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posted Oct 5, 2017, 6:28 AM by ByllesbyAssociation
(Doug Monson, Mankato area writer)

Carp on carp crime: Let’s use koi to clean up Minnesota Waters

Not long ago, the Free Press, as well as many other news outlets, reported on the Lake Elysian
carp koi kill, the result of a koi herpes virus (KHV).

Minnesota Department of Natural Resources officials speculate the virus was present in the
Waseca County lake due to someone releasing a goldfish or koi from a home aquarium or

As the news of the fish kill made the rounds, many articles focused on why the carp died, but
never stated how amazing it is that this disease had no effect on the other fish species in the

Most people recognize the common carp as a nuisance or rough fish. They leave them on the
shores with the belief the practice will eliminate one more rough fish from their favorite fishing
hole. According to the University of Minnesota’s Aquatic Invasive Species Research Center, a
single female can carry 3 million eggs in a lifetime-basically the catch and kill practice is as
effective as “using paper towels to catch water”.

Another fun fact about carp-the invasive species destroy ecosystems. MASRC research shows
that the common carp are more damaging to water quality than human watershed
development. How?

Researchers analyzed data from over 2,000 Minnesota lakes, covering three major ecoregions
of the Great Plains, Eastern Temperate Forests, and Northern Forests. They also conducted
whole lake experiments in six lakes in which they established what the current carp
populations were, surveyed plant cover and identified species richness both before and after
removing carp.

Researchers found that when common carp were prolific, plant cover was reduced to
less than 10 percent and species biodiversity was halved. By analyzing the impacts of
other human-caused stressors, the researchers revealed that carp had a GREATER
IMPACT on aquatic plant biodiversity than human watershed development did (urban and

The study also showed that removing common carp increased plant cover, species
richness and water clarity.

In our region of the state, this research is important. Carp burrow into lake sediments and in
the process uproot aquatic vegetation, increasing water turbidity and releasing large
quantities of sediment-bound nutrients, which stimulate algal blooms.

MAISRC estimates more than 70 percent of the lakes in southern Minnesota have lost their
plant cover and suffer from excessive algal blooms due to carp’s foraging activity. Common
carp also have a devastating impact on waterfowl habitat.

While those who combat common carp have focused on the reproductive cycle to eradicate
the fish, or have engaged in seining, I’m convinced researchers need to further examine the
first-known introduction of KHV in a wild fish environment in Minnesota. If KHV can wipe out 
large populations of carp in a wild fishery without harming other species of fish, why not
study it more to see if it can be safely replicated?

Replicating the virus without introducing actual koi to Minnesota lakes could be part of the
process of eradicating common carp. Operation Koi would be phase one. Phase two would be
controlling the spawning grounds in shallow lakes and wetlands where carp are able to move
to other bodies of water. And phase three would be the introduction of a bluegill stocking

MAISRC research shows that lakes with high populations of bluegills have low populations of
carp because bluegill feed heavily on carp eggs. And for those of you asking if sunfish would
do the trick, the answer is yes, because bluegills are sunfish.

Common carp are a difficult problem to solve, but one that needs to be examined as the state
pushes to improve its water quality. To ignore the possibilities of KHV would be a mistake.

Besides, its only a matter of time before a passionate Minnesota angler decides to break the
law and release koi into his or her favorite fishing hole, regardless of if the fish are infected or

Let’s save Minnesota anglers from themselves and study the possible benefits of KHV.

Note: Byllesby anglers have reported increased numbers of sunfish/bluegills caught in
the past few years as carp have been systematically been removed from the lake. Algae
blooms have also been noted as being less frequent.
Oct 5, 2017, 6:28 AM