From 1968 to 1996, early life-stage mortalities occurred in coho and chinook salmon, lake trout and brown trout and steelhead from the Great Lakes; however, their causes were not conclusively determined. "Early Mortality Syndrome" (EMS) describes several of these syndromes affect sac fry, swim-up fry, and feeding fry. Clinical signs include loss of equilibrium, swimming in a spiral pattern, lethargy, hyperexcitability, hemorrhage, and death. Within a species, mortality rates vary amongst fry from different female parents. Annual EMS mortality ranged from 10 to 30% until January 1993 when 60 to 90% of coho in Wisconsin Illinois, Indiana, and Michigan hatcheries died from the late eyed-egg stage through the feeding fry stage. These catastrophic losses prompted the Fish Health Committee and the Board of Technical Experts of the Great Lakes Fishery Commission to invite experts to address the possible causes: hatchery cultural techniques, broodstook management, genetics, pathogens, nutrition, ecosystem changes, and known contaminants such as polychlorinated biphenyls (PCBs). Early Mortality Syndrome can be prevented or reversed when eggs or fry are exposed to thiamine. Whether EMS results from a simple dietary deficiency or is due to interactions between thiamine and other environmental factors is unknown. Cayuga Syndrome and M74 are 2 other early life-stage mortality syndromes in which eggs contain very low levels of thiamine and affected fry respond to thiamine treatments. Cayuga Syndrome affects Atlantic salmon in New York Finger Lakes, and M74 affects Atlantic salmon from the Baltic Sea.
Rolland, RM; Gilbertson, M; Peterson, RE