We don't have a crawfish season up here, so it is typically mussels purchased live, then frozen, and supplemented with Vitachem a few times a week. At least that's what I did for shell workouts. A couple people that I know also had their Mbu trained to large hard pellets. To ensure the highest nutrient value, or at least the lowest thiaminase values most seafood should generally be fed within 30 days of freezing. Freezing does not stop this enzyme from breaking B1 down. Mussels generally contain thiaminase , some crayfish from certain US waters do as well. If one is supplementing with B1 at least a few times a week it shouldn't be an issue.