Pencil fish

{{Short description|Genus of fishes}} {{Automatic taxobox | name = Pencilfish | image = Nannostomus.jpg | image_caption = ''Nannostomus trifasciatus'' | display_parents = 2 | taxon = Nannostomus | authority = Günther, 1872 | type_species = ''Nannostomus beckfordi'' | type_species_authority = Günther, 1872 | synonyms = {{Genus list | Archicheir | C. H. Eigenmann, 1909 | Poecilobrycon | Eigenmann, 1909 | Nannobrycon | Hoedeman, 1950 }} | synonyms_ref = <ref name = "Cof family">{{Cof family|family=Pyrrhulininae|access-date=6 August 2025}}</ref> }}

'''''Nannostomus''''' (from the Greek ''nanos'', meaning "small", and the Latin ''stomus'', relating to the mouth)<ref name="Innes" /> is a genus of fish belonging to the characin family Lebiasinidae. All of the species in this genus are known as '''pencil fish''', a popular name that was initially only applied to two species in the 1920s, ''Nannostomus unifasciatus'' and ''Nannostomus eques''. By the late 1950s, however, the term was applied to all members of the genus.<ref name="Innes">{{Cite book |last=Innes |first=William T. |url=https://hdl.handle.net/2027/coo.31924003400623 |title=Exotic Aquarium Fishes |publisher=Innes Publishing Co |year=1935 |edition=First |location=Philadelphia |pages=157–162 |hdl=2027/coo.31924003400623 |author-link=William T. Innes}}</ref><ref name="Vorderwinkler">{{Cite book |last=Vorderwinkler |first=William |title=Pencilfishes |publisher=TFN Publications |year=1965 |location=Neptune, NJ}}</ref><ref name="Innes, Wm.">{{Cite magazine |last=Innes |first=William T. |date=November 1940 |title=''Poecilobrycon unifasciatus'' |magazine=The Aquarium |publisher=Innes Publishing Co |publication-place=Philadelphia}}</ref> 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.<ref name="WeitzmanCobb">{{Cite journal |last1=Weitzman |first1=Stanley H. |last2=Cobb |first2=J. Stanley |title=A Revision of the South American Fishes of the Genus ''Nannostomus'' |url=https://repository.si.edu/bitstream/handle/10088/5196/SCtZ-0186-Hi_res.pdf?sequence=1&isAllowed=y |journal=Smithsonian Contributions to Zoology |publication-date=1975 |volume=186 |access-date=2023-07-08}}</ref> 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''.<ref name="Weitzman:3">{{Cite journal |last=Weitzman |first=Stanley H. |title=Three new species of fishes of the genus ''Nannostomus'' from the Brazilian states of Para and Amazonas (Teleostei, Lebiasinidae) |url=https://archive.org/details/threenewspecieso0000weit/page/n1/mode/2up |journal=Smithsonian Contributions to Zoology |publication-date=1978 |volume=263 |access-date=2023-07-08}}</ref> 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:<ref name = "Cof genus">{{Cof genus|genus=Nannostomus|access-date=6 August 2025}}</ref> * ''Nannostomus anduzei'' Fernández & S. H. Weitzman, 1987 * ''Nannostomus beckfordi'' Günther, 1872 (golden pencil fish) * ''Nannostomus bifasciatus'' Hoedeman, 1954 (two-lined pencil fish, whiteside pencil fish) * ''Nannostomus britskii'' Weitzman, 1978 (spot stripe pencil fish) * ''Nannostomus digrammus'' (Fowler, 1913) (two-stripe pencil fish) * ''Nannostomus eques'' Steindachner, 1876 (brown pencil fish, Diptail) * ''Nannostomus erythrurus'' (C. H. Eigenmann, 1909) * ''Nannostomus espei'' (Meinken, 1956) (Espe's pencil fish, barred pencil fish, brown pencil fish) * ''Nannostomus grandis'' Zarske, 2011 * ''Nannostomus harrisoni'' (C. H. Eigenmann, 1909) (Harrison's pencil fish, black stripe pencil fish) * ''Nannostomus limatus'' Weitzman, 1978 (elegant pencil fish) * ''Nannostomus marginatus'' C. H. Eigenmann, 1909 (dwarf pencil fish) * ''Nannostomus marilynae'' Weitzman & Cobb, 1975 (Marilyn's pencil fish, greenstripe pencil fish) * ''Nannostomus minimus'' C. H. Eigenmann, 1909 (least pencil fish) * ''Nannostomus mortenthaleri'' Paepke & Arendt, 2001 (coral-red pencil fish) * ''Nannostomus nigrotaeniatus'' Zarske, 2013 * ''Nannostomus nitidus'' Weitzman, 1978 (shining pencil fish) * ''Nannostomus rubrocaudatus'' Zarske, 2009 (purple pencil fish) * ''Nannostomus trifasciatus'' Steindachner, 1876 (three-stripe pencil fish) * ''Nannostomus unifasciatus'' Steindachner, 1876 (one-line pencil fish)

==Description== [[File:Nannostomus eques.jpg|thumb|300px|left|''Nannostomus eques'' (brown pencil fish, diptail)]]

Most species are slender, pencil-shaped fish ranging in size from under {{Convert|1|to|2|in|cm|abbr=on|disp=x| long (}}). ''N. marginatus'', ''N. rubrocaudatus'', and ''N. mortenthaleri'' possess shortened, blockier outlines reminiscent of pencil stubs.<ref name="Innes" /> All but one species, ''Nannostomus espei'', have one to five horizontal black or brown stripes with gold or silver iridescence appearing above the primary stripe. Most also display red, orange, or maroon highlights on their fins, and many have flashes of these colors on their bodies as well. The recently described ''N. mortenthaleri'' and ''N. rubrocaudatus'' are especially vividly colored. ''N. espei'' is unique in that the horizontal stripes are only weakly present and are supplanted by five dark comma-shaped blotches. Other species take this appearance at night, but only ''N. espei'' displays the pattern permanently and in daylight.<ref name="Weitzman:Nannostomina" >{{Cite journal |last=Weitzman |first=Stanley H. |title=Review of South American Characid Fishes of Subtribe Nannostomina |url=https://repository.si.edu/bitstream/handle/10088/16927/USNMP-119_3538_1966.pdf?sequence=1&isAllowed=y |journal=Proceedings of the United States National Museum |publisher=Smithsonian Institution Press |publication-place=Washington DC |publication-date=1967-12-30 |volume=119 |issue=3538 |archive-url=https://web.archive.org/web/20230708190351/https://repository.si.edu/bitstream/handle/10088/16927/USNMP-119_3538_1966.pdf?sequence=1&isAllowed=y |archive-date=2023-07-08 |access-date=2023-07-08 |url-status=bot: unknown }}</ref>

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.<ref name="Innes" />

Sexual dimorphism occurs in the genus to varying degrees. In some species, the males are more brilliantly colored, especially the fins. In other species, dimorphism is far less evident. However, the anal fin is generally a reliable indicator of gender. For most species, the anal fin of adult males is enlarged and elongated (as in ''N. espei'', ''N. eques'', etc.) and/or more colorful (as in ''N. harrisoni'', ''N. marginatus'', etc.). The popular aquarium species, ''N. trifasciatus'', is an exception in this regard.

==Distribution== The genus as a whole has a vast distribution in South America, from Colombia, Venezuela, and the Guyanas in the north, to the southern Amazon basin and Bolivia in the south, to Peru in the west, and Belém, Brazil in the east.<ref name="WeitzmanCobb" /> Several of the individual species have a distribution nearly as vast. As a result, many of the species are polymorphic and manifest marked color variations depending on the population. Over the years, some of these color variants have been erroneously described as separate species. Such names as ''Nannostomus ocellatus'', ''N. anomalus'' and ''N. auratus'', among many others, are now known to be junior synonyms for the various species.

==In the aquarium== To date, only two species, ''N. beckfordi'' and ''N. harrisoni'', have been commercially raised for the aquarium trade in fisheries, mostly in Asia. All of the remaining species that find their way to home aquaria are wild-caught from South American waters. ''Nannostomus'' species thrive in home aquaria when provided with soft, moderately acidic water, low nitrate levels, and temperatures in the range of {{cvt|22|-|28|C|F}}. The addition of aquatic plants is recommended, including floating varieties as they reduce the likelihood of fish jumping, a common occurrence for some of the species, especially ''N. espei'' and ''N. unifasciatus''. They should be kept in schools of at least six, or in a community aquarium with other species of ''Nannostomus'', other small peaceful characins, or corydoras. Aquariums with a strong water current, large tankmates, or swift-moving species should be avoided. If kept in a thickly planted single-species aquarium with the above water parameters, most species will spawn, eggs will not be eaten, and fry will be found growing in the floating plants. Baby brine shrimp, live or frozen, and other small-sized foods are required for both fry and adults.<ref name="Innes" /> They are also avid biofilm grazers and, for most of the species, algae are under-reported staples of their diet.

In most species, the males establish small territories and defend them. Their defensive actions are usually harmless, but in two species, ''N. mortenthaleri'' and ''N. trifasciatus'', antagonistic behavior directed at conspecifics can be harmful if sufficient space and plant cover is not provided.

Once acclimated to the aquarium and provided with suitable conditions, they are hardy, often living for five or more years.<ref name="Weitzman:Nannostomina" />

==References== {{Reflist}}

Category:Lebiasinidae Category:Nannostomus Category:Fishkeeping Category:Freshwater fish of South America Category:Taxa named by Albert Günther