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.