CichlidFish.com - Fish That Think.

I came accross an interesting post. One that personally I hope I never need to encounter in my own tanks.

The main questions asked was.

What is the quickest, and least painful method for Euthinising a sick or dying fish.

Personally, after reading through the post, I would use the Freezing method. Curious as to what the other members here would use, or have used.

Hi all, I'm a newbie here but the euthanasia question is one that interests me as a biologist. And I apologise if this post comes across a little graphic...
Freezing or slow cooling is considered humane mostly because it is easy for us - we can't see what the fish is going through, but 'no visible behaviour' does not equate to 'calm and happy'. Fish have very slow metabolic rates, and slow freezing leads to large crystal formation in tissues which in most organisms we know about, is extremely painful. Large fish, particularly, would get crystal formation in eye tissue well before the brain shut down (nasty thought).
Boiling (I have heard this one suggested) is also completely unacceptable, for very similar reasons.
Decapitation is often considered but we do know that fish (and some other animal groups too - snakes for example) can survive decapitation for several hours. Decapitation alone is not a quick death for a fish. If you decapitate a fish you should also immediately destroy it's brain - mash it's head flat, for example. A wooden Popsicle stick will do it for small ones, a board and a hammer for larger ones, or simply stun the fish against a hard object (a step works well) and then pierce the top of the head with a sharp object (scissors, sharp knife) to ensure the brain is immediately and completely destroyed. You can wrap the fish in a cloth for a good grip.
The most humane death possible, as for most companion animals, is anaesthetic overdose. You need to contact a vet for the chemicals and advice on dose rate in most cases. Benzocaine at 200-300mg/litre water is a lethal dose for most species (exceptions may include labyrinth fish etc) and is absorbed through the gills. Some anaesthetics (tricaine methanesulphonate for example) reduce the pH of water, and the solution should be buffered with sodium bicarbonate.
Clove oil is a safe sedative for fish and can be used to render fish unconscious or euthanase them: a good description of its use is available from Aquatic-hobbyist at [url]http://www.aquatic-hobbyist.com/profiles/misc/cloveoil.html[/url]

Finally, it is always worth thinking about what methods are available to you, think through your own ability to do the deed, and if there are materials (like clove oil) you can keep in your (hopefully secure!) emergency cabinet for those times we all hope we never have to face. The most humane farewell to a friend becomes a torture if it is delayed 3 hours while you look it up or shop for supplies.

Hope this helps.

I heard that alka salza for upset stomachs will knock a fish unconcious is this true? I truelly hope that I never have to use any methods to put one of mine to sleep, but totally agree that I should know how to just in case the situation arouse where I needed to!

Hi Lisa

I have not heard of using alka seltzer, yet it might knock a fish out due to depriving the fish of oxygen. However even if it worked, the fish would still need to be "dispatched".

Hi Fuzzy,
I had heard that the alka selza would knock the fish out and then putting it in the freezer would be less painfull for the fish. Not sure if this is true, thanks for your response. Excuse my spelling. I have a certificate to proove I'm a twat, a dyslexic twat 

How are you doing? What kind of fish do you keep?

Hi Lisa,

I have oscars, and a couple plecos, in the past I was manily into comunity fish tanks, but a couple year back,
I decided to get some Oscars. I do have pics of them in the gallery, but I am not sure if the galleries up or not.

The best way to euthanise a fish is by freezing.

It is not painful, stressful, and it is incredibly quick. A fish will not even know what was going on.

As the fish's body gets colder it slows down more and more. The brain shuts off and then the fish dies.
It's like going to sleep for them.


Many times I've had to cull stock due to an outbreak of disease, where treatments have been attempted for two months. After the two month point where no improvement is seen and the fish are still stressed a decision is made to cull them. It is too costly to keep treating and the fish are suffering a lot.

For anyone interested in knocking fish out to reduce stress during moving house etc, AQUI-S is a very powerful anasthetic. I don't know if it is accessible privately but I got my hands on it through working in the commercial industry.
NB: If used a close eye needs to be kept on Dissolved oxygen, making sure it doesn't fall below 80%.
NBB: Try not to keep a fish under for too long as an extended knock out time can cause it to shut down completely.

Fish recover from the anasthetic as soon as they are placed in AQUI-S free water.