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One-lined pencilfish

Nannostomus unifasciatus

Also known as One Line Pencilfish

FreshwaterFish

One-lined pencilfish (Nannostomus unifasciatus)
Lochrian · CC BY-SA 3.0

Care at a glance

Temperature
73–82°F
23–28°C
pH
5.5–7.0
Adult size
1.6 in
4 cm
Minimum tank
17 gal
65 L
Temperament
Peaceful
Social behavior
Shoaling
Swim level
Middle
Difficulty
Medium
Breeding
Egg scatterer
Rarity
Rare
Family
Lebiasinidae
Origin
Brazil, Bolivia, Colombia

Overview

The one-lined pencilfish is a shy, peaceful pencilfish for a quiet planted tank. It is a step up from the easiest fish and suits a keeper with a little experience.

Did you know

The one-lined pencilfish, like other pencilfish, changes its look at night. Once the lights go out, the horizontal stripe fades and a blotchy, broken pattern takes over, then it reverses in the morning. If you check the tank after dark, you might think you are looking at a different fish.

Caring for the one-lined pencilfish

Keep at least six one-lined pencilfish together in a tank of 17 gal (65 L) or more. They are shy and do poorly alone. A quiet, well planted tank with gentle flow suits them, and some floating plants and dim light help them settle in.

Give them warm, soft water on the acidic side, at 73 to 82°F (23 to 28°C) and a pH of 5.5 to 7.0. Their mouths are small, so feed fine foods such as micro pellets and crushed flake. Small live or frozen foods like baby brine shrimp suit them too.

One-lined pencilfish hold in the upper and middle water and stay peaceful. A calm community of small, gentle fish suits them. Like many pencilfish, they scatter eggs and give no parental care, and breeding in the aquarium is not well documented for this species.

Good to know

The one-lined pencilfish belongs to the family Lebiasinidae. It has a long, slender body and a single dark stripe from snout to tail. It is known for resting and swimming at a slight head-up angle.

In the wild

The one-lined pencilfish lives in slow, soft, acidic waters across the Amazon and Orinoco systems, in Brazil, Bolivia and Colombia. These are tannin-stained streams and flooded forest with leaf litter and submerged roots.

Weekly picks

Tank mates

The one-lined pencilfish is a peaceful, shoaling species that keeps to the middle. These picks share a community profile with it, are safe together in both directions, and overlap on water type, temperature and pH.

Check the full mix in the stocking calculator

Common questions

What size tank does a one-lined pencilfish need?

A one-lined pencilfish needs at least 17 gal (65 L). It spends most of its time in the middle.

What temperature and pH does a one-lined pencilfish need?

A one-lined pencilfish is comfortable at 73–82°F (23–28°C) with a pH of 5.5–7.0.

What does a one-lined pencilfish eat?

A one-lined pencilfish has a small mouth, so it eats fine foods such as micro pellets and crushed flake. It also takes small live or frozen foods like baby brine shrimp.

How big does a one-lined pencilfish get?

An adult one-lined pencilfish reaches about 1.6 in (4 cm).

Does a one-lined pencilfish need a group?

Yes. A one-lined pencilfish is a shoaling species and should be kept in a group, not singly.

How does a one-lined pencilfish breed?

One-lined pencilfish scatter their eggs and give them no parental care, like many pencilfish. Breeding in the aquarium is not well documented for this species.

Related species