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Virus affecting carp enters Rock River ecosystem

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Ted Peck
August 10, 2014

A couple of significant carp die-offs in the Rock River’s headwaters near Horicon Marsh late last month have been caused by the koi herpes virus, according to DNR fisheries biologist Laura Stremick-Thompson.

Stremick-Thompson said this virus impacts only koi—a colorful carp cousin and common carp. The koi herpes virus is the carp equivalent of Ebola, with a mortality up to 80 percent.

The biologist said this is the first time koi herpes has been reported in Wisconsin waters. Previous outbreaks have been reported in Indiana, New York, Michigan and a couple of other states in recent years, but Stremick-Thompson said infected fish could not have migrated here from other states.

“This looks like the work of a phantom stocker who didn’t want to feed fish in a koi pond anymore and decided freeing the fish in Rock River would be the kindest thing to do,” she said.

Unfortunately, well-intentioned deeds often have disasterous unintended consequences.

Stremick-Thompson said there are no barriers which can prevent infected fish from swimming downstream and passing the virus on to other carp. Transmission is most pronounced in 70-75 degree water—the habitat parameter that will exist in the Rock River for at least another six weeks.

The first thought that comes to many anglers’ minds is that anything that would take out 80 percent of Rock River’s carp and leave all other species swimming healthy and happy would be a good thing.

The downside of this situation is that the surviving 20 percent of those bugle-mouthed bass will be resistant to the virus. Carp are notoriously hearty fish, able to thrive in even the nastiest conditions.

Resistance to the koi herpes virus is just one more factor resulting in a strain of super carp.

When one species vacates a niche in a riverine ecosystem, another species moves in to fill the void. Wouldn’t it be wonderful if this finny critter was smallmouth bass or walleyes?

“Unfortunately, 20 percent of a large number is still a large number,” Stremick-Thompson said. “Carp will remain a major player in the Rock River system.”

The biologist said she was “virtually certain” more carp fish kills will occur at points downstream this summer and into the future.

Imagine the stench of 80 percent of all Lake Koshkonong’s carp floating belly up in the August sunshine.

“Now that the koi herpes virus has been confirmed in the Rock River, it will not go away,” Stremick-Thompson said “There is no known cure for this virus. In future years, young carp which don’t have antibodies to the disease will be susceptible to the koi herpes virus. Carp fish kills will be the new normal in the Rock River system.”

It is hard to imagine anybody who is not totally evil doing anything to hurt our natural resources. The phantom koi stocker will never be apprehended. We all get to suffer forevermore from this freshwater “Free Willy” action.

Over the past couple of years, the DNR has cracked down on transporting unused minnows home from a day on the water in an attempt to stop the spread of the dreaded VHS disease, which impacts a number of fish species.

Water in the bilge or livewell of a boat can also carry invasives such as zebra mussels and Eurasian milfoil.

Thirty years ago, zebra mussels arrived in this country in bilge water of a freighter from the Black Sea. These little mussels and a cousin called the quagga mussel have displaced native mussel species and have had a profound impact in waters all across Wisconsin.

Every person who uses our natural resources needs to adhere to common sense rules which are in place. The unintended consequences of a good deed gone bad can be devastating.

The arrival of the koi herpes virus in Rock River carp is a sobering cautionary tale, indeed.

Ted Peck, a certified Merchant Marine captain, is an outdoors columnist for The Gazette. Email him at tedpeck@acegroup.cc.



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