|A group near Bonito, Brazil|
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 that is native to the Paraguay-Paraná River basin, but it has been introduced by aquaculture activities in a wider area. 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 62 cm (2.03 ft) in length and 20 kg (44 lb) in weight. The other member of its genus, P. brachypomus, can be distinguished by its larger scale-size and the lower number of lateral scales (less than 110).
Piaractus mesopotamicus is an omnivore. Young individuals usually feed on micro-crustaceans, while adults feed on plant material and insects. Main food items for adults are nuts and seeds that fall from trees in flooded forests. It tolerates water temperatures between 15 and 35 °C (59–95 °F), but stops feeding when it falls below 18 °C (64 °F).
- "Piaractus mesopotamicus". Integrated Taxonomic Information System. Retrieved 24 January 2006.
- Froese, Rainer; Pauly, Daniel (eds.) (2017). "Piaractus mesopotamicus" in FishBase. March 2017 version.
- Nico, L.; and B. Loftus (7 October 2012). Piaractus mesopotamicus. USGS Nonindigenous Aquatic Species Database, Gainesville, FL. Retrieved 13 March 2017.
- 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.
- Mulca, P. (26 April 2013). Piaractus mesopotamicus. PezAdicto Retrieved 13 March 2017.
- OPEFE (27 December 2011). genus Piaractus. Retrieved 2 March 2017.
- Nico, L.; P. Fuller; and M. Neilson (22 October 2013). Piaractus brachypomus. USGS Nonindigenous Aquatic Species Database, Gainesville, FL. Retrieved 2 March 2017.
- El Pato Web: Especies del Paraná (in Spanish)