A grass carp, or Ctenophayngodon idella, is a freshwater fish belonging to the Cyprinidae family. It is native to China and southern Russia, but it has been imported to many other countries and is now found throughout much of the world. It is often called white amur in the United States, an attempt to avoid the negative aspects that many associate with carp. These fish have been imported to many areas to eat invasive plants.
These herbivorous fish grow to an average weight between 15 pounds and 20 pounds (6.8 kg to 9.1 kg), but can reach 60 pounds (27 kg) or more in large bodies of water and with an abundance of food. They can be identified by their oblong bodies, silvery-green color and large scales. Unlike other species of carp, grass carp have no barbels on their faces, and they have no spines on their dorsal fins. They live for an average of 10 to 12 years, though they may live much longer in some areas. Larger grass carp actually consume far less than smaller ones, making younger fish preferable for aquatic plant control.
Grass carp have voracious appetites, consuming more than 40 percent of their weight in plants each day, and they will eat many different types of plants. They have been introduced to more than 20 countries in an attempt to control invasive aquatic weeds and have become invasive themselves in many areas, including the United States. As a result, it is often required that any imported grass carp be triploid, meaning they cannot reproduce.
These types of carp live in large bodies of slow-moving or still water, including lakes, ponds, marshes and large rivers. Spawning, however, occurs in fast-moving water, because the eggs are heavy and will sink and die in still water. Water that moves quickly will keep the eggs afloat as they drift downstream, keeping them alive for the 20 to 40 hours that it takes them to incubate.
If these fish overtake a body of water, they can destroy both plant life and the homes of rare snails and other invertebrates. In addition, large carp can jump up to 10 feet (3 m) in the air and have caused serious injury to boaters. They can cause a significant drop in the amount of waterfowl and native fish, as well. Once grass carp has become established in a body of water, they can be difficult to eliminate, and they are not easy for fishermen to catch, because they are very wary and stay in secluded areas. Bait such as corn, dough balls and earthworms have proved successful in catching these reclusive fish.