I babysat my Science Class' pet Garter Snake in grade 7, and it only ate feeder fish. Quite interesting to watch. However, it produced the most stinky, runny poo you ever saw/smelled. It was terrible! I was super grateful when I first saw Salzedo's perfectly formed, solid snakey-poo in the corner of his enclosure one day. Gooooo rats!!!
I'd not every try feeding a fish to a snake. I know the results!