Fish virus threatens aquaculture industry

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Capital News Service
LANSING – Although no fish with internal bleeding or bulging eyes have been reported by fish farms in Michigan or elsewhere in the Great Lakes region, symptoms of a highly contagious virus that has bruised the profits of many businesses.
Federal regulation of viral hemorrhagic septicemia – or VHS – caused a business disruption years ago that some fish farmers say continues to haunt them, but aquaculturists hope new management methods can combat disease risks and help stabilize the fledgling industry.
Since it was first detected in the region almost a decade ago, VHS has been found in wild fish in all five Great Lakes, Lake St. Clair, the St. Lawrence River and several area inland lakes, according to the Minnesota Department of Natural Resources.

The Animal and Plant Health Inspection Service, a division of the U.S. Department of Agriculture, identified 28 Great Lakes fish species that are susceptible to the virus. They include walleye, rainbow trout, yellow perch and smallmouth bass.
It’s primarily transmitted by infected fish that shed the virus into the water.
In response to VHS, the federal government halted interstate movements of live fish among the eight Great Lakes states for two weeks in 2006, said Nicholas Phelps, a University of Minnesota Extension aquaculture specialist.
As a result, Harrietta Hills Trout Farm near Cadillac lost 70 percent of its market overnight – even though it didn’t have any sick fish and annually certified its products as VHS-free, said owner Dan Vogler.
“We had to completely remake ourselves during that time period, and it resulted in extreme financial hardship,” said Vogler, adding that the sharp revenue drop prompted longstanding uncertainty that still comes up in discussions with banks and mortgage lenders.
If the federal government had consulted industry representatives and considered existing disease protocols, financial damage to aquaculturists could have been avoided, he said.
Phelps said the federal order was revised later in 2006 to allow interstate shipment of live fish that are certified free of the virus. The order was lifted last June to avoid redundancy with state agencies, which continue to regulate disease testing and prevention among fish farms.
Identifying potential disease carriers and creating effective regulations is not easy, said Allyn Spear, a research microbiologist with the U.S. Department of Agriculture.
“It becomes really difficult to get a handle on how often do we need to test, what species do we need to test and how restrictive do we need to be,” Spear said. “There is definitely an effort to make sure that the regulations are not too burdensome on producers.”
To accomplish that task, the National Aquaculture Association and Animal and Plant Health Inspection Service last month proposed a non-regulatory framework for how producers can best monitor health and prevent disease.
Phelps said VHS is a horrible disease that has been costly and time-consuming for many people, “but it has allowed for educational opportunity and, I think, advanced the industry moving toward something that is a little safer and, in the long run, sustainable.”
Phelps develops risk-based management methods for VHS. In 2014, he published research that recommended dividing each state into regulatory zones based on how close or connected they are to infected waters.
Michigan and Minnesota use this method, Phelps said. It allows low-risk farms to save time and money through less frequent testing.
Research is also improving detection of VHS. Recently, Phelps and other Great Lakes researchers led by the Agriculture Department developed new testing measures.
This new test is 100 to 1,000 times more sensitive and costs only $10 per sample instead of the $17 for current testing, Phelps said. And it reduces turnaround time from one month to a few days.
Despite its benefits, the test is allowed for in-state certification only in Minnesota so far, and it doesn’t qualify for interstate certification, said Phelps.
A downside is that such methods require killing fish to test their tissue.
However, research on a non-lethal alternative was recently published by Emily Cornwell, a veterinary student and postdoctoral fellow at Cornell University. It uses small tissue samples from fins or gills.
Although her method needs years of review before it could be approved for regulatory testing, it’s valuable in disease surveillance, Cornwell said.
Different species of wild fish in Lake Erie and the St. Lawrence River differ in susceptibility, Cornwell said.
For example, hybrid striped bass, which are farm-raised in New York, are moderately susceptible, she said. Tiger muskellunge are also fairly susceptible. But walleye are fairly resistant.
“I think potentially if you are raising a species that is particularly susceptible, you may want to pay even more attention to your biosecurity protocol,” Cornwell said.
Spear and fellow researchers are writing a four-year plan to study VHS prevention in yellow perch raised on fish farms. Wild perch have decreased for a variety of reasons, leaving a potential market for Great Lakes aquaculture, he said.
The project would investigate the possibility of breeding fish that are more genetically resistant to infection. Previous research demonstrated that resistance can be passed to offspring, and similar selective breeding programs reduced bacterial cold-water disease in U.S. trout, Spear said.
Another component of the project is to develop a vaccine for the strain of VHS found in the Great Lakes. Researchers will study how cells of infected fish react to the virus so they can artificially trigger the same immune response.
“If we can understand how the fish naturally sounds the alarm, then we can make sure that, when we design a vaccine, we are pressing those same buttons, and if anything we might be ringing the alarm louder,” Spear said.
An important goal is to make vaccines more affordable and easier to administer, he said. Techniques for incorporating vaccines into tank water may be preferred to traditional methods of injecting individual fish, particularly in treating highly vulnerable young fish.
Holly Drankhan writes for Great Lakes Echo.
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28 species of Great Lakes fish found with VHS:

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