TankBud

Purple pencilfish

Nannostomus rubrocaudatus

Also known as Redtail pencilfish

FreshwaterFish

Purple pencilfish (Nannostomus rubrocaudatus)
Elizabeth Barrett / animal.photos · Used with permission

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
20 gal
75 L
Temperament
Mostly peaceful
Social behavior
Shoaling
Swim level
Middle
Difficulty
Medium
Breeding
Hard
Rarity
Common
Family
Lebiasinidae
Origin
Peru, upper Amazon (Marañón River basin)

Overview

Keep them in a group of at least ten, in a tank of 75 liters or larger with a long footprint for swimming room. They are mostly peaceful and sit in the middle of the water column, schooling together, though males get territorial toward rivals, so a bigger group spreads out the squabbling and brings out bolder color. Water should run warm, 24 to 28 C, soft, and acidic to neutral at a pH of 5.5 to 7. They are timid and small, so skip the general community and pair them with other small, calm tankmates. Feed small live or frozen foods like baby brine, microworms, and daphnia, plus fine dry foods.

In the wild

Purple pencilfish come from soft, acidic blackwater in the upper Amazon, in the Maranon River basin of Peru. These are dim, tannin-stained waters over leaf litter, shaded and slow moving. To match that, give them a planted tank with dense growth, floating cover, dark substrate, and leaf litter or other tannins to tint the water. Keep it warm at 24 to 28 C with a pH from 5.5 to 7, and use gentle filtration like an air-driven sponge filter, since they dislike strong flow.

Good to know

This is a small pencilfish in the family Lebiasinidae, reaching about 3 cm and rarely more. It is an egg scatterer with no parental care, so adults will eat their own eggs. Most fish you find are wild caught, and breeding in the home tank is uncommon without a dedicated setup.

Did you know

Like other pencilfish, they swap their daytime pattern for a nighttime one. After the lights go out the bold horizontal stripe fades and a blotchy resting pattern takes over, then the stripe returns by morning. If you peek with a dim light at night you will sometimes catch them mid-change, looking like a different fish.

Weekly picks

Tank mates

Purple pencilfish is a mostly 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 Purple pencilfish need?

A Purple pencilfish needs at least 20 gal (75 L). It spends most of its time in the middle.

What temperature and pH does a Purple pencilfish need?

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

How big does a Purple pencilfish get?

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

Does a Purple pencilfish need a group?

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

Related species