Posted on Mar 16, 2021

EcoEducation: Investigating Biological Control of Common Carp

You may have heard about the concerns in many states about invasive carp.  First introduced for game and food (Carp is the most introduced fresh water fish), we now know that carp create a lot of environmental harm.  They not only compete for food with native fish and excrete a lot of nutrients promoting algae, but they also root in vegetation causing a turbid state in the water blocking sun.  This can affect the levels of oxygen in the water by inhibiting photosynthesis of aquatic plants. 70% of lakes in Minnesota are impacted by carp.  
We heard from Isaiah Tolo, graduate research assistant at the U of M about his research into biological methods for controlling carp population.  There are a few methods currently in use - all of which have shortcomings.  Netting and electrofishing are labor intensive and impractical for large lakes.  Poisoning affects all species.  Bluegills eat carp eggs, but they also eat eggs of other fish species.  Isaiah's research investigates the use of species specific viruses to control carp population. 
The research began with identifying viruses that affect carp by collecting dead carp from lakes that had a "mortality event"  They found that many of the dead carp had the koi herpevirus present.  Prior to this, it was unknown that the virus was in Minnesota.  There had been worldwide occurrences of the virus since the 1990s and it was identified in the United States in 1997.  There are many lakes in Minnesota now where the virus is known.  Lake Elysian is estimated to have 50% of the carp population infected with the koi herpevirus and it is from this lake that the researchers worked to isolate the virus to be able to test further.  
Isaiah and his team strove to understand if the virus would infect other species and they found that there was no transmission or replication.  Transmission did occur between carp when they came in direct contact.  The estimated results of using the koi herpevirus to control the carp population would be a 9% population reduction.  While this does not seem like much, in a population of millions of pounds of fish, this would be a free way to remove carp from the system. It is a very promising augmenting approach  - safe and no cost.  There is still more testing to do - to understand how the virus acts if fish are stressed, continue to test transmission with other species, and investigate how to get more yield. 
There is a natural expansion of the virus happening.  Some carp populations in the Mississippi river are getting older, suggesting that the virus could be having an effect.