Pencil Fish – A Complete Care Guide

Are you thinking of adding a pencil fish to your fish tank? If so, you’ll want to read this complete care guide first. In this guide, we’ll cover everything you need to know about keeping pencil fish healthy and happy in your tank. We’ll discuss their habitat, diet, and care requirements, as well as how to properly set up and maintain a tank for pencil fish. So whether you’re a beginner aquarium keeper or just thinking about getting a pet pencil fish, read on for all the information you need to make sure your little aquatic friend stays healthy and happy!

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


Scientific NameNannostomus spp.
Common NamesPencil fish
OriginSouth America
Care LevelModerate
ActivityLow to Moderat
Lifespan3 to 5 years
TemperamentPeaceful but aggressive feeders
Tank LevelBottom to medium level
Minimum Aquarium Size10 gallons
Temperature Range64°F to 82°F
Water Hardness4 to 8 KH
pH Range6.0 to 7.5
Filtration/Water FlowModerate
Water TypeFreshwater
BreedingEgg layer
Difficulty to BreedModerate
CompatibilityCommunity tanks
OK, for Planted Tanks?Yes

Origin and Habitat

Like many other fish in the aquarium hobby, pencil fish originate from South America. These fish have a wide range and can be found throughout parts of the Amazon River basin as well as in Venezuela, Peru, Guyana, Suriname, and Colombia. There, they can be 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 can be kept in a community tank, but hobbyists tend to 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.


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.


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 can be 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 can be 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 can be 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 can help keep waste off the substrate and improve oxygenation but is not necessary for the success of the fish.


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 may 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 can be 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:

Because of their ability to be more aggressive, pencil fish are a popular tank mate for South American dwarf cichlids, like Apistogramma. Pencil fish can help 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 may help decrease tensions.

Food and Diet

Pencil fish are omnivores but are mostly carnivorous. Feeding these aquarium fish can be 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 may also be supplemented.

All uneaten food should be removed.


Pencil fish aren’t the easiest species of freshwater fish to breed, but it has been done before. Beckford’s pencil fish seem to 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 can be 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 may also be offered.

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


Of the 19 species of pencil fish known, many have made their way into the aquarium trade. These fish are generally 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

Pencil Fish In A Planted Tank
  • 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

Dwarf Pencil Fish Planted Tank
  • 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

Coral Red Pencil Fish in Aquarium
  • 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

Golden Pencil Fish in Aquarium
  • 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 probably the most common species to come across in fish stores. These fish are usually 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

Probably 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 can be used to fill up a planted aquarium with intense coloration.

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.

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