Piranhas, with their sharp teeth and frenzied meat-eating habits, have a fearsome reputation as predators. Even their name means "tooth fish" in a South American Indian dialect. The 25 known species of these fish thrive in South American rivers, lakes and streams.

Piranhas spawn during the rainy season from December through March. The fish engage in a courtship ritual in which the fish swim in circles. Spawning piranhas turn a lighter color, while their bellies become redder.

Each females lays as many as 1,000 eggs in shallow nests on the bottom of of river or lake bed. The male then deposits sperm on the eggs to fertilize them.

Both the male and female piranhas watch over the fertilized eggs, which take two or more days to hatch. The warmer the water, the faster the hatching time.

The newly hatched piranhas, known as fry, rely on a yolk sac for nutrition during the first days of life. As they mature, the juvenile fish use water plants as cover and survive on small crustaceans, worms and insects.

Adult piranhas can grow from 6 to 24 inches in length, depending on the species. They reach this length in 12 to 14 months. A common species, the red-bellied piranha, can weigh up to five pounds and live as long as five years. Adults will spawn at around one year of age.