One-lined Pencilfish

Care at a glance

Overview

Keep at least six together in a tank around 65 liters, since they're shy and do poorly alone. They hold in the upper and middle water and stay peaceful, so they suit a calm community of small, gentle fish. Keep water warm, in the mid to upper 20s C, soft, and acidic to neutral. Their mouths are small, so feed fine foods like micro pellets, crushed flake, and small live or frozen items like baby brine.

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. Match that with a quiet, well-planted tank, gentle flow, and soft water on the acidic side. Some floating plants and dim light help them settle in.

Good to know

This is a pencilfish in the family Lebiasinidae, reaching about 4 cm with a long, slender body and a single dark stripe from snout to tail. It's known for resting and swimming at a slight head-up angle. Breeding in the aquarium isn't well documented for this species. Like many pencilfish, it scatters eggs and gives no parental care.

Did you know

Pencilfish change their look at night. The horizontal stripe fades and a blotchy, broken pattern takes over once the lights go out, then it reverses in the morning. If you check the tank after dark you might think you're looking at a different fish.

Related species

• 

  Hockeystick pencilfish

  Nannostomus eques

  1.4 in (3.5 cm)15 gal (55 L)72–82°F (22–28°C)
• Twostripe pencilfish

  Nannostomus digrammus

  1.4 in (3.5 cm)12 gal (45 L)75–82°F (24–28°C)

• 

  Three-lined pencilfish

  Nannostomus trifasciatus

  1.3 in (3.3 cm)15 gal (55 L)72–82°F (22–28°C)

• 

  Barred pencilfish

  Nannostomus espei

  1.2 in (3 cm)15 gal (55 L)72–82°F (22–28°C)

• 

  Coral red pencilfish

  Nannostomus mortenthaleri

  1.2 in (3 cm)15 gal (55 L)75–82°F (24–28°C)

• 

  Harrison's pencilfish

  Nannostomus harrisoni

  2.2 in (5.5 cm)16 gal (60 L)73–82°F (23–28°C)