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Encyclopedia / Tetras / Dwarf pencilfish
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Variations

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Dwarf pencilfish

Nannostomus marginatus · Dwarf pencil, One-lined dwarf pencilfish, Marginatus

Peaceful; ideal for small planted tanks with other tiny fish.

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3.5 cmAdult size ✓
23–28 °CTemperature ✓
5–7pH ✓
40 LSmallest tank ✓
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Tank mates
Check your own mix →
Not recommended
  • Tinfoil barb eats animals up to about 5 cm. Dwarf pencilfish only grows to 3.5 cm.
Not recommended
  • White cloud mountain minnow needs cool water and makes a lot of waste, while Dwarf pencilfish is tropical.
  • They need different temperatures (23–28 °C vs 14–22 °C). No setting suits both.
Not recommended
  • Giant gourami eats animals up to about 10 cm. Dwarf pencilfish only grows to 3.5 cm.
With conditions
  • Only a narrow temperature range suits both: 23–24 °C.
With conditions
  • Only a narrow temperature range suits both: 23–24 °C.
Compatible
Compatible
Compatible
Compatible
Compatible

307 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 ✓1–10 dGH
Group size ✓10 or more
Temperament ✓Peaceful
Swims at ✓Top
Care level ✓Moderate
Diet Omnivore
Lifespan ?Unknown
Size in shops 2–3 cm
Growth Medium

Behavior

Peaceful; ideal for small planted tanks with other tiny 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 noticeably slimmer (less stocky) than females; unlike its red relatives the sexes are coloured alike. In one Rio Negro form males have thickened anal-fin rays.

Health

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

Breeding

Egg-scatterer on plants · Moderate

Egg scatterer among fine-leaved plants or wool mops, rarely bred in aquaria; adults eat eggs and should be removed 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; first foods are Paramecium or 5-50 micron dry food. 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 – Guyana, Suriname & the Amazon basin
Rivers and lakesGuiana rivers and Amazon tributaries
HabitatShallow, vegetated streams
Native rangeAbout 1,200 km across
See it on the world map

The story of the dwarf pencilfish

An enduringly popular small pencilfish of Guyana, Suriname and the Amazon with three dark stripes; some forms (Guyana, Suriname, Rio Negro, Colombia) add a short red stripe above the central dark stripe, but males have no red between the stripes like N. mortenthaleri.

Carl Eigenmann described this pencilfish in 1909 from Guyana. It is the smallest pencilfish, reaching only about 3.5 cm. Its red, gold and black stripes make it a gem for nano tanks.

First described by Carl H. Eigenmann in 1909. Named for 'marginatus' means edged.

  • It is the smallest pencilfish, at about 3.5 cm.
  • Like other pencilfishes, it changes to a blotchy pattern at night.
  • It prefers dense plants and soft water.

Sources

16 facts checked with sources