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What is the best method of euthanising fish?

My very old female krib has been looking off colour for several months and has now developed dropsy.

She's too small to knock on the head, and I am a bit too sentimental to squash a fish I have kept for four years.

I have heard all sorts of things about clove oil and putting them in the freezer.


What's best?

Thanks.

Although I heard different opinions, I think the freezer is the best way to euthanise a cold blooded animal.
The other opinions had to do with the time involved before the animal actually dies. However, I'm not going to hit a fish with a hammer or stone, nor will I kill it in poisoned alcohol (in Dutch: spiritus). Have been there; awful sight.

How about bicarb/carbon dioxide?

Racoll,
Freezing is not the best way. A drop in a small jar containing vodka or gin will be very quick.
-Shane

I'm sure Shane is right, but I've empirically found that a glass of really cool water "calms" the fish quickly, so my method that I've been using for the last couple of fish is to stick a glass of water in the freezer for 15-30 min (not so long that it forms ice, but so that it's REALLY cold), then drop the fish in it. It only takes seconds for the fish to stop moving. Stick it back in the fridge for another while.

--
Mats

Freezer: I no longer use this method after I killed a large zebra cichlid that way. As the temperature dropped he started fighting like crazy, and continued for an hour.
Also, while freezing is probably fairly humane for tropical fish, who's organs fail as temperature drops under 10 Celsius or so, there's still a risk of pain if, say, proteins denature (e.g. muscles lock up in cramp).
Freezing is probably not at all humane for temperate and coldwater species, who will not die until their internal organs freeze.

Boiling is even worse, especially for large fish. IF you're lucky the fish is rendered unconscious by the sudden pain, if you're not... A fellow aquarist told me of how he tried to kill a large cichlid by dropping it in a pot of boiling water, and it kept banging on the lid for minutes.

Ethanol: From, unfortunately, extensive personal experience I can say that killing fish with ethanol is neither quick nor humane. Even a very small fish dropped in 95% ethanol will take minutes to stop struggling, and even at very low concentrations the fish show obvious signs of stress and discomfort (darting, tries to jump, labored breathing..). Formalin works much the same.

Decapitation, crushing, shooting, and/or breaking the neck & "pithing" the fish with a knife or needle: works well if you know what you're doing but there's a considerable risk of botching up if you don't.

My preferred method to euthanize would be MS222. It is a commercial fish sedative, and if overdosed the fish will fall asleep and die. It is however difficult to get hold of.
An alternative is Clove Oil (Eugenol). It can be found in health food stores, and is a powerful fish sedative. Put a couple of drops of clove oil in a liter of water. Shake. Put the fish in the water. Wait for at least one hour after the fish has stopped breathing until you discard the fish.

Thanks for the input guys.

I can't seem to find clove oil in my local Boots chemist. They have every other oil though They are pretty expensive too at about £6 per bottle.

I don't have any spirits in the house at the moment, as I'm trying to cut back a bit on the boozing.

I like the sound of the sodium bicarbonate mixture. My tank water is fairly acidic, so mixed with NaCO3 there should be enough CO2 to asphyxiate the fish pretty quickly.

Have you tried this grokefish?

On the NVC site (http://www.nvcweb.nl/ in Dutch) a vet has placed a summary about the possibilities.

freezing is very wrong, because the fish suffer a lot. I myself euthanasied a few cichlids because I had only males, and after half an hour I thought about discarding the corpses.

Wrong, they were still alife (luckely, 2 showed female dots in their fins, so I vcould save 4)

Thus freezing is very, very cruel, and I never did it again - I use the knife.

further possibilities are the clove oil and dedicated medicins, but those are not easily availeble, and I happen to have a few usefull knives

For a small fish, I just scoop them in the net and then in one swing bounce it off a hard surface with some force the multi trauma is quick and effective, a tad brutal but have never had one survive or any movement after.

Right, for the method of freezing (chilling, really), you'll need a SIGNIFICANTLY LARGER volume of water than the volume of fish - otherwise the warm fish will allow the temperature of the water to increase and thus slow down the fatal effect. This makes it feasible for small fish, but larger fish may not be so practical, if for nothing else than finding a fridge with scope for inserting a 5-10g bucket isn't that easy!

It's also essential that the water you put the fish into is really cool - 1 degree C/33'F is ideal.

--
Mats

IT might be worth having a read of this, it discusses several forms of Euthanasia and and the various factors involved in each.

http://www.lal.org.uk/pdffiles/LA2.pdf

Well I used the sodium bicarbonate method.

I dissolved a big spoonful in a jar of tank water.

Movement was frantic for about 20 secs, then motionless.

Gill movements slowed right down and stopped in less than 5 mins.

It was OK, but I don't know if I would do it again as I experienced similar as reported in the above document.

"Carbon dioxide This is not acceptable for euthanasia of fish as it causes intense activity prior to loss of consciousness and is slow
acting."


It seems the only truly humane method is with MS-222.

There must be an easier method available to the home aquarist.

Mike, have you used the clove oil method yourself?

racoll wrote: "Carbon dioxide This is not acceptable for euthanasia of fish as it causes intense activity prior to loss of consciousness and is slow
acting."

Yeah, I can't see suffocation as a nice way to go

put the fish in an apropriate size bucket and put a piece of paper on the surface of the water and they will go to sleep and not wake up i t also happens slow enough that the fish doesnt usually become frantic but it is basically a carbon dioxide method usually takes 3-6 hours