Jeff Lowe, age 11, of Rockland, Ontario, Canada, for his question:
CAN YOU TELL ME SOMETHING ABOUT THE PIRANHA?
The piranha, like almost all other fish, can probably hear sounds produced in the water. Fish can also hear sounds made on shore or above the water if they are loud enough. Fish have inner ears which are enclosed in chambers on each side of the head. Each ear is made up of a group of pouches and tubelike canals. Piranha and other fish have no outer ears or eardrums.
One of the most dreaded fish in the world is the piranha, which is also called the caribe. It is a bloodthirsty fish which can be found in South America's Amazon River.
Many scientists say that the piranha is more dangerous than a shark. The fish range in size from only about four inches to 18 inches long, but they attack their victims in great numbers.
Sometimes as many as several thousand piranhas travel together in a group. They have been known to tear all the flesh off the skeleton of a large animal or even a human in only a few minutes.
There are about 20 different kinds of piranha. Some of them are bluish gray or yellow in color while others can be green or spotted with red or gold.
The piranha is a member of a group of fish called the characin family. And all of them have teeth that are razor sharp.
One member of the family only eats plants. But the rest of the varieties maintain diets that include blood.
Piranhas have highly developed senses of smell. The olfactory organs, or organs of smell, are made up of two pouches, one on each slide of the snout. The pouches are lined with nerve tissue that is highly sensitive to odors from substances in the water.
A nostril at the front of each pouch allows water to enter the pouch and pass over the tissue. The water leaves the pouch through a nostril at the back.
Piranhas also have taste buds in various parts of their mouths.
The fish also have a well developed sense of touch. Nerve endings throughout the skin react to the slightest pressure and change of temperature.
The piranha starts its life as an egg. In the egg, the undeveloped fish feeds on the yoke until it is ready to hatch.
The carnivorous piranha usually feeds on water animals, worms and shellfish. But above all, they eat other fish.