Other varieties are Black piranha (Serrasalmus rhombeus), Ruby-throated, Piraya piranha, etc. Among all the species Black piranha has the most strong jaws. The most dangerous variety is red bellied piranha. They like to live as groups. Other fish could not put with piranha together. They are not much danger when they along. Normally they do not bit human. But if you try to touch with hands they might bite your hand. They will be more dangerous if they kept hungry for long time.
Piranha is carnivorous. You have to provide them such foods, in example Bloodworms like foods or small fish, prawns and meat. But do not give meat regularly. Some fish have trained to eat common fish food. Ask it from the seller when you buy. Piranha is a good hunter. They like to hunt live preys.
Piranha is very active. Therefore they need a lot of room to move here and there. A 4 feet long, 1.5 feet wide and 1.5 feet high tank is enough to 4 fish. Use a good filter. Tanks may contaminated while they eating foods. They can live long time without any illness if the water is in good condition. Therefore keep the tank water clean. Remove half of water and fill with fresh water once a week. No need of aquarium plants but you can arrange a natural environment using wooden pieces and stones.
What is the difference between Piranha and Pacu?
Pacu is close to the shape and color of piranha. Most of the people confused on identifying both. Most expressed character of piranha is triangular shaped, sharp teeth. Teeth of Pacu are more wider and little bit of square shaped. Teeth of Pacu has a likeness to human teeth. The lower jaw of piranha is more wider and extrude a little. But in Pacu both upper and lower jaws are in same length. In mature status Pacu is bigger than piranha. Maximum size of Pacu is about 28 inches.
CAUTION
If you keep piranha as a pet fish keep in mind not to release or not let them to release to natural water reservoirs or rivers, if your country has no natural piranha. If it so, the other species of (may be endemic or endangered) fish or aquatic creatures can be vanished. It is important to be act accountable.