The tailspot tetra (''Bryconops caudomaculatus'') is a freshwater fish that lives in the coastal river regions of upper South America. Both its common and scientific names reference the distinct spot of color present on the tail fin, which is one of its defining characteristics. It is a small fish, reaching 4.8 in (12.4 cm) at its longest. Despite its small size, it is an active swimmer, with a preference for fast-flowing waters.

Description

The tailspot tetra, like the rest 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 ...

'', has a slender body described as "

smelt Smelt may refer to: * Smelting, chemical process * The common name of various fish: ** Smelt (fish), a family of small fish, Osmeridae ** Australian smelt in the family Retropinnidae and species ''Retropinna semoni'' ** Big-scale sand smelt ''At ...

-like", similar to members of sister genus ''

Piabucus ''Piabucus'' is a genus of freshwater tetras in the family Iguanodectidae. All three species are found in South America, largely the Amazon and its major tributaries. None of them are longer than half a foot long, with the largest reaching a max ...

''. It reaches 4.8 in (12.4 cm) in

total 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 ...

(with the tail fin included), and a corresponding weight of 20.1 grams. Its back scales are tinted orange to dark-orange, fading into silver on the belly when the fish is alive. Upon close inspection, the scales are also revealed to have a scattering of minute dots. The spot of bright orange on the basal half of the caudal fin is what gives the tailspot tetra its common name. The scientific name also reflects this - "caudo-" is in reference to the caudal fin (the tail fin), and "-maculatus" means "spotted" (compare with the word "immaculate", which means "without blemishes"). Though it is more vivid in life, this spot of color may turn pale upon preservation of a given specimen.Machado-Allison, Antonio & Buckup, Paulo & Chernoff, Barry & Royero, Ramiro. (1993)
Las especies del genero Bryconops Kner, 1858 en Venezuela (Teleostei, Characiformes)
14. 1-20. Visually, the tailspot tetra is easy to confuse with congeners '' B. magoi'' and '' B. collettei'', which means that they have often been misidentified as ''B. caudomaculatus''.Chernoff, Barry & Machado-Allison, Antonio. (2005)
Bryconops magoi and Bryconops collettei (Characiformes: Characidae), two new freshwater fish species from Venezuela, with comments on B. caudomaculatus (Günther)
Zootaxa. 1094. 10.11646/zootaxa.1094.1.1. (This is part of the reason they are considered to be in the same species complex.) Recent congener '' B. florenceae'' was also previously misidentified as ''B. caudomaculatus'' before its distinction as a separate species. 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 ...

is usually incomplete. Some specimens of ''B. caudomaculatus'' display a particularly truncated lateral line that makes them appear more visually similar to '' B. durbini''. Another recently named congener, '' Bryconops piracolina'', is visually similar, but with a difference in the lateral line - it has a smaller number of pored lateral line scales than ''B. caudomaculatus''.

Taxonomy

In 1864,

Albert Günther Albert Karl Ludwig Gotthilf Günther FRS, also Albert Charles Lewis Gotthilf Günther (3 October 1830 – 1 February 1914), was a German-born British zoologist, ichthyologist, and herpetologist. Günther is ranked the second-most productive re ...

gave the tailspot tetra the scientific name ''Tetragonopterus caudomaculatus'' when he first described it as a new species. The genus '' Tetragonopterus'' is closely related to the genus ''Bryconops'', and therefore an element of viability remains in Günther's original placement. Ichthyologist

Carl H. Eigenmann Carl Henry Eigenmann (March 9, 1863 – April 24, 1927) was a German-American ichthyologist of the late nineteenth and early twentieth centuries, who, along with his wife Rosa Smith Eigenmann, and his zoology students is credited with identifyin ...

placed ''B. caudomaculatus'' into the genus ''Creatochanes'', which was later classified as 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. caudomaculatus'' no longer belongs; Instead, it is considered ''Bryconops'' (''Bryconops'') ''caudomaculatus''. The tailspot tetra is the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

of the ''Bryconops caudomaculatus''

species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

, which includes ''B. caudomaculatus, B. disruptus, B. durbini, B. collettei,'' and ''B. magoi''. This complex is not official, but species have been placed in it based upon

phenotypic In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...

similarities and a history of synonymy with ''Bryconops caudomaculatus''. Due to striking visual similarities and subsequent routine misidentification, ''B. florenceae'' (named in 2021) is a candidate for the complex, though this has not been professionally recognized. The genera ''Bryconops'', ''

Iguanodectes ''Iguanodectes'' is a genus of freshwater fish found in tropical South America, with eight currently described species. They are all small tetras, none longer than 5 inches, and often have attractive silvery or striped scales, which makes them a t ...

,'' and ''

'' were previously in the family

Characidae Characidae, the characids or characins is a family of freshwater subtropical and tropical fish, belonging to the order Characiformes. The name "characins" is the historical one, but scientists today tend to prefer "characids" to reflect their st ...

, which is incredibly variable and has many genera

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 ...

. In 2011, however, research by Oliveira et al. prompted the three to be moved to the family

Iguanodectidae Iguanodectidae is a family of freshwater fish in the order Characiformes that lives in South America. It is home to the subfamily Iguanodectinae (Eigenmann, 1909) and the monotypic ''Bryconops'' clade. Several species in the family, such as the ...

, which was revived from Eigenmann's previous work.Oliveira, C., Avelino, G.S., Abe, K.T., Mariguela, T.C., Benine, R.C., Orti, G., Vari, R.P., & Correa e Castro, R.M. (2011)
Phylogenetic relationships within the speciose family Characidae (Teleostei: Ostariophysi: Characiformes) based on multilocus analysis and extensive ingroup sampling.
� ''BMC Evolutionary Biology, 11: 275. doi: 10.1186/1471-2148-11-275'' The tailspot tetra's classification as a

characiform 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.: "Relationshi ...

fish in the family Iguanodectidae is its current accepted position.

Habitat and ecology

The tailspot tetra is an active swimmer, with a physiology that reflects this despite its small size. Its chosen habitat is also linked to its swimming strength, as it has a noted preference for fast-flowing waters with rocky substrate. It is also not an uncommon sight in a contrasting home - slow-moving blackwater environments. Its morphology differs based upon where it lives (in a running water channel as opposed to a

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') a ...

); studies have shown that examination based upon physical aspects can correctly classify at least 75% of any given specimens' habitats.Langerhans, Brian & Layman, Craig & LANGERHANS, AIMEE & Dewitt, Thomas. (2003)
Habitat-associated morphological divergens in two Neotropical fish species
Biological Journal of the Linnean Society. 80. 689 - 698. 10.1111/j.1095-8312.2003.00266.x. More of the body weight is shifted backwards for tailspot tetras that live in lagoon habitats, and the mouth is slightly more upturned for channel-dwelling tetras. A study in January of 2022 tested the effects of

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...

in the tailspot tetra's environment, as aluminum is soluble in acidic waters and has been linked to cardiotoxic damage after prolonged exposure. Researchers determined that an aluminum concentration of 3.0 mg/L has a high likelihood of leading to an

atrioventricular block Atrioventricular block (AV block) is a type of heart block that occurs when the electrical signal traveling from the atria, or the upper chambers of the heart, to ventricles, or the lower chambers of the heart, is impaired. Normally, the sinoatr ...

in ''B. caudomaculatus'', meaning that the heart's ability to beat effectively gets compromised due to interruption (blockage) of the responsible electrical impulse.

Prey and predators

As part of its omnivorous diet, the tailspot tetra will actively leap from the water to target flying insects, especially during the twilight hours. It also has a marked taste for insects that have not yet matured, as opposed to the mature terrestrial forms that have moved onto land. It is unknown if varying habitats, and therefore varying morphologies, have a distinct effect on specific diet composition, though it is speculated that this could be the case. In turn, the tailspot tetra is not only a regular part of the

food chain A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), det ...

as a source for animals that eat small fish, but it is also preyed upon by

parasites Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted structurally to this way of lif ...

. In 2011, ''B. caudomaculatus'' was discovered to be the host for a new species of

trematode Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host ...

(parasitic flatworm), ''Auriculostoma foliaceum'' (which is currently accepted as ''Creptotrema foliaceum'').

Conservation status

Though the tailspot tetra's conservation status has not been evaluated, it is known to be taken from the wild in places including

Guyana Guyana ( or ), officially the Cooperative Republic of Guyana, is a country on the northern mainland of South America. Guyana is an indigenous word which means "Land of Many Waters". The capital city is Georgetown. Guyana is bordered by the ...

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 ...

, and

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 ...

for export in the aquarium industry, especially in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...

.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. Despite this, it remains common in many places, including areas disrupted by the construction of the Balbina Hydroelectric Dam in

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 ...

. Its ability to adapt to its surroundings combined with a flexible diet make it unlikely to become endangered.

References

{{Taxonbar, from=Q5554627 Characiformes Fish described in 1864 Taxa named by Albert Günther Tetras