Joined: 4-July 05
Location: Bangor, North Wales
Posts: 2
fidhw is the writer of this.
Sorry for the length of this post!
As a biologist and lifetime animal keeper the subject of euthanasia is one that, sadly, has cropped up occasionally, and I've posted on the subject of fish euthanasia in a couple of places before. In my opinion, the question of which method to use on fish is too often 'which is easiest for me' rather than 'which is easiest for my fish'. I apologise in advance if readers find this post a little graphic - I have tried to be as clear as I can - because it's important to understand what you are doing. The most common methods I've heard mentioned are:
1. Just flushing the fish away. This is easy for the keeper, and the fish will *eventually* die. Probably from shock, chlorine poisoning or anoxia, if it survives that then it may get macerated in a processing machine or die in a toxic settling tank. As you may be able to tell, I don't see this as a valid option for a single instant!
2. Freezing or boiling. Of these two, freezing is probably slower (depends on the size of the fish) and is easier for the fish keeper since they don't have to watch. Slow freezing in water is the commonest method. What many people don't realise is that freezing a live animal in a domestic freezer is slow enough to allow large ice crystals to form in the tissues (eyes, brain) and that this may well happen before the fish dies. Fish are poikilothermic, and do not become unconscious when hypothermic like mammals (i.e. people) do. We do not know how painful this process is for a fish (although we know it is extremely painful in humans!). We do not know much about fish consciousness, or whether the fish is aware of freezing to death. Personally, I don't much like this one either...
3. Simple decapitation. This is another difficult one - it's not simple to do (for the fish keeper) and the fish head and brain can live for up to an hour after separation from the body (a talent they share with snakes).
4. Stunning, and destruction of the brain. This is effective, can be fast if done carefully and sympathetically, and works for even large fish. For small fish the brain can be destroyed by mashing the head (really flat, sorry to be so graphic) using a brick, rolling pin etc. and a stone step or floor. For larger fish you can wrap the body in a cloth for grip, stun the fish by whacking it hard on a stone step or with a rolling pin and then destroy the brain using the point of a sharp knife inserted into the head. Wiggle the knife tip about to make sure the brain is completely destroyed while the fish is unconscious.
5. Alcohol poisoning - alcohol is an irritant and very toxic to fish, causing bleeding from the gills before death. Fish do not become paralytically drunk as we would. Alcohol exposure appears to kill fish rapidly but I am not aware of any research into it's effects or whether it is humane.
6. Anaesthetic overdose. Without a doubt this is the most humane method I know of. Like any other pet, a large fish deserves respect as an organism, and if you know the fish must be euthanased, talk to your vet. The recommended anaesthetic for fish euthanasia is tricaine methanesulphonate. Since it tends to reduce pH it is used as a bath immersion at 300mg/litre buffered with 600mg/litre sodium bicarbonate. Once the fish appears to be dead the brain should be destroyed as in no. 4 above.
7. Clove oil. Since clove oil is an anaesthetic it should really be listed with other anaesthetics, but it differs in that it is available from pharmacies to the general public, and as such can be kept in your fish medicine cabinet. Clove oil contains eugenol (the sedative/anaesthetic chemical). Unfortunately, it is not soluble in water so prepare it as follows: mix 2-3ml clove oil with 8ml vodka (makes a milky suspension), pour into a clean bucket and add 1 gallon tank water and stir gently. Transfer your fish to this bucket and wait. This is a lethal concentration of eugenol, which will first induce anaesthesia and then death. If you need to use a stronger mixture use more clove oil but no more vodka as the alcohol will cause bleeding and irritation to your fish.
I have used clove oil euthanasia several times for my own fish and other peoples', and am happy that it causes minimal distress and works well. I wait until the fish is dead (no gill movement, no response to touch), then wait another hour, then either destroy the brain or freeze the remains (depending on the size of fish) to be absolutely sure.
Final note, in my poinion any keeper of animals has a responsibility to think about their options for euthanasia should it become necessary, prepare themselves mentally and keep any necessary equipment on hand. If you don't feel you can do this yourself, that's fine: but you probably know someone who can. Remember that the most humane farewell to an old friend becomes a torture if it is delayed several hours for research or a trip to the pharmacy.
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