''Bryconops melanurus'', sometimes called the tail-light tetra, is a small species of freshwater fish from

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

that primarily preys on insects. It lives in small schools and is an active swimmer, which means that it requires open space in its habitat. Nonetheless, it does not demonstrate a strong preference for any one biotope within its native range.

Description

''Bryconops melanurus'' reaches a maximum total length of about 13.2 cm (5.2 in), which puts it on the larger side of the genus '' Bryconops''. The head is slender, with a pointed snout, and ''B. melanurus'' lacks a

humeral spot Humeral spot (from Latin ''humerus'', pertaining to the shoulder) is a mark or pattern found on several species of fish, typically above the pectoral fin Fins are distinctive anatomical features composed of bony spines or rays protruding f ...

of the kind frequently seen in congeners (such as '' B. humeralis'' and '' B. inpai''). ''B. melanurus'' shares aspects of its jaw structure, which is rather lengthened, with ''B. inpai'', '' B. affinis'', and '' B. giacopinii''. (This was used to place ''giacopinii'' in the genus ''Bryconops'' instead of its originally described ''Autanichthys''.) ''Bryconops melanurus'' is a silvery, slender fish with a darker back. The caudal fin has distinctive markings, but lacks a well-formed ocellus (eyespot). There is a dark stripe about the width of the pupil that veers from the center of this fin up towards the dorsal lobe, and the caudal-fin margins are dusky. The rest of the fin is either light in pigment (usually yellowish) or entirely clear. ''Bryconops melanurus'' has noted morphological similarities with congeners '' B. transitoria'' and '' B. gracilis'', but can be differentiated based on morphometric specifics and differences in fin structure; for instance, ''B. transitoria'' has 23-27 anal-fin rays, whereas ''B. melanurus'' has 28–29. ''B. melanurus'' is also known to be similar to '' B. cytogaster'', but ''cyrtogaster'' has a deeper body and a greater number of anal-fin rays (30-31). While it lacks a common name accepted by the wider scientific community, hobbyists know it as the tail-light tetra. It should not be confused with the head-and-tail light tetra, ''Hemigrammus ocellifer'', which is a different fish in the same order, Characiformes.

Taxonomy

''Bryconops melanurus'', when originally described by German naturalist

Marcus Elieser Bloch Marcus Elieser Bloch (1723–1799) was a German physician and naturalist who is best known for his contribution to ichthyology through his multi-volume catalog of plates illustrating the fishes of the world. Brought up in a Hebrew-speaking Jewish ...

in 1794, was named ''Salmo melanurus'', and was listed as a salmon native to

Suriname Suriname (; srn, Sranankondre or ), officially the Republic of Suriname ( nl, Republiek Suriname , srn, Ripolik fu Sranan), is a country on the northeastern Atlantic coast of South America. It is bordered by the Atlantic Ocean to the north ...

. (In modern taxonomy, the name '' Salmo'' applies to a genus in the family Salmonidae that encompasses trout and salmon from

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

. ''B. melanurus'' is not native to Europe, nor is it a salmon.) By 1926, it had been moved to the genus ''Creatochanes'', which is reflected in a paper by English ichthyologist John Roxborough Norman. ''Creatochanes'' is no longer considered a standalone genus, and is instead a

subgenus In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a species name, in parentheses, placed between t ...

of ''Bryconops'' to which ''B. melanurus'' belongs. (This makes its full name ''Bryconops (Creatochanes) melanurus''.) DNA barcoding has revealed that ''B. melanurus'' is most closely related to ''B. transitoria'' and '' B. caudomaculatus'', moreso the former than the latter.

Habitat and ecology

The type locality of ''B. melanurus'' is

, but no specific river was given in the original description. Specimens have been cited from the Caraipé, Curuá,

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, and

Moju Moju is a municipality in the state of Pará in the Northern region of Brazil. See also *List of municipalities in Pará This is a list of the municipalities in the state of Pará (PA), located in the North Region of Brazil. Pará is divided ...

rivers in modern accounts, as well as the Tapajós. Within this range, it seems to demonstrate no preference for any one

biotope A biotope is an area of uniform environmental conditions providing a living place for a specific assemblage of plants and animals. ''Biotope'' is almost synonymous with the term "habitat", which is more commonly used in English-speaking countrie ...

in particular, but does prefer living in groups.

Diet

''Bryconops melanurus'' feeds primarily on insects. This is in line with the rest of the genus, members of which are largely invertivores, with a few noted herbivores on the list. Specific dietary habits are unclear, but may be similar to habits of congeners '' B. inpai'' and '' B. magoi'', which feed on terrestrial insects that are either washed into the river or that fall from trees hanging above.

Conservation status

''Bryconops melanurus'' has not been evaluated by the

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

. While it is known to be exported from

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = Seal (emblem), National seal , national_motto = "Fi ...

for use in the aquatics industry,Prang, Gregory. (2007)
An industry analysis of the freshwater ornamental fishery with particular reference to the supply of Brazilian freshwater ornamentals to the UK market
Uakari. 3. 10.31420/uakari.v3i1.18. and it has a presence in hobbyist communities, it is not thought to be endangered. Aquarists know it not to fare particularly well in tank settings, partially because it is an active swimmer that needs plenty of space.

References

{{Taxonbar, from=Q11680346 Fish described in 1794 Characiformes Fish of South America Fish of Venezuela Taxa named by Marcus Elieser Bloch