Alright guys, now I have to ask, because all you have discussed begs the question, why does it matter?
If you're going to kill the fish anyways, why does it matter how you kill the fish? Because it feels less pain? Because you feel less pain?
You need to step back and realize that there are plenty more fish in the sea, and that's that is all it is, a fish you took from the sea. Sometimes when you love something, you have to just hit it with a hammer.
Because current research shows that fish feel pain, and you show compassion by being humane in killing an animal. Of course, some people wont care, to them it is just a fish. But to some, they are beloved pets just like any dog or cat. Would you put your dog in a freezer to humanely put it to sleep?