Coral-red pencilfish Care Guide: Diet, Tank Mates, Diseases, Breeding & More

Updated: November 1, 2022

The coral-red pencilfish is a beautiful freshwater fish that is perfect for the nano aquarium.

This species is peaceful and relatively easy to care for, making them a great choice for beginner fishkeepers.

But even though they’re easy to care for, there are still a few things you need to know before you add them to your tank.

In this guide, we’ll teach you everything you need to know about coral-red pencilfish care. tank size, diet, lifespan, and more!

Species overview

Coral-red pencilfish (Nannostomus mortenthaleri) are a freshwater fish that are found in the Orinoco River basin in South America.

They inhabit blackwater streams and rivers which are slow-moving and have a very low pH. The leaves and other plant matter in these habitats release tannins and other chemicals which give the water its dark color.

This species is peaceful and relatively small, which makes it a good choice for a community tank. They are also relatively easy to care for, which is another plus.

The main draw of the coral-red pencilfish is its beautiful coloration. The fish is mostly red with a black stripe running down the length of its body. This contrasting coloration is quite striking and makes this fish a real standout in any aquarium.


Coral-red pencilfish

As the name would suggest, the most defining feature of this fish is their color. The vast majority of their body is a deep coral red.

The only time you’ll see much color variation is on the tips of their dorsal and caudal fins as well as their ventral fins. These fins have a beautiful yellow hue that really makes this fish stand out.

Coral-red pencilfish have a very elongated and thin body. This gives them a hydrodynamic shape that helps them zip around the water with ease.

Their dorsal fin is tall and starts almost at the very back of their bodies. This fin is rather pointed at the end and tapers down gradually as it goes towards the head.

The anal fin is much shorter and also starts near the back of the body. This fin is more rounded than the dorsal fin.

The caudal fin is forked and symmetrical.

One unique thing about this fish is that they have a very long snout. This snout is almost as long as the rest of their bodies!


Coral-red pencilfish have a lifespan of up to 6 years in captivity. This is actually quite long for a fish of this size.

As with all fish, their lifespan will be impacted by the quality of care they receive. If they are kept in suboptimal conditions, their lifespan will be significantly shorter.


The average Coral-red pencilfish size is about 2 inches in length, with males being slightly larger than females. Despite their small size, they still need a fair amount of space to swim and hide. As a result, a 10 gallon tank is the bare minimum you can get away with.


Tank Size

The recommended minimum tank size for coral-red pencilfish is 10 gallons. However, we recommend going up to a 20 gallon tank if you can swing it. This will give you a little bit more room to work with when it comes to stocking your tank.

Water Parameters

Coral-red pencilfish come from the blackwater rivers of Brazil. These habitats are characterized by being murky, with very little visibility. The water is also stained brown from tannins and other dissolved organic matter.

This gives the water a slightly acidic pH, high hardness, and low alkalinity.

While you can’t recreate the exact environment, you can get close. It’s important to remember that these fish come from slow-moving waters. As such, they do not like a lot of current in their tank.

Here are some ideal water parameters for coral-red pencilfish.

  • Water temperature: 75 to 85 degrees Fahrenheit
  • pH levels: 6.0 to 7.0
  • Water hardness: 2 to 12 dGH
  • Alkalinity Levels: 2-6 dKH

What To Put In Their Tank

When it comes to setting up the interior of their tank you have a few options. The first is to go with a planted tank. These fish love being around vegetation, so it’s a great way to provide them with some enrichment.

The second option is to go with a more traditional setup. This would involve adding some rocks and driftwood to the inside of the aquarium.

We recommend a mixture of both if you can manage it. This will give your fish plenty of places to hide and explore.

The substrate you use is up to you. These fish don’t have any specific requirements, so feel free to use whatever you’d like.

Just make sure that it’s not too sharp or abrasive. Something like sand or small gravel would be ideal.

Common Diseases

The Coral-Red Pencilfish is a rather hearty and disease-resistant fish. They’re not immune to everything, but they’re definitely not as susceptible to illness as some other freshwater species.

The most common disease that these fish experience is ich. This is a parasites that will cause your fish to develop white spots on their body, fins, and gills.

If left untreated, ich can be quite serious (even deadly). However, it’s relatively easy to treat if you catch it early.

The best way to prevent your Coral-Red Pencilfish from getting sick is by maintaining a clean and stable tank. These fish are rather tolerant of different water conditions but they still need clean water to thrive.

If you notice anything out of the ordinary with your fish (white spots, abnormal behavior, etc.) be sure to consult a vet as soon as possible. The sooner you act, the better the chance is that your fish will make a full recovery.

Behavior & Temperament

Coral-red pencilfish (Nannostomus mortenthaleri) are a peaceful, shy species that does best when kept in groups. They are typically timid and will spend a lot of time hiding, so it’s important to provide them with plenty of hiding places in their aquarium.

Coral-red pencilfish are also known to be jumpers, so a tight-fitting lid is a must.

This species is a bit more sensitive than some of the other pencilfish, so it’s important to acclimate them slowly to their new environment.

Once they’re acclimated, they’ll be a little more active and you may see them swimming around in the middle or top of the water column. They are also known to be good jumpers, so a tight-fitting lid is a must.

In terms of temperament, coral-red pencilfish are relatively peaceful. They may squabble with each other from time to time, but they typically don’t bother other tank mates.

Tank Mates

The coral-red pencilfish is a peaceful and relatively small freshwater fish. As a result, it can be kept with a wide variety of tank mates.

The main thing to consider is that these fish come from slow-moving waters in the Amazon. As a result, they’re not built for high-speed chases and might get stressed out by more active fish.

It’s also important to remember that coral-red pencilfish are schooling fish. They do best when kept in groups of at least six individuals. This will help reduce aggression and make them feel more comfortable.

Some compatible tank mates for coral-red pencilfish include:

  • Tetras
  • Rasboras
  • Danios
  • Gouramis
  • Corydoras Catfish
  • Plecos


Coral-red pencilfish are beautiful little freshwater fish that make a great addition to any aquarium. They’re not the easiest fish to breed, but it can be done with some patience and the right setup.

To start, you’ll need a breeding tank that’s at least 10 gallons. The water should be soft and acidic, with a temperature between 76 and 82 degrees Fahrenheit.

Next, you’ll need to add some plants. Live plants are best, but you can also use artificial plants. Just make sure that they’re safe for freshwater aquariums.

When it comes to decor, use your imagination. Driftwood, rocks, and caves all make great hiding places for these fish. Just make sure that there are plenty of places for them to hide.

Now it’s time to add the fish. You’ll need at least six fish, and it’s best to have two males for every female.

Once the fish are in the tank, you’ll need to wait for them to reach maturity. This usually takes around six months.

When they’re ready to breed, the males will start to chase the females around. The females will lay their eggs in plants or on rocks. After that, the males will fertilize them.

Once the eggs are fertilized, the parents will lose interest and swim away. The eggs will hatch in about three days.

At this point, you’ll need to remove the parents from the tank. They will eat the fry if given the chance.

The fry will feed on microscopic organisms in the water. You can supplement their diet with baby brine shrimp or other commercially-available foods.

As they grow, you can slowly start to introduce them to flake food and other aquarium-safe foods.


Coral-red pencilfish are absolutely beautiful fish that make a great addition to any freshwater tank. They’re not too difficult to care for, but there are a few things you need to be aware of.

Overall, we think they’re a great choice for any aquarist who wants to add a splash of color to their tank. Just be sure to do your research and be prepared to care for them properly!