The National Academy of Sciences published a report on the presence of thiaminase in fish for the fox and mink farming industry. Fish are a cheap food and readily eaten by these mammals but they too develope neuroligical problems when fed thiaminase containing fish species. Follow the links below for a two page list that will help you choose thiaminase free fish for your snakes. The first page is primarily thiaminase bearing species so you can see what to avoid. The bottom of that page and all of the second page list the thiaminase free species. This is from: NAP, Nutrient Requirements of Mink and Foxes, Second Revised Edition, 1982.
Use the zoom feature on the right when you get there to make reading the pages easier!