The Grass carp, (Ctenopharyngodon idella), also known as the White Amur, is an herbivorous, freshwater fish. It is cultivated in China for food but was introduced in the United States for aquatic weed control. It is a species of carp native to Siberia and northern China. The name White Amur derives from the Amur River, where the species is believed to have originated.
Grass carp have an elongate, chubby body form that is torpedo shaped. The terminal mouth is slightly oblique with non-fleshy, firm lips, and no barbels. The complete lateral line contains 40 to 42 scales. The dorsal fin has 8 to 10 soft rays, and the anal fin is set closer to the tail than most cyprinids. The body color is dark olive, shading to brownish-yellow on the sides with a white belly and large slightly outlined scales.
The species was deliberately introduced into the United States in 1963 for aquatic weed control. It was introduced into New Zealand along with stocks of goldfish but the distribution is carefully controlled to prevent it from becoming a more widespread pest. Adults of the species feed exclusively on aquatic plants. The grass carp grows very rapidly, and young fish stocked in the spring at 8 inches will reach over 18 inches by fall, and adults often attain nearly 4 feet in length and over 40 pounds in weight.
When used for weed control, often the fish introduced to the pond or stream are sterile, triploid fish. The process for producing triploid fish involves “shocking” eggs with heat or electricity. In the wild, grass carp only breed in fast-moving rivers.