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Encyclopedia / Tetras / Ruby tetra
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Variations

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Ruby tetra

Axelrodia riesei · Riesei

Peaceful; shy.

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2.1 cmBody length, without tail ✓
24–28 °CTemperature ✓
4–6.5pH ✓
54 LSmallest tank ✓
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Tank mates
Check your own mix →
Not recommended
  • Tinfoil barb eats animals up to about 5 cm. Ruby tetra only grows to 2.1 cm.
Not recommended
  • White cloud mountain minnow needs cool water and makes a lot of waste, while Ruby tetra is tropical.
  • They need different temperatures (24–28 °C vs 14–22 °C). No setting suits both.
Not recommended
  • Betta eats animals up to about 2.5 cm. Ruby tetra only grows to 2.1 cm.
With conditions
  • Only a narrow temperature range suits both: 24–25 °C.
With conditions
  • Only a narrow temperature range suits both: exactly 24 °C.
Compatible
Compatible
Compatible
Compatible
Compatible

201 species in our list are a good match.

Facts checked against sources on 16 Oct 2026. ✓ means a source backs it; ? means no reliable source yet. See sources

Care and water

Hardness ✓1–5 dGH
Group size ✓10 or more
Temperament ✓Peaceful
Swims at ?Middle
Care level ✓Moderate
Diet Omnivore
Lifespan ?Unknown
Size in shops 1.5–2 cm
Growth Medium

Behavior

Peaceful; shy.

Food

Micro foods like baby brine shrimp.

Tap a food to see what it is.

Male or female

Adult males are slightly smaller and more intensely coloured; mature females are rounder-bodied, especially when full of eggs.

Health

Common problems. Tap one to see the signs. This is a guide, not a diagnosis.

Breeding

Egg-scatterer (rarely bred) ·

Egg scatterer that spawns among fine-leaved plants in soft, acidic water; once in condition adults spawn daily, and a few fry may appear unaided in a mature, planted tank.

Pairing

Needs a large group in mature, stable conditions; pairing is hard to control.

Setup

Roomy, planted tank with very soft acidic water (pH 5-6.5), subdued light and fine-leaved plants or a spawning mat.

What starts it

Rain-season style changes: soft cool water changes, a small temperature rise and heavy live feeding.

Eggs

20-50 eggs

Raising the fry

Infusoria then brine shrimp nauplii; survival is poor without very clean water.

Common mistakes
  • Hard tap water
  • Overcrowding the breeding tank
  • Poor water quality
Full breeding guide, day-by-day plan and simulator →

Where it lives in the wild

RegionOrinoco basin – eastern Colombia (Río Meta region)
Rivers and lakesUpper Río Meta and nearby Orinoco tributaries
HabitatClear and blackwater forest streams and savanna pools
Native rangeAbout 400 km across
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The story of the ruby tetra

A tiny red tetra from Colombia (upper Río Meta) that needs a mature, soft-water tank; its red colour often fades in captivity.

French ichthyologist Jacques Géry described this tiny red tetra in 1966. It comes from the Orinoco drainage of eastern Colombia, where it lives among vegetation in small streams. Its glowing red colour has made it a favourite among nano-aquarium keepers.

First described by Jacques Géry in 1966. Named for Genus honours aquarium publisher Herbert R. Axelrod.

  • Adults rarely exceed 2 cm, making it one of the smallest tetras in the hobby.
  • Its red colour intensifies in dim light and soft, slightly acidic water.
  • It is best kept in groups, which makes the small fish feel safer and colour up.

Sources

15 facts checked with sources