I'm really sorry to hear about your pond fish
I've had mine for 4 yrs - I can only imagine how you feel.
Mink will kill for the sheer pleasure of it - they've decimated my chicken and pheasant pens before.
Don't give up on live trapping that animal just yet. Mink have large territories (esp males), and can often take a week to 10 days to make the "circuit" back to their den. They like fresh foodstuffs, so it wouldn't hurt to freshen the bait daily, in the trap. Try some sardines...
Good luck trapping that varmint!
~Tamara