Amazing Piranha

Fish World | Amazing Piranha | Piranhas belong to the subfamily Serrasalminae, which is also closely related omnivorous fish such as pacus. Traditionally, only the four genera Pristobrycon are Pygocentrus, and Serrasalmus Pygopristis considered true piranhas, due to their specialized teeth. However, a recent analysis showed that if the piranha group is monophyletic, should be restricted to Serrasalmus, Pygocentrus and part of Pristobrycon, or extended to these taxa plus Pygopristis, and Catoprion Pristobrycon striolatus contain. Pygopristis appeared to be more akin to Catoprion than the other three piranha genera.

The total number of piranha species is unknown and controversial, and new species continue to be described. Estimates range from less than 30 to over 60.

Piranhas are found in the Amazon, the Orinoco, in rivers of the Guyanas, in the Paraguay-Paraná, and São Francisco river systems. Some species of piranha have a broad geographic range, occurring in more than one of the major basins mentioned above, while others are more restricted distributions.
Aquarium piranhas are introduced in parts of the United States, with occasional specimens found in the Potomac River, Lake of the Ozarks in Missouri, and even as far north as Lake Winnebago in Wisconsin, although they usually do not survive cold winters. Piranhas are also discovered in the Kaptai Lake in southeastern Bangladesh. Research is conducted to determine how piranha have moved to such distant corners of the world from their original habitat. Some rogue exotic fish traders are thought to have released in the lake to prevent prisoners from antipoaching forces.
Piranhas are normally about 14 to 26 cm long (5.5 to 10.25 inches), although some individuals are reported to be up to 43 cm (17.0 inches) in length.
Serrasalmus, Pristobrycon, Pygocentrus Pygopristis and are most easily identified by their unique dentition. All piranhas have a single row of sharp teeth in both jaws, the teeth are tightly packed and interlocking (via small cusps) and used for rapid puncture and shearing. Individual teeth are typically broadly triangular, pointed and blade-like (flat in profile). There is little variation in the number of nodules, in most species, the teeth are tricuspid with a larger middle cusp which individual teeth are similar triangular. The exception is Pygopristis who pentacuspid teeth and a middle cusp usually only slightly larger than the other is slipping. In the scale-eating Catoprion, the shape of their teeth is clearly different and the premaxillary teeth in two rows, as in most other serrasalmines
Piranhas are important ecological components of their environment. Although largely confined to lowland drainages, these fish are widespread and inhabit diverse habitats within both lotic and LENTIC environments. Some piranha species are abundant locally and multiple species often occur together. As both predators and scavengers, piranhas influence the local distribution and composition of fish assemblages. Certain piranha species consume large quantities of seeds, but unlike the related Colossoma and Piaractus, herbivorous piranhas thoroughly chew and fully digest all seeds eaten and not function as dispersers.

Piranha has a reputation as ferocious predators hunt their prey in schools. Recent research, however, that "started with the premise that they school as a means of cooperative hunting", discovers that they are timid fish trained to protect their own predators such as cormorants, dolphins and caimans. Piranhas are "basically like ordinary fish with big teeth."

Research into the species Serrasalmus aff. brandtii and Pygocentrus nattereri in Viana Lake, which is formed during the wet season when the Rio Pindar (a tributary of the Rio Mearim) floods, has shown that these types of plant material to eat at some stage in their lives, they are not strictly carnivorous fish

Scientific classification 

Kingdom: Animalia 
Tribe: ChordataActinopterygii 
Division: NeopterygiiInfra 
Class: Teleostei 
Order: Characiformes
Family: Characidae 
Subfamily: SerrasalminaeGery, 1972 
Species: Piranha