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. 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. Additionally, P. brachypomus is widely farmed and has been introduced to other regions. In South Florida they are invasive in rivers, canals or lakes.

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.

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