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Euthanizing FW Fish

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TwoTankAmin

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It has been a fairly long time since I had to euthanize one of my fish. For the most part I have had to remove dead fish as opposed to having to euthanize them. I have always read about using clove oil, but it took me 23 + years finally to get a bottle of 100% pure syzygium aromaticum. I had a suffering kerri tetra I needed to euthanize. It is a small fish.

So I found instructions on line and followed them. This was the basic procedure for use with fish 4 inches or less. I have removed the wordy less needed parts :

Method 1: The Clove Oil Bath​

This stuff works wonders and is recommended by the American Veterinary Medical Association as a humane way to kill fish. You see, it works like the anesthetics that vets use, which are not available to the public. It puts your fish to sleep before killing it without suffering.

Step 1: Catch Your Fish​

Fill up your bucket with water from your aquarium – a gallon will do for most fish, although larger fish might need more.
Catch your fish and place it inside the container. Be gentle and cause as little stress as possible.
I did this.

Step 2: Mix The Clove Oil​

You can’t add your clove oil just yet. You see, it’s an oil. And if you add it now, it would simply float on the surface of the water.
So, grab a small container – pill containers work great. Fill the container with water from your tank and add 4 drops of clove oil.
Note: This is for fish less than 4 inches in length, increase the amount of drops for larger fish.
Put a lid on it and give the container a good shake, until the water turns a milky white color. Your clove oil is now mixed.
I did this.

Step 3: Add The Clove Oil Mixture​

Slowly add the clove oil mixture to the container with your fish while stirring gently with your hand. You should see the milky mixture spread throughout the container.
After a few minutes, your fish should stop moving. It may even go belly up…
But it’s not dead just yet… It’s simply knocked out. If you look closely at your fish’s gills, you should see them still moving – a sure sign that your fish has been put to sleep.
If your fish is still swimming around after 5 minutes, add a couple more drops of the clove oil mixture.
I did this. But, as soon as I began adding the oil the fish became "excited" and was swimming somewhat wildly. For a bit. I had to make a second mix using only 3 drops and after adding this the fish sank to the bottom. I waited 5 mins. and it was in the same place and its gill flap was moving.

Step 4: Add A Stronger Dose​

Now that your fish is asleep, it’s time to put him to rest for good.
Scoop some water out of the container with your fish and add another 12 drops of clove oil mixture. Just like before, shake it up until the clove oil mixes thoroughly.
Add the clove oil mixture to the container with your fish and wait.
It should take less than 30 minutes before your fish’s gills stop moving. Once the gills don’t move for 10 minutes, the fish has been successfully put down.
If you still see gill movement after 30 minutes, add more mixture.
It may take some time, but many aquatic life experts find this the most comfortable method of euthanizing a sick or injured fish and in accordance to ethical standards.

I did this. But, when I added this stronger dose the fish became allert and begam swimming erratically around the bucket. This continued for a while. Probably under 90 seconds but it seemed like more . Then the fish stopped and sank to the bottom. I waited 30 minutes and there was no gill movement. I waited at least another 20 minutes and still no movement. So I flushed the fish.

My Comments:

The next time I have to try this method I will use 5 or 6 drops to anesthetize. I need to be sure the fish is asleep. I think I also need to add the initial anesthetic dose more slowly. I think the reaction of the fish may have been due to my adding too fast.

There are other options one might choose if you know the fish is out cold. Freezing would be one. This should never be done unless the fish has been anesthetized first. There are two other methods of humane euthanization. It is suggested that even if one opts to use one to condsider doing the clove oil anesthesia first. I am not one who can do the Smash or the Stab method,

I also think I would prefer to do a quick freeze after anesthesia. I would remove the knocked out fish and some of the water to a smaller container and put it into out freezer set to 0°F (-17.78C), The smaller container should drop the water temp pretty fast, so the fish should feel nothing.

Finally. Clove oil is not effective for larger fish. This requires a more powerful anesthetic which means a vet must be involved.

You can read the entire article with full details on doing the Smash or the Stab methods. It also explains what methods for euthrnizing which one should never use and why not.
https://fishlab.com/how-to-kill-a-pet-fish/
 
Don’t flush fish, bury them in the garden or put them in the bin.
Flushing fish can block drains. Also the fish, or the water it was flowing in, can still sometimes carry diseases which are then transmitted to local fish and wildlife – that can prove to be destructive.
 
That’s an awful, inaccurate method.

The Clove Oil dosage for euthanasia is 25 drops per litre of water. Any less is just an anaesthetic dosage and the fish will wake up again at some point.
Put a litre of water into container #1. Then take some of that litre and mix in ALL 25 DROPS by violent shaking (in container #2 with a lid). Then put the fish in container #1, then slowly pour in the mix from container #2. Panic is inevitable but will only last a few seconds.
 
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Given that there's some disagreement on this issue, I figured I'd do my own research on the matter and report back. This is the science section of the forum after all. I found one research paper and a couple protocol documents from universities with research labs. The euthanasia protocols are managed by the Institutional Animal Care and Use Committee (IACUC), a federally mandated regulatory body for institutions that use live animals. The IACUC follows the American Veterinary Medical Association's (AVMA) guidelines for euthanasia of animals.

For zebrafish and other small tropical fish, respiratory failure begins at 400mg/L of eugenol, so that is the minimum recommended dose for euthanasia. McGill University does not (to my knowledge) follow AVMA guidelines, but it's a Canadian institution, so they might have their own regulatory system. Regardless, their internal animal welfare guidelines for fish state that 1-3mL of eugenol should be mixed with 10mL of ethanol (oils are soluble in alcohol—this should be relatively pure ethanol, think Everclear, not some random bourbon or something) and then that solution is added to 1L of water. The paper I found states that 0.4mL/L of eugenol/clove oil can be used for euthanasia, but I'd personally rather go with the higher doses recommended by the AVMA and McGill. The use of mL and mg is important because different manufacturers will have different products with different droppers, meaning drop sizes are inconsistent between brands and therefore not a great measuring tool for this application. The recommended number of drops might result in a different dosage if you're using a product that has a slightly smaller dropper than the person who developed the dosage you're trying to follow.

It's also recommended to follow up with a physical euthanasia method, either decapitation or pithing. McGill additionally recommends using very dim light or an opaque container during the euthanasia. They don't go much into the actual procedure of the process, but at least with McGill, it seems like the solution is prepared beforehand and then the fish is immersed. All of the sources comment on the importance of using products with known concentrations since clove oil often is not pure eugenol, the active ingredient. 85-95% eugenol is recommended.

Sources also stress the fact that clove oil is not recognized or regulated as a product for human consumption. Notre Dame University even goes the length to say that fish euthanized with clove oil should NOT be disposed of in a way that might allow people or other animals to consume it (so no dumping it into waterways and no burial where other animals might dig it up), and that clove oil solutions cannot be disposed of in bodies of water or sewer systems. Eugenol and isoeugenol are known carcinogens. The safest disposal method for people without access to laboratory hazardous waste disposal systems seems to be absorbing the liquid with sand or diatomaceous earth and then disposing of that mixture in the garbage.

Here are the sources if people are interested
Paper (only abstract available): https://pubmed.ncbi.nlm.nih.gov/27683808/
Notre Dame University guidelines (equivalent to AVMA guidelines): https://freimann.nd.edu/assets/262662/fullsize/iacuc_clove_oil_aneseuth_pol16_2_.pdf
AVMA guidelines for animal euthanasia (eugenol/clove oil is on page 38): https://www.avma.org/sites/default/files/2020-02/Guidelines-on-Euthanasia-2020.pdf
McGill University guidelines: https://www.mcgill.ca/research/file...atic_amphibian_euthanasia_-_march_2022_v2.pdf
 
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Given that there's some disagreement on this issue, I figured I'd do my own research on the matter and report back. This is the science section of the forum after all. I found one research paper and a couple protocol documents from universities with research labs. The euthanasia protocols are managed by the Institutional Animal Care and Use Committee (IUCAC), a federally mandated regulatory body for institutions that use live animals. The IUCAC follows the American Veterinary Medical Association's (AVMA) guidelines for euthanasia of animals.

For zebrafish and other small tropical fish, respiratory failure begins at 400mg/L of eugenol, so that is the minimum recommended dose for euthanasia. McGill University does not (to my knowledge) follow AVMA guidelines, but it's a Canadian institution, so they might have their own regulatory system. Regardless, their internal animal welfare guidelines for fish state that 1-3mL of eugenol should be mixed with 10mL of ethanol (oils are soluble in alcohol—this should be relatively pure ethanol, think Everclear, not some random bourbon or something) and then that solution is added to 1L of water. The paper I found states that 0.4mL/L of eugenol/clove oil can be used for euthanasia, but I'd personally rather go with the higher doses recommended by the AVMA and McGill. The use of mL and mg is important because different manufacturers will have different products with different droppers, meaning drop sizes are inconsistent between brands and therefore not a great measuring tool for this application. The recommended number of drops might result in a different dosage if you're using a product that has a slightly smaller dropper than the person who developed the dosage you're trying to follow.

It's also recommended to follow up with a physical euthanasia method, either decapitation or pithing. McGill additionally recommends using very dim light or an opaque container during the euthanasia. They don't go much into the actual procedure of the process, but at least with McGill, it seems like the solution is prepared beforehand and then the fish is immersed. All of the sources comment on the importance of using products with known concentrations since clove oil often is not pure eugenol, the active ingredient. 85-95% eugenol is recommended.

Sources also stress the fact that clove oil is not recognized or regulated as a product for human consumption. Notre Dame University even goes the length to say that fish euthanized with clove oil should NOT be disposed of in a way that might allow people or other animals to consume it (so no dumping it into waterways and no burial where other animals might dig it up), and that clove oil solutions cannot be disposed of in bodies of water or sewer systems. Eugenol and isoeugenol are known carcinogens. The safest disposal method for people without access to laboratory hazardous waste disposal systems seems to be absorbing the liquid with sand or diatomaceous earth and then disposing of that mixture in the garbage.

Here are the sources if people are interested
Paper (only abstract available): https://pubmed.ncbi.nlm.nih.gov/27683808/
Notre Dame University guidelines (equivalent to AVMA guidelines): https://freimann.nd.edu/assets/262662/fullsize/iacuc_clove_oil_aneseuth_pol16_2_.pdf
AVMA guidelines for animal euthanasia (eugenol/clove oil is on page 38): https://www.avma.org/sites/default/files/2020-02/Guidelines-on-Euthanasia-2020.pdf
McGill University guidelines: https://www.mcgill.ca/research/file...atic_amphibian_euthanasia_-_march_2022_v2.pdf
Bravo! Thank you for this
 
We have out own septic system. So the minimal amount of clove oil involved will never be where and animals can get at it. A very high volume of water goes through our septic system a lot of which is due to my fish tanks. just batching the RO/DI water we do dumps a lot of gallons in terms of the rejected water v.s. the volume of pure water we keep and use.

I have disposable pipettes in both 1 and 3 ml sizes and will not do drops in the future should I need to put down another fish. I will also use lees water and a smaller container tominimize how much clove oil I need to use. I have not had to do this often over the years. Also lets not get silly here re the potential "hazards" of clove oil use in my case. We are talking about under 20 small drops of pure clove oil going into and through a system which holds many 100s of gals of water and also has many more 100s of gallons going through it every day.

It is winter here and the ground is frozen. So burial is not a viable option. It even changes my ability to pump water out of windows when doing water changes on tanks where this is my normal practice. There are no bodies of water near me that a dead fish could end up in.

When I dumped the water and the small tetra down the toilet it had been lying in the bottom of the bucket with no gill movemement for well over an hour. I have no doubt it was dead. This was a tiny fish and smashing it would have turned it to jelly. The water goes underground into a buried septic tank. That overlows underground into a leech field and the water sill either be use by plants/trees or it will work it way deeper over time and end up back in the aquifer. So we are talking dilution in ppt (parts per trillion) or more.

I read the guidline pdf for animal euthanasia. It has a specific section on clove oil (had to delete the supscript numbers for the references as the superscript won't work here They are in the pdf if you want to check them):

M2.14 EUGENOL
Cloves contain a number of essential oils, including eugenol, isoeugenol, and methyleugenol. Eugenol comprises 85% to 95% of the essential oils in cloves, and has been used as a food flavoring and a local anesthetic for human dentistry. Eugenol is classified as a “generally regarded as safe” food additive by the FDA and as an exempted least-toxic pesticide active ingredient by the US EPA. Eugenol exhibits antifungal, antibacterial, antioxidant, and anticonvulsant activity. Some other components of clove oil, such as isoeugenol, are equivocal carcinogens based on studies in rodents. Clove oil and its extracts have become popular as anesthetic agents for freshwater and marine fish because of their wide availability, low cost, and shorter induction times when compared with MS 222. When compared with MS 222 as an anesthetic agent, eugenol was found to have a more rapid induction, prolonged recovery, and narrow margin of safety, as it can cause rapid onset of ventilatory failure at high concentrations (> 400 mg/L).

The anesthetic mechanism of clove oil and its derivatives has been poorly studied, but they appear to act similarly to other local anesthetics by inhibition of voltage-sensitive sodium channels within the nervous system. Studies of rodents indicate this class of agents may cause paralysis in addition to their anesthetic effects.

Advantages—(1) Clove oil and its derivatives are widely available, are relatively inexpensive, and are not controlled substances. (2) These agents have a short induction time. (3) Clove oil and its derivatives are effective at a wide range of water temperatures. (4) Eugenol has low risk for human toxicity at concentrations used for euthanasia of fish.

Disadvantages—(1) Clove oil and its derivatives are not FDA approved for use as an agent of euthanasia. (2) Animals euthanized with clove oil products are not approved for human consumption. (3) Some clove oil derivatives are potential carcinogens. (4) The impact of clove oil residues in euthanized fish on the environment or scavenger species has not been determined.

General recommendations—Clove oil, isoeugenol, and eugenol are acceptable agents of euthanasia for fish. It is recommended that, whenever possible, products with standardized, known concentrations of essential oils be used so that accurate dosing can occur. These agents are not acceptable means of euthanasia for animals intended for consumption.
 
Thank you, @TwoTankAmin for bringing this important topic to light! And thank you too, to @Seisage for your detailed contributions as well! It's an ugly topic. So it gets ignored. But unlike domestic animals (dogs, cats, etc.) we as care takers end up being responsible for determining the best end of life scenario for our exotic captives. Care for the well, and even the ill, gets discussed a lot. But how an organism can humanly end it's existence does not. I think it needs to be more openly discussed, so I thank you both! Much as any keeper should have an exotics vet, and should have basic medicine on hand, a keeper should likely also have the means to aid a dying animal on hand as well.
 
Thank you, @TwoTankAmin for bringing this important topic to light! And thank you too, to @Seisage for your detailed contributions as well! It's an ugly topic. So it gets ignored. But unlike domestic animals (dogs, cats, etc.) we as care takers end up being responsible for determining the best end of life scenario for our exotic captives. Care for the well, and even the ill, gets discussed a lot. But how an organism can humanly end it's existence does not. I think it needs to be more openly discussed, so I thank you both! Much as any keeper should have an exotics vet, and should have basic medicine on hand, a keeper should likely also have the means to aid a dying animal on hand as well.
These posts prompted me to order a vial of clove oil from Amazon should the need arise. I hope no time soon.
 
Finally. Clove oil is not effective for larger fish. This requires a more powerful anesthetic which means a vet must be involved.
How large are we talking? I've used this clove oil method on a fairly large common goldfish that was dying, and it was effective, no panic reaction, but to be fair, the fish was very close to death anyway... it may have just been the past the point of being able to react.

But I've seen people I won't name on youtube (@GaryE , you know the one, I know!) use clove oil to sedate a rather large Asian arowana in order to do some DIY fish surgery on fins, and an eye I believe, if I remember rightly. It did appear to sedate the fish, and then removing the fish from the clove oil and he held the fish near a strong filter output, so fresh water was flowing over the gills and the fish gradually came around.

Apparently it's common for keepers of some expensive and exotic fish to use clove oil for sedation only and then reviving, and being careful not to overdose and kill the fish? I don't know how common DIY fish surgery happens, but I wouldn't feel capable to do that, personally. But I'd imagine it would still work if a fish that size needs to be euthanised?

It's not nice to have to do it, but I can't leave an animal to suffer and pass painfully when we do have a method that lets the fish pass peacefully. Have also used it on guppies without issue. I've had to do it more times than I'd wish, but I also inherited an ancient overstocked tank with old tank syndrome, and a nearly 40 year old pond full of fish, so I got into the hobby to try to fix those issues. Plus fish store livebearers are so often riddled with worms, I wasn't aware of that then, and had to deal with more losses than I'd like to remember, and a few tank crashes.

I researched and watched some videos about how to do it first, and agree with you that the times I've heard on the forum where the fish has panicked is likely if the oil isn't mixed well, and/or is added too quickly.

I've used the "smash" method once. When I didn't have clove oil, and a guppy was suffering and beyond saving. Just put some paper towel on a surface, had a heavy book nearby, netted fish, placed on paper towel and folded paper towel over it and used the book to end it quickly. Not nice to do, and I wouldn't want to have to do it again, but I figured at least it would be fast, and ended his suffering as fast as I could. I now keep clove oil handy with containers that I only use for clove oil, and hope that I don't need to use either method again.


That’s an awful, inaccurate method.

The Clove Oil dosage for euthanasia is 25 drops per litre of water. Any less is just an anaesthetic dosage and the fish will wake up again at some point.
Put a litre of water into container #1. Then take some of that litre and mix in ALL 25 DROPS by violent shaking (in container #2 with a lid). Then put the fish in container #1, then slowly pour in the mix from container #2. Panic is inevitable but will only last a few seconds.

Given that there's some disagreement on this issue, I figured I'd do my own research on the matter and report back. This is the science section of the forum after all. I found one research paper and a couple protocol documents from universities with research labs. The euthanasia protocols are managed by the Institutional Animal Care and Use Committee (IUCAC), a federally mandated regulatory body for institutions that use live animals. The IUCAC follows the American Veterinary Medical Association's (AVMA) guidelines for euthanasia of animals.

Love that you did that deep dive, thank you! That was fascinating. Most above my head, but still interesting and I like to see the research to back it up. :)
 
This may sound crude, but why can’t one net a sick fish out, and quickly behead it with a knife?
As long as you are quick, it should only last a second..no stress involved.
 
This may sound crude, but why can’t one net a sick fish out, and quickly behead it with a knife?
As long as you are quick, it should only last a second..no stress involved.
That's a perfectly acceptable method of euthanasia, although it'd still be recommended to sedate the fish with an anesthetic dose of clove oil first to make the process a little less stressful, and it would help with keeping the fish still so you can aim correctly with the knife. But yes, decapitation is just as good as clove oil, as long as it's swift. I think most sources also recommend following up with pithing which, put bluntly, is basically stabbing the brain with something sharp to make sure all neural connections are destroyed. There's more of a technique to it, you have to insert the sharp object at a particular position, but it's just a way to ensure a swifter death.

It's a particular issue with reptiles, since their neural connections are set up in such a way that can allow them to remain conscious for quite a while after decapitation. I think it's something to do with their metabolism, but it's where the old saying about a rattlesnake head still being able to bite you after decapitation comes from. Not sure how similar fish are in that regard, but given they're cold blooded like reptiles, I think the pithing is a good safeguard.
 
However you do this, it's harsh.

But for reference, while I have no use for essential oils and naturopathy, such stores are a good source of clove oil if you need it.
 
In the UK, clove oil is usually stocked by pharmacies as it's an old remedy for toothache.
 
It was taken off the pharmacy treatment/toothache shelves around here a few years ago, but if your pharmacy has an aromatherapy display, it's often in there. To me, it's the smell of doomed fish...
 

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