Pacu Fish
A piranha relative with flat, square human-looking molars — used for cracking nuts that fall into the river
No photo available for Pacu Fish
Superpower
The pacu has teeth that are structurally and visually nearly identical to human molars — flat, square, multi-cusped crushing teeth arranged in rows in both jaws. When a pacu opens its mouth, the resemblance to a human smile is immediate and deeply unsettling. The teeth evolved for crushing hard-shelled nuts and seeds that fall into South American rivers — pacu are among the most important seed dispersers in Amazonian forest, swallowing fruits whole and depositing seeds far from the parent tree. They can crack Brazil nuts that require a vice grip to open.
Overview
Pacu (Colossoma macropomum and related species) are large South American freshwater fish closely related to piranha but primarily herbivorous. They grow up to 88cm and 25kg — large enough that when they bite, the human-tooth resemblance becomes medically relevant. Several fishermen in Papua New Guinea, where pacu were introduced as a food fish, have reportedly been bitten. They're also popular aquarium fish whose owners frequently release them when they outgrow their tanks, establishing invasive populations in North America and Europe.
Found in
Rivers and flooded forests of the Amazon and Orinoco basins in South America. Introduced populations exist in Papua New Guinea, the US, and several European countries from aquarium releases. Prefer slow, warm water with access to flooded forest.
Things worth knowing
- 1
Pacu teeth are so human-like that they have repeatedly caused alarm when fish are found — wildlife officials in New Jersey received panicked reports after a pacu was caught, with callers convinced a human had somehow ended up in the water.
- 2
Pacu are among the most important seed dispersers in Amazonian forest — trees that drop fruit into rivers have evolved to rely on pacu to swallow and transport seeds. Some Amazonian tree species have declining reproduction in rivers where pacu have been overfished.
- 3
During flood season in the Amazon, pacu swim into flooded forest and feed directly on falling fruit — following the sounds of fruit dropping into water. They can detect a nut hitting the surface from significant distances.
- 4
Pacu are sometimes called 'vegetarian piranhas' — but they're not strict vegetarians. They eat invertebrates, smaller fish, and carrion when plant food is scarce.
- 5
The largest pacu ever recorded weighed 40kg — roughly the size of a large dog, with a set of flat human molars capable of cracking Brazil nuts.