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Alligatorweed
(Alternanthera philoxeroides)
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Photo credit: Pam Fuller, USGS, Bugwood.org
Grass Carp
(Ctenopharyngodon idella)
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Species at a Glance
The grass carp, also known as the white amur or the waan ue, is one of the largest minnows in the family Cyprinidae. It is also a member of the Asian carp complex, which includes the black, bighead, and silver carp. It was introduced into the United States to help control the growth of aquatic weeds in aquaculture facilities, but escaped into natural systems and is now widespread throughout the U.S.
Identification
The body of the grass carp is oblong in shape but considered slender for most carp. It typically reaches 29-36 kg (65-80 lbs), although individuals as large as 45 kg (100 lbs) have been reported. Scales are large, with dark edges and a black spot at the base. The scaleless head lacks barbels. Overall color is olive to silvery-white, while the fins are a clear to gray-brown. The dorsal fin is composed of three simple rays and seven branched rays.
Similar Species
The grass carp may be confused with the common carp (Cyprinus carpio), which can be distinguished by the presence of barbels around the mouth. The common carp is also more golden in color and has spiny modified rays on the dorsal and anal fins.
Habitat
The grass carp prefers shallow and quiet waters, typically 0.9-3 m (3-10 ft) deep, such as ponds, lakes, pools and backwaters of large rivers.
Spread
Once introduced, the grass carp can spread to distant water bodies by tributaries, waterways, river systems, canals, and dams. This carp is also still intentionally stocked in aquaculture facilities; however, it must be stocked in the triploid form, which means it is sterile and unable to reproduce. Some states require a permit to stock the carp, and stocking is only permitted in ponds to prevent its spread through waterways and river systems.
Distribution
Native to eastern Asia, including China and Russia, the grass carp was introduced in many countries for aquaculture plant control. It is now widespread in 45 states in the U.S., including all Mid-Atlantic states. Reproductively sterile triploid grass carp can be stocked In Delaware, New Jersey, New York, Pennsylvania, Virginia, West Virginia, and North Carolina with a permit. In Maryland, use of diploid or triploid grass carp is prohibited.
Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.
Environmental Impacts
While the grass carp does help to reduce unwanted aquatic vegetation, it also alters the food web because it feeds voraciously on desirable plant species, reducing the amount of food available to native invertebrates and fishes. Excreted plant material can also increase nutrient levels in the water that cause harmful algal blooms and affect water quality.
Video
Note
Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).