I have luckily never had to resort to having to "put my fish down" but if I was presented with such a situation I would probably go for the blunt force trauma to the head. I used to live in Florida and fished alot for supper and before I would even begin "cleaning" the fish I would use that method so that the fish wouldn't have to suffer the pain of me removing all of their scales or skin ect.. It is a hard decision to make with any pet but seeing as I get quite attached to my little fishy buddies I would definately want whatever method chosen to be as quick as possible. My suggestion to you though would be what many have already suggested... Don't give up yet, there still may be hope.