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What is a Pencil Fish?

By Jason C. Chavis
Updated Mar 05, 2024
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A Pencil Fish is a freshwater fish found throughout South America. Known scientifically as Nannostomus, it is commonly used as an aquarium fish due to its coloring and shape. They are relatively small, ranging in size from only one to two inches (2.5 - 5.1 cm).

The Pencil Fish is native to most of the northern area of South America, particularly the Amazon basin. Countries such as Colombia, Venezuela, Bolivia and Brazil maintain a strong market on these types of fish. Although the Pencil Fish is traditionally found in these areas, they have been adapted to the climate of Asia as well. Today, they are found nearly worldwide due to their use in aquariums.

In the past, scientists have attempted to categorize the different types of Pencil Fish based strictly on the coloring of their bodies. This has been found to be apocryphal, as the fish are all basically identical. Today, researchers have determined that there are simply 17 distinct species which comprise the Nannostomus genus, most notably the Nannostomus beckfordi and Nannostomus harrisoni, used in trade.

Depending on the variety of Pencil Fish, the coloring and patterns vary significantly. Many have black or brown horizontal stripes with tinges of gold or silver. Others have a variety of blotches covering their bodies. The fins of the various species are usually vividly colored and can come in nearly any shade. These fins can be long or short depending on the sex and species.

While native populations of South America had known of the Pencil Fish, it wasn't added to the scientific records until 1872. Numerous scientists recorded the existence and species types through drawings and writings for years. It wasn't until 1933, however, that actual photographs of the fish were published in scientific journals. William T. Innes was the photographer, known widely for his work on taxonomy. Over the years, the different species were often mistaken for different genus types, but in 1975, they were merged into the unified genus Nannostomus.

The Pencil Fish is best kept in aquariums with temperature ranges of 72°F (about 22°C) to 82°F (about 28°C). While they can be used as general community fish, they thrive most readily when associated with other species of the same genus. Owners of these fish should feed the animals brine shrimp and algae as well as keep aquatic plants in the tanks to help with oxygen production.

Frequently Asked Questions

What is a Pencil Fish and where can it be found?

Pencil Fish is a common name for several small, slender freshwater fish species belonging to the genus Nannostomus, which are part of the family Lebiasinidae. They are native to the slow-moving, acidic waters of the Amazon Basin in South America. Their habitat includes countries like Brazil, Peru, and Colombia, where they thrive in densely planted areas with plenty of hiding spots.

How did the Pencil Fish get its name?

The Pencil Fish earned its name due to its elongated, narrow body shape that resembles a pencil. This distinctive physical trait, along with their horizontal stripes, makes them easily recognizable. Their slender form is an adaptation to their environment, allowing them to navigate through dense vegetation and tight spaces in their natural habitat.

What size aquarium is suitable for Pencil Fish?

For Pencil Fish, a minimum tank size of 10 gallons is recommended, but a larger aquarium is preferable to provide ample swimming space and to accommodate a school of these social fish. According to aquarium experts, maintaining a group of at least six Pencil Fish helps to promote natural behavior and reduces stress, enhancing their well-being in captivity.

What do Pencil Fish eat?

In the wild, Pencil Fish are omnivores, feeding on small insects, crustaceans, and plant matter. In captivity, they thrive on a varied diet that includes high-quality flake food, micro pellets, and live or frozen foods such as brine shrimp and daphnia. It's important to offer small portions that they can consume within a few minutes to prevent overfeeding.

Are Pencil Fish good community tank mates?

Pencil Fish are generally peaceful and make excellent community tank mates, especially when paired with other non-aggressive species that thrive in similar water conditions. They are best kept with small, peaceful fish to avoid predation, as their small size makes them vulnerable. Care should be taken to ensure that water parameters are consistent, as Pencil Fish can be sensitive to changes.

How do you breed Pencil Fish in captivity?

Breeding Pencil Fish in captivity requires setting up a separate breeding tank with soft, acidic water and fine-leaved plants or a spawning mop for egg laying. The water temperature should be slightly warmer than their regular tank to encourage spawning. After spawning, parents should be removed to prevent them from eating the eggs, which typically hatch within 24 to 36 hours.

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