Glowlight rasbora

Quick facts

Adult size

3 cm

Lifespan

can live up to 5 years

Tank zone

mid

Temperament

peaceful

Difficulty

beginner

Schooling

recommended 8+ (critical minimum 6, thrives at 12+)

Water parameters

Temperature

23–28°C

pH

5.5 to 7.5

Hardness

1 to 10 dGH

Tank requirements

Minimum volume

40 L

Minimum length

45 cm

Flow

low

Lighting

moderate

Substrate

any

Driftwood

preferred

Hiding spots

needed

Feeding

Diet: omnivore, feeds primarily at the mid.

Micro pellets, crushed flake, frozen baby brine shrimp, frozen cyclops, frozen daphnia, and live microworms or vinegar eels. The mouth is very small; standard flake and pellets are too large unless crushed. They feed in the upper and midwater column. Live food triggers the best feeding response and is worth offering regularly. In community tanks with larger fish, glowlight rasboras get outcompeted at feeding time. Targeted feeding with a pipette or feeding in a corner where only the small fish gather helps. Feed twice daily in very small amounts. Biofilm grazing supplements their diet in mature tanks with live plants.

Compatibility

• Tiny fish (under 3 cm) that belongs in a nano setup or a carefully chosen community. Any fish large enough to eat them will. Stick with other nano species: ember tetras, chili rasboras, pygmy corys, celestial pearl danios, and shrimp.
• Peaceful and undemanding in terms of social behavior. They school loosely and don't squabble. Groups of 8+ bring out the best color and the most confident behavior.
• The orange-red stripe fluoresces under certain lighting conditions, particularly blue-shifted or UV-enhanced LED setups. This makes them unusually visible for such a small fish.
• Good companion for planted shrimp tanks. They ignore adult shrimp and most shrimplets. The main risk is competition for micro-foods in tanks where both shrimp and tiny fish need the same small-particle diet.

Habitat

Native to forest streams in Sumatra and Borneo in Indonesia. Found in slow-moving, shallow water over leaf-litter substrates with dense bankside vegetation and overhanging canopy. The water is soft, acidic, and tannin-stained. The species (Trigonostigma hengeli) is closely related to the harlequin rasbora (T. heteromorpha) and looks like a smaller, sleeker version of it. The body is translucent pinkish-gold with a bright orange-red neon stripe along the lateral line and a smaller dark triangular mark behind it. Under the right lighting, the stripe glows intensely, especially against a dark background. Males are slimmer and slightly more vivid than females. Adult size is about 2.5 cm, making this one of the smallest rasboras regularly available. The species has been in the trade since the early 2000s and has gained popularity as nano fishkeeping expanded. Both wild-caught and tank-bred specimens are available. They're often confused with Trigonostigma espei (the lambchop rasbora), which is slightly larger and has a more prominent dark mark.

Breeding

Egg depositor that attaches eggs to the undersides of broad leaves, similar to harlequin rasboras. The pair performs an inverted spawning where the female turns upside down under a leaf (Cryptocoryne or Anubias leaves are preferred) and deposits a few adhesive eggs while the male fertilizes them. Clutch sizes are small (10-30 eggs per spawning event). Water must be soft and acidic (pH 5.0-6.5, GH below 5) for successful egg development; eggs laid in harder water often fungus. Remove adults after spawning. Eggs hatch in 24-36 hours. Fry are extremely tiny and need infusoria or paramecium for the first 5-7 days before graduating to baby brine shrimp nauplii. Breeding is achievable but requires attention to water chemistry and patience with the small clutch sizes. Most hobbyists find it easier to buy more than to breed them.

Common problems

Size-related vulnerability is the main concern. At under 3 cm, these fish are fragile. Netting them is risky (use a cup), aggressive tankmates are dangerous, and sudden parameter swings hit them harder than larger species. Ich can appear after transport stress; treat with temperature elevation rather than medication, as chemical doses designed for larger fish can overdose nano species. Internal parasites from wild-caught specimens cause wasting; treat with praziquantel. Color loss happens in tanks with bright overhead lighting and pale substrate. Dark substrate, floating plants, and subdued or warm-toned lighting bring out the neon stripe. The species is sensitive to water quality; keep nitrate below 20 ppm and maintain a regular water change schedule.

Bioload

Bioload coefficient: 0.3 (very small nano rasbora; smaller than chili rasbora).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size