There are approximately 20 species of piranha found living in the Amazon River. They do not live in the Nile.
The Amazon River (US // or UK //; Spanish and Portuguese: Amazonas) in South America is generally regarded as the second longest river in the world and is by far the largest by waterflow with an average discharge of about 209,000 cubic meters per second (7,381,000 cu ft/s), greater than the next seven largest rivers combined (not including Madeira and Rio Negro, which are tributaries of the Amazon). The Amazon, which has the largest drainage basin in the world, about 7,050,000 square kilometres (2,720,000 sq mi), accounts for approximately one-fifth of the world's total river flow. The river would have the biggest drainage basin in the world even just counting Brazil, which it enters with only one-fifth of the volume that will finally be discharged into the Atlantic.
In its upper stretches, above the confluence of the Rio Negro, the Amazon is called Solimões in Brazil; however, in Peru, Colombia and Ecuador, as well as the rest of the Spanish-speaking world, the river is generally called the Amazon downstream from the confluence of the Marañón and Ucayali rivers in Peru. The Ucayali-Apurímac river system is considered the main source of the Amazon, with its main headstream being the Carhuasanta glacial stream flowing off the Nevado Mismi mountain.
Serrasalmus rhombeus (Redeye Piranha, and see below), is a fish of the piranha family Serrasalmidae found in South America in the Amazon and Orinoco river basins, the north and eastern Guiana Shield rivers, and northeastern Brazilian coastal rivers. Its length is up to 41.5 cm.
Serrasalmus nattereri (non Günther, 1864)
The red-bellied piranha or red piranha (Pygocentrus nattereri) is a species of piranha native to South America, found in the Amazon River Basin, coastal rivers of northeastern Brazil, and the basins of the Paraguay and Paraná. They are omnivorous foragers and feed on insects, worms, crustaceans and fish. They are not a migratory species, but do travel to seek out conditions conducive to breeding and spawning during periods of increased rainfall. Red-bellied piranhas often travel in shoals as a predatory defense, but rarely exhibit group hunting behavior. Acoustic communication in common, and is sometimes exhibited along with aggressive behaviors. At this time, the red-bellied piranha is not considered to be a threatened species by the IUCN, and therefore, there are no conservation strategies in place to target this species. Through media influence, the red-bellied piranha has developed a reputation as a ferocious predator, though this is not actually the case. They are a popular aquarium fish.
The Nile (Arabic: النيل, an-Nīl; Ancient Egyptian: Iteru & Ḥ'pī; Coptic Egyptian: ⲫⲓⲁⲣⲱ, P(h)iaro; Amharic: ዓባይ?, ʿAbbai) is a major north-flowing river in northeastern Africa, generally regarded as the longest river in the world. It is 6,853 km (4,258 miles) long. The Nile is an "international" river as its water resources are shared by eleven countries, namely, Tanzania, Uganda, Rwanda, Burundi, Democratic Republic of the Congo, Kenya, Ethiopia, Eritrea, South Sudan, Sudan and Egypt. In particular, the Nile is the primary water resource and life artery for Egypt and Sudan.
The Nile has two major tributaries, the White Nile and Blue Nile. The White Nile is longer and rises in the Great Lakes region of central Africa, with the most distant source still undetermined but located in either Rwanda or Burundi. It flows north through Tanzania, Lake Victoria, Uganda and South Sudan. The Blue Nile is the source of most of the water and fertile soil. It begins at Lake Tana in Ethiopia at 12.03583°N 37.26472°E / 12°02′09″N 037°15′53″E and flows into Sudan from the southeast. The two rivers meet near the Sudanese capital of Khartoum.