''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 considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

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 ''Bryconops'' is a genus of freshwater fish in the family Iguanodectidae from South America. It consists of small fish, all under half-a-foot long, with slender bodies and silvery scales, though there is some mild color variation. Several species ...

''. 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. In insects, the humeral spot may be found on the Glossary_of_entomology_terms#Costa, cost ...

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 Characiformes is an order of ray-finned fish, comprising the characins and their allies. Grouped in 18 recognized families, more than 2000 different species are described, including the well-known piranha and tetras.; Buckup P.A.: "Relationsh ...

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, officially the Republic of Suriname, is a country in northern South America, also considered as part of the Caribbean and the West Indies. It is a developing country with a Human Development Index, high level of human development; i ...

. (In modern taxonomy, the name ''

Salmo ''Salmo'' is a genus of ray-finned fish from the subfamily Salmoninae of family (biology), family Salmonidae, and is part of the tribe (biology), tribe Salmonini along with the sister genera ''Salvelinus'' and ''Salvethymus''. Almost all ''Salmo ...

'' applies to a genus in the family

Salmonidae Salmonidae (, ) is a family (biology), family of ray-finned fish, the only extant member of the suborder Salmonoidei, consisting of 11 extant genera and over 200 species collectively known as "salmonids" or "salmonoids". The family includes salmo ...

that encompasses trout and salmon from

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

. ''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 John Roxborough Norman (1898, Wandsworth, London – 26 May 1944, Berkhamsted, Hertfordshire) was an English ichthyologist. He started as a clerk in a bank. His lifetime affliction with rheumatic fever began during his military service during the ...

. ''Creatochanes'' is no longer considered a standalone genus, and is instead a

subgenus In biology, a subgenus ( 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 the ge ...

of ''Bryconops'' to which ''B. melanurus'' belongs. (This makes its full name ''Bryconops (Creatochanes) melanurus''.)

DNA barcoding DNA barcoding is a method of species identification using a short section of DNA from a specific gene or genes. The premise of DNA barcoding is that by comparison with a reference library of such DNA sections (also called " sequences"), an indiv ...

has revealed that ''B. melanurus'' is most closely related to ''B. transitoria'' and, slightly more distantly, '' B. caudomaculatus''.

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 Curuá 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 Brazil, o ...

Madeira Madeira ( ; ), officially the Autonomous Region of Madeira (), is an autonomous Regions of Portugal, autonomous region of Portugal. It is an archipelago situated in the North Atlantic Ocean, in the region of Macaronesia, just under north of ...

, 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 Brazil, off ...

rivers in modern accounts, as well as the

Tapajós The Tapajós ( ) is a river in Brazil. It runs through the Amazon Rainforest and is a major tributary of the Amazon River. When combined with the Juruena River, the Tapajós is approximately long. Prior to a drastic increase in illegal gold mi ...

. 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 flora (plants), plants and fauna (animals), animals. ''Biotope'' is almost synonymous with the term habitat (ecology), "habitat", which ...

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) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...

. While it is known to be exported from

Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...

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 Bryconops Freshwater fish of Venezuela Taxa named by Marcus Elieser Bloch