''Piabucus caudomaculatus'' is a small freshwater fish inhabiting the rivers of

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

. It was the first member of the family Iguanodectidae to be reported from

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

, and it remains endemic to the region, found solely in the

Mamoré river The Mamoré is a large river in Brazil and Bolivia which unites with the Beni to form the Madeira, one of the largest tributaries of the Amazon. It rises on the northern slope of the Sierra de Cochabamba, east of the city of Cochabamba, and is k ...

basin. It displays a preference for slow-moving waterways and has a largely insectivorous diet.

Description

''Piabucus caudomaculatus'' reaches a maximum of 9.6 cm (3.8 in) standard length (SL). This makes it the smallest member of the genus. The largest is ''

Piabucus dentatus ''Piabucus dentatus'', also called the chin tetra or the coastal piabucus, is a small freshwater fish from the rivers of South America. It has a wide range that includes multiple coastal drainage systems, and was once mistakenly cited from Peru ...

'', at 12.9 cm (5.1 in) SL, and the second-largest is ''

Piabucus melanostoma ''Piabucus melanostoma'', sometimes called the chin tetra, is a small species of freshwater fish from the rivers of South America. It is the second-largest species of the genus, but still only reaches about 12 cm (4 in) long. Occasionally found ...

'', at 11.5 cm (4.5 in) SL. Members of ''

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 ...

'' are characterized by a deep chest and long pectoral fins, which sets them apart from otherwise-similar members of sister genus ''

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 ...

''. ''Piabucus caudomaculatus'' lacks an

adipose fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as s ...

. There is a spot of dark pigmentation on the lower jaw, a feature it shares with ''Piabucus melanostoma''. There is another dark spot that extends from the caudal peduncle to the middle caudal-fin rays. Piabucus_melanostomus

Visually, ''P. caudomaculatus'' bears similarities to congener ''P. melanostoma'', but there are several differentiating characteristics in their respective morphometries. These include differences in lateral line scales (75-76 in ''caudomaculatus'' and 82-87 in ''melanostoma''), dorsal-fin rays (8 or 9 vs. 11), and anal-fin rays (36-38 vs. 44-46). As well as in appearance, the two species are similar in dentition, both bearing a single tooth row in the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

Sexual Dimorphism

Males from all three species of ''Piabucus'' develop lappets (fleshy extensions) and small hooks on the foremost few rays of the anal fin. Similar sexual dimorphism is seen in all members of family Iguanodectidae, and is somewhat more common in related 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 ...

''."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

Taxonomy

''Piabucus caudomaculatus'' has retained its original name since discovery, given to it by Richard P. Vari in 1977. It is the most recent addition to the genus. While the other two species of ''Piabucus'' demonstrate intraspecific genetic variation that suggests unnamed species of ''Piabucus'', ''P. caudomaculatus'' is largely confirmed to be monophyletic.

Etymology

"Caudo-" means "tail", and "-maculatus" means "spotted" (consider the word "immaculate", which means "without spots or blemishes"). The specific name for ''P. caudomaculatus'' originates in the dark spot of pigment across the caudal peduncle and the middle caudal-fin rays. The generic name "Piabucus" is a Latinization of the Brazilian word "piabucu", which refers to various small fishes of similar shape. ''Piabucus caudomaculatus'' lacks a widely-accepted common name, but hobbyists have reported a ''Piabucus'' species with strong resemblance to ''P. caudomaculatus'' being sold under the name "chin tetra". In an evaluation of non-native species, the South African government referred to it as the "spot-tailed slender tetra".

Distribution and habitat

''Piabucus caudomaculatus'' is only known from

, in the

basin. Its type locality is a small, muddy waterway known as the Rio Matucare (Matucare river). The Mamoré river system generally has a high sediment load, and is considered a whitewater river, high in inorganic solids and particulates. The Matucare specifically is a small river, sometimes referred to as an arroyo (which is usually a smaller creek or stream) in literature and cartography.Author unknown.
San Joaquin
' (Map). 1:100,000. Series H632, sheet 3944. Washington, D.C.: U.S. Defense Mapping Agency, 1988. ''Piabucus caudomaculatus'' demonstrates a general preference for slow-moving streams, including blackwater environments as well as its usual whitewater.

Diet and ecology

Little is known of ''P. caudomaculatus'' in terms of diet or interactions with other fish species, but it is largely insectivorous. The Mamoré river and its tributaries are dense in aquatic vegetation, which provides an adequate breeding habitat for the invertebrates and insects upon which ''P. caudomaculatus'' feeds.

Presence and behavior in aquaria

It is unknown if ''P. caudomaculatus'' has an active presence in the aquarium industry, though fish bearing a strong resemblance to it are sometimes seen for sale. These could either be specimens of ''P. caudomaculatus'' or one of its congeners, but specific identity is infrequently confirmed.

Conservation status

''Piabucus caudomaculatus'' is considered a species of least concern 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 ...

. Still, its habitat faces various

anthropogenic hazard Anthropogenic hazards are hazards caused by human action or inaction. They are contrasted with natural hazards. Anthropogenic hazards may adversely affect humans, other organisms, biomes, and ecosystems. They can even cause an omnicide. The f ...

s. While rivers in the Mamoré basin are unaffected by dams or levees, there is still notable degradation of natural resources, including pollution from gold mining and an increased risk of entanglement in fishing nets. As it is a small species with a wide range, ''P. caudomaculatus'' is nonetheless unlikely to face increased survival pressures of particular remark.

References

{{Taxonbar, from=Q5638812 Fish described in 1977 Taxa named by Richard Peter Vari Characiformes Fish of South America Fish of Bolivia