One of my buddies in med school did a research project where he had to pith the fish and then take the samples immediately after the fish died. It was the same method.
He was a VERY precise guy, and is now an eye surgeon, so I suspect he got it exactly right every time.
I suspect I might miss every now and then, but I believe it is considered one on the most humane methods to euthanize research animals. Like our "taste" experiment, you typically don't want stress chemicals in your research animal tissues.
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