Piranhas are medium-sized, carnivorous tropical fish native to South America. There is some considerable confusion over the definition of the piranhas. The common name has been hopelessly applied to any and all voracious carnivorous fish, whether or not it is biologically a member of the piranha subfamily, the Serrasalminae. Even further complicating the definition of piranhas is the aquarium trade, which often applies upwards of five or six common names for a single species, and often uses the same common name for up to ten different species. The result is a horrible mess of confusion, frustration and tears. What follows is a discussion of the piranhas as best defined by modern biological classification.

General Biology

The name Piranha, or more appropriately Piraña, is etymologically from the Tupi-Guarani, and means toothed-fish (pira=fish, ranha=tooth). They are also often called Caribe, named after the Carib natives who were known to the Spanish explorers (conquerors) to be both fierce and cannibalistic.

They are deep-bodied laterally-compressed (imagine a dinner plate) fish with very prominent jaws. They are best known for their highly developed and very sharp teeth, which can grow to be 3/4 cm long. Their teeth are so sharp that people who have been bitten claim not to have felt the contact at all, and in fact until they saw the blood had no idea they were hurt. Piranhas have well developed lateral lines, and a prodigious sense of smell. Their vision, on the other hand, is quite poor. They are thus well adapted to living in the murky waters of South American rivers.

Neonate piranhas feed on invertebrate prey (zooplankton, insects) but as they grow they quickly shift to higher animals like fish, birds and rodents. They school, and attack in packs. When piranhas attack a larger prey, they go into a frenzy, causing the water around them to roil and turn red with blood. In this feeding frenzy, they often bite one another, and are known to be voraciously cannibalistic.

The above description of their feeding behaviour is generally valid for the genera Pygocentris and Serrasalmus. It falls to pieces, however, with the other members of the subfamily, the genera Pristobrycon and Pygopristis, which are totally herbivorous. They feed on fruit and seeds that fall from trees into the water, and can be kept in captivity on commercial bird seed1.

The piranha is a preferred prey of many birds and larger predators in South America. In particular, it is targeted by the caiman and crocodile during the end of the rainy season (as the rivers and tributaries dry up, the piranhas are easy prey).

Conservation status

Unlike many other species native to South America, the piranha is not threatened by humans. In fact, the piranha presents the opposite problem for the conservation biologist: they are quite hardy animals and have been transported all over the globe due to the aquaculture hobby. These animals are released into the wild relatively infrequently, but have managed to survive in both North American and European waterways. Luckily enough, they are normally killed by the cold winter; they do not survive if the water temperature drops below 230C. However, there is considerable concern about a possible introduction leading to a permanent population in the southern United States (California, Texas and Florida), resulting in the banning of the species from some southern states.

Relationship to humans

The piranha, despite horrible movies to the contrary, has never been a confirmed predator of human beings. However, humans are often injured by piranhas, especially when fishing either for the species or for another fish in the same waterway. In many areas in South American, the piranha is fished locally for food. They apparently taste remarkably like the crappie, and are remarkably easy to catch (a line, a hook and any animal protein will do).

Taxonomy

There is a great deal of confusion as to what constitutes the piranha family, subfamily or genus. What is presented below is the best classification currently available based on both classic morphlogical and modern genetic techniques.

Order: Characiformes 2
Family: Characidae
Subfamily: Serrasalminae

Genus Pygocentrus (the true piranhas)
P. piraya -- Red piranha
P. cariba -- Black-spot piranha
P. nattereri -- True piranha


Genus Pristobrycon
P. aureus
P. baratai
P. striolatus -- Striolated piranha
P. maculpinnus
P. careospinus
P. calmoni


Genus Serrasalmus
S. spilopleura -- Gold piranha
S. rhombeus -- Red-eyed piranha
S. maculatus
S. altispinnis
S. altuvei
S. brandti
S. compressus
S. eigenmanni
S. elongatus -- Slender piranha
S. irritans
S. gibbus
S. gouldingi
S. hastatus
S. hollandi
S. humeralis
S. manueli
S. marginatus
S. medinai
S. nalseni
S. neveriensis
S. nigricans
S. sanchezi
S. serrulatus


Genus Pygopristis
P. calmoni
P. denticulata -- Lobetoothed piranha
P. striolatus


1 Wonderful little facts, such as these, help to contribute to the aforementioned weeping and frustration.
2 Formerly part of the Cypriniformes, the same family as the goldfish, carp etc.


Information culled from ...
* http://www.fishbase.org
* http://www.wetwebmedia.com
* http://www.angelfire.com/biz/piranha038/