Many methods have been suggested over the years most are unintentionally cruel and this defeats the whole object of euthanasia where suffering is meant to be minimal.
Putting the fish in a small body of water and then placing it in the freezer where the fish is meant to relax and go to sleep until it passes away quite peacefully!
Freezing to death over an hour or two is not a calm peaceful death, it is more like slow painful torture.
A sharp blow to the head is another old classic, in actual fact this rarely works with just a single blow and catching then having to handle the fish prior to clubbing it to death will hardly be stress free.
Flushing, this really shouldn't need any explanation as to why it is wrong.
Feeding to a larger fish, some would have us believe that this is natures way. But there are a couple of very good reasons why it shouldn't be done.
Is to use an over dose of anaesthetic. If the fish is in pain, and yes despite popular opinion it has been scientifically shown that fish do respond to pain meaning that they must feel it in order to respond to it.
The anaesthetic will almost instantly reduce the level of pain the fish feels, it will then render the fish unconscious within less than one minute and finally the fish will die but it will be completely unaware of anything.
Fish anaesthetic is only available to veterinary surgeons, educational institutions and where animals and fish are used for science. They aren't available to the general public. There are two alternatives both of which do the same job and very effectively.
Oil of cloves is widely available from chemist shops where it is sold as a toothache remedy. It is a very effective fish anaesthetic and can be used to sedate fish in order to treat them or using a higher dose it can be used for euthanasia.
Oil of cloves doesn't mix very well with water. Some people have got around this problem by using a wetting agent such as alcohol in the form of vodka which allows the water and oil of cloves to mix.
Unfortunately the alcohol is a great irritant to the fish and causes a great deal of distress to the fish when this method is used. A myth has grown around this method which states that the oil of cloves simply sedates the fish but it is the alcohol which dispatches it. This simply isn't the case.
There is absolutely no need to use any alcohol in fish euthanasia.
Recently an article suggested that it was alcohol which killed the fish after it was simply sedated by the oil of cloves, this is incorrect. the oil of cloves will euthanise the fish on its own both quickly and painlessly.
Oil of cloves can easily be mixed with water by using a small amount of tepid water and adding the correct dose of the oil of cloves to the tepid water and vigorously shaking the mix and then adding it to the container with the fish.
2-phenoxyethnol is not as readily available but it is sold by koi dealers as a koi sedative. It is more effective than oil of cloves and is used in exactly the same way.
2-phenoxyethnol should be used in accordance with the instructions for sedation and the dose doubled for euthanasia. Oil of cloves should be used at 10 drops /litre for sedation and at 25 drops per litre for euthanasia.
Place the sick fish in a small body of water with a known volume. Add the correct dose of anaesthetic to a small amount of tepid water and shake it vigorously until the two liquids mix and then pour it in to the container with the fish. Death occurs very quickly but leave the fish in the mix for at least thirty minutes. This will ensure that the fish really is dead and not simply under heavy sedation.
Some fish will occasionally panic when they begin to lose their equilibrium, this isn't a sign of pain. This stage will only last a few seconds if it occurs at all, simply make sure that the fish cannot escape from the container during this time.
The fish in the video was NOT killed. It wasn't mistreated simply to make a video. The fish in the video was actually sedated in order to prevent it from harming itself while it was being treated for a deep ulcer on its face.
The fish was purchased (cheaply) due to the ulcer and it went on to make a full recovery and is still alive and well today.
Euthanasia is a sensitive subject for most people but there are times when it has to be considered rather than let unnecessary suffering continue when there is no hope of the fish making a recovery. Try to look at it as a final act of kindness for an old friend.
Please don't take the attitude that where there is life there is hope because that may lead to untold suffering which is completely unnecessary to a terminally ill or incurable fish.