[Zephyr]

Yep, I've known this. Most of the fish we have for feeders are thiaminase (or thiamin, whichever it is) filled, so...
In the wild where I find my garters, the natural lake and artificial pond are overrun with introduced goldfish, and yet the snakes have no apparent problems.
I'd say that it's fine to feed rosies as part of the diet, but not all. I believe they have a lower ammount of thia whatever than goldfish by a large percent.