Chesapeake Bay Introduced Species Database

Ctenopharyngodon idella

Common name(s):
Grass Carp
Grass Carp are freshwater herbivores. They eat aquatic plants and were imported to the United States, Europe, Africa, Japan, Mexico, and other areas to control unwanted aquatic plants. They are native to China and Russia and are cultivated in China for food. They were first brought to the United States in 1963 from Malaysia by researchers at the United States Fish and Wildlife Service Fish Farming Experimental station. At the time people thought that if the fish were only used in lakes and other slow moving water bodies they would not become established because they need large swift-flowing rivers to reproduce. But, they were wrong and very soon they had established breeding populations in the lower Mississippi drainage. They've now been introduced to 45 states. The fact that Grass Carp eat aquatic vegetation is useful in areas with high densities of introduced aquatic weeds. But Grass Carp don?t discriminate between aquatic weeds and valuable native submerged vegetation, they eat them all. Trying to balance the desire to control aquatic weeds and introducing a nonnative fish that eats native plants led to efforts to develop nonreproductive fish for weed control. These sterile triploids are stocked in some states, such as Virginia and banned in others, including Maryland. So far there is no evidence of reproduction by these triplod fish in the Chesapeake Bay watershed.
Image courtesy of Pavel Dvorak.


Ctenopharyngodon idella


Potentially Misidentified As:

Common Names:

Grass Carp


Most fish stocked in the United States now are sterile triploids, produced by subjecting eggs to a temperature shock after fertilization, resulting from retention of the second polar body and an extra set set of chromosomes. This results in increased cell size; red blood cells are used for testing. Electronic particle sizers are used to verify triploidy and for inspection of eggs by the United States Fish and Wildlife Service, which certifies fish as triploid (Allen and Wattendorf 1987; Griffin 1991).

This data was last modified on Wednesday, July 17th, 2013.
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