>>2429809>Hold fish upside down and smack it's head very hard on a rock a few times to stun it>knife through the brain/brainstem to make it not feel pain anymore and stop flopping>gut it from ass to gills, cutting across the vein of one of the gills to bleed it out>remove all organs immediately>and there's your dead and clean fishThe most humane and the safest way overall. You don't want it to be flopping while your cleaning it, so the brain blow is neccesary.
Don't let rigor mortis set it if it's not bled or gutted yet either. Stringers are kind of fucked, so I'm usually bopping trout on the head or just killing and cleaning them entirely these days before they go on it.