I found putting a fish in a blender and pressing puree does the job and I can't imagine a feeling a thing if someone put me in a blender and pressed puree. Most probably think I'm sick for saying this......but seriously think about it.
heh i didn't really think of it that way lol... but i do like to use my blender from time to time for food and well even after a good cleaning still not sure if i wouldn't do this

i do eat fish alot but not in a puree form...
What if the fish hits the blades caudal fin-first? Then you're going to have to blend it's whole body before its even dead. Sounds pretty damned excruciating to me. I can't imagine dropping that fish down on the blades before you started the process would feel too good either...