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

Trigonostigma hengeli is a small rasbora from the peat-stained waters of Sumatra and Borneo. Meinken described it as Rasbora hengeli in 1956, and Kottelat and Witte moved it into the genus Trigonostigma in 1999. The name honours J. van Hengel, a Dutch ornamental-fish dealer in Amsterdam who passed specimens to Meinken. It is one of three closely similar Trigonostigma in the trade, all built around a dark wedge-shaped flank mark, and the three are routinely mixed up. The harlequin, T. heteromorpha, is the largest and pinkest, with a broad solid triangle; T. espei is coppery red with a slimmer, lambchop-shaped mark; and T. hengeli is the smallest and palest, its body close to colourless apart from a bright orange flash running along the top and front of the lambchop. A fourth species, T. somphongsi, is very rare and may be gone from the wild. The trade name glowlight rasbora is shared with an unrelated fish, Trigonopoma pauciperforatum, so the same common name points to two different species. Maximum size is about 3 cm, and males are a touch slimmer and brighter than females.

Breeding

Like the rest of its genus, the glowlight rasbora lays its eggs on the underside of broad leaves rather than scattering them, and the adults give no parental care afterward. Spawning needs soft, acidic water, roughly pH 5 to 6 and very low hardness; eggs laid in harder water tend to fungus. A common trigger is to condition a pair on live food and then do a larger, slightly cooler water change, after which they often spawn the next morning. Clutches are small. The fry are tiny and take infusoria-grade food before they can manage baby brine shrimp. Removing the adults after spawning improves the odds, and many keepers find buying more fish simpler than raising them.

Common problems

Their size is the main vulnerability. At around 3 cm these are delicate fish: net them with a cup rather than a mesh, keep them away from boisterous or aggressive tankmates, and avoid sudden swings in water chemistry, which hit small fish harder. New arrivals sometimes break out with ich after the stress of transport; raising the temperature is safer than dosing, since medication amounts meant for bigger fish can overdose a nano species. Wild-caught fish can carry internal parasites that cause slow wasting. Colour washes out under bright overhead light over pale substrate, while dark substrate, floating plants, and warmer-toned light bring the orange stripe forward. As with most blackwater fish, steady water quality and routine water changes keep them in good shape.

Bioload

Further reading

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