Raskolnikov said:Freezing takes too long, and every tropical fish that I've euthanized that way showed signs of extreme stress; flopping and flipping all over the place and frantically thrashing. IME, smashing the head or whole body is the fastest means to death that the average person has at their disposal, and therefor the least stressfull to the fish.
Not everyone can do that. Some people can not do that even if they had to.