http://www.gsas.org/Articles/1998/he...uthanasia.html
Greater Seattle Aquarium Society
Northwest Aquaria Article Archive
Title As You Wish: Euthanasia (Part 1)
by Heather Candelaria
[SNIP]
Pain is not a basic straight forward event, it is much more complex than I intend to go into right now, but the basic fact that is important to know is that pain generally occurs as a result of some sort of damage being done to the body or cells of an animal.
Pain evolved as a sort of warning system, to tell an organism that damage is occurring to its body and that evasive action is a good idea. Getting away from the source of the pain is therefore a very important drive directing all animals capable of feeling pain.
With this in mind, I would like to express my opinion about the `humane' and `painless' method of euthanizing a fish; the freezing method.
[SNIP]
By the time the cellular walls are bursting I’m pretty sure that the fish has taken its last gasp, but a great deal of damage (pain) occurs before death does.
I think the best way to put a fish out of its misery is the fastest way possible. Dropping Mr. Bubbles into a blender is not the nicest (or cleanest) method of euthanasia, but as far as Mr. Bubbles is concerned, it is all over with before he has time to even notice.