''Bryconops allisoni'' is a species of freshwater fish known from the rivers of

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

. It is a recent addition to the genus (2019), currently considered a member ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

''. Its name honors

Antonio Machado-Allison Antonio is a masculine given name of Etruscan origin deriving from the root name Antonius. It is a common name among Romance language-speaking populations as well as the Balkans and Lusophone Africa. It has been among the top 400 most popular male ...

, an ichthyologist responsible for a great deal of work on the genus ''Bryconops''.

Description

The holotype, or first collected specimen, of ''Bryconops allisoni'' was 7.25 cm SL (

standard length Fish measurement is the measuring of individual fish and various parts of their anatomies. These data are used in many areas of ichthyology, including taxonomy and fisheries biology. Overall length * Standard length (SL) is the length of a fish m ...

). Other collected specimens range from 2.76 to 6.86 cm. This makes it slightly smaller than other members of the genus, which usually range from 6 to 8 cm SL. The body is generally slender, deepest in the region of the dorsal fin, and the snout is relatively long, about 23-29% of the length of the head. The scales of ''B. allisoni'' are silvery with a greenish iridescence, and parts of the snout are tinted brown. (Silver or greenish coloration is not uncommon in the genus as a whole.) It bears an iridescent-green lateral stripe that turns black when it advances onto the caudal fin, and the caudal fin also has a red blotch of pigment just above this stripe; the dorsal fin may have a spot of red, and the adipose fin is red entirely. The pelvic, anal, and dorsal fins are almost completely clear with scattered chromatophores (color cells). The presence of a stripe on the caudal peduncle on the caudal fin is a feature shared with '' B. chernoffi'', '' B. inpai'', and '' B. melanurus'', but various factors differentiate said species. In ''B. inpai'' and ''B. melanurus'', the stripe is longer, advancing onto the dorsal lobe of the caudal fin, and ''B. allisoni'' has more predorsal scales than ''B. chernoffi'' (10-12 vs. 8–9, respectively).

Sexual dimorphism

Mature males of ''B. allisoni'' are equipped with bony hooks on select fin-rays. This is a feature seen in many other members of ''Bryconops'', though the specific appearance may vary depending on the species, sometimes more accurately being described as barbs or spines;"THE FISH FAMILIES". Field Guide to the Fishes of the Amazon, Orinoco, and Guianas, edited by Peter van der Sleen and James S. Albert, Princeton: Princeton University Press, 2017, pp. 95-96. https://doi.org/10.1515/9781400888801-009 for instance, hooks are well-defined on the anal fin of congener '' B. munduruku'', but there are smaller spines on ''munduruku's'' dorsal and pelvic fins. Otherwise, there are no documented morphometric or coloration differences between males and females.

Taxonomy

''Bryconops allisoni'' has been considered a member 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 specie ...

'' since its description in 2019. There are two

subgenera 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 ...

in ''Bryconops'', ''Bryconops'' and ''Creatochanes'', and B. allisoni exhibits

synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

of both; multicuspid teeth on both

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...

e and well-denticulated

gill raker Gill rakers in fish are bony or cartilaginous processes that project from the branchial arch (gill arch) and are involved with suspension feeding tiny prey. They are not to be confused with the gill filaments that compose the fleshy part of the ...

s from ''Creatochanes'', but a shorter jaw structure associated with ''Bryconops''. Therefore, ''B. allisoni's'' subgeneric status is yet undetermined. It is still considered a member of the genus ''Bryconops'' ''

''. The specific name "allisoni" is in honor of

Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...

n ichthyologist

, who has written or co-authored a large amount of literature concerning the taxonomy of ''Bryconops''.

Distribution and ecology

''Bryconops allisoni'' is only known from the lower

rio Tapajós Rio or Río is the Portuguese, Spanish, Italian, and Maltese word for "river". When spoken on its own, the word often means Rio de Janeiro, a major city in Brazil. Rio or Río may also refer to: Geography Brazil * Rio de Janeiro * Rio do Sul, a ...

, appearing solely in small, right-bank tributaries. It is the most recent species described therein; excluding ''B. allisoni'', there are thought to be at least nine species cited from the middle and lower Tapajós basin. The congener ''B. munduruku'' specifically was also originally described from a right-bank tributary of the Tapajós, and ''B. allisoni'' occurs syntopically with congener ''B. melanurus''.

Conservation status

''Bryconops allisoni'' 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 ...

. Based on patterns seen in other members of the genus, it may be under threat of various anthropogenic hazards, including

illegal mining Illegal mining is mining activity that is undertaken without state permission, in particular in absence of land rights, mining licenses, and exploration or mineral transportation permits. Illegal mining can be a subsistence activity, as is the cas ...

and farmland settlement. The Tapajós main has been subject to such intense mining activity in the past that portions of it have turned entirely brown due to sediment addition and disturbance. However, its type locality, the Corredor Ecológico stream, is a tributary of the Tapaós located in the Tapajos National Forest, a large area of protected land. Therefore, there are already measures in place that may aid in its survival as a species.

References

{{Taxonbar, from=Q115774127 Bryconops Fish described in 2019 Freshwater fish of Brazil