Information regarding carp-exclusive fish kill in Waterville area

May 29, 2020

Hi all, we and several DNR offices have been getting inundated with calls regarding Lake Frances in the city of Elysian. There has been a carp-exclusive fish kill ongoing in the lake for the past two to three weeks. That being the case it is prudent to send this out to all our Waterville Fisheries Newsletter contacts to make you aware of the situation and so you have a better understanding of carp only kills.

The cause of the carp kill on Frances has been verified to be Carp Edema Virus (CEV). This is a virus that has been monitored since 2017 and found to be present in a couple dozen carp kills in Minnesota and Iowa in recent years. There is a graduate student from the UMN Minnesota Aquatic Invasive Species Research Center that tested and verified the cause of the kill on Frances. This graduate student has been studying this virus since the large fish kill that happened on Lake Elysian just before Independence Day in 2017, which made state-wide news as the first positive case of Koi Herpes Virus (KHV) in Minnesota public waters. KHV is another virus that so far exclusively impacts common carp. His studies of Lake Elysian show the viruses continue to manifest themselves in the lake. Carp numbers are down in Lake Elysian, yet persisting.

What we have learned is that although CEV and KHV are relatively new to Minnesota in regard to positive test results, these viruses may have been around for some time given the widespread nature of positive testing, and we just were not testing for it. Historically, DNR had tested fish from carp only kills but those kills were often attributed to Columnaris, which is a bacterial infection caused by the bacteria Flavobacterium columnare. With this recent discovery of KHV and CEV and more specific testing for viruses the Columnaris diagnosis of previous carp only fish kills may have merely been a secondary infection and likely not the primary cause of the kills. Recent testing has indicated KHV and CEV or in some cases both viruses, have been the cause of most carp only kills.

We are still learning about these viruses but the bottom line is it seems these viruses are present in many lakes in Minnesota, and have not had a negative impact on other fish species or humans. Given carp are an in-lake habitat destroying bottom feeding species some may be hoping these viruses wipe out all carp. Keep hoping. J What I can tell you is that KHV and CEV caused carp only kills have not resulted in 100% carp kills, and most often 50% of carp or less die from the disease from what we have observed. Fish that survive the viruses develop immunity, but from my understanding that immunity is not passed on to offspring, so the impacts of KHV and CEV can persist in lakes. Typically, KHV onset occurs with water temps near 70 F, which is around the first couple weeks of June in southern Minnesota. CEV onset can occur at cooler temps apparently.

Some have questioned if humans should eat fish from a lake where a carp only kill has occurred. From what we know these viruses do not impact humans or other fish species so you should be fine eating fish captured from Lake Frances or any other lake that has tested positive for KHV or CEV or that is experiencing a carp only fish kill. Use your normal protocol for preparing fish, hand washing, etc. Dead fish that wash up on shore should be composted or disposed of properly.

If you observe fish kills please contact the Minnesota Duty Officer at 651-649-5451 or 1-800-422-0798 to report the kill so the proper agencies can be notified: