Hi
So many times I have heard and read about the problem wth thiaminase (lack of B1-vitamin), when feeding with goldfish.
Therefor I tried an experiment. I had a fairly nice clutch of Thamnophis sirtalis sirtalis "Florida blue" and raised 10 animals on the wild form of goldfish (Carassius carassius)only, without adding any vitamins. I used freshly killed and chopped fish and had no bad experiences. They grew fast to maturity, and showed no signs of illness.
I am aware of the problems using frozen goldfish and would newer try that.
Now I am raising another clutch of Thamnophis s.sirtalis "Chilton road, Montevallo, Chilton county Alabama" on wild goldfish alone, and so far they are ALL doing very well.
I use freshly killed goldfish and remove the fish after 1 hour. Maybe the brakedown of B-vitamin hasn`t come to a critical state so quickly. I don`t know .....just my experience
Best wishes
Søe