The problem with thiaminase is when you feed items that contain thiaminase exclusively. While that smelt I feed may contain thiaminase I also feed shrimp, octopus, squid, silverfish, scallops, and enrich with vits. Thiaminase blocks thiamine(B1), so if you are feeding a variety and they are able to get B1 from other sources it will be no problem. Krill also has thiaminase and the basis to the the over fear of thiaminase is that many predator fish; eels, lions, scorps, anglers, and even puffers; will settle in and only eat krill exclusively. I can't remember the brand name off hand, but one lfs brand may be smelt rather than true silversides. So people that exclusive feed these 2 items may have an issue in the long run.