Ornamental goldfish that escaped or were released into a lake just south of the Twin Cities likely infected and killed off large numbers of carp, according to state conservation officials.
A virus from the koi goldfish also has been found in at least eight other southern Minnesota lakes in the past year, the state Department of Natural Resources (DNR) said Friday.
Staff from the DNR's Lake City fisheries office went to Lake Byllesby near Cannon Falls after dead fish washed up on shore. They collected samples and brought them to the agency's pathology lab and to the Minnesota Aquatic Invasive Research Center at the University of Minnesota.
The labs confirmed that the fish died from infection with the koi herpes virus, which only afflicts common carp and koi, an ornamental member of the carp family raised in East Asia for centuries and kept by some people in aquariums and outdoor ponds.
The virus kills carp by damaging their gills and skin. It cannot be transferred to humans or to other animals.
The virus has been detected at other southern Minnesota lakes, including Jonathan, Washington, Elysian, Tetonka, Gorman, Dora, Sabre and Cottonwood, the DNR said. The agency once caught a koi near Albert Lea that was 9 to 11 inches long.
The virus "likely found its way into Minnesota waters by the release or escape of ornamental koi," a statement from the DNR read. "Releasing ornamental fish into the wild is illegal and can upset the balance of natural systems."
Ideally, unwanted living aquarium fish and plants should be donated. Minnesota Sea Grant and the Minnesota Aquarium Society have hosted fish and plant surrenders. Information is available at seagrant.umn.edu/news.
Meanwhile, U researchers are trying to determine whether the virus might be an option for controlling the carp population, which can cause serious damage to aquatic ecosystems.
Most fish kills this time of year are due to natural processes, not outside forces, the DNR said.
Fish kills can be reported to the state at 651-649-5451 or 1-800-422-0798. Property owners with dead fish on their shoreline can bury them or leave them for other wildlife to consume. The DNR said it does not collect and remove dead fish.