The fish virus was detected in ovarian fluid samples taken from coho salmon used to produce eggs for DNR's ongoing Lake Michigan stocking programme.
After receiving test results indicating the presence of VHS in females donating to two batches of eggs, these eggs and others that lacked complete data were destroyed as a precaution despite undergoing federally approved disinfection procedures as part of the department's established biosecurity measures.
Ron Bruch, DNR fisheries chief, said no impact is expected on spring 2016 stocking plans. This year's successful spawning run resulted in the collection of approximately 25 per cent more coho eggs than anticipated and this additional volume should cover the number of eggs that were destroyed, providing for the 2016 stocking of 400,000 yearlings.
"Wisconsin DNR is committed to maintaining the integrity of our hatchery system, as well as the health of state fisheries, and our fish health surveillance work is a key part of that commitment," Mr Bruch said.
"Our testing and biosecurity protocols exceed state and federal standards and our operational firewalls prevent wild brood stock from coming in contact with young fish in our hatcheries. The conservative approach taken by destroying the eggs was implemented as an additional precaution."
The Root River facility serves as one of the state's two sources of wild steelhead or rainbow trout eggs and also serves as a collection point for coho eggs. VHS, which has been found in the Great Lakes since 2003 and, since 2007, in the Wisconsin waters of Lake Michigan, Superior and Winnebago. The virus can kill fish by weakening their blood vessels, although no large scale die-offs of game fish have been observed in these waters since the disease was first detected.
DNR officials credited a partnership with the US Fish and Wildlife Service for providing an efficient means of laboratory sample processing and disease detection. As part of the fall egg collection procedures at Root River, as well as at Strawberry Creek Chinook Facility in Sturgeon Bay and the C.D. "Buzz" Besadny Anadromous Fish Facility near Kewaunee, ovarian fluid samples are sent to the La Crosse Fish Health Center for analysis. The lab uses cell culture testing to detect VHS, a process that takes 30 days to complete and the only process recognised by the USDA for confirmation of the presence or absence of the virus in a sample.
"We are applying the best scientific practices to monitor and ensure the health of the fishery," Mr Bruch said.
"I am not surprised we found VHS in Lake Michigan coho salmon, given the presence of the disease in other game fish such as brown trout and chinook. The finding validates our proactive disease surveillance programme to protect our hatchery system as well as our wild fish stocks."
DNR has been in communication with the US Department of Agriculture and state Department of Agriculture, Trade and Consumer Protection regarding the VHS detection and preventive actions. DATCP is responsible for regulating the health of fish that are found on private fish farms and DNR hatcheries while USDA has oversight on trade restrictions involving VHS.
"The DNR is very thorough in its efforts to ensure fish health beyond state and federal requirements and we are working with the department's fisheries management team to ensure the health of fish being raised in Wisconsin," said state Agriculture Secretary Ben Brancel.
"We appreciate DNR's surveillance efforts as a way to further understanding of VHS and its impact."
