Something strange was happening. Dead fish were washing up on the shores of the Great Lakes. The cause was determined to be viral hemmorhagic septisemia (VHS), a virus that infects approximately 38 species of both marine and freshwater fish. As stated above, it was introduced into the Great Lakes in the early 2000s and there are concerns about it spreading eastward. The symptoms include hyperactivity, twisting of the body, and erratic swimming. In its most severe form, fish become lethargic with bulging eyes, liver and kidey abnormalities, and bleeding in the eyes, skin, gills, fin bases, skeletal muscles, and interal organs. It is unknown how it was introduced into the Great Lakes, but according to http://www.seagrant.umn.edu, genetic evidence suggests it may have been transported in water from ships or migration from infected fish. Aquaculture and bait transportation have also been liked to the virus’ spead. Shawn Good, a Fisheries Biologist with the Vermont Fish and Wildlife, also said it was likely introduced through bait transportation. He said bait fish were caught, sold to shops, and subsequently sold to anglers. It is found in all the Great Lakes as was as lakes in Ohio, New York, Michigan, and Wisconsin.
It is native to eastern and western Europe, Japan, the Pacific coast (California to Alaska), and the North Atlantic coast. Good said that fish which are found where the disease is native do seem to be more resistant as a result of having evolved with it. The disease fares best in cold water and is unable to survive in warm blooded animals. Thus, it is not one that humans can catch. While it is not unsafe for people to eat fish with VHS, Good said it is not something he would recommmend.
Good said no threatened or endangered species are at risk. However, he also said it can affect different species in different ways. Some appear to be just carriers. Some are not affected at all, while others seem to be prone to it. The reasons for this are unknown. Good also said the virus can exist outside of a host for a couple of weeks, thus giving it time to spread. However, he also said survivors can pass the resistance traits to their offspring thus potentially creating a population which may be more resistant in the long run. He also said its effect on overall populations can vary. Muskellunges (esox masquinongy) or “muskies” are large predatory fish which can grow up to up to five feet and weigh up to 60 pounds. They are considered rare even in a healthy population and Good said they were seriously impacted by the disease in the St. Lawrence River and it would likely take 20 years for the population to recover. However, other species which are faster growing, such as sunfish and bass recover much more quickly.
According to http://www.seagrant.umn.edu, there are also concerns with the impacts to aquaculture. When fish are confined and stessed, as they are in an aquaculture setting, the disease can be much more serious. Good also stated that fish in a weakened condition tend to be more vulnerable and said that approximately 20 years ago, hatcheries in Europe took a serious hit from the disease. This was at least in part due to taking eggs from wild stock. As a result, this practice was temporarily stopped, quarantine areas were created, and water sterilization was also added. Good said that due to these preventative measures, that so far as he knew, no U. S. hatchery had an outbreak.
While it can be a serious disease, taking precautions such as the ones stated above can do much to limit the spread. Good said that many of the Great Lakes states, including New York, Ohio, Pennsylvania, Wisconsin, and Michigan had passed laws making it illegal to move fish from an infected area and he said there were similar laws in Vermont. He said by following these laws it may be possible to prevent the further spread of the disease.
The Nature Journal 