Pacu is a South American freshwater fish found in most rivers and streams in the Amazon and Orinoco river basins of lowland Amazonia, but they have also been reported as far as Papua New Guinea, where it was artificially introduced to aid the local fishing industry. Pacu is related to the meat-eating piranha, both sharing the same subfamily Serrasalminae, although they have different food habits. The piranha is a carnivorous species while the pacu is omnivorous with vegetative tendencies. The difference is evident in the structure of their teeth. Piranha have pointed, razor-sharp teeth whereas pacu have squarer, straighter teeth, that eerily resemble those of humans.

Pacu uses its teeth mainly to crush nuts and fruits, but sometimes they also eat other fish and invertebrates. They usually eat floating fruits and nuts that drop from trees in the Amazon, and on a few occasions were reported to attack the testicles of male swimmers mistaking them to be floating nuts. This has earned them the name of "ball-cutter" after they castrated a couple of local fishermen in Papua New Guinea. So when the fish was spotted in a few odd lakes in Denmark and later in Washington, New Jersey and Illinois last year, a mild panic ensued.

While they are not aggressive carnivores like the piranha, their crushing jaw system can be hazardous. One toddler needed surgery after a pacu 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.

Pacus are legal to own in the United States, can be bought in aquarium stores and are easy to raise. The trouble is many aquarium owners are unaware that pacus can grow up to 4 feet long, which is way too large for a typical home aquarium. When pet pacus outgrow their fish tank, many owners end up dumping the fish in nearby lakes.

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Aside from pacu the Sheepshead fish (Archosargus probatocephalus) also has human teeth but a little too many.

Photo credit: Scientificamerican.com

A fully-grown adult sheepshead has well-defined incisors sitting at the front of the jaw, and molars set in three rows in the upper jaw and two rows in the lower jaw. It has strong, heavy grinders set in the rear of the jaw too, which are particularly important for crushing the shells of its prey. As with humans, this unique combination of teeth helps the sheepshead process a wide-ranging, omnivorous diet consisting of a variety of vertebrates, invertebrates and some plant material.

Sheepshead fish are also called convict fish due to the black and white bands that run down its silvery body. Photo credit