From the Sticky:
Scientific Name: Serrasalmus elongatus
Common Names: Elongated Piranha, Elong, Pike Piranha.
Distribution: In many different types of waterways in Venezuela/Colombia and Amazonian Brazil.
Size: 10 inches (Captive), 14 inches (wild)
Captivity: This is one of the most active and fast swimming of the species. Therefore they need at least 100 gallons (or more) to themselves and a very strong current to swim against. A temperature of 24-30C, and pH of 5.5-7.5 is required.
Personal Comment: This is normally a very aggressive piranha and very bold once settled. Very efficient filtration and a very strong current is needed to keep this fish in good health and active.