A bighead carp caught near Lake Michigan in June likely lived nearly its whole life in waters from the Great Lakes, tests show.
The nine-kilogram fish captured in Lake Calumet on June 22 was the first Asian carp caught on the wrong side of underwater electric barriers near Chicago intended to keep the invasive species from moving up the Mississippi River system into the Great Lakes and adjoining waters.
Researchers at the Southern Illinois University Carbondale Fisheries and Illinois Aquaculture Center analyzed the chemical markers in the inner ear bones of the fish and released the results Thursday.
As fish grow, their bones incorporate chemicals from their environment, and therefore contain the unique signature of the waters where the fish lived.
"It is very plausible that this fish originated in the Illinois River and then moved or was transported to Lake Calumet or Lake Michigan during the early portion of its life," Jim Garvey, the centre's director, said in a statement.
John Rogner, assistant director of the Illinois Department of Natural Resources, said the test results suggest the fish may have been put there by humans.
East Asian Buddhists sometimes release fish as a religious practice.
Asian carp used to be sold live for food in supermarkets. However, the sale of live carp has now been banned in Ontario and many U.S. states and their live transport across state lines is banned across the U.S.
Fears for fishery
Many fear that if the bighead and silver carp from Asia get into the Great Lakes, they could out-compete native fish like lake trout and walleye, decimating the Great Lakes fishing industry on both sides of the border, which is worth an estimated $7 billion.
Both Asian carp species are voracious eaters and prolific breeders. Since being accidentally released into the Mississippi River in the 1990s, in some places they now constitute up to 90 per cent of the fish mass in the river.
The capture of the six-year-old, 88-centimetre-long bighead in June bolstered alarming suspicions that Asian carp had managed to get around the electric barriers designed to stop their migration into the Great Lakes system.
Researchers at the University of Notre Dame have detected bighead and silver carp DNA on the Great Lakes side of the barrier since the fall of 2009.
The barriers, first installed in 2004 by the U.S. Army Corps of Engineers, consist of equipment that produces an electric field of pulsing current. The field is uncomfortable for the fish to swim through, encouraging them to turn back.Google map showing Chicago area near carp capture
View Asian carp invasion in a larger map