Nannostomus unifasciatus
| One-lined pencilfish | |
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| Nannostomus unifasciatus | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Characiformes |
| Family: | Lebiasinidae |
| Genus: | Nannostomus |
| Species: | N. unifasciatus |
| Binomial name | |
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Nannostomus unifasciatus Steindachner, 1876 |
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Nannostomus unifasciatus, (from the Greek: nannos = small, stomus = mouth; from the Latin: unifasciatus = one band), commonly known as the one-lined pencilfish, is a freshwater species of fish belonging to the genus Nannostomus in the Lebiasinidae family of Characins. They are popular in the aquarium trade due to their small size, beautiful color pattern, unique swimming posture and relative hardiness. With its long, pencil-shaped profile, its single jet black stripe reminiscent of the graphite core of a pencil, and its eraser-colored caudal fin, this is the species for which the popular name, 'pencilfish', was first coined in the 1920s, later to be applied to all the species of the genus Nannostomus.
Steindachner first described the species in 1876, making it the second of what are now nineteen species in the genus to be described. The taxonomy for the entire genus was for many decades the subject of heated debate, resulting in numerous conflicting revisions, leaving the genus for long periods in a state which has been aptly described as 'chaotic.'N. unifasciatus was often at the center of this controversy and this for several reasons.N. unifasciatus, is broadly distributed throughout the Amazon basin, in Brazil, the Guiana Shield, Colombia, Venezuela, and northern Bolivia. As a result, the species is polymorphic with many geographic populations manifesting subtle morphological differences, most frequently regarding color. Over the years, some of these color morphs have been erroneously described as separate species. Further taxonomic confusion arose when various authors erected other genera for Nannostomus unifasciatus and its congeners, Nannostomus eques and Nannostomus harrisoni. Confounding the situation still further, Dutch naturalist, J. J. Hoedeman published a paper in The Amsterdam Naturalist in 1950 that put forth that N. unifasciatus and N. eques were one and the same species. Consensus was finally achieved when, in his seminal paper on the genus Nannostomus in 1975, Dr. Stanley H. Weitzman restored Steindachner's taxonomy and expanded upon it, reaffirming the status of N. unifasciatus and N. eques as distinct and individuated species, and placing N. unifasciatus and all of its congeners in one genus, Nannostomus. As a result, 'Poecilobrycon ocellatus,' 'Nannobrycon unifasciatus,' and similar epithets formerly applied to the species, are now relegated to junior synonyms to N. unifasciatus. A population of the species has also been discovered on the island of Trinidad, but it is believed to have been introduced.
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