Electronic Thesis and Dissertation Repository

Thesis Format



Master of Science




Neff, Bryan D.


Thiamine deficiency from the consumption of invasive, high-thiaminase prey fishes is considered to be a major barrier for lake trout restoration in the Great Lakes. In fishes, an understudied aspect of thiamine deficiency is its effect on cardiac function. I examined the effects of dietary thiaminase on cardiac function and morphology in lake trout, specifically as they relate to thermal tolerance. Two hatchery strains of lake trout (Seneca and Slate) were raised on a control or thiaminase diet for nine months. The thiaminase diet was associated with significant ventricle enlargement, impaired cardiac function, and reduced thermal tolerance; these effects were more pronounced in Slate strain fish. Similar cardiac morphological changes were observed in wild-caught lake trout from the Sudbury Basin. These results suggest that dietary thiaminase impairs cardiac function and alters cardiac morphology in fishes, and that such changes may become increasingly important as water temperatures increase through climate change.

Summary for Lay Audience

Thiamine (vitamin B1) is an essential vitamin that animals must obtain from their diet. In mammals, a deficiency of thiamine can result in severe cardiac disorders including heart failure and changes in heart size. However, little is known about how thiamine deficiency affects the cardiac system of fish. In lake trout from the Laurentian Great Lakes and Sudbury Basin, thiamine deficiency is thought to contribute to current population declines. In these ecosystems, the source of this vitamin deficiency comes from the consumption of invasive prey species — alewife and rainbow smelt — that contain high concentrations of a thiamine-degrading enzyme called thiaminase. Understanding how the consumption of thiaminase impacts cardiac function is critical in advancing ongoing lake trout management efforts, as cardiac function and morphology are integral to the thermal tolerance of fishes. In this thesis, I investigated the connection between thiaminase consumption, cardiac function, cardiac morphology, and thermal tolerance in two hatchery strains of lake trout that are currently targeted for reintroduction in the Great Lakes. I found that raising lake trout on a diet containing thiaminase for nine months resulted in impaired cardiac function, increased heart size, and reduced thermal tolerance. I also found notable differences between lake trout strains, where a strain originating from a population that historically fed on high-thiaminase prey fishes was more tolerant of the thiaminase diet. I expanded my laboratory findings to the field where I found that wild lake trout from the Sudbury Basin displayed similar cardiac structural changes in lakes where high-thiaminase prey fishes are the main forage items. Results from this research show that the consumption of dietary thiaminase from invasive species can impair cardiac function and alter cardiac morphology, which may translate to lower survival in the wild, especially as water temperatures increase with climate change.