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Dwarf Pencilfish (Nannostomus Marginatus) Care Guide

Need to add more peaceful fish to your community tank? The nannostomus marginatus can make a great buddy for your freshwater aquarium.

This tiny fish is so popular amongst aquarists for a great reason. The part of the Lebiasinidae family has such unique characteristics and beauty.

For most parts, it is very easy to take care of them. If you are a beginner, you don’t need any special skills to care for your little buddy. However, breeding can be more daunting than caring. We will explain why later in this post. But before going further, let’s see the overview of the dwarf pencilfish to learn more about it.

Species Overview

Level of CareEasy
Life Expectancy2-5 years.
Size3 – 4 cm (1.18 – 1.57 inch)
Tank Size4.4 gallons
Tank EnvironmentVery soft and acidic water with the decorations of  decaying leaves and wood
Tank MatesCorydoras catfish and small loricariids

The nannostomus marginatus is categorized as a freshwater aquarium fish. This proposition alone is a winning point since you could just add this fun little creature to your nano or small tank and it will thrive.

You could add a larger tank if you tag these buddies along with the other various tank mates. These fish will effectively add more interesting colors that you can enjoy from time to time.

Natural Habitat

The tiny pencilfish has been emerging in popularity since 1928. The first domestication record is traced back to European merchants who gave the “dwarf pencilfish” the name because of its tiny size.

Although it was revolving around Europe, the original location of the fish was in the Suriname and Guyana river basin.

According to the researchers, they found their natural habitats in the small rivers and streams which come from the main riverbed. In these spots, there are a lot of hides and shades thanks to the fallen leaves, branches of trees, and plants.

And they will likely love to live in similar habitat in your community aquascape.


Nannostomus marginatus is the tiniest and most beautiful representative of the Lebiasinidae family.

It has a slim and elongated body with a small mouth and larger eyes. And you will notice its spindle shape first as the fish moves around in the water.

The other unique appearance lies in its tail fin, which is transparent enough so that many aquarists wonder how powerful the magic that this tiny fish has.

The fins are red. The tail fin has a grayish tint. Unlike the other species in the same part of the family, these tiny buddies do not come with fatty fins.

What I like the most about the appearance of this dwarf fish is its natural night coloring. The day coloring might look indifferent. But when the night comes, you will be surprised by the coloration that it presents to you.

While the stripes of your tiny buddies get paler, the central stripe will dash a lot. As you use the dark substrate in your community tank, you will see the maximum coloration of the fish. And it will be a fulfilling feeling to experience.

Challenges of Adopting

The dwarf pencilfish buddies have been popular in the world of aquarists. There are tons of reasons to keep these in your tank. These tiny fish have great coloring, a peaceful temper towards their kind and others, a tiny size, and are easy to care for and feed.

Nano and small aquarium users often face many challenges in finding the appropriate dwellers for their tanks.

If you are looking for the best nano tank residents, the nannostomus marginatus is a fantastic choice.

The size of this fish is about 3 cm at max. You could keep the fish in a group since it is a schooling fish. The small tank size is also enough for your pet and its tank mates.

The challenge of caring for this fish is to maintain the water parameters and prevent disruptions that will affect the fish’s life. And for the new tank owner, it is very imperative to make the tank mature first before proceeding.

Bringing your tiny fish to a completely new tank will be strange and challenging for them. In the worst case, they could die.


In captivity, the tiny pencilfish’s life span could be around five years. But it can be less. The reason is simple. Since the fish size is small, its fast metabolism makes it die sooner.

Tank Setup

As mentioned, it is easy to take care of dwarf pencilfish and make them thrive for a long time. For a small school of tiny fish, you can prepare as little as 4.4 gallons or 20 liters of water. The larger the group, the larger the size of the tank that you need to prepare for them. Keep at least 10 of the specimens for each group of fish.


The decoration is straightforward. The best way to decorate your aquarium is to replicate the real habitat of the fish maximally. Here is how you can do it.

The bottom part of the tank should be a dark color. Then you can add some plants in moderate numbers.

Do not overcrowd the tank since it will limit the space for the schooling fish to swim and explore the space.

Add the plants moderately and it will be enough for your fish and their buddies. The fish will look better in large groups. So, it does not hurt to prepare a larger tank at home.

In their natural habitat, they school in the thick flora aquascape. Similar conditions will be much more favorable for them. You could add thin tank plants. You can feed them food nearby these plants since these are their favorite places. You can also add stones where algae can grow. They are also fond of algae as their main staple.

2 dwarf pencilfish

Water Parameters

Good water parameters will be the main keys to the wellness and survivability of your nannostomus marginotus tiny fish and their tank mates.

These dwarf fish can survive and thrive with simple tap water. You can also use water conditioners that are sold in the marketplace to make the water drinkable. After using the conditioner, there is no need to conduct a complex procedure to settle the water for your fish.

According to experts, the recommended water temperature is around 23 to 26° Celsius.

Meanwhile, the pH levels are around 4 to 7. However, the most recommended pH value for this fish to survive is from 6 to 6.8. The hardness should be around 8dGH, although your pencilfish can survive in up to 15 dGH water hardness.

In their natural habitats, these dwarf buddies usually live in soft waters. But in captivity, these fish can adapt very well to hard water. Even though you have harder water in the tank, the fish can still tolerate the conditions. But it does not mean you can overlook this matter. Exposing your dwarf pencilfish to the hardest water for a long time can affect their life expectancy.


Consider having a high-quality filter that can maintain clean water. But do not use a filter with strong water flow. They need slow water flow to thrive. The most appropriate filter type for this purpose is a canister filter.

Nannostomus Marginatus Tank Mates

Your dwarf pencilfish buddies are the upper and middle dwellers of your community tank. They are schoolmates. So, you will want to keep them in a group of six at least. You could enlarge the group members if you have a larger aquarium.

It will be fun to see them darting from one corner to another. They are spread when they look for food. But they will flock again after done.

The number proportions of genders should also be ideal. Males of this species are highly competitive. So, you will want to keep fewer males than females in the tank.

The good tank mates for your marginatus are species that are similar in size to them.

The good nature of these fish allows you to choose many fish, such as:

And so on…

Any similar-sized fish that is peaceful can be their best tank mates. So, you won’t need to worry about introducing them to the other dwellers.

Dwarfs in an aquarium

Food & Diet

These fish are omnivorous.

They are not so picky when it comes to the foods that they eat.

They have small mouths so tiny foods can be the most prevalent for them. Their favorite foods are small crustaceans like daphnia.

The other alternative could be mini blood worms. But I won’t suggest you give them live foods since there have been many cases where the fish ended up getting sick after eating live foods.

Frozen foods are preferable. There are also commercial foods specially designed for this fish. You could use them to keep them healthy.

Breeding Guidelines

Your nannostomus marginatus fish tend to spawn anytime they want.

But the tricky part is when the adults have laid the eggs. They tend to eat them.

Although the females can lay hundreds of eggs at once, there will only be a few left in the end. Then you will have to take precautions to save the juveniles.

You could also separate them in the spawning tank with 2 females and one male. The juveniles are slow-moving.

You could give them brine shrimp to eat.

They grow slowly in the first week. But you can look at the significant growth in only two months.