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 species ...

'', 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 maxi ...

''. 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, for data used in many areas of ichthyology, including taxonomy and fishery biology. Overall length Standard length (SL) is the length of a fish measured f ...

(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 epithelia ...

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 ''Bryconops piracolina'' is a small fish that inhabits the waters of Brazil. It is slender and silvery in color, like many fish in ''Bryconops'', but can be distinguished from other members by way of its dorsal fin, which has a black patch of col ...

'', 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 , also Albert Charles Lewis Gotthilf Günther (3October 18301February 1914), was a German-born British zoologist, ichthyologist, and herpetologist. Günther is ranked the second-most productive reptile tax ...

gave the tailspot tetra the scientific name ''Tetragonopterus caudomaculatus'' when he first described it as a new species. The genus ''

Tetragonopterus ''Tetragonopterus'' is a genus of fish in the family Characidae native to South America. It is the only member of the subfamily Tetragonopterinae. The subfamily was originally much larger as previously defined, and contained many of the genera ...

'' 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 ichthyology, ichthyologist of the late nineteenth and early twentieth centuries, who, along with his wife Rosa Smith Eigenmann, and his zoology students is credited wit ...

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

type species In International_Code_of_Zoological_Nomenclature, 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 spe ...

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 (physical form and structure), its developmental processes, its biochemical and physiological propert ...

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,'' and ''

'' were previously in the family

Characidae Characidae, the characids, is a family of freshwater subtropical and tropical fish belonging to the order Characiformes. They are found throughout much of Central and South America, including such major waterways as the Amazon and Orinoco Riv ...

, which is incredibly variable and has many genera

incertae sedis or is a term used for a taxonomy (biology), 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 contains three genera: ''Iguanodectes, Piabucus'', and ''Bryconops''. Several species in the family, such as the green line lizard tetra (' ...

, 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. '' The tailspot tetra's classification as a

characiform Characiformes is an order of Actinopterygii, 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 ...

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'') an ...

); 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 2022 tested the effects of

aluminum Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium 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, often starting with an autotroph (such as grass or algae), also called a producer, and typically ending at an apex predator (such as grizzly bears or killer whales), detritivore (such as ...

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

parasites Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...

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

trematode Trematoda is a Class (biology), class of flatworms known as trematodes, and commonly as flukes. They are obligate parasite, obligate Endoparasites, internal parasites with a complex biological life cycle, life cycle requiring at least two 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, officially the Co-operative Republic of Guyana, is a country on the northern coast of South America, part of the historic British West Indies. entry "Guyana" Georgetown, Guyana, Georgetown is the capital of Guyana and is also the co ...

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 ...

, and

Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...

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 Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

.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, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

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

References

{{Taxonbar, from=Q5554627 Bryconops Fish of Guyana Freshwater fish of Peru Freshwater fish of Venezuela Fish described in 1864 Taxa named by Albert Günther Tetras