One-Lined Pencilfish

Nannostomus unifasciatus

One-Lined Pencilfish is a peaceful middle-to-top swimmer.

PeacefulMiddle to top swimmerBeginner – Intermediate

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Need help with One-Lined Pencilfish?

Explore compatibility, care or problems using this guide and your aquarium’s conditions.

Quick facts

Adult size: ≤ 1.6" (≤ 4 cm)
Aquarium size: 16 US gal (60 L) or larger / ≥ 29.5" (≥ 75 cm) minimum length
Care level: Beginner – Intermediate
Temperament: Peaceful
Swimming zone: Middle to top swimmer
Temperature: 73–82°F (23–28°C)
pH: 4–7
GH: 1–10 dGH
Diet: Omnivore
Lifespan: up to 5 years

Care requirements

Care level: Beginner – Intermediate.

Lifespan: up to 5 years.

Aquarium size and space needs

Minimum aquarium size: 16 US gal (60 L) or larger / ≥ 29.5" (≥ 75 cm) minimum length. Plan the layout and stocking within that limit.

Water parameters

Suitable water: temperature 23–28 °C, pH 4–7, GH 1–10 dGH.

Temperament and compatibility

One-Lined Pencilfish is peaceful and suits calm community fish.

Swimming zone and behavior

This fish uses the middle to upper part of the aquarium, so leave enough open swimming space for movement and feeding.

Feeding

As an omnivore, One-Lined Pencilfish should receive a varied diet rather than one repeated food type.

Micropredator of tiny aquatic invertebrates; offer daily small live/frozen prey such as Artemia nauplii or Moina; dry food only if suitably small.

Before adding this fish

Plan for an aquarium of 16 US gal (60 L) or larger / ≥ 29.5" (≥ 75 cm) minimum length.
Avoid aggressive or highly competitive fish.
Offer a varied diet suited to this species’ documented feeding habits.

Similar fish profiles

Use these profiles to compare fish with similar care level, size, temperature range, or swimming behavior.

Barred Pencilfish Nannostomus espei Same genus Same family Similar care level Beginner – Intermediate ≤ 1.2" (≤ 3 cm) 72–82°F (22–28°C) Bleeding Blue Tetra Hyphessobrycon margitae Similar care level Same temperament Same swimming zone Beginner – Intermediate 1.6–2" (4–5 cm) 73–79°F (23–26°C) Black Arrow Royal Tetra Inpaichthys luizae Similar care level Same temperament Same swimming zone Beginner – Intermediate ≤ 1.6" (≤ 4 cm) 72–79°F (22–26°C) Black Heart Tetra Hyphessobrycon copelandi Similar care level Same temperament Same swimming zone Beginner – Intermediate ≤ 1.6" (≤ 4 cm) 75–82°F (24–28°C) Black Line Tetra Hyphessobrycon scholzei Similar care level Same temperament Same swimming zone Beginner – Intermediate ≤ 1.6" (≤ 4 cm) 72–82°F (22–28°C) Blueberry Tetra Hyphessobrycon wadai Similar care level Same temperament Same swimming zone Beginner – Intermediate ≤ 1.6" (≤ 4 cm) 75–81°F (24–27°C)

FAQ

How large does One-Lined Pencilfish get?

One-Lined Pencilfish reaches ≤ 1.6" (≤ 4 cm).

What aquarium size does One-Lined Pencilfish need?

Use an aquarium of at least 16 US gal (60 L) or larger / ≥ 29.5" (≥ 75 cm) minimum length.

Is One-Lined Pencilfish peaceful?

Yes. One-Lined Pencilfish is recorded as peaceful and is best planned with calm community fish that do not harass it or dominate the feeding area.

What temperature is suitable for One-Lined Pencilfish?

Keep it between 23 to 28 °C.