Glowlight rasbora

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Feeding

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.

Origin and habitat

Native to Sumatra and Borneo, Indonesia. The species is named after J. van Hengel, a Dutch ornamental fish importer-exporter in Amsterdam who sent specimens to Meinken for identification. Closely related to the harlequin rasbora (T. heteromorpha) and lambchop rasbora (T. espei); all three are frequently confused with each other. Telling them apart: T. heteromorpha has a pinkish body with a broad dark triangle; T. espei is bright copper/reddish with a thinner lambchop-shaped mark; T. hengeli is the smallest, with an overall greyish/colorless body and a flash of bright orange pigmentation along the upper and front edges of the lambchop marking. Mostly transparent with an intensely bright neon orange iridescent line over a slimmer peduncle mark. Max 3 cm SL. The "glowlight rasbora" trade name can cause confusion because it's also used for Trigonopoma pauciperforatum. Males are slimmer with slightly more vivid coloring than females. T. somphongsi is the fourth, extremely rare member of the genus, possibly extinct in the wild.

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

Further reading

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