''Piaractus mesopotamicus'', the small-scaled pacu, Paraná River pacu or simply pacu (a name shared with other species), is a South American

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

that is native to the

Paraguay Paraguay, officially the Republic of Paraguay, is a landlocked country in South America. It is bordered by Argentina to the Argentina–Paraguay border, south and southwest, Brazil to the Brazil–Paraguay border, east and northeast, and Boli ...

Paraná River The Paraná River ( ; ; ) is a river in south-central South America, running through Brazil, Paraguay, and Argentina for some ."Parana River". Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica Inc., 2012. Web. ...

basin,Nico, L.; and B. Loftus (7 October 2012)
Piaractus mesopotamicus.
USGS Nonindigenous Aquatic Species Database, Gainesville, FL. Retrieved 13 March 2017. but it has been introduced by

aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. Nelu ...

activities in a wider area.A. A. Agostinho, L. C. Gomes, H. I. Suzuki, H. Ferreira Júlio Jr: ''Migratory fishes of the Upper Paraná River basin, Brazil.'' Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura (Nupelia). Universidade Estadual de Maringá. Maringá, Paraná, Brazil. In its native range it is also known as the pacú chato, pez chato ("flat fish") or mbiraí-piraí. ''Piaractus mesopotamicus'' is a robust fish, with ovoid shape, flattened laterally. Its colour is dark grey to silver, with a white belly and a yellow breast. It reaches up to in length and in weight. The other member of its genus, '' P. brachypomus'', can be distinguished by its larger scale-sizeOPEFE (27 December 2011)
genus Piaractus.
Retrieved 2 March 2017. and the lower number of lateral scales (less than 110).Nico, L.; P. Fuller; and M. Neilson (22 October 2013)
Piaractus brachypomus.
USGS Nonindigenous Aquatic Species Database, Gainesville, FL. Retrieved 2 March 2017. ''Piaractus mesopotamicus'' is an

omnivore An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize t ...

. Young individuals usually feed on micro-

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s, while adults feed on plant material and insects. Main food items for adults are nuts and seeds that fall from trees in

flooded forest Freshwater swamp forests, or flooded forests, are forests which are inundated with freshwater, either permanently or seasonally. They normally occur along the lower reaches of rivers and around freshwater lakes. Freshwater swamp forests are foun ...

s. It tolerates water temperatures between , but stops feeding when it falls below .

References

El Pato Web: Especies del Paraná
(in Spanish) Serrasalmidae Fish of South America Paraná River Fish described in 1887 Taxa named by Eduardo Ladislao Holmberg {{characiformes-stub