Koi or pet goldfish released in MN lake responsible for carp die-off, DNR says

An ornamental koi or pet goldfish is believed to be responsible for a large-scale die-off of thousands of common carp in a lake in southern Minnesota last month.

The Minnesota Department of Natural Resources and the University of Minnesota said the koi herpesvirus (KHV) was the main cause of the fish kill in Waseca County’s Lake Elysian in late June. It is the state’s first documented case of the virus in a wild fish population.

The DNR believes the virus was likely introduced by an ornamental koi or pet goldfish that was released or escaped into the lake.

“Many people don’t realize that koi are essentially just colorful carp, so ultimately the same species and not native to Minnesota,” Craig Soupir, a DNR official, said in a news release. “What this incident tells us is the virus can be introduced by human action – a goldfish or koi was likely released from a home aquarium or pond into Lake Elysian or a connection waterway.”

The virus can cause disease in koi and common carp, but is not believed to affect other fish species or humans. Goldfish can be carriers of the virus but typically do not show signs of the disease.

In light of the incident, the DNR is reminding people that introducing ornamental or pet fish into the wild is illegal and has consequences. Anyone looking to dispose of exotic fish is urged to contact their area DNR fisheries, wildlife office or local humane society.