Impacts of Diet on Thiamine Status of Lake Ontario American Eels

The Lake Ontario-upper St. Lawrence River (LOUSL) population of American Eels Anguilla rostrata (hereafter, eels) was once one of the most important groups of the species but is now in a state of serious decline. Given that thiamine deficiency has been observed in almost all of the top predators in Lake Ontario, we assessed the potential that a diet-induced thiamine deficiency associated with consumption of Alewives Alosa pseudoharengus could be involved. Muscle thiamine was measured in eels from throughout the LOUSL corridor and was compared with putative threshold effect levels established from the literature. Mirex concentrations were used to separate Lake Ontario-resident eels from non-Lake Ontario-resident eels. Stable isotope analyses of eel muscle samples and potential prey, including Alewives, were combined with mixing model software to infer the diets consumed by Lake Ontario eels. Although residence in Lake Ontario was associated with a significant decline in muscle thiamine concentration, estimated Alewife consumption by eels was unexpectedly low. Instead, mixing model results indicated that crayfish and Round Goby Neogobius melanostomus were the major prey. Both taxa are known to contain thiaminase and have the potential to cause thiamine deficiency, but there are no reports of thiamine deficiency associated with Round Goby consumption, thus implicating crayfish. There was no recovery in thiamine levels prior to the initiation of oceanic migration. As a result, thiamine levels of Lake Ontario-resident eels prior to migration were only slightly above putative threshold effect levels for pathological and behavioral effects in Japanese Eels Anguilla japonica, but this would require confirmation with American Eels. Since thiamine levels are expected to decline further during migration, additional effects on eel behavior, reproduction, and survival seem probable. Because of panmixia, such effectswhen combined with the relatively high reproductive potential of Lake Ontario-resident eelsmay have consequences for the entire species. Received August 24, 2012; accepted May 28, 2013