|MadSci Network: Neuroscience|
First, please allow me to apologize for the lateness of this answer--I was out of town for an unexpected trip when the question arrived.
And a good question it is--it sent me scrambling to MedLine and the medical library. In looking for specific species of fish which have an "anti-thiamine" effect (primarily via an enzyme called thiaminase), there are reports that it is found in tuna and goatfish (Hilker and Peter, 1968). From an epidemiology study I read (Bovet et al., 1998), it appears that this activity is present in many kinds of raw and fermented fish, but there is nothing I can find that names individual species. The enzyme is destroyed by heating, and cooked fish does not lower blood thiamine levels (Vimokesant et al., 1982). A contributory factor in all of this is that raw and fermented fish tends to be eaten in areas where polished rice is a large part of the diet. Polishing means that the vitamin-rich husk is removed.
For your corollary question, yes, alcohol consumption can contribute to this--basically the data I have seen suggests that alcohol (100 g/day or more) also lowers blood thiamine levels (Bovet et al., 1998). At least one animal study suggests that the effects of alcohol on memory functions are more pronounced when the subject is also thiamine deficient (Crowe and Kempton, 1997), suggesting that there might be some additional interactions.
You might be able to find additional information at one of the nutrition or public health departments in Australia or Southeast Asia (primarily Thailand), as that is where many of these studies originate.
For further reading you might try (*=referenced above):
Try the links in the MadSci Library for more information on Neuroscience.