here's a pinned topic on the subject with some more info, help you make up your mind.
No way in hell would I be able to cut my fishes head off, or bash it over the head, or stick somthing into its brain. Wouldn't you be terrified if you saw a sharp object coming after you? Or a bolder about to drop on your head?
I think putting some type of liquid in the tank to make him fall asleep or somthing, or drop the tanks temperater by adding ice. I feel this would make his organs shut down. Instead of dumping im in ice cold water and shocking him and then having him die.
I dunno. Such barbaric ways of killing fish.