Koi herpesvirus may have caused Kent Lake die-off

Back in June, an estimated 300 to 500 common carp died in Kent Lake in Oakland and Livingston counties. Although the spring viremia of carp virus (SVCV) was originally thought to be the culprit behind the die-off, testing and laboratory analysis failed to detect SVCV.

However, samples from the fish kill showed the presence of koi herpesvirus (KHV), which may have contributed to the fish kill, according to the state Department of Natural Resources (DNR).

KHV is a highly contagious viral disease that can cause significant morbidity and mortality in common carp, which are sometimes selectively bred for the ornamental fish industry, where the carp is known as koi.

First detected in England in 1996, KHV has been found all around the world and was responsible for the large-scale carp die-offs seen in Ontario in 2007 and 2008. Although not previously found in wild fish samples in Michigan, KHV was detected in a private koi pond near Grand Rapids in 2003.

A herpes-type virus, KHV can produce 80 to 100 percent mortality in diseased populations. While it appears to only cause disease and mortalities in common carp and koi, the virus can infect goldfish and crucian carp. The virus does not cause any human health effects. The impact of KHV on native minnow species is currently unknown at this time.

Common disease symptoms include pale and necrotic gills; lethargy; sunken eyes; erratic swimming; a notch in the “nose” of the fish; and patches of discolored skin.

Death can happen within one to two days following the onset of symptoms with most fish dying within 6 to 24 days.

“The disease is easy to confuse with other diseases such as viral hemorrhagic septicemia, so laboratory analysis is needed to confirm this disease,” said Gary Whelan, DNR Fish Production Manager. “While there are no treatments for this disease, the DNR is evaluating potential steps to manage it.”

Infections are transmitted via the presence of the virus in the water, in fecal material, and in sediments; it can also be transmitted fish-to-fish.

The disease was likely introduced into Michigan waters by the release or escape of infected ornamental fish.

“This disease outbreak is another example of why the DNR reminds anglers and boaters that they need to drain bilges and live wells upon leaving a boat launch,” said Jim Dexter, Acting Chief of the DNR’s Fisheries Division. “Anglers should clean their boats, disinfect their gear, and not move live fish, to reduce the possibility of any fish diseases being transferred to new locations.”