Pacu (Portuguese pronunciation: [paˈku]) is a common name used to refer to several species of omnivorous South American freshwater serrasalmid fish related to piranhas. Pacu and piranha do not have similar teeth, the main difference being jaw alignment; piranha have pointed, razor-sharp teeth in a pronounced underbite, whereas pacu have squarer, straighter teeth and a less severe underbite or a slight overbite. Pacu, unlike piranha, mainly feed on plant material and not flesh or scales. Additionally, the pacu can reach much larger sizes than piranha, up to 1.08 m (3 ft 6+1⁄2 in) in total length and 40 kg (88 lb) in weight.
Name The common name pacu is generally applied to fish classified under the below listed genera. Among these, several genera contain species where commonly used English names include the word pacu, as listed.
Subfamily Colossomatinae Colossoma – black pacu, black-finned pacu, giant pacu Mylossoma Piaractus – red-bellied pacu, small-scaled pacu Subfamily Myleinae Mylesinus Myleus Myloplus Ossubtus – parrot pacu, eaglebeak pacu Paramyloplus Prosomyleus Tometes Utiaritichthys Subfamily Serrasalminae Metynnis Each of these groups contains one or more separate species. For example, the fish often found in pet stores, known as the black pacu and red-bellied pacu, typically belong to the species Colossoma macropomum and Piaractus brachypomus, respectively. A species popular among fish farmers is Piaractus mesopotamicus, also known as Paraná River pacu or small-scaled pacu. Pacu is a term of Tupi-Guaraní origin. When the large fish of the genus Colossoma entered the aquarium trade in the U.S. and other countries, they were labeled pacu. In the Brazilian Amazon, the term pacu is generally reserved to smaller and medium-sized fish in the Metynnis, Mylossoma, Mylesinus and Myleus genera. Colossoma macropomum are known as tambaqui, whereas Piaractus brachypomus is known as pirapitinga. In Peru, both of the species (Colossoma macropomum and Piaractus brachypomum) are called pacú and gamitana. Piaractus mesopotamicus of the Paraná-Paraguay basin is also called pacú in Paraguay and Argentina.
Classification
Pacu, along with their piranha relatives, are a characin fish, meaning a kind of tetra, belonging to the Characiformes order. The ongoing classification of these fish is difficult and often contentious, with ichthyologists basing ranks according to characteristics that may overlap irregularly. DNA research sometimes confounds rather than clarifies species ranking. Ultimately, classifications can be rather arbitrary. Pacu, along with piranha, are currently further classified into the family Serrasalmidae (formerly a subfamily of Characidae). Serrasalmidae means "serrated salmon family" and refers to the serrated keel running along the belly of these fish. However, dental characteristics and feeding habits further separate the two groups from each other.
Native distribution and habitat Pacus are native to tropical and subtropical South America. They inhabit rivers, lakes, floodplains and flooded forests in the Amazon, Orinoco, São Francisco River and Río de la Plata Basins, as well as rivers in the Guianas. Here they form part of the highly diverse Neotropical fish fauna. Their habitat preferences varies significantly depending on the exact species. Several species are migratory.
As exotic species
Pacus have been introduced to the wild in many places outside their native range, both in South America and other continents. They are sometimes released to increase the local fishing, but others are released by aquarists when they outgrow their aquarium. This is illegal in many countries and strongly advised against. When becoming established they can be invasive species that damage the local ecosystem. In many regions where individuals have been seen they are unlikely to survive long-term because of temperature. Among the large pacu species (Colossoma and Piaractus), the most cold-adapted species is Piaractus mesopotamicus, which tolerates water down to 15 °C (59 °F), but stops feeding below 18 °C (64 °F).
United States Pacus have become established in Puerto Rico and singles have been caught in numerous U.S. states. Discoveries have been reported in Alabama, Arizona, Arkansas, California, Colorado, Florida, Georgia, Hawaii, Iowa, Idaho, Illinois, Indiana, Kansas, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, New Jersey, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, South Carolina, Texas, Utah, Washington, Wisconsin, and Wyoming. Among the numerous recent records are a pacu caught in the California Delta, near Stockton in 2015, two in Lake St. Clair in 2016 and a single in Lake Huron in 2016. Some state wildlife authorities have advised home aquarists who wish to get rid of overgrown pacu to cut the heads off the fish and dispose of them as garbage. Habitattitude, a U.S. national initiative led by the Aquatic Nuisance Species (ANS) Task Force, recommends humanely disposing the fish through a veterinarian or pet retailer, returning them to retailers, or donating them to a local aquarium society, school, or aquatic business. Additionally, aquarium-raised fish can be eaten (see Food fish).
Europe In August 2013, a pacu was discovered in Scandinavian waters; a fisherman pulled a 21 cm (8+1⁄2 in) specimen from the Øresund, a semi-brackish strait between Sweden and Denmark. An angler fishing on the river Seine in Paris, France, caught a pacu in August 2013. In June 2016, a 20 cm (8 in) pacu was caught in a city pond in Tula, Russia. In June 2017, a pacu was accidentally caught during a fishing contest at the Port of Drobeta Turnu Severin, Romania. The fish bit one of the fishermen, leading to a general warning being issued in the region, until the origin of the fish can be determined. In August 2017, a pacu was caught in the stream Motala Ström in Norrköping, Sweden. In July 2019, two pacus were caught near Baia Mare, Romania. In September 2020, a 50 cm (20 in) pacu weighing approx. 3 kg (7 lb) was caught in Zegrze Reservoir in Poland. In February 2024, a dead pacu was found in Garadice Lough, Ireland. In Summer 2025 a pacu got fished out of the Jagst River near Crailsheim in southern Germany.
Asia Pacus have become established in tropical Asia, including Vietnam, Malaysia, Bangladesh, Thailand, and India.
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