Three-Lined Pencilfish Care Guide: Tank Setup, Diet, Tank Mates, and More

Table of Contents

• Key Takeaways
• Species Overview
• Classification
• Origin & Natural Habitat
• Appearance & Identification
• Average Size & Lifespan
• Care Guide
• Tank Mates
• Food & Diet
• Breeding & Reproduction
• Common Health Issues
• Common Mistakes to Avoid
• Where to Buy
• Frequently Asked Questions
• Closing Thoughts
• Recommended Video
• References

The three-lined pencilfish is one of the most popular and widely available pencilfish species in the hobby. Its clean pattern of three bold horizontal stripes, accented with patches of red and gold, makes it an elegant addition to any peaceful nano or planted tank. Like all pencilfish, it has that characteristic habit of hovering at an angle in the water, giving it a distinctive look that sets it apart from typical tetras.

This species has been a staple of the hobby for decades, and for good reason. It’s small, peaceful, and visually striking without demanding the extreme water conditions that some of its Nannostomus relatives require. Here’s everything you need to know about keeping the three-lined pencilfish.

Key Takeaways

• One of the most commonly available pencilfish species in the hobby
• Beautiful striped pattern with red and gold accents between the black bands
• Small species (1.5 inches max), ideal for nano and planted tanks
• Prefers soft, acidic water for best coloration
• Peaceful and calm, best kept in groups of 8 or more

Species Overview

Field	Details
Scientific Name	Nannostomus trifasciatus
Common Names	Three-Lined Pencilfish, Three-Striped Pencilfish, Three-Banded Pencilfish
Family	Lebiasinidae
Origin	Amazon basin, Rio Negro, Guyana
Care Level	Moderate
Temperament	Peaceful
Diet	Omnivore (micropredator)
Tank Level	Mid to Top
Maximum Size	1.5 inches (4 cm)
Minimum Tank Size	10 gallons (38 liters)
Temperature	75-82°F (24-28°C)
pH	5.0-7.0
Hardness	1-10 dGH
Lifespan	3-5 years in captivity
Breeding	Egg scatterer
Breeding Difficulty	Moderate
Compatibility	Peaceful community / specialist
OK for Planted Tanks?	Yes

Classification

Taxonomic Level	Classification
Order	Characiformes
Family	Lebiasinidae
Subfamily	Pyrrhulininae
Genus	Nannostomus
Species	N. trifasciatus (Steindachner, 1876)

Nannostomus trifasciatus was described by Franz Steindachner in 1876. The species name translates to “three-banded,” referring to the three horizontal stripes that give this fish its common name. There are several regional color variants that differ in the intensity and extent of their red and gold markings.

Note on family placement: Pencilfish belong to Lebiasinidae, which is separate from Characidae. This family was not affected by the 2024 Melo et al. revision. Nannostomus has been taxonomically stable for decades.

Origin & Natural Habitat

The three-lined pencilfish has a broad range across the Amazon basin in Brazil, with populations in the Rio Negro, Rio Madeira, and other major tributaries, as well as in Guyana. Different collection points produce fish with varying amounts of red and gold coloring, leading to some sought-after locality variants.

In the wild, they inhabit slow-moving blackwater streams and flooded forest margins with soft, acidic water stained dark with tannins. They’re found in areas with dense aquatic vegetation, submerged roots, and leaf litter. These are typically shaded, low-flow habitats where the fish hover among the vegetation.

Most fish in the trade today are captive-bred, though wild-caught specimens from specific localities are sometimes available from specialty importers.

Appearance & Identification

The three-lined pencilfish features three bold, dark horizontal stripes running from the snout to the caudal fin. Between these dark bands, the body shows bright patches of gold, cream, and red. The intensity of the red varies between populations and individuals, with some fish showing vivid crimson patches and others displaying more subdued coloring.

The body shape is typical of pencilfish: elongated, slender, and torpedo-shaped. Like all Nannostomus species, three-lined pencilfish often hover at an oblique angle in the water, which is perfectly normal behavior.

Like other pencilfish, this species displays a nocturnal color pattern. When the lights go off, the horizontal stripes fade and are replaced by a series of faint vertical bars. This is normal and the daytime pattern returns when lights come back on.

Sexual dimorphism is subtle. Males tend to be slightly slimmer and more intensely colored, particularly in the red areas. The anal fin of males often has a slightly different shape with a more rounded edge. Females are fuller-bodied when mature.

Average Size & Lifespan

Three-lined pencilfish reach about 1.5 inches (4 cm), making them well-suited for nano tanks and smaller planted setups. They’re slightly larger than some other pencilfish species like N. marginatus.

With proper care, expect a lifespan of 3 to 5 years. Soft, acidic water and a varied diet are the biggest factors in longevity.

Care Guide

Tank Size

A 10-gallon tank is the minimum for a small group. For a school of 10 to 12 with additional tank mates, a 20-gallon long provides more swimming room and easier maintenance. These are not demanding in terms of space, but they benefit from a longer tank footprint over a taller one.

Water Parameters

Parameter	Ideal Range
Temperature	75-82°F (24-28°C)
pH	5.0-7.0
General Hardness	1-10 dGH
KH	0-4 dKH
Ammonia / Nitrite	0 ppm
Nitrate	Below 15 ppm

Soft, acidic water is recommended for this species, though the three-lined pencilfish is somewhat more tolerant of moderate water conditions than some of its relatives like N. mortenthaleri. The best coloration comes out in soft, tannin-stained water. Indian almond leaves, driftwood, and peat filtration all help achieve these conditions.

Water quality should be excellent. These are clean-water fish that don’t tolerate organic waste buildup. Small, frequent water changes (15 to 20 percent twice weekly) work well for maintaining stable conditions.

Tank Setup

A densely planted tank with subdued lighting brings out the best in this species. Floating plants are highly recommended to diffuse light and provide security. Dense vegetation along the sides and back gives the fish places to retreat, while leaving some open areas for them to hover and display.

A dark substrate enhances the color contrast of their striped pattern. Leaf litter on the bottom adds a natural touch and provides tannins. Low-light plants like Java fern, Cryptocoryne, Anubias, and mosses thrive in the same conditions these fish prefer.

Keep water flow gentle. Pencilfish are not strong swimmers and prefer calm water.

Tank Mates

Three-lined pencilfish are among the most peaceful fish in the hobby. They rarely interact with other species and spend most of their time hovering quietly in the mid to upper water column.

Good Tank Mates

• Other pencilfish species
• Small, peaceful tetras (ember, green neon, cardinal)
• Pygmy corydoras, habrosus corydoras
• Otocinclus
• Small rasboras (chili, espei)
• Dwarf Apistogramma species
• Cherry shrimp, Amano shrimp
• Small snails

Tank Mates to Avoid

• Active, boisterous species that would outcompete them for food
• Large or aggressive fish
• Fast-moving species that would stress them

Food & Diet

Three-lined pencilfish are micropredators with small mouths. They feed best on small, appropriately sized food items.

• Best foods: Live baby brine shrimp, daphnia, microworms, grindal worms
• Frozen foods: Cyclops, baby brine shrimp, daphnia
• Dry foods: Crushed high-quality flakes or micro pellets (most individuals accept these readily)

The three-lined pencilfish is somewhat more willing to accept dry foods than some of its relatives, making it one of the easier pencilfish species to feed. Still, regular offerings of live or frozen foods promote the best coloration and condition. Feed small amounts two to three times daily.

Breeding & Reproduction

Three-lined pencilfish can be bred in captivity with some effort and attention to water conditions.

Breeding Setup

• Breeding tank: 5 to 10 gallons with dim lighting
• Water: Very soft (1-3 dGH), acidic (pH 5.0-6.0), temperature 79-82°F
• Decor: Java moss, fine-leaved plants, or spawning mops
• Filtration: Gentle sponge filter

Spawning occurs among fine-leaved plants, with eggs deposited individually on plant surfaces. Clutch sizes are typically small (20 to 50 eggs). Adults will eat eggs, so dense plant cover is essential or remove adults after spawning is observed.

Eggs hatch in approximately 24 to 36 hours. Fry are very small and require infusoria or liquid fry food as a first food, transitioning to baby brine shrimp nauplii after a week or so. Growth is slow, as is typical for pencilfish.

Common Health Issues

• Water chemistry stress: While more tolerant than some pencilfish, they still do best in soft, acidic water. Hard, alkaline conditions lead to dull coloring and increased disease susceptibility.
• Ich and velvet: Can occur during acclimation. Slow, gradual introduction to new water conditions is important.
• Starvation in community tanks: Their calm, deliberate feeding style means they can lose out to faster fish. Make sure food is reaching them.
• Stress from boisterous tank mates: These are quiet fish that stress easily around active, fast-moving species.

Common Mistakes to Avoid

• Hard, alkaline water: They’ll survive but won’t show their best coloration. Soft, acidic conditions make a visible difference.
• Bright lighting: Washes out their colors and makes them shy. Subdued lighting with floating plants is essential.
• Food too large: Their mouths are small. Standard flakes should be crushed, and pellets should be micro-sized.
• Groups too small: Pencilfish are more confident and display better behavior in groups of 8 or more.
• Mixing with fast feeders: They’re deliberate, slow feeders that get outcompeted by aggressive eaters like barbs or larger tetras.

Where to Buy

Three-lined pencilfish are one of the more commonly available pencilfish species and can be found through many online retailers. Check these trusted sources:

• Flip Aquatics
• Dan’s Fish

Frequently Asked Questions

Why does my three-lined pencilfish change color at night?

All pencilfish species display a nocturnal color pattern. When the lights go off, the bold horizontal stripes fade and are replaced by faint vertical bars. This is completely normal and not a sign of illness. The daytime pattern returns when the lights come back on.

Why does my pencilfish swim at an angle?

This is characteristic behavior for all Nannostomus species. Pencilfish naturally hover at an oblique, slightly head-up angle. It’s normal and not a sign of swim bladder problems or illness. If a pencilfish suddenly starts swimming normally (horizontally), that might actually be a cause for concern.

Can three-lined pencilfish be kept with other pencilfish species?

Yes, different Nannostomus species can be kept together in the same tank. They generally don’t interact with or show aggression toward other pencilfish species. A mixed pencilfish community in a planted blackwater tank is a beautiful setup.

Closing Thoughts

The three-lined pencilfish is a great entry point into the world of pencilfish. It’s more widely available and slightly more forgiving than some of the rarer species, while still offering the elegant appearance and fascinating behavior that makes this group so appealing. A school of these fish hovering at angles among the plants in a dimly lit blackwater tank is one of the most peaceful and attractive sights in the nano fish hobby.

If you’ve never kept pencilfish before, the three-lined is a great place to start. If you’re already a fan, it’s a species you probably already appreciate. Either way, it’s a fish that earns its place in any peaceful community or specialist setup.

Recommended Video

Check out our Tetra Tier List video where we rank popular tetra species for the home aquarium:

References

• Froese, R. and D. Pauly, Eds. FishBase. Nannostomus trifasciatus. Accessed 2025.
• SeriouslyFish. Nannostomus trifasciatus species profile. Accessed 2025.

Explore More Tetras

The three-lined pencilfish is just one of dozens of characin species we cover in our complete species directory. Whether you’re into pencilfish or classic schooling tetras, our guide has you covered.

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