by Sandra Parker

Created on: May 03, 2009   Last Updated: November 18, 2010

While most people know what a piranha is, many have not even heard of its cousin, the pacu. Even though these fish are related, there are several distinct differences between them.

Pacu is a term associated with several freshwater South American fish species that are all closely related to the piranha. Pacu are popular in many home aquariums and have been billed as a "vegetarian piranha".

The primary difference between Pacu and their cousins, the piranha, is their choice of diet. Many Pacu are thought to be herbivorous, though most are omnivorous, eating small fish, insects and other bits of meat in addition to plants and seeds. Piranhas are also omnivorous, but have a preference for eating meat. For the piranha, any tidbit of meat is fair game, whether it be a sickly cow, or a keeper's unfortunately misplaced fingers.

The teeth of both the pacu and piranha are similar to each other, though the alignment of their jaws is quite different. The piranha has razor sharp teeth and a lower jaw that juts out farther than their upper jaw, thus giving them an underbite and more leverage when tearing meat from the bones of their prey. Pacu tend to have straighter, squarer teeth, more like humans, and in most cases have a much less pronounced underbite, and possibly even having an overbite. This gives them the advantage when crushing seeds and plant materials.

Size is also a major difference. In the wild, Pacu can reach an average length of 3 feet. Piranhas are generally much smaller coming in at a mere 2-15 cm. Pacu have a much gentler nature and are kept in many aquariums around the world. All but the most experienced aquarists tend to stay far away from piranha.

Lastly, piranhas are only found in the Amazon basin, the Orinoco, and in the river systems of the Guyanas, Paraguay-Parana, and Sao Francisco. Pacu are also found in these areas, but because of irresponsible disposal by keepers, they can now be found worldwide.

All in all, both fish are fascinating in their adaptability to their surroundings, being that both fish can survive on either vegetation or meat and their ability to thrive and even benefit alongside humans. Both species have very powerful jaws and command great respect from anyone trying to keep them in captivity. Both species present challenges to their keepers, the pacu in size and the piranha in their bloodlust.

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