''Bryconops disruptus'' is a small freshwater fish of 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 t ...

. It is only found in the Rio Negro in

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 souther ...

. Like the rest of the genus ''Bryconops'', ''B. disruptus'' is silvery in color, with a relatively deep chest and a notable set of teeth. The specific epithet "disruptus" refers to the incomplete lateral line.

Description

''Bryconops disruptus'' is one of the smallest members of ''

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 ...

'', measuring about 6.4 cm (2.5 in) in

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 ...

. The only species smaller is ''

Bryconops durbinae ''Bryconops durbinae'', sometimes listed under the name ''Bryconops durbini'', is a small species of freshwater fish in the family Iguanodectidae. It is the smallest species of the genus ''Bryconops''. Like all members of Iguanodectidae, it inha ...

'', which reaches 3.1 cm (1.2 in) in standard length. It is similar in coloration to ''

Bryconops caudomaculatus 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 ...

'', including a similar caudal ocellus (an eyespot on the tail fin), but is overall a darker silver and has a more consistently incomplete lateral line. The number of pored lateral line scales varies wildly, ranging from 9 to 23. Due to the presence of a caudal ocellus, ''B. disruptus'' bears an outward resemblance to ''B. caudomaculatus'', and its small size and general shape make it reminiscent of ''B. durbinae''. However, it can be told apart by various factors; these include fewer precaudal vertebrae (16 in ''B. disruptus'' versus 17–18 in ''B. caudomaculatus'') and the lack of a caudal ocellus in ''B. durbinae''.

Taxonomy

''Bryconops disruptus'' has been identified as a member of the genus ''

'' since its description in February 1997. Originally, the genus ''Bryconops'' was considered a member of 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 s ...

, but research in 2011 prompted a move into the family

, alongside the genera ''

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 ...

'' and ''

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 ...

''. ''B. disruptus'' is currently classified as an iguanodectid. ''Bryconops caudomaculatus'', a closely-related congener, is at the center of an informal

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 ...

that formed around a history of mistaken identity or synonymy. ''B. disruptus'' is a part of this species complex, having drawn multiple comparisons to ''B. caudomaculatus'' in its original description. The specific epithet "disruptus" is in reference to the lateral line, which is regularly incomplete or interrupted. ''B. disruptus'' has no accepted common names.

Habitat and ecology

''Bryconops disruptus'' solely inhabits the Rio Negro, a

blackwater Blackwater or Black Water may refer to: Health and ecology * Blackwater (coal), liquid waste from coal preparation * Blackwater (waste), wastewater containing feces, urine, and flushwater from flush toilets * Blackwater fever, an acute kidney disea ...

tributary of the Amazon river. The Rio Negro has very low mineral content, and is very acidic, with a pH ranging from 2.9 to 4.2. The riverbed is stable, with low erosion and very few suspended particulates in the water, and the flora and fauna are generally sparse outside of species like ''B. disruptus''. Blackwater habitats generally have low oxygen content, which shows that ''B. disruptus'' does not need well-oxygenated waters to survive. This is because blackwater conditions are caused by the decay of plant matter leaching

tannin Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' (from Anglo-Norman ''tanner ...

s into the water, and the microbial activity responsible for said decay consumes a great deal of the available dissolved oxygen. ''Bryconops disruptus'''s preference for acidic and/or blackwater environments is something it shares with more than a few of its congeners. One of these is '' Bryconops collettei'', which is found both in more acidic blackwaters and rather less acidic clear waters. Another example is '' Bryconops colaroja'', which inhabits waters in the

Guiana Shield The Guiana Shield (french: Plateau des Guyanes, Bouclier guyanais; nl, Hoogland van Guyana, Guianaschild; pt, Planalto das Guianas, Escudo das Guianas; es, Escudo guayanés) is one of the three cratons of the South American Plate. It is a ...

that lean towards acidity.Echevarría, G. 2019. ''Bryconops colaroja''. The IUCN Red List of Threatened Species 2019: e.T118038882A118038887. https://dx.doi.org/10.2305/IUCN.UK.2019-3.RLTS.T118038882A118038887.en. Accessed on 7 May 2022.

Conservation status

The Rio Negro is the world's largest blackwater river, which means that ''B. disruptus'' has a wide native range. Though ''B. disruptus'' hasn't been evaluated by the IUCN, there is no concern that it will run out of habitable territory anytime soon.

References

{{Taxonbar, from=Q5642700 Fish described in 1997 Characiformes Fish of South America