The Grass Carp are also called White Amur, belongs to the minnow family. A name developed and used to avoid the negative connotations of “carp.” This large import from China is primarily a freshwater herbivore introduced for aquatic weed control. In many parts of the country it is considered an invasive species and stocking/transporting it is illegal. However, it is still stocked for to control weeds, typically as sterile, triploid fish. The process to create sterility is not usually 100% effective, so the young are usually tested for triploidy before being sold.
Amur have a torpedo shaped body with moderately large scales. The head is scaleless. Coloring ranges from silver to olive in color on the back, shading to white on the belly. Its mouth is terminal, no barbells, with non-fleshy, firm lips. The dorsal fin has 8 to 10 soft rays. Anal fins are closer to the tail than most other minnows.
In its native habitat, Grass Carp are fish of large, turbid rivers and associated floodplains. They have a wide degree of temperature tolerance. Spawn at occurs at temperatures 68 to 86 degrees Fahrenheit. As these minnows spawn in flowing water and do not reproduce well in lakes and ponds. Reproductive success requires an adequate flow of oxygen rich water. Wild populations do exist in many waters of the United States.
Juvenile grass carp rely primarily on phytoplankton for food, but have been reported to eat small invertebrates and crustaceans. Adults feed primarily on aquatic vegetation, consuming up to three times their weight in food each day. Grass carp are rapid growers, with fish stocked at eight inches in the spring reaching 18 inches by fall. Adults can obtain sizes in excess of four feet and fifty pounds. They are known to exceed one hundred pounds in China.
Grass Carp in Colorado
Courtesy of NDIS Species Diversity, Colorado Parks and Wildlife
Habitat: The grass carp is herbivorous, eating copious amounts of aquatic vegetation. It is not known if the species can successfully spawn in the rivers of the United States.
Description: A robust, thick-bodied minnow; head broad, blunt; mouth large, terminal; scales very large, dark-edged; anal fin close to caudal fin, distance from the front of the anal fin to the tip of snout is 3 times or more longer than the distance from the front of the anal fin to the base of caudal fin; 40-45 lateral line scales. Grass carp are golden or olivaceous in color on the back, fading to a yellow-white on the stomach. The scales on the back and side are dark-edged. As the fish age, colors gradually darken. A large minnow, adults can exceed 20 inches in length and 5 pounds in weight.
Range in Colorado: Native to Asia, the species was introduced into the United States to control rooted aquatic vegetation. Grass carp have been released in a few locations in Colorado, regulated by a permit system administered by the Division of Wildlife. The species is prohibited from the western slope of the state.
Status: This species is not listed.