Thanks all, especially aSnakeLovinBabe.
I am more concerned for the moment. He ate last friday, but so far is expressing no interest in the dead minnow. I will try to get some earthworms or night crawlers tomorrow. Should I remove the fish from his water bowl and put it in his "dish" (mayonnaise jar lid, thoroghly washed). Good to know about the guppies; The PetSmart near me only sells comets and rosies, but getting salmon in Portland, OR isn't especially hard, so hopefully he'll like that, and as you say, it would actually be cheaper and more convenient. I'll mix it up with worms, and 'plonks' too. I work in medical science, and though I don't have any mouse colonies, I know a few ppl who do, and could get a good pinky source pretty easily. A week and a half into garter ownership, drama! LOL