Coral red pencilfish

Nannostomus mortenthaleri

Also known as Red Arc Pencilfish

FreshwaterFish

Care at a glance

Temperature
75–82°F
24–28°C
pH
5.5–7.0
Adult size
1.2 in
3 cm
Minimum tank
15 gal
55 L
Temperament
Peaceful
Social behavior
Shoaling
Swim level
Middle
Difficulty
Medium
Breeding
Medium
Rarity
Rare
Family
Lebiasinidae
Origin
Peru

Overview

Keep them in a shoal of six or more in a small planted tank of about 55 liters, where the males will color up and spar over rank without doing harm. They hold the middle of the water and are peaceful, so pair them only with other gentle, small species. Aim for the mid to high 20s C and a soft, acidic to neutral pH. Their mouths are small, so feed micro foods like crushed flake, micro-pellet, and tiny live or frozen items.

In the wild

Coral red pencilfish come from slow, clear streams in the Peruvian Amazon, around the Rio Nanay. The water is soft and acidic, full of leaf litter, roots, and fine plants. A blackwater-style setup with dim light, tannins, and lots of planting suits them and brings out their red. Gentle flow only, since these are small, delicate fish.

Good to know

This pencilfish sits in the family Lebiasinidae and stays tiny at around 3 cm. Males show the deepest red, while females are paler and rounder. It was only described in 2001, and it is a micropredator that eats very small invertebrates in the wild. Breeding is possible but takes effort.

Did you know

Rival males put on a near-constant color show, sparring and flaring to sort out rank, and they turn their brightest red during these standoffs. A single male kept alone never reaches that intensity because there is nobody to compete with.

Weekly picks

Tank mates

Coral red 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 Coral red pencilfish need?

A Coral red pencilfish needs at least 15 gal (55 L). It spends most of its time in the middle.

What temperature and pH does a Coral red pencilfish need?

A Coral red pencilfish is comfortable at 75–82°F (24–28°C) with a pH of 5.5–7.0.

How big does a Coral red pencilfish get?

An adult Coral red pencilfish reaches about 1.2 in (3 cm).

Does a Coral red pencilfish need a group?

Yes. A Coral red pencilfish is a shoaling species and should be kept in a group, not singly.

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