Nannostomus (from the Greek nanos, meaning "small", and the Latin stomus, relating to the mouth) Several species have become popular aquarium fish due to their attractive coloration, unique shape, and interesting demeanor.

Taxonomy

The genus Nannostomus was first described by Günther in 1872, with the type species N. beckfordi. In 1876, Steindachner described three more species, N. unifasciatus, N. eques (pictured below), and N. trifasciatus (pictured above). In 1909, Carl H. Eigenmann described N. marginatus, N. minimus, N. erythrurus and N. harrisoni. Several of these have been popular with aquarists since the early 20th century, partly due to enthusiastic articles written about them and photographs taken by William T. Innes that were published as early as 1933.

Over the years, the genus was split by subsequent authors into other genera, including Poecilobrycon and Nannobrycon. After nearly a century of debate on the subject, Dr. Stanley Howard Weitzman and Dr. J. Stanley Cobb restored earlier taxonomy and expanded upon it, unifying all species under Nannostomus in 1975. This comprehensive revision of the genus has now been widely accepted. Weitzman is also responsible for describing five of the more recently introduced species, N. marilynae, N. limatus, N. nitidus, N. britskii and N. anduzei. Twenty species are now known, most of which are also familiar to aquarists. Several other unidentified Nannostomus species have been imported over the years; many were found as bycatch with other small characins, but their taxonomic status is yet to be determined.

Species

Nannostomus contains the following species:

  • Nannostomus anduzei <small>Fernández & S. H. Weitzman, 1987</small>
  • Nannostomus beckfordi <small>Günther, 1872</small> (golden pencil fish)
  • Nannostomus bifasciatus <small>Hoedeman, 1954</small> (two-lined pencil fish, whiteside pencil fish)
  • Nannostomus britskii <small>Weitzman, 1978</small> (spot stripe pencil fish)
  • Nannostomus digrammus <small>(Fowler, 1913)</small> (two-stripe pencil fish)
  • Nannostomus eques <small>Steindachner, 1876</small> (brown pencil fish, Diptail)
  • Nannostomus erythrurus <small>(C. H. Eigenmann, 1909)</small>
  • Nannostomus espei <small>(Meinken, 1956)</small> (Espe's pencil fish, barred pencil fish, brown pencil fish)
  • Nannostomus grandis <small>Zarske, 2011</small>
  • Nannostomus harrisoni <small>(C. H. Eigenmann, 1909)</small> (Harrison's pencil fish, black stripe pencil fish)
  • Nannostomus limatus <small>Weitzman, 1978</small> (elegant pencil fish)
  • Nannostomus marginatus <small>C. H. Eigenmann, 1909</small> (dwarf pencil fish)
  • Nannostomus marilynae <small>Weitzman & Cobb, 1975</small> (Marilyn's pencil fish, greenstripe pencil fish)
  • Nannostomus minimus <small>C. H. Eigenmann, 1909</small> (least pencil fish)
  • Nannostomus mortenthaleri <small>Paepke & Arendt, 2001</small> (coral-red pencil fish)
  • Nannostomus nigrotaeniatus <small>Zarske, 2013</small>
  • Nannostomus nitidus <small>Weitzman, 1978</small> (shining pencil fish)
  • Nannostomus rubrocaudatus <small>Zarske, 2009</small> (purple pencil fish)
  • Nannostomus trifasciatus <small>Steindachner, 1876</small> (three-stripe pencil fish)
  • Nannostomus unifasciatus <small>Steindachner, 1876</small> (one-line pencil fish)

Description

thumb|300px|left|[[Nannostomus eques (brown pencil fish, diptail)]]

Most species are slender, pencil-shaped fish ranging in size from under ). N. marginatus, N. rubrocaudatus, and N. mortenthaleri possess shortened, blockier outlines reminiscent of pencil stubs.

The adipose fin is present in some species and absent in others, while in certain species, such as N. eques, its presence or absence varies between individuals.

All species swim horizontally, except N. unifasciatus and N. eques, which assume an oblique, 'snout-up' posture.