What do you feed? That is a fish was was fed seafood containing thiamine only. If you have a diversified menu with lots of thiamine free foods, then some thiamine is fine, but you don’t want it to be only thiamine containing food. A varied diet is the key. I believe that thiamine is found mostly in saltwater fish, I’m not so sure about muscles. There are freshwater muscles aNd clams, I had clams in my front ditch until the drought dried it up. Unfortunately In Maryland you cannot harvest freshwater mollusks, although there is a grey area concerning ditch cleaning on your own property.