A review of early mortality syndrome (EMS) in great lakes salmonids: Relationship with thiamine deficiency

Early mortality syndrome or EMS that affects salmonids in the Great Lakes e xhibits many of the same clinical signs as Cayuga syndrome, that affects At lantic salmon (Salmo. salar) in the New York Finger Lakes and the M74 syndr ome that affects Atlantic salmon from the Baltic Sea. These similarities ma y reflect their shared characteristics of associated low thiamine concentra tions in eggs and therapeutic responsiveness to exogenous thiamine treatmen t. When egg thiamine levels fall below a species-specific threshold clinica l signs include loss of equilibrium, depression of respiration and reduced heart rate. Although feeding studies with thiamine deficient diets have yet to confirm a thiamine cause-effect relationship, EMS-like symptoms can be induced with thiamine antagonists. Patterns of temporal variability of EMS among Great Lakes' salmonids over the last 3 decades have been similar. In coho salmon (Oncorhynchus kisutch), EMS was negatively correlated with alew ife (Alosa pseudoharengus) abundance in Lake Michigan. We hypothesize that this may reflect quantitative or qualitative changes in the alewives eaten because despite their fluctuating abundance they have remained the preferre d diet item. The limited data available for other salmonids suggest similar trends.