Egg-thiamine Status and Occurrence of Early Mortality Syndrome (EMS) in Atlantic Salmon from the St. Marys River, Michigan

Early mortality syndrome (EMS) is the term used to describe the mortality of juvenile salmonids due to thiamine deficiency within the Great Lakes basin. EMS appears to be related to the presence of thiaminase found in prey fish such as alewives Alosa pseudoharengus, rainbow smelt Osmerus mordax, and gizzard shad Dorosoma cepedianum. Since 1985, the Michigan Department of Natural Resources, in conjunction with Lake Superior State University's Aquatic Research Laboratory, has raised Atlantic salmon Salmo salar for stocking in the St. Marys River region near Sault Ste. Marie, Michigan. The current study correlates egg-thiamine concentrations from 45 individual family groups with egg and larval mortality as well as length, weight, and condition data obtained from spawning females. Thiamine concentrations were measured at three stages of egg-development using a newly developed rapid reversed-phase solid-phase extraction (RP-SPE) method of thiamine analysis. Results suggest a threshold average total egg-thiamine concentration of approximately 1.0 (nmol/g egg) for normal larval survival. Thiamine analysis indicated no significant change in egg-thiamine concentrations from prefertilization to the eyed stage of development. Female parent weight showed an inverse relationship with egg-thiamine levels. Thiamine immersion of larval sac-fry eliminated the occurrence of EMS for this study population. Due to low cost and ease of use, the RP-SPE method for large scale egg-thiamine analysis has the potential to impact basin wide management decisions with respect to salmonid stocking programs.