Carp have been part of Chinese culture and aquaculture for thousands of years. They are one of the most important food fishes, and they are also celebrated in Chinese literature and art. In their home range of eastern China, the carp can tolerate a variety of environments, including lakes and reservoirs, but they seem to prefer large rivers. They spawn in the spring, usually in flowing water with a rocky bottom; a female can lay more than 500,000 eggs. Young bighead and silver carp grow rapidly and are sexually mature within a few years. Large individuals can be 4 feet long and weigh 70 pounds.
“Interestingly for fish this size, they are not predators. Rather, they filter water through their specialized gills to consume plankton, algae and other particles,” says senior aquarist Kurt Hettiger, who tends the Asian carp in Shedd’s Local Waters gallery.
And that is why these swimming vacuum cleaners are such a threat: They are depleting the food web at its very foundation. In some stretches of the Illinois River, fish populations are dominated by two species. You guessed it: bighead and silver carp.
Since the beginning of the 20th century, Asian species of carp have been introduced in more than 70 countries, either inadvertently or for aquaculture
or research purposes. They were imported to the United States in the early 1970s by aquaculture facilities in southern states, including Arkansas, to help manage water quality. Asian carp were efficient at controlling algae and plankton growth in aquaculture ponds containing catfish and other food fish.
Unfortunately, some escaped or were transplanted into the waters of the Mississippi River basin. Once in natural waters, Asian carp thrived. In addition to their efficient feeding and breeding habits, they are, for the most part, untroubled by predators—few native species can take on these behemoths past their first year. Asian carp have been spreading through the Mississippi basin, and today, they have been confirmed in at least 18 states.
Coincidentally, 18 possible entry points in five states have been identified as gateways for movement of Asian carp into the Great Lakes. One hotspot for possible entry is the Chicago Sanitary and Ship Canal, which provides a direct connection between carp-infested Illinois rivers and Lake Michigan. In 2002, the Army Corps of Engineers built the first of three electric fish barriers in the CS&S Canal to keep bighead and silver carp at bay a scant 60 miles from Lake Michigan. Since 2009, genetic evidence of Asian carp has been found in waters beyond the barrier, including in Lake Michigan, although no established carp populations have been found.
Today, the Asian carp situation is complex, with no easy solutions. Much is at stake economically and environmentally no matter what preventive measures are pursued. One of the best things you can do to help is learn more and teach others. You can start at Shedd Aquarium’s informative invasive species exhibit in the Local Waters gallery. Shedd is a great—and, we hope, the only—place to see Asian carp in Chicago.
To wrap up National Invasive Species Awareness Week, tomorrow we’ll feature a native fish that is targeted by an invasive species but is also benefiting from it.
—Sam Bugg, Daniel P. Haerther Center for Conservation and Research