Pencilfish: Complete Care Guide (Nannostomus spp.)

What It Is Actually Like Living With Pencilfish

The Pencilfish is more active and aware of its surroundings than most people expect. In a properly set up tank, it shows behaviors that generic care guides never mention.

Feeding becomes a routine both you and the fish look forward to. The Pencilfish learns your schedule and responds to your presence near the tank within the first few weeks.

Maintenance is consistent, not difficult. Regular water changes and parameter monitoring become second nature. The fish rewards consistent care with better color, more activity, and visible health.

Over time, you notice personality traits unique to your individual fish. Some are bold explorers. Others are cautious observers. That individual personality is what turns casual fishkeeping into a genuine hobby.

Table of Contents

• What Most Care Guides Get Wrong About Pencilfish
• Frequently Asked Questions
• Overview
• Classification
• Origin and Habitat
• Appearance
• Care
• Types
• Is the Pencilfish Right for You?
• How the Pencilfish Compares to Similar Species
• Final Thoughts
• The Reality of Keeping Pencilfish
• What It Is Actually Like Living With Pencilfish

Pencilfish are precision feeders that pick food off surfaces with surgical accuracy. They do not compete well with aggressive eaters. Put them in a tank with barbs or fast tetras and they starve while everything else gets fat. Success with pencilfish means building the tank around their feeding behavior.

Pencilfish do not compete for food. Build the tank around them or watch them starve.

Expert Take

Pencilfish are one of the most underappreciated groups in the hobby. Once you keep a group in a proper blackwater setup, you realize why dedicated nano keepers obsess over them.

The Reality of Keeping Pencilfish

They hover. That is the point. Pencilfish spend much of their time motionless or drifting slowly through the water column, often at a slight upward angle. If you want a fish that constantly swims and schools, pencilfish will feel “lazy.” But their hovering behavior is fascinating once you appreciate it. They are ambush micro-predators picking tiny organisms from the water.

Night colors are different from day colors. Many pencilfish species change their color pattern dramatically at night. The daytime stripes and colors fade and are replaced by bars or blotches. This is normal and one of the most interesting aspects of keeping them.

They need calm tank mates. Fast, aggressive fish stress pencilfish into hiding. They are best kept with other calm species like corydoras, small rasboras, or other pencilfish. In a hectic community tank, they fade into the background and you lose everything that makes them special.

Biggest Mistake New Owners Make

Keeping them with active, boisterous tank mates. Pencilfish are quiet, deliberate fish. In a tank full of barbs or large tetras, they hide, refuse to eat properly, and slowly decline.

Key Takeaways

• Pencil fish are one of the more peaceful barb fish available in the aquarium trade
• They grow from 1.5 to a little over 2 inches depending on the type
• They enjoy schooling and prefer to be in groups of at least 5
• They do great in community tanks are won’t eat plants

Overview

Scientific Name	Nannostomus spp.
Common Names	Pencil fish
Family	Lebiasinidae
Origin	South America
Diet	Omnivore
Care Level	Moderate
Activity	Low to Moderat
Lifespan	3 to 5 years
Temperament	Peaceful but aggressive feeders
Tank Level	Bottom to medium level
Minimum Aquarium Size	10 gallons
Temperature Range	64°F to 82°F
Water Hardness	4 to 8 KH
pH Range	6.0 to 7.5
Filtration/Water Flow	Moderate
Water Type	Freshwater
Breeding	Egg layer
Difficulty to Breed	Moderate
Compatibility	Community tanks
OK, for Planted Tanks?	Yes

Classification

Order	Characiformes
Family	Lebiasinidae
Genus	Nannostomus
Species	Multiple species (Gunther, 1872)

Origin and Habitat

Like many other fish in the aquarium hobby, pencil fish originate from South America. These fish have a wide range and is found throughout parts of the Amazon River basin as well as in Venezuela, Peru, Guyana, Suriname, and Colombia. There, they is found schooling above a leaf-littered substrate or in and out of dense vegetation.

Unlike the many other species they’re found swimming alongside, pencil fish aren’t the most colorful fish. That isn’t to say that these fish aren’t worth keeping, though!

Pencil fish are not commonly found in typical fish stores. They’re easy to keep and is kept in a community tank, but hobbyists will shy away from them. The fact of the matter is that there are more exciting and colorful fish available. However, a school of pencil fish can encourage other fish to come out of hiding and provide an interesting topic for onlookers.

Pencil fish belong to the Nannostomus genus, meaning small mouth. As we’ll see, these fish have very small mouths that can make stocking tank mates easy but feeding difficult. As of now, there are about 19 discovered species, many of which have made their way into the home aquarium.

Appearance

Pencil fish aren’t the biggest or brightest fish you’ll see in the aquarium. However, these fish are still interesting to look at and can definitely bring excitement to the tank where other species can’t.

These fish get their name from their very slender bodies with two pointed ends. Oftentimes, these fish will have thick lateral stripes that help give them a pencil-like appearance. Pencil fish come in relatively plain colors, like browns, yellows, and muted reds. Some of the more intensely colored species may resemble a cherry barb (Puntius titteya).

On average, pencil fish grow to be about 1.5 – 2.0 inches. There are few differences between males and females; males typically have more intense coloration while females are plainer and rounder in shape.

Care

Though not common to see in the aquarium setting, pencil fish are pretty easy to care for. They are small schooling fish with low activity levels that can make a great alternative to a more traditional school of tetras or rasboras.

The only challenging aspect of keeping pencil fish is fed.

Tank Size

Pencil fish are small fish that don’t need a lot of open swimming space. They’ll float around the middle and bottom portions of the tank in a loose school, investigating each other and the environment around them.

While these freshwater fish only grow to be a couple of inches, they need to be kept in schools. Because of this, the minimum tank size recommended is 10 gallons for the smallest pencil fish species. It is strongly recommended to get upwards of a 29 gallon aquarium to allow for tank mates.

Pencil fish are one of the few fish that does better in a tall tank than in a long tank. Different species of pencil fish prefer different regions of the water column, allowing hobbyists to mix and match for a full spectrum from top to bottom.

Aquarium Setup

Like many other Amazonian species, pencil fish thrive in a planted aquarium. These fish love to pick through leaf litter and forage vegetation for any algae growth. The waters of their natural habitat are typically stained with tannins from driftwood and detritus littering the sandy substrate. These conditions should be matched in the aquarium as best as possible.

Pencil fish are bold and curious fish, but appreciate a backdrop of plants to occasionally swim through. The best part about these fish is that they are considered a dither fish, motivating other shyer-planted tank species to come to the front of the aquarium.

At the same time, pencil fish is kept in a simple tank setup. These aquarium fish are also suitable for beginners that might not be ready to tackle a full freshwater ecosystem with live plants just yet.

Water Parameters

Pencil fish are tropical fish that need relatively consistent water parameters. They need a constant water temperature between 72-82°F with slightly acidic and soft water. pH should remain between 6.0-7.5 with water hardness between 4-8 KH.

Water pH and water hardness may be lowered by using dried botanicals that release tannins. Not only does this improve water quality, but leaf litter can also be used to provide your fish with food and protection.

Filter and Aeration

Pencil fish do not create a lot of waste, but a lot of waste is created due to their feeding.

Pencil fish have very small mouths that sometimes make it hard for them to accept traditional fish flake foods or pellets. Because of this, hobbyists often need to crush up foods or give protein-rich live foods. On top of this, many pencil fish refuse to eat off the bottom of the substrate. This can lead to some waste management issues.

The best filtration for pencil fish will be a sponge filter, hang-on back filter, or canister filter that is rated for at least 2x the aquarium size. Additional aeration helps keep waste off the substrate and improve oxygenation but is not necessary for the success of the fish.

Lighting

Like most South American fish, pencil fish appreciate the coverage. Most of the small rivers and streams that run throughout the continent are stained black from botanicals. This makes for very shaded water that helps fish swim in the open.

Pencil fish will do best with dimmed lighting along with some floating plants. Larger background plants also be used to create more areas of refuge. This will help your pencil fish be more present in the aquarium, which will subsequently encourage other fish to be brave, too.

Community Tank Mates

In general, pencil fish are considered peaceful fish that is kept with a variety of tank mates. However, there are a few stories about a school of pencil fish being very aggressive to each other and to other fish.

It should be noted that pencil fish can become considerably aggressive for several reasons. Pencil fish can become territorial during feeding times and breeding periods. Try to keep your fish well fed and feed in a separate part of the tank away from the other species. Add additional fish if there is intraspecies aggression.

That being said, pencil fish luckily have very small mouths and they can’t do a ton of damage, especially if they can’t catch the other fish. Some of the best pencil fish tank mates include:

• Tetras
• Barbs
• Rasboras
• Corydoras
• Platies
• South American cichlids

Because of their ability to be more aggressive, pencil fish are a popular tank mate for South American dwarf cichlids, like Apistogramma. Pencil fish helps cichlids be more in the open and there is little need to worry about potential fry being eaten.

How Many Should You Get?’

Pencil fish are social schooling fish and need to be kept in groups of at least 6 or more. If you are having intraspecies aggression, then adding more pencil fish to the group helps decrease tensions.

Food and Diet

Pencil fish are omnivores but are mostly carnivorous. Feeding these aquarium fish is slightly more challenging than keeping more common tropical fish, but is relatively straightforward.

There are two things to consider when feeding your pencil fish. One is that they have very small mouths. Two is that these fish are unlikely to eat off the bottom of the tank. This means that small foods that don’t sink fast are ideal.

A varied diet can include live and frozen food, like brine shrimp, daphnia, and microworms. A high-quality fish flake food or pellet may be broken up into smaller pieces. For the most part, these fish will get all the green nutrition they need from the natural flora growing in the aquarium, but an algae flake or pellet along with blanched vegetables also be supplemented.

All uneaten food should be removed.

Breeding

Pencil fish aren’t the easiest species of freshwater fish to breed, but it has been done before. Beckford’s pencil fish do be the easiest to breed (video source).

Pencil fish are egg scatters that don’t provide any care for their young; the eggs are laid, fertilized, and hatched, leaving the fry to fend for themselves. For the best results, a breeding tank is recommended.

This breeding tank should be dimly lit with a dark substrate and plenty of aquatic plants. A sponge filter will keep the aquarium clean and oxygenated without the threat of sucking up babies. When ready, move a group of pencil fish to the aquarium. This is necessary as it is very difficult to tell males apart from females.

Slowly adjust the water temperature to about 84° F. Feed a high-protein diet. Eventually, males should start to intensify in color. Females may begin to deposit their eggs among the leaves, which will then be fertilized by the male.

It is strongly recommended to remove the adult pencil fish from the aquarium once the eggs have been laid. The eggs hatch and fry and become free-swimming after about a week. The fry should be able to sustain itself on the microorganisms available in the tank, especially if a sponge filter is available. However, crushed-up fish flakes also be offered.

Eventually, the fry will be able to be removed from the breeding tank.

Types

Of the 19 species of pencil fish known, many have made their way into the aquarium trade. These fish are inexpensive, but certain species fetch more money than others.

It should also be noted that pencil fish are still largely wild-caught, which can make for a more difficult transition to the home aquarium.

1. Diptail

• Scientific Name: Nannostomus eques
• Adult Size: 1.5 inches
• Color Pattern: Brown, black, tan
• Unique Traits: Lateral black stripe

Also known as the brown pencil fish or hockey stick pencil fish, the diptail pencil fish has a very natural appearance. These fish live in the Amazon and are excellent micro predators. They are one of the shyer species of pencil fish and will spend their time hunting for small organisms around the tank.

At first glance, this fish might resemble a Siamese algae eater (Crossocheilus oblongus) or Otocinclus catfish.

2. Dwarf

• Scientific Name: Nannostomus marginatus
• Adult Size: 1 inch
• Color Pattern: Brown, black, yellow, red
• Unique Traits: Lateral black stripes and red-tipped fins

The dwarf pencil fish is a favorite for nano hobbyists. Some experienced pencil fish keepers like to keep these fish in as little as 5-gallon aquariums.

The dwarf pencil fish originates from Guyana and Suriname with very acidic and soft water. They have been found in pH as low as 4.0.

3. Coral Red

• Scientific Name: Nannostomus mortenthaleri
• Adult Size: 1.5 inches
• Color Pattern: Brown, white, red, black
• Unique Traits: Broad lateral red stripe outline in black

The coral red pencil fish is one of the most popular species of pencil fish in the hobby. These fish are small with a brilliant stripe of red across their bodies. They originate from Peru-given their second most common name, the Peruvian red pencil fish-and appreciate a densely planted aquarium that helps bring out their intense coloration.

4. Golden

• Scientific Name: Nannostomus beckfordi
• Adult Size: 1.5 inches
• Color Pattern: Brown, yellow, black, red
• Unique Traits: Lateral black stripe with red fins

Also known as Beckford’s pencil fish, the golden pencil fish is the most common species to come across in fish stores. These fish are plain in color but can turn incredible shades of red in correct environmental settings and/or during spawning periods.

These fish originate from northeast regions of South America but have been successfully commercially bred.

5. Purple

• Scientific Name: Nannostomus rubrocaudatus
• Adult Size: 2 inches
• Color Pattern: Red, blue, black, brown
• Unique Traits: Lateral black stripes with bluish-white to red gradient

one of the most expensive pencil fish available, the purple pencil fish might not be what you expect (video source). These fish are not completely purple as their name suggests. Instead, purple pencil fish have a bluish-white to red gradient from their head to their tail which can appear purple under certain lighting.

Although these Peruvian fish might not be purple, they are one of the larger pencil fish species that is used to fill up a planted aquarium with intense coloration.

Is the Pencilfish Right for You?

Before you add a pencilfish to your tank, it’s worth asking whether this species actually fits your setup and your goals. Here’s a quick breakdown to help you decide.

This species is a good fit if:

• You have a large enough tank to manage territories. Cramped conditions amplify aggression.
• You’re comfortable managing aggression through stocking ratios, line of sight breaks, and tank layout.
• You can commit to regular water changes. These fish produce more waste than many smaller species.
• You’re not planning a peaceful community tank. Pencilfishs need tank mates that can hold their own.
• You enjoy watching active, interactive fish. Cichlids have personality that smaller species simply don’t match.
• You have backup plans. Sometimes a particular fish just doesn’t work out, and you need a way to rehome it.
• You’re feeding a varied, high-quality diet. Color and health depend on nutrition.

If most of those points line up with your setup, the pencilfish is worth serious consideration. If several don’t, it’s better to choose a species that matches your tank now rather than trying to make it work.

How the Pencilfish Compares to Similar Species

Want an easy community fish? This is not it. Want a species that rewards dedicated care? The Pencilfish delivers if you put in the work.

Choosing between similar species is tricky. Here’s how the pencilfish stacks up against some common alternatives.

The pencilfish occupies a specific niche in the aquarium hobby, and direct comparisons really depend on what you’re looking for. In my experience, the most common question people ask is whether they should choose the pencilfish or something similar that’s more widely available. The answer usually comes down to three things: tank size, water parameters, and what other fish you’re keeping. If your setup matches what the pencilfish needs, it’s hard to beat. If not, there are alternatives worth exploring.

Final Thoughts

When thinking of freshwater fish to add to your aquarium, pencil fish might not be at the top of your list. They might not even be on your list at all. Over the next few years, this will likely change. Pencil fish are great beginner fish that are small and easy to keep.

Hobbyists may run into some initial problems during feeding times and when picking the right tank mates, but pencil fish can either fill up their own space in the aquarium or be used to encourage other shyer species.

References

• Seriously Fish — Species profiles and care data
• FishBase — Taxonomy and scientific data
• Practical Fishkeeping — Husbandry and care advice