Piranha

The piranha is a freshwater fish that lives in the rivers and lakes of South America. It has sharp, triangle-shaped teeth and a flat, round body shaped like a dinner plate. There are more than 30 species of piranha. Most live in the Amazon River and other warm rivers in Brazil, Peru, Venezuela, and Argentina. The most famous species is the red-bellied piranha, which has silver scales and a bright orange-red belly.

An adult red-bellied piranha grows about 12 inches long. That is roughly the length of a school ruler. Its teeth are small but razor sharp. They fit together like the blades of scissors, which lets a piranha bite clean chunks out of its food. When a tooth wears out or breaks, a new one grows in to replace it.

Piranhas are known for swimming in groups called shoals. A shoal can have dozens or even hundreds of fish. For a long time, people thought piranhas traveled in groups to hunt together, like underwater wolf packs. Newer research suggests something different. Scientists now think piranhas shoal mostly for safety. Larger animals, like river dolphins, caimans, and big catfish, hunt piranhas. Staying in a group helps them watch for danger.

Their reputation as killers is mostly a myth. Most piranhas eat fish, insects, snails, and fallen fruit. Some species are almost completely vegetarian. They do eat meat when they find a dead or injured animal in the water, and a hungry shoal can strip a carcass in minutes. But healthy humans who swim in piranha rivers are almost never attacked. Serious injuries are rare.

The scary reputation comes partly from President Theodore Roosevelt. In 1913, he traveled through the Amazon and watched local people feed a chopped-up cow to piranhas in a blocked-off stretch of river. The fish had been trapped and starved for days. When the meat hit the water, they tore it apart. Roosevelt wrote about the scene in a popular book, and the image of the bloodthirsty piranha stuck in people's minds for the next hundred years.

Piranhas also play a useful role in their rivers. They eat sick and injured fish, which helps keep other fish populations healthy. They spread seeds when they eat fruit that falls from trees during the rainy season flood. People in South America have fished for piranhas as food for thousands of years. Grilled piranha is still served in many Amazon towns today.