Early Life Stage Mortality Syndrome in Fishes of the Great Lakes and Baltic Sea

<em>Abstract.—</em>Muscle and egg samples from returning adult female Lake Michigan coho salmon <em>Oncorhynchus kisutch </em>were collected for thiamine analysis. Three groups of five females having low (2.5%), medium (42.4%), or high (92.6%) mean fry survival were selected for this study. Egg and muscle samples were collected at spawning and analyzed by high-performance liquid chromatography analysis for free thiamine, thiamine monophosphate (TP), and thiamine pyrophosphate (TPP). Egg concentrations of ascorbic acid, iron, zinc, magnesium, and potassium were measured. Twenty-five contaminants were also measured in muscle tissue of adult females. Total thiamine levels in eggs were similar between the medium and high survival groups but significantly lower in the low survival group. Eggs from the high and medium survival groups had higher levels of free thiamine and TP (<EM>P </EM>< 0.01) than eggs from the low survival group. There were no significant differences among the three groups in egg TPP. Muscle concentrations of TPP, TP, and total thiamine were similar among the three survival groups (<EM>P </EM>> 0.10). Correlations between fry survival and egg free thiamine (<em>r </em>= 0.61) and TP (<em>r </em>= 0.52) were observed. Fry survival was not correlated with adult muscle concentration of any form of thiamine or contaminant measured. Among the three groups, no differences in egg concentration were found for ascorbic acid, dehydroascorbic acid, iron, magnesium, zinc, and potassium. This research supports the hypothesis that low egg thiamine is an important factor in early mortality syndrome.