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Encyclopedia / Tetras / Coral red pencilfish
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Coral red pencilfish

Nannostomus mortenthaleri · Coral red pencil, Red pencilfish, Mortenthaleri

Peaceful; small shy schooling fish.

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3 cmBody length, without tail ✓
24–28 °CTemperature ✓
5–7pH ✓
81 LSmallest tank ✓
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Tank mates
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Not recommended
  • Tinfoil barb eats animals up to about 5 cm. Coral red pencilfish only grows to 3 cm.
Not recommended
  • White cloud mountain minnow needs cool water and makes a lot of waste, while Coral red pencilfish is tropical.
  • They need different temperatures (24–28 °C vs 14–22 °C). No setting suits both.
Not recommended
  • Pearl gourami eats animals up to about 3 cm. Coral red pencilfish only grows to 3 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

247 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 ✓Top
Care level ✓Moderate
Diet Omnivore
Lifespan ?Unknown
Size in shops 2.5–3.5 cm
Growth Medium

Behavior

Peaceful; small shy schooling fish.

Food

Small live and frozen foods such as baby brine shrimp and daphnia, plus fine flakes.

Tap a food to see what it is.

Male or female

Adult males are slimmer and far more colourful than females, with bright red between the upper two dark stripes, and show a white mark at the front of the dorsal fin from a young age.

Health

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

Breeding

Egg-scatterer on plants · Hard

Egg scatterer among fine-leaved plants or wool mops, rarely bred in aquaria; give each pair its own patch of spawning medium and remove adults after 2-3 days.

Pairing

Keep a group with several females and condition on live foods; pairs form on their own.

Setup

20-30 L tank with soft acidic water (pH 5.5-6.5), dense fine-leaved plants or java moss, dim light and a gentle sponge filter.

What starts it

Soft acidic water, dim light and daily live baby brine shrimp; spawning is usually in the morning.

Eggs

Adults are removed after 2-3 days and the first fry appear a day or two later; adult patterning develops after about 8 weeks. No egg count found in the sources checked.

Raising the fry

Feed infusoria, then fine fry food and newly hatched brine shrimp; fry are tiny and need very small food.

Common mistakes
  • Hard alkaline water
  • Strong flow
  • Leaving adults with the eggs
Full breeding guide, day-by-day plan and simulator →

Where it lives in the wild

RegionSouth America – northeastern Peru
Rivers and lakesTributaries near Iquitos
HabitatShallow blackwater forest streams
Native rangeAbout 150 km across
See it on the world map

The story of the coral red pencilfish

A red-and-black pencilfish found only around the Nanay and Tigre rivers in Peru, named after exporter Martin Mortenthaler who collected the first specimens; described in 2001 as a subspecies of the dwarf pencilfish and assessed Critically Endangered by IUCN.

Hans-Joachim Paepke and Klaus Arendt described this pencilfish in 2001 from fish exported from Peru. Males are bright coral red with black stripes, making it one of the most colourful pencilfishes. It was named after Peter Mortenthaler, an ornamental fish exporter in Iquitos.

First described by Hans-Joachim Paepke & Klaus Arendt in 2001. Named for Named after Peter Mortenthaler, an ornamental fish exporter in Iquitos, Peru.

  • Males are bright coral red.
  • It was only described in 2001.
  • It comes from a small area of the Peruvian Amazon.

Sources

16 facts checked with sources