The dry season is in full force on a floodplain in Venezuela. Since January, the sheets of water that covered the land have been drying, and by the beginning of April much of the water has evaporated. Fish are crowded into the small remaining pools. Many have died for lack of water and oxygen. But few of the fish in these pools are adult piranhas. Where are they?
No one knows for sure, but scientists think that the piranhas have migrated to deeper water downstream. They will return very soon after the rainy season starts, a month from now.
Wedding Finery(ThePiranha’s Year)
When the piranhas return, both male and female adults will be wearing different colors than they do during the rest of the year, because they will be ready to breed. The Orinoco red-bellied piranha, usually silver and red, turns black with glittering purple or gold flecks. The black piranha turns even darker. Many colorful piranhas are more colorful and beautiful than usual. The female piranhas spawn, or lay eggs, during the rainy season.
Piranhas probably court each other, like their relatives the tetras do. Tetra males and females go through a set of paired movements, as though they were dancing together, before they spawn. It is likely that piranhas do something similar. Right now, scientists know very little about how wild piranhas breed. They are probably sexually mature, or old enough to reproduce, when they’re about a year old.
Spawning
No one is really sure about the spawning habits of wild piranhas. In aquariums, some females just lay their eggs on the floor of the tank, but others have been seen readying a nest. These spend a great deal of time choosing a spot near water plants and then cleaning it with their fins. When the fish lay their eggs, the eggs stay stuck to the plants. Then the males swim near and deposit sperm on the eggs. In the wild, it may be that piranhas behave differently. No one is sure whether the fish also guard their nests or the newly hatched piranhas. Some scientists think they do, but very few people have actually seen them behaving this way.
Young Piranhas at Home
In the wild, the young piranhas hide among the stems and roots of the water plants. These plants cover the riverbank and form floating clumps on the surface of the water. The tiniest piranhas, less than 1 inch (about 2 centimeters) long, spend their entire time there. They swim slowly through the thick tangle of plants, looking for tiny crustaceans, immature insects, and aquatic worms. When the little piranhas are a bit bigger, they sometimes venture away from the plants to hunt small fish. They come back to rest and hide among the plants at night. The plants protect the little piranhas from larger piranhas and other predators, as well as from one another.
The plants may serve another purpose for the piranhas. The clumps of plants often break loose and
float down the river. When the plants float away, tiny piranhas and other fish passengers go with them. Eventually the plants bump into something and stop moving, and the fish settle down in their new home. In this way, piranhas are distributed throughout the lowland waterways of South America. Some people think that a way to control piranhas where they are pests might be to destroy or move the plants instead of trying to kill the fish.
Piranhas and People
Piranhas have a frightening reputation, but people have been getting along with them and making use of them for thousands of years. Their jaws are still used as cutting tools and their teeth as razors by some of the rain forest people of South America.
Some groups of people use piranhas as undertakers. The Orinoco River floods its banks and turns the surrounding grasslands into floodplains. When the earth is underwater, dead people can’t be buried. Instead, the bodies are left in the water. Within a few hours, only a skeleton is left. The skeleton is then retrieved, and the bones are dried, dyed, and decorated. When the land dries, the bones are finally buried. This may be another reason that one of the piranha’s names is caribe-cannibal.
Piranhas are also an important food. In Brazil, fishermen bait “trotlines,” fishing lines tied between two poles or trees in a lake. Each string has several hooks tied to it that hang just below the surface of the water. A fisherman sets out as many as 15 of these trotlines at a time. Some fishermen bait their hooks with shrimp and jiggle the poles. When the piranhas come to eat the shrimp, the fishermen lift them out of the water and club them on the head. If the fishermen threw the piranhas into the boat before they did that, the men could easily get bitten.
Many people consider piranhas pests and would like to get rid of them. Piranhas make fishing difficult. They eat fish that are caught in a net or on a pole. They destroy nets with their teeth, and sometimes bite through fishhooks. People herding animals across rivers worry that parts of the animal that hang underwater might be bitten. And although few swimmers get bitten by piranhas, care must be taken around the fish. When hungry piranhas are crowded into a small area, it could be unsafe to be among them.
A Useful Fish
But in some ways, piranhas are actually friends of the fishing industry. Piranhas can’t usually catch and kill healthy fish. It is often the slower, weaker, or diseased fish that they catch. In this way, they keep the fish population strong and stop fish epidemics from spreading. And because piranhas eat dead creatures, they dispose of flesh that would otherwise poison the water.
You might not think that fish have anything to do with trees, but piranhas are friends of the forest, too. They are important in the ecology of the more than two million square miles (nearly five million square kilometers) of Amazon rain forest, the largest tropical rain forest in the world. Piranhas eat seeds that fall into the water and then swim away. They expel some of the seeds undamaged in their waste matter. If the seeds fall into a proper environment, they may sprout, spreading the forest.
Rain forests are very special environments. They are home to almost half of the species of plants and animals on earth. They are also home to some groups of people. Many useful products-some varieties of fruit, wood, fiber, and the drugs quinine and curare-are found nowhere else.
The tropical forests of the world are disappearing so quickly that the larger blocks of forest may be gone within 20 years. Trees are being cut down to make room for humans, their farm animals, their industries, and their homes. As a result, scientists are afraid that destroying the tropical forests will make the world an unfit place to live.
In some places, piranhas have been poisoned to get rid of them, but no one really knows what the long-term results of this action will be. Like the tropical forests they help to maintain, the piranhas are irreplaceable and unique.
Scientists are just beginning to discover facts about the behavior and life cycle of piranhas. The more that is known about them, the less people will fear these fascinating, mysterious fish.
