Fish Heads, Fish Heads...
In case you needed to know, Pharyngula has given a lesson on how to euthanize a fish. It's actually a cute post. Alright, maybe not cute, but that's the only word I can think of right now.
It's funny how scientists become "expert exterminators" in the eyes of the public. I had someone who wanted me to put their cat asleep for them. Apparently if you have access to the drugs and the know how, it makes you worthy of such a painful decision. I've had numerous members of the public ask me how to get rid of rats, mice, and snakes in various regions around their houses--some have even asked me to draw out designs for homemade traps.
When I was an undergrad, I arrived late to lab. My group had designated me the animal slayer because of my tardiness and their weaniness (they were all boys, by the way), and I had to behead and pith the frog. Have I ever told you all that I am a frog lover, through and through? I vowed I would never do it again.
Alright, so I lied to myself. Go figure, it's not the first time. I've had to behead quite a few animals since that dreaded frog massacre. It always used to bother me, the decapitating-live-animals thing, until one day when someone rattled off the story about how executioners would hold up the heads of decapitated people so that the heads could see their bodies (France has got some bad karma). Now it doesn't bother me--it devastates me.
Regardless, I will not give you any advice on how to kill anything. I will tell you how to catch things without killing them, but that's as far as it goes.