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Four species of large Asian carps (grass, bighead, silver and black) have been imported into the U.S. for use in the aquaculture industry, and biologists are raising more and more concerns about their effect on native fish and shellfish when released or escaped to the wild. In fact, in the fall of 1999, fish kills in isolated ditches adjacent to the Upper Mississippi River on the Mark Twain National Wildlife Refuge in southern Illinois included large numbers (97%) of Asian carps, but only one individual each of four native fish species. After that incident, reports came in of commercial fishermen having to abandon fishing sites on the Missouri River because they were catching so many Asian carps that they found it impossible to raise their nets. The common carp, introduced by European immigrants in the 1800’s as a food fish, has become so widespread in the U.S. that in most areas it is considered part of the native fauna. The fear is that in time the other four Asian carps will become as widely distributed and abundant, wreaking widespread havoc with native fish and shellfish habitats and foods.