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

Grass carp (Ctenopharyngodon idella) is an exotic species which was imported into the United States in 1963 to control aquatic vegetation. Individuals 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 collected grass carp in other portions of the upper Mississippi River system. The presence of juveniles (some less than 20 mm long) and adults (some diploid) in our collections leads us to believe that grass carp are reproducing in the Illinois River, and their larvae are finding suitable nursery areas in backwaters. Naturalized, reproducing grass carp populations probably exist as far north as 209 km into the Illinois River. Collections of juveniles by other researchers indicate reproduction and recruitment may also be occurring in upper Mississippi River Reaches 25, 26 and the Open River Reach below Lock and Dam 27.