There are seven types of carp that fall under the name Asian Carp.
grass carp (Ctenopharyngodon idella), common carp (Cyprinus carpio), silver carp (Hypophthalmichthys molitrix), largescale silver carp (Hypophthalmichthys harmandi), bighead carp (Hypophthalmichthys nobilis), black carp (Mylopharyngodon piceus), common goldfish (Carassius auratus)
These fish, along with our familiar common carp, were first farmed in Asia thousands of years ago. The farmers of the Southern United States began aquaculture operations in the 1970's as the demand for high protein feed stock and natural fertilizer were growing rapidly.
While these fish were raised for direct consumption in Chinese systems the modern aquaculture system in America was raising a product to feed to other food plants and animals. The market for carp as food never caught on except in small areas of the U.S.
The other difference is that the fish in the ancient systems were closer to a wild fish as it had not been crossed with other carp species.
The fish in carp aquaculture today are seen as the seven species listed above. Although they are distinct they are not natural. The removal of eggs and sperm from adult fish is simple and with thousands of chances of fertilization per cross a few are going to develop into viable adults.
These are food animals and they eat like animals bred to be large and fat in the shortest time possible.
The carp once contained in ponds and pools in the southern aquaculture operations slowly escaped as flood waters reached their enclosures. This began as early as the mid 1970's and progressed sporadically until several years of devastating floods in the early 1990's caused the release of a huge number of fish.
The detritus produced by the flood was a feast for these fish and as they drained back into the river basin they could not have wished for a better environment. That is, if fish wish.
The route of these fish is directly up the Mississippi River and its tributaries. Including the Illinois Sanitary and Ship Canal. It sounds worse than it is but it does carry Chicago's sewage waste away from Lake Michigan and the city.
This was not the way it was originally planned by nature. Normally, the Calumet River would flow into Lake Michigan a short distance west of Chicago at the Continental Divide. City planners changed the flow of the river to a lake outlet that flowed to the new canal and eventually the Mississippi River. The canal made the trip to the Gulf of Mexico much shorter than the trip around the peninsula of Florida.
This was a convenient way to flush away the sewage of Chicago. Previously it had been dumped into the lake. After many rounds of a mystery illness over the years the culprit was found. The sewage dumping was being carried by underwater currents during heavy rains and polluting the drinking water supply with sewage.
The canal is a direct route to a body of water that would otherwise be an impossible journey in a natural system.
The Asian Carp has already reached Lake Michigan according to some evidence. Genetic testing reveals the signature of Asian Carp but the fish has not officially reached the lake.
An attempt at keeping the fish out with an underwater electric fence is seen as a success. But the system has broken down occasionally and is without power for a few minutes. The foraging whiskers of a carp sense prey by touch and electrical signal. The carp could possibly sense a lack of energy in the barrier and cross unobserved in the murky water.
The aggressive feeding and territorial nature of these fish makes them sure to out compete native fish and introduced sport fish. This development would cost the commercial and recreational fishing industries a significant portion of the billions of dollars they contribute to the economy each year.
These fish can also reach 100 pounds like the common carp. The fish escape predators by leaping from the water and often land in boats as the wake disturbs the fish. Several serious injuries have been reported from leaping carp.
The spread of these fish can be seen on this animated map.