Pencilfish, scientifically known as Nannostomus, is a genus of fish that belongs to the Lebiasinidae family of Charasins. All species are slender and pencil-shaped and range between 2.5 -5cm in length. All Pencilfish swim in a horizontal attitude, except for Nannostomus unifasciatus  and Nannostomus eques, which assume a more oblique, snout-up posture. In most of the species the males are brilliantly coloured, particularly on their fins, and gender can usually be recognised by the enlarged, elongated and brilliantly coloured anal fins of the males.

 The genus is distributed over  large areas across most of South America, from the northern Columbia,Venezuela and the Guyanasto the Amazon basin and Bolivia in the south, Peru in the west and Brazil in the east.

 In their natural habitat, Pencilfish live in soft, acidic waters with a pH of 5.5-6.8, with low nitrate levels and warm temperatures ranging from 25° to 28°C. This should of course be emulated in their tank. Pencilfish do best in a well planted aquarium with moderate lighting and a dark substrate, which tends to display their colours better. They do best in a group of at least 6 of the same species. In most species, the males will establish a territory and defend it, but this is mostly harmless posturing. Once acclimatised to their aquarium, and providing the water conditions are ideal, Pencilfish are very hardy and can live up to five years.


Pencilfish are peaceful and do well with tankmates such as other Nannostomus species, tertras, rasboras corydoras, plecos and more. If kept in a densely planted species tank with the ideal conditions, they will readily spawn and not eat the eggs. The fry is normally found amongst the floating plants. Baby brine shrimp, live or frozen, as well as other small sized foods is necessary for both adults and fry.

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