Dieter - See Tillit et al. 2005, Journal of Aquatic Animal Health, 17:13-25. Gizzard shad are the primary forage of Walleyes in western Lake Erie in autumn. Rainbow smelt are an important summer forage species for Walleye and steelhead. Alewives have not been abundant in Lake Erie for a couple of decades (in 82 trawls this year not even 1 was caught). 

These predators gain their required B1 via food. So, one explanation could be that as their food had low B1, they have low levels, as well. In this case the thiamine content of the prey should be analyzed. If they are B1 deficient, you should go to the next stage for diagnosis.

Thiamine antagonists are different. Sulfite is one. High sulfite ingestion in preys may cause thiamine deficiency, which will pass to the predators. The other antagonist is thiaminases. I don't know if the preys you mentioned had thiminase activity or not. It should be checked. Also, some thiaminases are produced by bacteria. Bacterial thiaminases are cell surface enzymes that must dissociate from the membrane before being activated; the dissociation can occur in ruminants under acidotic conditions. Rumen bacteria also reduce sulfate to sulfite, therefore high dietary intakes of sulfate can have thiamine-antagonistic activities

Dear Wolf-Dieter N Busch,

Since we have focused on thiamine deficiency in the ecosystem for a number of years now, I would like to say that we do not know the background to the ongoing deficiency. Yes, there is a number of working hypothesis published, although if there is a common cause to this deficiency, we still do not know its common background. This is substantiated by the simple fact that many bird species, aquatic and "terrestrial", are affected nowadays, please see attached article. Furthermore, we want to stress that thiamine deficiency is a underestimated problem in our ecosystems.

Very best regards

 Lennart Balk