#1. Clove oil:
Of all of the methods I have read about or heard about this one is the most painless for the fish and the fish keeper combined. Most of my information on this method is courtesy of RTR via the boards.
Clove oil can be mixed in water, the recommendation from RTR is 1-3 drops per liter of water, mixed well , and then the fish placed in it. Clove oil will anesthesize the fish, and a little more will make it permanent. If I understand RTR correctly if the fish is left in the clove oil even at 1-3 drops per liter, it will eventually prove fatal. In other words fish that are being anesthesized for other reasons should not be left in the clove oil mix for any length of time after they go to sleep.
While studying this method I found the recommendation in several places to mix the clove oil with Vodka so it would mix with the water well. Vodka is an irritant to fish, and thus makes this method far less humane. Furthermore when I questioned RTR about possibly using clove oil in the tank for netting purposes. He made it very clear that clove oil is stable, and could not be removed without a 100% water change. So based on the fact that RTR and others who use this for anesthesia don?t recommend vodka, and clove oil can?t be removed, it would stand to reason that the vodka is not necessary, and shouldn?t be used as it will cause discomfort. Just mix the clove oil well in the first place. The only folks I have seen who debated clove oil as being inhumane were folks who assumed it was used with vodka. Vodka is the problem, not the clove oil, according to my research.
The only downside to clove oil is cost. I can?t imagine that the cost is very high, and wouldn?t think that it would be an issue. However there will be methods discussed later that are just as humane for the fish although a bit harder on the fish keeper, and cost nothing. Clove oil is available in the toothache section of most pharmacies.