Via a discussion on the Garter Snakes Facebook group, here is a discussion thread on Thamnophis.com that discusses the risk of pre-packaged frozen fish that has been treated with sodium triphosphate (also known as sodium tripolyphosphate), a preservative that is considered safe by the FDA. But what’s safe for people isn’t necessarily safe for other animals. If this is confirmed (and I’m not saying it is, yet), then it’s one more thing to worry about with fish — except this time it’s with frozen fish fillet, which doesn’t normally have thiaminase or parasite concerns.