''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 fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or hor ...

that is native to the

Paraguay Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tavakuairetã Paraguái, links=si), is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to th ...

Paraná River The Paraná River ( es, Río Paraná, links=no , pt, Rio Paraná, gn, Ysyry Parana) is a river in south-central South America, running through Brazil, Paraguay, and Argentina for some ."Parana River". Encyclopædia Britannica. Encyclopædia Br ...

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. lot ...

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 has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutr ...

. Young individuals usually feed on micro-

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

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 found ...

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