**The title, authors, and abstract for this completion report are provided below.  For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**

Thiamine status and diet of sub-adult salmonines

in lake ontario

John D. Fitzsimons² and Dale Honeyfield³

²Fisheries and Oceans Canada

Burlington, Ontario

L7R 4A6

³US Geological Survey

Wellsboro, Pennsylvania

April 2008

ABSTRACT:

Lake Ontario salmonines are affected by a diet-induced thiamine deficiency resulting from thiaminase that destroys thiamine. The disease is related to consumption of alewives and rainbow smelt that have high levels of thiaminase, but there is no information on the ontogeny of the disease which is necessary for evaluating impacts on affected stocks. We collected lake trout and Chinook salmon from Lake Ontario, over a broad range of sizes during 2005-2006 and analyzed stomach contents and stable isotopes (δ¹³C and δ¹⁵N) in their muscle tissue as measures of diet, and related changes in diet to changes in muscle thiamine concentration. We compared ontogenetic changes in Lake Ontario to changes in the same species in Lake Superior where rainbow smelt and alewives are much less abundant, and lake trout from Spray Lake, an alpine lake where alewives and rainbow smelt are absent. The transition to piscivory in Lake Ontario was associated with dramatic age- and size-related declines in muscle thiamine concentrations in both lake trout and Chinook. Based on a combination of stomach and stable isotope analysis, these declines appear to be related but are not proportionate to consumption of alewives and rainbow smelt although it was not possible to determine the relative role of each. Lake Superior lake trout also showed ontogenetic changes in muscle thiamine concentrations and limited evidence of thiamine deficiency. Low thiamine concentrations in intermediate sized lake trout in this lake were suggestive of high consumption of alewives or rainbow smelt. Increased thiamine concentrations in larger lake trout, suggested a switch to thiaminase-free prey. We conclude that salmonines in Lake Ontario that consume alewives or rainbow smelt may be at risk to adverse effects throughout the entire period of their ontogeny that they are piscivorous. As a result we recommend studies to evaluate the potential effects posed by current thiamine levels to survival throughout this period.