Fish Disease Joins Growing List of Invasive Species in Great Lakes

For fisheries biologist Gary Whelan, invasive species fall into two groups—the ones you can see and the ones you can’t. The second group is the one that worries him.

“I’m concerned about the ones I can’t see,” says Whelan, a fish production manager for the Michigan Department of Natural Resources (MI DNR). “Organisms belonging to the microbial world are showing up at an increasing rate. These are the ones that create challenges.”

Among the organisms that have entered Michigan waters in the last seven years are koi virus (affecting carp and koi), largemouth bass virus, and the parasite Heterosporis sp. (affecting yellow perch and walleye). In 2005, fisheries managers added another virulent pathogen—Viral Hemorrhagic Septicemia or VHS.

VHS is a viral fish disease affecting more than 40 species of marine and freshwater fish in North America. Most recently, VHS has been confirmed in 18 species of fish in the Great Lakes region. The virus, which causes hemorrhaging of a fish’s internal organs, has been responsible for several large-scale fish kills.

VHS is not a human pathogen. It is, however, an international reportable animal disease by the O.I.E. World Organization for Animal Health that requires notification of and action by USDA Animal and Plant Health Inspection Service (APHIS). The discovery of VHS in a number of Great Lakes fish species prompted USDA-APHIS to issue an order on October 14, 2006 that temporarily halted the movement of 37 species of live fish in the Great Lakes states.

The federal action had an immediate economic impact on the commercial fishing, baitfish, and aquaculture industries. An amended federal order issued by USDA-APHIS on November 14, 2006 allowed movement of live fish following testing and certification that they were free of VHS.

The MI DNR stresses that it is critical to make every attempt to slow the spread of VHS in Great Lakes and inland waters. In this respect, anglers and boaters play a pivotal role by cleaning boats and fishing gear when leaving a water body. (See sidebar)

While the actions will help contain VHS, the virus is here to stay, says Whelan: “Like it or not, we’re going to be managing this virus forever.”

Quick Facts about VHS

Where has VHS been found?
In the Great Lakes region, VHS has been confirmed in fish collected from the St. Clair River, Lake St. Clair, Lake Erie, Niagara River, Lake Ontario (Bay of Quinte, Ontario and Rochester, NY areas), the St. Lawrence River, and most recently Lake Huron (near Cheboygan, Rogers City and Alpena).

What fish species in the Great Lakes are affected by VHS?
VHS has caused large fish kills in freshwater drum, muskellunge, round gobies, gizzard shad, and yellow perch from specific locations. VHS has also been confirmed in smaller mortality events in lake whitefish, walleye, smallmouth bass, black crappie, and bluegill.

A number of other species have been identified as carrying VHS although mortalities have not been seen in these species. These include: Chinook salmon (Lake Huron); rock bass (Lake St. Clair); silver redhorse (Lake St. Clair); northern pike (Lake St. Clair); shorthead redhorse (Lake St. Clair); burbot (Lake Ontario) silver redhorse (Lake St. Clair); spottail shiners (Lake St. Clair), and emerald shiners (Lake Erie and the Niagara River).

How does VHS affect fish?
VHS Type IVb is most active in cold water (less than 15 degrees C), which is why mortalities are often seen in the spring. Fish exhibit hemorrhaging of the skin including large, red patches particularly on the sides and anterior portion of the head. However, the MI DNR notes that infected fish will sometimes exhibit very minor external hemorrhaging or no external signs. Internally, organs are often congested with multiple hemorrhages in the liver, spleen, and intestines. The cause of death is usually internal organ failure, particularly the kidneys, or the inability to manage chemical elements in their bodies. Sick fish will often appear listless, swim in circles, or hang just below the surface, according to MI DNR staff observations. Fish that survive infection can be carriers of the virus throughout their lives. VHS is transmitted by urine, feces, and reproductive fluids.

See: AIS Library

Source: Viral Hemorrhagic Septicemia (VHS) in the Great Lakes. 2007. Michigan Sea Grant.

> Next Article