EVIDENCE OF GRASS CARP (CTENOPHARYNGODON-IDELLA) REPRODUCTION IN THE ILLINOIS AND UPPER MISSISSIPPI RIVERS

Grass carp (Ctenopharyngodon idella) is an exotic species which was im ported into the United States in 1963 to control aquatic vegetation. I ndividuals escaped from ponds and subsequently spread into streams in the Mississippi River basin. We have been collecting grass carp in the Illinois River since 1990, and some of our associates have also colle cted grass carp in other portions of the upper Mississippi River syste m. The presence of juveniles (some less than 20 mm long) and adults (s ome diploid) in our collections leads us to believe that grass carp ar e reproducing in the Illinois River, and their larvae are finding suit able nursery areas in backwaters. Naturalized, reproducing grass carp populations probably exist as far north as 209 km into the Illinois Ri ver. Collections of juveniles by other researchers indicate reproducti on and recruitment may also be occurring in upper Mississippi River Re aches 25, 26 and the Open River Reach below Lock and Dam 27.