Glowlight tetra

Quick facts

Adult size

4 cm

Lifespan

can live up to 5 years; captive average is 3-4

Tank zone

mid

Temperament

peaceful

Difficulty

beginner

Schooling

recommended 6+ (critical minimum 4, thrives at 8+)

Water parameters

Temperature

22–28°C

pH

5.5 to 7.0

Hardness

1 to 10 dGH

Tank requirements

Minimum volume

75 L

Minimum length

60 cm

Flow

low

Lighting

dim preferred

Substrate

any

Driftwood

preferred

Hiding spots

needed

Feeding

Diet: omnivore, feeds primarily at the mid.

Eats anything. Flake food, micro pellets, frozen bloodworm, frozen daphnia, frozen brine shrimp, live baby brine shrimp. Feeds in the midwater column. Small mouth but slightly larger than neon tetras, so standard-sized flake works without crushing. Not picky, not demanding, not competitive. In community tanks they eat their share without fighting for it. Twice daily in moderate amounts is fine.

Compatibility

• Peaceful schooling tetra that fits into any community tank with non-aggressive species. A reliable, low-drama fish that does what it's supposed to do and causes no problems.
• Schools well with other small tetras, rasboras, and danios. In mixed tetra tanks, glowlights tend to stick together rather than schooling with other species.
• Good companion for dwarf cichlids (apistogramma, rams) because they stay in the midwater zone and don't invade cichlid territories on the bottom. Also fine with corydoras, otocinclus, and all shrimp species.
• The glowing orange-red stripe shows best against dark substrates and under warm-toned lighting. On pale gravel under white LEDs, they look washed out and boring.

Habitat

Native to the Essequibo River basin in Guyana, South America. Found in slow-moving forest streams with soft, acidic water stained by tannins, over sandy substrates with dense leaf litter. The species was first imported to the aquarium hobby in the 1930s and has been a mainstay ever since. The common name refers to the bright orange-red stripe that runs from the snout through the eye to the base of the tail, which under good lighting looks like a glowing filament. The stripe is an iridescent structural color (similar to neon tetras) and appears to glow under certain lighting angles. Tank-bred in massive commercial quantities; wild-caught specimens are rare in the trade. The fish is almost identical in care requirements to neon tetras, with the advantage of being slightly hardier and less prone to disease. Adult size is about 4 cm, lifespan 3-5 years in typical conditions. Body shape is classic tetra: laterally compressed, torpedo-shaped, translucent. Males are slimmer; females are fuller-bodied when mature.

Breeding

Egg scatterer. Condition pairs with frozen food for a week. The breeding tank needs soft, acidic water (pH 5.5-6.5, GH below 6), dim lighting, and fine-leaved plants or spawning mops. Temperature at 26–27°C. Spawning occurs at dawn, triggered by the first light reaching the tank. The pair scatters 100-200 eggs among the plants. Eggs are photosensitive; keep the tank dark for the first 24 hours. Remove adults immediately after spawning, as they eat eggs enthusiastically. Eggs hatch in 24-30 hours. Fry need infusoria for the first 3-4 days, then transition to baby brine shrimp. Growth is moderate; sellable size in about 3 months. Glowlight tetras are slightly easier to breed than neon tetras because they're less sensitive to water chemistry extremes and the fry are marginally larger. Still requires dedicated effort and a separate breeding setup.

Common problems

One of the hardiest small tetras in the hobby. Significant disease problems are uncommon in established tanks with stable water. Ich can appear in newly purchased fish; treat with temperature elevation (30°C) or standard medication. Fin rot and columnaris (bacterial infections) happen when water quality degrades, but glowlights are usually among the last fish to show symptoms because they're just that tough. The main issue is cosmetic: poor coloring in suboptimal conditions. The species needs dark substrate, subdued lighting, and soft water to look its best. On bright white gravel under full-blast LEDs, the stripe fades to a dull orange-brown and the fish look unremarkable. Tannin-stained water from driftwood or Indian almond leaves enhances the color noticeably. Old age brings gradual fading of the stripe intensity; fish over 4 years lose some of their visual impact.

Bioload

Bioload coefficient: 1.0 (identical adult size and activity profile to neon tetra).

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