Rainbow tetra - Nematobrycon lacortei

Scientific name: Nematobrycon lacortei

Common name: Rainbow tetra

Family: Characidae

Usual size in fish tanks: 3 - 4 cm (1.18 - 1.57 inch)

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Recommended pH range: 6 - 7.2

Recommended water hardness: 4 - 17°N (71.43 - 303.57ppm)

0°C 32°F30°C 86°F

Recommended temperature range: 22 - 28 °C (71.6 - 82.4°F)

The way how these fish reproduce: Spawning

Where the species comes from: South America

Temperament to its own species: peaceful

Temperament toward other fish species: peaceful

Usual place in the tank: Middle levels

General Information

The Rainbow Tetra (Nematobrycon lacortei) is a small, peaceful characin endemic to western Colombia, with natural records from the Río San Juan system – notably the Río Calima. It inhabits slow, plant-rich tributaries with subdued light. Keep it in a proper shoal (≥6–8) to reduce intra-species sparring and to see confident, natural schooling behavior.

Food and Feeding

An unfussy micro-predator/omnivore. Offer quality flakes or micro-granules as a staple, and rotate live or frozen foods such as brine shrimp nauplii, daphnia, cyclops, and mosquito larvae for colour and condition. Feed small portions once or twice daily so all food is eaten within a few minutes to protect water quality.

Sexing

Males are usually slimmer, more intensely coloured, and have slightly longer dorsal/anal/caudal fins. A reliable cue is eye colour: males show red irises, while females are bluish-green. Juveniles resemble females until maturity.

Breeding

An egg-scattering spawner with no parental care. Use a separate dimly lit breeding tank with fine-leaved plants (e.g., Java moss) or spawning mops. Soft, slightly acidic water helps. Remove adults after spawning to prevent egg predation. Eggs hatch in ~24–36 hours; fry become free-swimming a few days later and should start on infusoria, then newly hatched brine shrimp.

Lifespan

Typically 3–5 years in stable, clean aquaria with a varied diet and low stress.

Tank Requirements & Water Parameters

Minimum tank length: 60–75 cm (24–30″) for a shoal; larger footprints improve stability and schooling.
Temperature: 22–28 °C (71.6–82.4 °F).
pH: ideally slightly acidic to neutral (≈6.0–7.0).
Hardness: soft to medium.
Environment: dark substrate, plenty of live plants (including floaters) to diffuse light, leaf-litter/tannins, gentle filtration (filter) and calm flow.
Maintenance: weekly 25–30% water changes; avoid parameter swings.

Compatibility & Tank Mates

Peaceful shoaler suited to quiet community tanks. Combine with similarly sized, non-aggressive species (small rasboras/tetras, Corydoras, small peaceful dwarf cichlids). Avoid long-finned or very slow fish if males display fin-nipping, and avoid large or predatory species.

Behaviour & Usual Place in the Tank

Mid–upper water column: active shoalers that spend most time in the middle of the tank, often venturing upward among plants. Provide open lanes through vegetation for natural “glide and shimmer” movement.

Short Description

Rainbow Tetra (Nematobrycon lacortei) is a Colombian endemic, best in soft, slightly acidic, planted aquaria with subdued light. Keep in groups, feed varied small foods, and expect striking coloration with stable, clean water.

Q&A

How do I sex them? Males have red eyes, extended fins, and stronger colours; females show bluish-green eyes and deeper bellies.
Top, middle, or bottom? Mostly mid–upper levels among plants; not a bottom sitter.
Minimum group size? Keep at least 6–8; larger groups (10 ) spread any male sparring and look more natural.