An investigation into the cause of a summer fish kill on the St. Joseph River near Elkhart and Mishawaka has concluded the cause was a combination of fish pathogens.
“Our test results show pathogens, and not pollution, were the primary cause of death for several hundred common carp,” said Bill James, chief of fisheries for the Department of Natural Resources.
The fish die-off, which occurred in July and August, triggered a joint investigation by the DNR, the State Board of Animal Health (BOAH), and the Elkhart County Health Department.
The Animal Disease Diagnostic Laboratory at Purdue University tested tissue samples and found that in addition to bacterial and parasite issues, the carp were suffering the effects of a pathogen know as Koi herpes virus (KHv).
Unusually warm weather also is believed to be a contributing factor.
“The carp that died were pushed beyond their normal defense limits by rapidly rising water temperatures, bacteria, parasites, and ultimately the Koi herpes virus,” James said.
Indiana State Veterinarian Dr. Bret D. Marsh said, “The pathogens involved in this case are specific to selected species of fish and are not an imminent health threat to other fish in the river. Neither are they a source of health problems in people if fish taken from the river are eaten.”
Marsh added that the Koi herpes virus was not identified previously in Indiana waters but was found in many of the fish collected in this case.
The investigation shows the dynamic nature of life in rivers and the uncertainty for stable and apparently healthy fish populations. KHv is on the world watch list because it is known to cause significant losses in wild populations and captive environments where specially bred carp, commonly referred to as Koi, are used in the aquarium industry.
The bacteria and parasite identified are common in the aquatic environment and by themselves normally don’t cause fish die-offs. However, when fish are stressed heavily by a virus, such as KHv, these other common pathogens can contribute to losses.
The new Great Lakes fish virus–viral hemorrhagic septicemia (VHS)–was not detected.
James said the situation is a reminder to boaters, anglers and other watercraft users that they can play an important role in preventing the spread of unwanted organisms from one body of water to another. The DNR advises boaters and anglers to clean, drain and dry all equipment when moving from one waterway to another, and only release fish into the body from which they came.
For more information on keeping Indiana lakes and rivers healthy, visit www.invasivespecies.IN.gov on the DNR website.