HomeFreshwater aquarium fishTetras & characinsOneline pencilfish Oneline pencilfish (Nannostomus unifasciatus) Scientific name: Nannostomus unifasciatus Steindachner, 1876 The Oneline pencilfish (Nannostomus unifasciatus) is a freshwater fish of the family Lebiasinidae that grows to about 5.5 cm (2.2 in). It is easy to keep and peaceful, suits community aquariums and needs a tank of at least 40 L (11 US gal), water at 24–29°C (75–84°F) and a pH of 5.5–7.0. Native range: South America, Parts of the Amazon river basin of Bolivia and Brazil. The upper Orinoco river basin of Venezuela, and Guyana. Oneline pencilfish care at a glanceCare levelEasyTemperamentPeacefulCommunity tankExcellentAdult size5.5 cm (2.2 in)Minimum tank40 L (11 US gal)Temperature24–29°C (75–84°F)pH5.5–7.0Hardness0–12 dGH (0–214 ppm)DietOmnivore. Accepts flakes, frozen foods and live foods. BiologyFeeds on worms, crustaceans and insects.Source: FishBase, licensed CC BY-NC 4.0. Species factsScientific nameNannostomus unifasciatusFamilyLebiasinidae (Pencilfishes)OrderCharaciformes (Characins)ClassActinopterygii (Ray-finned fishes)Maximum length3.8EnvironmentFreshwater;; pH range: 5.5 - 7.0; dH range: ? - 4 benthopelagicClimateTropicalDistributionSouth America: Parts of the Amazon basin of Bolivia, Brazil, and probably Colombia; the upper Orinoco basin of Venezuela, and Guyana.Conservation status (IUCN)Not EvaluatedThreat to humansHarmlessUsesAquarium: commercial More tetras & characinsStriped headstanderAnostomus anostomusBarred pencilfishNannostomus espeiMarbled headstanderAbramites hypselonotusGolden pencilfishNannostomus beckfordiRedspotted tetraCopeina guttataMarbled hatchetfishCarnegiella strigataSee all tetras & characins SourcesTaxonomy, distribution and biology data: FishBase (Froese, R. and D. Pauly, eds.), licensed CC BY-NC 4.0. Aquarium care parameters compiled, checked and converted to metric and imperial units by Guppies.za.net.Last updated 28 September 2026