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Coral Red Pencilfish

Scientific Name: Nannostomus mortenthaleri
Family: Lebiasinidae, Sub-Family Pyrrhulininae

About the Coral Red Pencilfish

Species Type: Freshwater Fish
Category: Characins

Care Level: DifficultThis fish may have multiple properties that make a fish moderately difficult to care for and is therefore only recommended to experienced fishkeepers who have had success in dealing with species that may have particular care requirements.

Origin: Occurs only in small forest tributary streams of the Rio Nanay, Peru. It may also occur in the Rio Tigre near Santa Elena in Loreto Department, Peru. The Rio Nanay is a very slow-moving blackwater stream that annually floods its banks into the surrounding forest. The substrate of the main river channel is sand and mud with a layering of leaves; bogwood abounds, as fallen trees, branches and roots.

Compatibility/Temperament: Peaceful; males will challenge each other and may nip slightly, and tend to drive females hard. Well suited to a species biotope tank or a community aquarium of small, peaceful characins, rasbora, small catfish and loaches, dwarf cichlids.


This beautiful pencilfish will sparkle in a well-planted aquarium with a dark substrate and subdued light; floating plants will greatly increase its sense of security. The tank should be well-planted, and have branches or twigs. This fish should always be kept in a group, with at least an even ratio of females to males to prevent the males from driving individual females too hard. Requires sufficient swimming space, and generally remains in the middle to upper levels mainly among plants where it will browse continually--when not displaying or chasing each other--for bits of food. It will spend time near the substrate, especially at feeding time, searching for food particles.

Males are generally more colourful than females; the outside edge of the anal fin is bright red and the anterior base of the dorsal fin is white in males. This is one species of characin in which the girth of the fish is not indicative of females except when carrying eggs. This species is not widespread in its habitat, and to date it has not been commercially spawned, though several aquarists have had successful spawnings. Since all available fish are wild-caught, particular attention must be given to the water parameters.

This species does not possess an adipose fin. In common with all pencilfish, the mouth is always open, and the fish have a diurnal colour pattern. During darkness, the horizontal lines break up into a series of dashes. This has been observed in blind fish, showing that it is an automatic response and not controlled by the fish.

This fish was first discovered in 2000 in a collection of fish from the Rio Nanay near the town of Alvarenga in Peru. First described as a sub-species of Nannostomus marginatus by Paepke & Arendt (2001), it was subsequently established as a valid distinct species by Weitzman in 2001. The species epithet honours the Austrian aquarist Martin Mortenthaler who owns the fish export company Aquarium Rio Momon which made the collection in which this beautiful pencilfish was discovered.

All pencilfish are found in the tribe Nannostomini in the subfamily Pyrrhulininae. Three different genera (Nannostomus, Nannobrycon and Poecilobrycon) were used at various times until Weitzman & Cobb (1975) placed all species in the single genus, Nannostomus, erected by Gunther in 1872 with N. beckfordi as the type species; Gery (1977) separated them into two genera, Nannostomus and Nannobrycon, largely on the basis of the swimming position. Weitzman & Weitzman in Reis et al. (2003) reassigned the species into the single genus Nannostomus which now includes all described pencilfish. The genus name Nannostomus comes from the Greek meaning "small mouth."


Gery, Jacques (1977) "Characoids of the World," TFH Books.

Reis, R.E., S.O. Kullander & C.J. Ferraris Jr. (2003), "Check list of the freshwater fishes of South and Central America."

Weitzman, Stanley H. (1966), "Review of South American Characid Fishes of Subtribe Nannostomina," Proceedings of the United States National Museum (Smithsonian Institution), Volume 119, Number 3538.

Weitzman, Stanley H. & J.S. Cobb (1975), "A revision of the South American fishes of the genus Nannostomus Gunther (family Lebiasinidae)," Smithsonian Contributions to Zoology No. 186.

Weitzman, Stanley H., J. Melgar & Marilyn Weitzman (2001), "The geographical color forms of the Dwarf Pencilfish Nannostomus marginatus and a related coral red form," Tropical Fish Hobbyist, May 2001, pp. 73-85.

Coral Red Pencilfish Diet

Will usually accept prepared foods including flakes and small frozen foods like daphnia, and bloodworms. Wingless fruit flies would be a suitable live food treat.


Attains 1.2 inches.

Minimum Tank Suggestion

20 gallon, or 15 gallon long.

Ideal water parameters for Coral Red Pencilfish

Soft (hardness below 10 dGH) acidic (pH below 7.0) water, temperature 24-28C/75-82F. Preferred ranges are less than 5 dGH and 5-6.5 in pH. pH values for the Rio Nanay system are below 6, averaging 5.2 to 5.5.

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