''Ossubtus'' is a genus of fish in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Serrasalmidae The Serrasalmidae (serrasalmids) are a family of characiform fishes, recently elevated to family status. It includes more than 90 species. The name means "serrated salmon family", which refers to the serrated keel running along the belly of these ...

. It contains a single species, ''Ossubtus xinguense'', the parrot pacu or eaglebeak pacu, The species is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

rapids Rapids are sections of a river where the river bed has a relatively steep gradient, causing an increase in water velocity and turbulence. Rapids are hydrological features between a ''run'' (a smoothly flowing part of a stream) and a ''cascade''. ...

in the

Xingu River The Xingu River ( ; pt, Rio Xingu, ; Mẽbêngôkre: ''Byti'', ) is a river in north Brazil. It is a southeast tributary of the Amazon River and one of the largest clearwater rivers in the Amazon basin, accounting for about 5% of its water. ...

basin in the

Brazilian Amazon Brazilian commonly refers to: * Something of, from or relating to Brazil * Brazilian Portuguese, the dialect of the Portuguese language used mostly in Brazil * Brazilians, the people (citizens) of Brazil, or of Brazilian descent Brazilian may also ...

.Andrade, M.C., Sousa, L.M., Ota, R.P., Jégu, M. & Giarrizzo, T. (2016)
Redescription and Geographical Distribution of the Endangered Fish ''Ossubtus xinguense'' Jégu 1992 (Characiformes, Serrasalmidae) with Comments on Conservation of the Rheophilic Fauna of the Xingu River.
''PLoS ONE, 11 (9): e0161398.'' This

endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...

is primarily a

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

Description

The body of ''Ossubtus xinguense'' is ovoid in shape. The profile of the snout is blunt. In young fish, the mouth is terminal (pointing forward); however, as the fish grows, the mouth turns downward and becomes strictly ventral in individuals longer than . This gives the mouth a beak-like appearance. It reaches up to in total length and about in weight.

Range and habitat

''Ossubtus xinguense'' is restricted to

in the

basin in the Brazilian Amazon. It has been confirmed from Volta Grande do Xingu in the lower Xingu River and lower

Iriri River The Iriri River ( pt, Rio Iriri, ; Mẽbêngôkre: ''Kororoti'', ) is a large tributary of the Xingu River in Brazil, in the state of Pará. It is long making it the 116th longest river in the world (with Krishna River, India) and the 15th long ...

near its confluence with Xingu, but possibly also occurs further upstream on these rivers (perhaps as far as

São Félix do Xingu São Félix do Xingu is a Municipalities of Brazil, municipality in the states of Brazil, state of Pará in the Northern Region, Brazil, Northern region of Brazil. The city is served by São Félix do Xingu Airport. With an area of , ...

). This species is strictly

rheophilic A rheophile is an animal that prefers to live in fast-moving water. Examples of rheophilic animals Insects *Many aquatic insects living in riffles require current to survive. *''Epeorus sylvicola'', a rheophilic mayfly species ( Ephemeroptera) ...

and found in rapids, but prefers sheltered,

Podostemaceae Podostemaceae (riverweed family), a family in the order Malpighiales, comprise about 50 genera and species of more or less thalloid aquatic herbs. Distribution and habitat They are found mostly in tropical and subtropical areas worldwide. Ma ...

-covered rocky crevices. Young individuals of up to can be observed in schools of 20–30 individuals, sheltered under broad stones.

Behavior

The species is primarily a

and a diet analysis of 10 specimens revealed mostly plant material, but also lower quantities of

macroinvertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate s ...

Shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...

, dead or alive, blood worm, vegetable matter,

brine shrimp ''Artemia'' is a genus of aquatic crustaceans also known as brine shrimp. It is the only genus in the family Artemiidae. The first historical record of the existence of ''Artemia'' dates back to the first half of the 10th century AD from Urmia La ...

and

daphnia ''Daphnia'' is a genus of small planktonic crustaceans, in length. ''Daphnia'' are members of the order Anomopoda, and are one of the several small aquatic crustaceans commonly called water fleas because their saltatory swimming style resembl ...

are consumed in

captivity Captivity, or being held captive, is a state wherein humans or other animals are confined to a particular space and prevented from leaving or moving freely. An example in humans is imprisonment. Prisoners of war are usually held in captivity by a ...

. The female is far more dominant than the male and will often seek

cave A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...

s into which no other fish may enter. This is believed to be due to reproductive dominance, once a suitable breeding location is found, the female will not surrender it.

Parasites

It is parasitized by '' Anphiira xinguensis'', an

isopod Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, an ...

e of the family

Cymothoidae The Cymothoidae are a family of isopods in the suborder Cymothoida found in both marine and freshwater environments. Cymoithoids are ectoparasites, usually of fish, and they include the bizarre "tongue-biter" ('' Cymothoa exigua''), which att ...

. This

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

is only known from ''Ossubtus xinguense'' where it lives in the gill chamber of the fish and develops a contorted

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...

, presumably in response to its host's cursive

ontogeny Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the stu ...

.Thatcher, E. (1995) ''Anphiira xinguensis'' sp. nov. (Isopoda, Cymothoiclae) a gill chamber parasite of an Amazonian serrasalmid fish, ''Ossubtus xinguense'' Jegu, 1992. ''Amazoniana'' XIII(314): 293-304. The intestines are also commonly infested with '' Rondonia rondon'', a

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...

that possibly is

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

rather than parasitic. Black spot disease is found in most ''Ossubtus xinguense''.

Status

This fish is

endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inva ...

,Jégu, M. & Zuanon, J. (2005)
Threatened fishes of the world: ''Ossubtus xinguense'' (Jégu 1992) (Characidae: Serrasalminae).
''Environmental Biology of Fishes, 73 (4): 414-414.'' but it has not been rated 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 ...

. A review in 2016 suggested that it is more widespread than previously believed and its historic rarity as museum specimens in part can be explained by its habitat (rapids), which are difficult to sample, but it remains threatened by dams such as the Belo Monte.

References

{{Taxonbar, from=Q1938699 Serrasalmidae Fish of South America Fish of Brazil Monotypic fish genera Taxa named by Michel Louis Arthur Marie Ange François Jégu Fish described in 1992