Piaractus mesopotamicus

Piaractus mesopotamicus, pirapitinga, the small-scaled pacu, Paraná River pacu or simply pacu (a name shared with other species), is a species of freshwater ray-finned fish belonging to the family Serrasalmidae, which includes the piranhas, pacus and related fishes. These fishes are endemic to the drainage basin of the Paraguay River in South America.

Piaractus mesopotamicus
Conservation status
Near Threatened  (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Characiformes
Family:	Serrasalmidae
Genus:	Piaractus
Species:	P. mesopotamicus
Binomial name
Piaractus mesopotamicus (Holmberg, 1887)[2]
Synonyms[3]
Myletes (Myleus) mesopotamicus Holmberg, 1887 Myletes mitrei C. Berg, 1895 Colosoma canterai Devincenzi, 1942

Taxonomy

Piaractus mesopotamicus was first formally described as Myletes (Myleus) mesopotamicus in 1887 by the Argeintine naturalist and novelist Eduardo Ladislao Holmberg with its type locality given as the Río Uruguay and Río Baradero, tributaries of the Rio Paraná in Uruguay.^[3] This species is classified in the genus Piaractus which belongs to the subfamily Colossomatinae within the family Serrasalmidae,^[4] which is classified in the suborder Characoidei of the order Characiformes.^[5]

Etymology

Piaractus mesopotamicus is a member of the genus Piaractus, this name combies the Greek pī́ar, meaning "fat", with aktís, which means "ray", an allusion to the adipose fin having fin rays. The specific name mesopotamicus means "between rivers", this probably alludes to Argernina's to Región Mesopotámica (or La Mesopotamia), a northeastern region situated between the rivers Paraná and Uruguay, where this fish is found.^[6]

Description

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.^[7] It reaches up to 62 cm (2.03 ft) in length^[8] and 20 kg (44 lb) in weight.^[7] The other member of its genus, P. brachypomus, can be distinguished by its larger scale-size^[9] and the lower number of lateral scales (less than 110).^[10]

Distribution

Piaractus mesopotamicus is endemic to the Paraguay-Paraná River basin,^[7][11] but it has been introduced by aquaculture activities in a wider area.^[8]

Biology

Piaractus mesopotamicus is an omnivore.^[8] Young individuals usually feed on micro-crustaceans, while adults feed on plant material and insects.^[8] Main food items for adults are nuts and seeds that fall from trees in flooded forests.^[7] It tolerates water temperatures between 15 and 35 °C (59–95 °F), but stops feeding when it falls below 18 °C (64 °F).^[8]