The Mystery Ailment
A mysterious ailment continues to kill a high percentage of newly hatched Great Lakes salmonid and trout, and the attrition rate appears to be growing.
Researchers call the mysterious condition "early mortality syndrome," or EMS. Fish become lethargic, wonÕt feed, swim in circles, and ultimately die at the bottom of their hatchery holding tanks. The affliction presently kills more than 70 percent of coho salmon, 60 percent of Chinook salmon, 35 percent of rainbow/steelhead trout and 80 percent of lake trout bred from Lake Michigan or Lake Ontario feral stocks.
The problem is not new, according to Wisconsin Department of Natural Resources Fish Health Specialist Sue Marcquenski. A similar condition called M-74 surfaced in the Baltic Sea more than 20 years ago.
"Our early mortality syndrome may have been present in the Great Lakes as early as 1971 or 1972," Marcquenski said. "Anecdotal reports in our records indicate the problem existed in coho from Lake Michigan."
EMS caused some hatchery mortality through the 1970s and '80s, but mortality numbers have increased dramatically in recent years, rising to as high as 90 percent in coho salmon at some hatcheries.
"That [the high numbers] started the most recent interest in determining what causes early mortality syndrome," Marcquenski said.
No known viral or bacterial pathogens have been diagnosed as the cause. Chemical contamination is a possibility, but "it would be hard to pin this on any one particular thing," according to James Kitchell, coordinator of the UW Sea Grant Living Resources research subprogram.
"Fifteen years ago, we had peak levels of contaminants in the Great Lakes, but EMS wasn't an issue," Kitchell said. "Now contaminant levels are down significantly - in some cases to one-tenth of previous levels - yet EMS is a problem. It doesn't make any sense."
Another theory suggests EMS may be due to nutritional deficiencies. Researchers have discovered that afflicted fish are deficient in thiamine. Correspondingly, thiamine treatments applied to newly fertilized eggs or larval fish seem to reduce EMS symptoms.
"We may be looking at the result of interactions among things like disease, nutrition, genetics and possible bioaccumulation of contaminants within the food web," Kitchell said. "But we just don't know." While thiamine supplements may be used to boost hatchery survival rates, Marcquenski stressed the ecological importance of solving the EMS mystery.
"If we don't understand why this is occurring, we just can't go on artificially supporting some of these high populations of trout and salmon in the Great Lakes," she said. "When we find these types of syndromes that affect the reproductive potential of a species and seem to indicate some type of environmental or food web or ecosystem perturbation, it's one of those warning signals that we all need to take a look at."
- Laurence Wiland
F E B R U A R Y 16-17
The 1996 Wisconsin Aquaculture Conference
Ramada Inn & Convention Center, Wausau, Wis. Sponsored by the Wisconsin Aquaculture Association; the Wisconsin Department of Agriculture, Trade and Consumer Protection; University of WisconsinÐMilwaukee Center for Great Lakes Studies, and UW Sea Grant. Contact Theresa at (608) 224-5137.F E B R U A R Y 21-22
Round Goby Conference
Clarion Hotel, Chicago, Ill. Update on the biology, impact and control of this new exotic fish. Sponsored by Illinois-Indiana Sea Grant, Purdue University and the University of Illinois at Urbana-Champaign, with funding from the National Oceanic and Atmospheric Administration. Contact Ellen Marsden at (708) 872-8677.M A R C H 5-7
Sixth International Zebra Mussel
and Other Aquatic Nuisance Species Conference Hyatt Regency Hotel, Dearborn, Mich. Conference will highlight current information on the biology and impact of zebra mussels and other aquatic nuisance species as well as the latest control options available, education efforts and policy guidelines. Hosted by Michigan Sea Grant. For a copy of the preliminary program and registration materials, call (800) 868-8776.M A R C H 8-9
Minnesota Aquaculture Conference and Trade Show
Radisson Arrowwood Resort, Alexandria, Minn. An opportunity for researchers, fish farmers, aquaculture vendors, students, seafood industry representatives, agency representatives and policy makers to interact. Sponsored by Minnesota Sea Grant, the Minnesota Department of Agriculture, Alexandria Technical College and the Minnesota Aquaculture Association. Contact Jeff Gunderson at (218) 726-8715; email: jgunderson@d.umn.edu.M A R C H 30
Great Lakes Declining Amphibians Conference
Milwaukee Public Museum, Milwaukee, Wis. The first meeting of the Great Lakes Working Group of the Declining Amphibian Populations Task Force (DAPTF), an international organization devoted to investigating the worldwide decline in amphibian populations. Regional working groups promote research and education, and act as information clearinghouses. The Great Lakes region encompasses the states of Minnesota, Wisconsin and Michigan. Contact Gary S. Casper at (414) 278-2766; email: gsc@csd.uwm.edu.A P R I L 9-10
Great Lakes Information Network Conference
Lansing Center, Lansing, Mich. Focuses on building Internet skills, exploring innovative uses of the Internet and, in particular, planning the future role of the Great Lakes Information Network (GLIN). Sponsored by the U.S. Environmental Protection Agency, the U.S. Army Corps of Engineers and the Great Lakes Commission. An online registration form is available at www.great- lakes.net/partners/glc/announce/gisconf.html, or by contacting Carol Ratza at (313) 665-9135.
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This page created February 1996
Last updated 9 February 1996. T. Yao
All contents copyright 1995 University of Wisconsin Sea Grant Institute
Designed by Tina Yao tlyao@seagrant.wisc.edu