Pacu (Portuguese pronunciation: [paˈku]) is a common name used to refer to several species of omnivorous South American freshwater serrasalmid fish related to piranhas.

[2] Additionally, the pacu can reach much larger sizes than piranha, at up to 1.08 m (3 ft 6+1⁄2 in) in total length and 40 kg (88 lb) in weight.

In the Brazilian Amazon, the term pacu is generally reserved to smaller and medium-sized fish in the Metynnis, Mylossoma, Mylesinus and Myleus genera.

[10] Pacu, along with their piranha relatives, are a characin fish, meaning a kind of tetra, belonging to the Characiformes order.

[5] Discoveries have been reported in Alabama,[15] Arizona,[16] Arkansas,[1] California,[17] Colorado,[18] Florida,[19][20] Georgia,[21] Hawaii,[5] Iowa, Idaho,[22] Illinois,[23] Indiana,[24] Kansas,[5] Kentucky,[25] Maine,[26] Maryland,[27] Massachusetts,[28] Michigan,[29] Minnesota,[30] Mississippi,[5] Missouri,[31] Nebraska,[32] New Hampshire,[33] New Jersey,[34] New York,[5] North Carolina,[35] North Dakota,[36] Ohio,[37][38] Oklahoma,[39] Pennsylvania,[40] South Carolina,[41] Texas,[42][43][44] Utah,[45] Washington,[46] Wisconsin,[47] and Wyoming.

[50] 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.

[52] 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.

Local people blame the fish for outcompeting native species, including juvenile crocodiles, as well as for several attacks on humans.

One toddler needed surgery after a pacu (misreported as a piranha) bit her finger at Edinburgh Butterfly and Insect World in Scotland.

Commenting on the incident, Deep Sea World zoological manager Matthew Kane warned, "Pacus will eat anything, even children's wiggling fingers.

[4] "Most UK dealers now refuse to stock this species due to the large size and expensive aquarium requirements it demands," according to Practical Fishkeeping magazine's Matt Clarke.

[66] Incapable of maintaining large aquaria, overwhelmed hobbyists are suspected of illegally releasing their pacu into wild waterways.

[67] In Appendix B of Through the Brazilian Wilderness[68] (see also online version[69]), Theodore Roosevelt advised, "For small fish like the pacu and piranha an ordinary bass hook will do."

"More recently, South American rivers including the Amazon have become a popular destination for recreational anglers, who go to fly fish for pacu.

[70] When bait-fishing in pacu-stocked ponds, anglers in Malaysia are advised to use circle hooks, size 2 or larger, and braided leather rather than nylon leaders which are easily broken by the pacu's teeth.

If the angler simply allows the line to tighten, the circle hook will slide to the side of the fish's mouth and embed its point there.

Both subsistence fishers and their commercial rivals compete in netting large quantities of pacu, which bring good prices at markets in Brazil and abroad.

[74] Research shows that the "flavor of [farmed] pacu is comparable to that of hybrid striped bass, tilapia, and rainbow trout, but superior to catfish.

[76] Nevertheless, their very strong jaws made for crushing plant seeds and the like means that fishermen and aquarists sometimes are warned about the powerful bite that may cause traumatic injuries.