How to kill a rock

[5th Tuition]

It' raining so here's something to ponder.

In anticipation of the return to great fall rockfishing, I have a question.
Often, when I get back to the pier from fishing and open the cooler, there are one or two rock still alive in the box.
Is there a humane way to kill them before I filet them? I was wondering if you could cut down behind the head and sever a spinal cord?
The other option would be to "whack em" with a club, but my neighbors might call "PETA" on me.
How do you accomplish "the act"?
5th (Marty)

p.s.
I realize I could just drag them behind the boat for a few more minutes, as this will surely kill them all dead (there's that dog with a bone thing again).