The Grass Carp (Ctenopharyngodon idella) is a herbivorous, freshwater fish. It is cultivated in China for food but was introduced in Europe and the United States for aquatic weed control. It is a species of carp native to Siberia and northern China.
The alternative name White Amur derives from the Amur river, where the species is believed to originate. This is not to be confused with the White Amur Bream (Parabramis pekinensis) which is not a particularly close relative as Cyprinidae go.
White amur 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. Broad, ridged pharyngeal teeth are arranged in a 2, 4-4, 2 formula. The dorsal fin has 8 to 10 soft rays, and the anal fin is set closer to the tail than most cyprinids. Body color is dark olive, shading to brownish-yellow on the sides with a white belly and large slightly outlined scales.
The grass carp grows very rapidly, and young fish stocked in the spring at 20 cm (8 inches) will reach over 45 cm (18 inches) by fall, and adults often attain nearly 1.2 m (4 feet) in length and over 18 kg (70-90 pounds) in weight. They grow 10 pounds a year at least. They eat up to 3 times their own body weight daily. They thrive in small lakes and backwaters that provide an abundant supply of fresh water vegetation.
The Grass Carp is considered an invasive species to North America. It is illegal to transport or own Grass Carp in all but twelve U.S. states because of the threat Grass Carp have on native plant species.
The species was introduced in the Netherlands in 1977 for aquatic weed control against overabundant weed growth. The release of grasscarp into national water is controlled and regulated by the Dutch Ministry of Agriculture, Nature and Foodquality. Because grasscarp only reproduce in water of 25C°, which is much higher than the water temperature reaches during the mating season in the Netherlands. Because of this, it's mandatory to maintain grasscarp populations by artificial means, which is done by the Dutch Ministry of Agriculture, Nature and Foodquality. Because of its special function in controlling weed growth, grasscarps should always be returned into the water alive and unharmed.
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 rapid change in temperature. The young are then tested for triploidy before being sold. Bait often consists of vegetables or fruits that are native to the area.