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Piaractus brachypomus also known as the red-bellied Pacu or pirapitinga, is a large species of pacu, a close relative of piranhas and silver dollars, in the serrasalmid family.[1][2] It is native to the Amazon basin in tropical South America, but it formerly included populations in the Orinoco, which was described in 2019 as a separate species, P. orinoquensis.[3] Additionally, P. brachypomus is widely farmed and has been introduced to other regions.[4] In South Florida they are invasive in rivers, canals or lakes.[5]
| Piaractus brachypomus | |
|---|---|
 | |
| Adult Piaractus brachypomus at Aquarium du palais de la Porte Dorée | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Characiformes |
| Family: | Serrasalmidae |
| Genus: | Piaractus |
| Species: | P. brachypomus |
| Binomial name | |
| Piaractus brachypomus (G. Cuvier, 1818) | |
| Synonyms | |
As with a number of other closely related species, P. brachypomus is often referred to as the red-bellied pacu in reference to the appearance of the juveniles. This has resulted in a great deal of confusion about the nature and needs of all the species involved, with the reputation and requirements of one frequently being wrongly attributed to the others.[6]
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In general, its behavior resembles that of the closely related tambaqui (Colossoma macropomum). It is migratory, but the pattern is poorly understood.[7] Spawning occurs at the beginning of the flood season between November and February.[8] Larvae of the Red-Bellied Pacu are found in whitewater rivers, but adults mainly live in flooded forests and floodplains of various river types, including those of both nutrient-rich and nutrient-poor.[7] Unlike the tambaqui, the Red-bellied pacu also occurs in the headwaters of nutrient-poor rivers (not just in the lower sections).[7]
It mainly feeds on fruits, seeds, and nuts, but it is opportunistic and will also take zooplankton, insects, crustaceans and small fish, especially in the dry season.[4][9] In general, more seeds are able to pass undamaged through the red-bellied pacu than the tambaqui, meaning that the former is overall a more efficient seed disperser.[10]
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Piaractus brachypomus can reach up to 88 cm (2.9 ft) in length and 25 kg (55 lb) in weight.[2]
Juveniles have a distinct red chest and stomach, and are easily confused with the carnivorous red-bellied piranha (Pygocentrus nattereri), but the two can be separated by their teeth, which are molar-like in Piaractus brachypomus.[1] This similarity is believed to be Batesian mimicry by P. brachypomus in an attempt of avoiding predation by other species.[4] Adults lack the bright red chest and belly, and resemble the tambaqui (Colossoma macropomum), but can be separated by several meristic and morphological features: The Red-Bellied Pacu has a smaller adipose fin that lacks rays, as well as differences in teeth and operculum.[1][11] The Red-bellied Pacu also has a more rounded head profile (less elongated and pointed).[11][12] The other member of its genus, P. mesopotamicus, can be distinguished by its smaller scale-size[13] and the higher number of lateral scales (more than 110).[1]
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The Red-Bellied Pacu supports major fisheries and based on a review by IBAMA, it was the 12th most caught fish by weight in the Brazilian Amazon in 1998 (just after the tambaqui).[7]
The Red-Bellied Pacu is often kept in aquaculture. Hybrids between this species and the tambaqui have been produced in aquaculture.[14] It can also hybridize with P. orinoquensis, but the offspring appears to be sterile.[3]
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