Glowlight tetra

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

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.

Origin and habitat

Native to the Essequibo River basin in Guyana and likely also the Corentyne basin at the Guyana-Suriname border. Found in forested tributaries like the Potaro and Mazaruni, not the main channel. The water is dark brown from tannins, soft, and acidic. Described by Durbin in 1909. Introduced to the aquarium trade as early as 1933. The genus Hemigrammus combines Greek hemi ("half") and gramma ("letter/signal"), a reference shared across the genus. Silver body with a bright iridescent orange-to-red stripe running from snout to tail base; the front of the dorsal fin matches the stripe color; other fins are silver to transparent. Size conflicting across sources: max 3.3 cm TL is recorded (noted as questionable, with 4cm also reported); 4–5 cm is the common hobby figure. A peaceful shoaling species. Commercially bred in huge numbers; captive stock adapts to a broad parameter range. Good tankmates include livebearers, danios, rasboras, other tetras, Corydoras, smaller loricariids, gouramis, and dwarf cichlids. Not safe with larger species that may eat it.

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

Further reading

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