By "backed up with science", I meant that euthanasia methods should be chosen based on having been proven, as well as such a thing is possible, to be humane. Science about, specifically, the humane treatment and euthanasia of fish. Not any random science that happens to involve fish.
I think as long as you are quick about it, then it is humane. When i was kid, my neighbor used to farm meat rabbits...
Instant destruction of the brain is humane, yes. Freezing isn't quick. You either have to destroy the brain all in one go, or use a chemical method that causes unconsciousness with minimal to no discomfort. Clove oil, done properly, is the latter, and is generally both less upsetting and easier to do for someone who's squeamish and/or attached to the animal in question when compared to something like pithing.
