Odontesthes bonariensis is a species of Neotropical silverside, an euryhaline fish native to fresh, brackish and salt water in south-central and southeastern South America, but also introduced elsewhere. It is often known by the common name Argentinian silverside or pejerrey (the latter is of Spanish origin, meaning "king fish," the Latin piscis given rise to "pez," fish, and "peje," a kind of fish, and "rey," king), but it is not the only species of silverside in Uruguay and Argentina and pejerrey is also used for many other silversides. It is a commercially important species and the target of major fisheries.

O. bonariensis resembles the other species in the genus Odontesthes, but it is larger, generally reaching up to 50 cm (1.6 ft) in total length, and exceptionally as much as 82 cm (2.7 ft) long and 5.2 kg (11 lb 7 oz) in weight (reports of even larger are unconfirmed and questionable).

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