Disclaimer:

The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: small-scaled pacu

Taxonomy: available through www.itis.gov

Identification: H. A. Britski (personal communication) considers Piaractus mesopotamicus one of three valid large pacu species (the others are P. brachypomus and Colossoma macropomum). Commonly used synonyms include Piaractus metrei, Colossoma metrei, and Colossoma mesopotamicus. In his taxonomic review, Machado-Allison (1982) used the name P. metrei (Berg 1895). This, however, is a junior synonym of P. mesopotamicus. At least some, and perhaps all, specimens taken in United States waters and identified as this species may actually have been the closely related Piaractus brachypomus. In addition, Piaractus specimens taken in United States waters have frequently been misidentified as red piranhas Pygocentrus nattereri.

Size: To about 85 cm SL, and reaches 20 kg in weight (Lovshin 1995).

Native Range: Restricted to the La Plata Basin, South America (Machado-Allison 1982), including the Paraguay/Parana rivers.

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Means of Introduction: All records probably represent aquarium releases.

Status: Failed in Florida and Oregon.

Impact of Introduction: The impacts of this species are currently unknown, as no studies have been done to determine how it has affected ecosystems in the invaded range. The absence of data does not equate to lack of effects. It does, however, mean that research is required to evaluate effects before conclusions can be made.

Remarks: The Florida specimen, originally reported as a piranha in newspaper accounts, was not preserved. That specimen was apparently destroyed and the fish was later identified as Colossoma metrei (= Piaractus mesopotamicus) based on a photograph (Courtenay, personal communication). Because of the close resemblance with other pacus, that identification should be considered tentative.
Voucher specimens: Oregon (OS 11983).

References: (click for full references)

Courtenay, W.R., Jr. - Florida Atlantic University, Boca Raton, FL.

Logan, D.J., E.L. Bibles, and D.F. Markle. 1996. Recent collections of continental exotic aquarium fishes in Oregon and thermal tolerance of Oriental weatherfish and pirapatinga. California Fish and Game 82(2):66-80.

Lovshin, L.L. 1995. The colossomids. p. 153-159. In C.E. Nash and A.J. Novotny (eds.). World animal science: production of aquatic animals: fishes. Elsevier Science, Amsterdam, The Netherlands.

Machado-Allison, A. 1982. Estudio sobre la subfamilia Serrasalminae (Teleostei, Characidae). Prte 1. Estudio comparado de los juveniles de las "cachamas" de Venezuela (generos Colossoma y Piaractus). Acta Biologica Venezuelica 11(3):1-101.

Other Resources:
US Fish and Wildlife Service Ecological Risk Screening Summary for Piaractus mesopotamicus

Author: Leo Nico, and Bill Loftus

Peer Review Date: 7/10/2012

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.