It sounds more like a weasel rather than a mink to me, but until you catch who knows? Did you happen to notice any white on it, tip of tail or undersides? If it is a mink do as pigmy suggested, as they like fresh fish. A weasel I am not so sure about except for a nice pellet gun to do the trick. Good Luck on getting rid of that varmit! I would also find the place it is getting in and patch it up so it can't find it's way back into it.