Essentially I might add quick is almost always better. putting a fish to sleep via clove oil is probably the best and most humane method I have heard of. otherwise whatever method it needs to be as near to instantaneous as possible IMO. Although I would do it if needed, taking a fish out and wrapping it in a wet paper towel is not quick, yes compared to other things it might be quicker, but still not quick or stress free. freezing is greatly arguable, seltzer is obviously stressful. So when you look at all of the arguments you end up back at clove oil Truly painless and stress free. I have spent most of my life around animals that were raised for food, euthanasia is not something that bothers me or is difficult for me to do however I cannot stand to see an animal suffer needlessly, and never could. I also really have trouble understanding people who can. my methods for fish, and most other animals would be seen as barbaric by anyone watching, but the animals don't suffer, and usually don't have time to know what hit them. I don't discuss my methods as most people will be much happier without knowing them. Not everyone is willing or able to be suddenly lethal to an animal and in those cases other methods are used. Spend the money on the clove oil, I can't imagine it's that expensive, and although I haven't tried it (no need since I learned about it) it sounds like the best way to go.
I might also add that while many people say to mix clove oil and vodka, I have not heard this from people like RTr. I have simply heard add clove oil to a quantity of water, mix well and add fish. My nderstanding is that clove oil is perfectly stable once added. this would indicate that the vodka thinning isn't at all necessary if the oil is mixed into the water welll.
dave