.

A dedicated breeding tank of around 20 to 30 litres is ideal. The water should be very soft, with a general hardness of 1–3 dGH, and acidic, with a pH of 5.0 to 6.0. Temperature should be at the warmer end of the species’ range, around 26–28 °C. Adding Indian almond leaves or peat extract to tint the water a pale amber helps replicate natural conditions and may stimulate spawning. The tank should contain broad-leaved plants such as Cryptocoryne species or Java Fern, as the fish will deposit their eggs on the undersides of these leaves. Dim lighting is preferable, and filtration should be provided by a gentle sponge filter to avoid sucking in eggs or fry.

Spawning typically occurs in the early morning hours. The pair will swim together, with the male closely following the female as she selects a suitable leaf. The female then inverts herself beneath the leaf and deposits a small number of adhesive eggs, which the male immediately fertilises. This process is repeated over the course of an hour or so, with the total clutch size usually numbering between 20 and 80 eggs.

Once spawning is complete, the adults should be removed promptly, as they will readily consume their own eggs if given the opportunity. The eggs typically hatch within 24 to 36 hours, and the tiny, nearly invisible fry will absorb their yolk sacs over the next two to three days before becoming free-swimming. First foods should be extremely small, infusoria or commercially available liquid fry food are suitable for the first week, after which the fry can be transitioned to freshly hatched baby brine shrimp and micro-worms. Growth is relatively slow, and the fry will begin to show adult colouration at around six to eight weeks of age.

Common Diseases

Glowlight Rasboras are generally hardy fish when kept in appropriate conditions, but they are susceptible to the same range of diseases that affect most tropical freshwater species. Maintaining stable water quality, avoiding overcrowding, and quarantining new arrivals are the most effective preventative measures.

Ich (white spot disease), caused by the protozoan parasite Ichthyophthirius multifiliis, is perhaps the most commonly encountered ailment. It presents as small white spots on the body and fins, accompanied by flashing (rubbing against surfaces) and lethargy. Treatment involves gradually raising the water temperature to around 28–30 °C and administering a suitable white spot medication. Early intervention is critical, as small fish can deteriorate quickly.

Fin rot, a bacterial infection characterised by fraying, discolouration, and erosion of the fins, is typically a secondary condition resulting from poor water quality or physical injury. Improving water conditions through more frequent water changes is often sufficient to resolve mild cases, though more advanced infections may require treatment with an antibacterial medication.

Columnaris, sometimes mistaken for a fungal infection due to its cottony white appearance, is another bacterial disease that can affect stressed or immunocompromised fish. It tends to appear around the mouth, gills, or body, and can progress rapidly if left untreated. Antibacterial treatments and improvements to water quality are the standard response.

Internal parasites can occasionally affect wild-caught specimens, presenting as weight loss, lethargy, or stringy white faeces despite normal feeding. Anti-parasitic medications designed for internal worms are effective when administered promptly. Quarantining wild-caught fish for two to four weeks before introducing them to the main display tank is strongly advisable to catch and treat such issues before they can spread.

Stress-related conditions, while not diseases in themselves, are worth mentioning. Glowlight Rasboras that are kept in overly bright, barren tanks, in groups that are too small, or with aggressive tank mates will often display chronic stress symptoms such as persistent paleness, loss of appetite, hiding, and increased susceptibility to opportunistic infections. Addressing the underlying environmental cause is always the first and most important step in resolving these issues.

FAQs

How many Glowlight Rasboras should I keep together?

A minimum group of eight is recommended, but these fish are significantly more confident and display far more natural behaviour in larger groups of twelve to twenty or more. In small groups, they tend to be nervous, scattered, and less colourful. If your tank has the space, always err on the side of a larger shoal, the visual impact and the welfare benefits are well worth it.

What is the difference between the Glowlight Rasbora and the Harlequin Rasbora?

Both belong to the genus Trigonostigma, but they are distinct species. The Harlequin Rasbora (T. heteromorpha) is somewhat larger, with a broader, more prominent dark triangular body marking. The Glowlight Rasbora (T. hengeli) is slimmer and smaller, with a narrower dark marking and a vivid neon-orange line running above it that is far more pronounced than in the Harlequin. There is also a third commonly available species in the genus, T. espei (Lambchop Rasbora), which is intermediate in appearance and sometimes confused with T. hengeli.

Can Glowlight Rasboras be kept in hard water?

While they can survive in moderately hard water up to around 10 dGH, they will not display their best colour or behaviour in such conditions, and breeding is extremely unlikely outside of soft, acidic water. If your tap water is hard, consider mixing it with reverse-osmosis water to bring the hardness and pH down to a more suitable level. For long-term health and the most vibrant display, soft water is strongly recommended.

Are Glowlight Rasboras suitable for a planted tank?

Absolutely. Glowlight Rasboras are ideal inhabitants for planted aquariums. They do not eat or uproot plants, they benefit from the cover and subdued light that dense planting provides, and their warm orange and copper tones create a beautiful contrast against green foliage. They are particularly well-suited to nature aquarium and Iwagumi styles, as well as Southeast Asian biotope setups.

Do Glowlight Rasboras jump out of the tank?

Small rasboras are not habitual jumpers, but they can leap from the water when startled or stressed. A tight-fitting lid or cover slides are advisable as a sensible precaution, particularly during the first few days after introduction when the fish may be more prone to panic. Ensuring gentle lighting and adequate cover at the water surface with floating plants also helps reduce the risk.

Related Guides

• Harlequin Rasbora (Trigonostigma heteromorpha) Care Guide, a close relative and popular alternative with very similar care requirements and a slightly larger profile.
• Lambchop Rasbora (Trigonostigma espei) Care Guide, the third commonly available species in the genus, often confused with T. hengeli and equally rewarding to keep.
• Chili Rasbora (Boraras brigittae) Care Guide, another tiny Southeast Asian rasbora perfect for nano and blackwater setups.
• Ember Tetra (Hyphessobrycon amandae) Care Guide, a similarly sized, warm-toned nano fish that makes an excellent companion species.
• Blackwater Aquarium Setup Guide, a comprehensive guide to creating the tannin-rich, soft-water environments in which Glowlight Rasboras truly thrive.