''Bryconops marabaixo'' is a small freshwater fish from the lower

Amazon Amazon most often refers to: * Amazons, a tribe of female warriors in Greek mythology * Amazon rainforest, a rainforest covering most of the Amazon basin * Amazon River, in South America * Amazon (company), an American multinational technology c ...

basin, native to the Rio Jari. It is small and silvery, with a dark-gray back, and its fins are mostly clear, though the caudal fin has a dark stripe on the lower margin of the dorsal lobe, and a spot of red pigment just above that. Like many other members of ''Bryconops'', it has 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 ...

, which is a mark near each pectoral fin. ''Bryconops marabaixo'' was officially named in 2020, though it was the secondary focus of the nominal article. The study that described it had the primary purpose of solidifying a proper description for congener ''

Bryconops cyrtogaster ''Bryconops cyrtogaster'' is a midsize species of freshwater fish found in the rivers of South America. It is overall silver, with an indistinct dark patch at the base of the tail fin that spreads onto the fin rays slightly. Originally described ...

'', to which it has some superficial resemblance.

Description

''Bryconops marabaixo'' is a relatively small member of its genus. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

, or first collected specimen, measured 6.17cm 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 ...

), and further specimens measured 5.04-6.09 cm SL. Most members of ''Bryconops'' are between 6 and 8 cm SL. The body, while compressed, is rather convex, especially in comparison to other members of ''Bryconops''. The scales are generally silver, with a blue-green tint, and they are darker on ''B. marabaixo's'' back; this color changes to a yellowish or pale-brown upon preservation of a dead specimen in alcohol. (A silver-to-greenish color is not uncommon in ''Bryconops''. A bluish tint is only otherwise seen in '' B. inpai'' and '' B. sapezal''.) In life, the dark coloration from the back extends to the caudal peduncle and somewhat onto the base of the caudal fin. The humeral mark is middlingly conspicuous. ''Bryconops marabaixo'' bears some morphological resemblance to congeners '' Bryconops chernoffi'' and '' Bryconops rheoruber''. In all three, there are 8-9 predorsal scales (as opposed to 10-17 in other ''Bryconops'') and a similar position of dorsal-fin origin. In ''marabaixo'' and ''chernoffi'', the

lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelial ...

reaches the interradial membrane (the fin membrane itself) of the caudal fin, where it does not in any other congeners. Nonetheless, differentiation from ''B. marabaixo'' specifically is simple because ''B. chernoffi'' and ''B. rheoruber'' both lack a humeral spot.

Taxonomy

The genus ''Bryconops'' has 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 ...

, ''Bryconops'' and ''Creatochanes''. ''B. marabaixo'' is characterized as belonging to ''Creatochanes'' by way of its teeth and

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; members of Creatochanes have 1-3 teeth in either side of the

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 the gill rakers are ossified (bony) and well-denticulated. Both traits are seen in ''B. marabaixo'', though it has a jaw structure more reminiscent of subgenus ''Bryconops''. ''B. marabaixo'' has no known synonyms, and has retained its original name since discovery.

Etymology

The specific epithet "marabaixo" originates from a collection of religious and festive practices, Marabaixo, that originated in

Amapá Amapá () is one of the 26 states of Brazil. It is in the northern region of Brazil. It is the second least populous state and the eighteenth largest by area. Located in the far northern part of the country, Amapá is bordered clockwise by Fr ...

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 ...

, the type locality of ''B. marabaixo''. It is strongly associated with the resistance and cultural strength of black Brazilians, who were originally settled in the region as slaves. The religious aspect is tied with the

saints In religious belief, a saint is a person who is recognized as having an exceptional degree of holiness Sacred describes something that is dedicated or set apart for the service or worship of a deity; is considered worthy of spiritual res ...

of the Catholic church.

Distribution and ecology

''Bryconops marabaixo'' is only present in the Rio Jari and the Rio Iratapuru. The latter is a tributary of the former. It is the only species of ''Bryconops'' to be found in the rio Jari, though most species of ''Bryconops'' are from other regions of the Amazon. The range of ''B. marabaixo'' seems to be limited by the Cachoeira de Santo Antônio, a major waterfall in a downstream portion of the Jari.

Conservation status

Though ''B. marabaixo'' has not been officially evaluated, a large portion of its native range, the Rio Jari, is within the

Nascentes do Lago Jari National Park Nascentes do Lago Jari National Park ( pt, Parque Nacional Nascentes do Lago Jari) is a national park in the state of Amazonas, Brazil. It protects an area of Amazon rainforest in the BR-319 highway area of influence. Location The Nascentes d ...

. This park is one of few left in the region that prioritizes biological diversity and preservation, as opposed to sustainable use of natural resources. Nonetheless, it is under threat of illegal activities that include an unlawful access road that cuts through various protected areas. While this is not an immediate threat to the aquatic environment of the region, it sets a precedent of deliberate anthropogenic hazard that may eventually extend into ''B. marabaixo's'' habitat.

References

External links

{{Taxonbar, from=Q115774180 Fish described in 2019 Characiformes Fish of South America Fish of Brazil