How to euthanize a fish

Discussion in 'Fish Disease Treatment and Diagnosis' started by Humblefish, Sep 19, 2016.

  1. Humblefish

    Humblefish Dr. Fish Staff Member Team R2R R2R Supporter R2R Excellence Award Partner Member 2018 Article Contributor Expert Contributor Louisiana Reef Club

    Nov 9, 2014
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    Navarre, FL
    I wanted to compile several different contributions into one thread, and make it a sticky. You have two options to use for euthanizing a fish: MS-222 or Pure Clove Oil.

    For MS-222 you can find more info and euthanasia dosage here:

    You can buy MS-222 from here:

    Below is video documentation from @Steve Jones showing euthanization of a sick wrasse using MS-222.

    Below are instructions from @Lionfish Lair on using pure Clove Oil (available at many drug stores) for euthanization:

    • Put 3 drops with a half pint of water and shake very well, so the oil and water make a fusion - otherwise the oil will just float on top of the water and for the euthanasia to work the fish has to get the oil into its system.
    • Add the mixture to the water that the fish is in (1 gallon of water should be more than enough) and stir it around slowly with your hand. The fish should become lethargic and sleepy. When the fish goes "belly up" it is asleep - not dead.
    • Then add 3 more drops of clove oil. Add another mixture of 2 to 3 drops of oil in water.
    • The fish feels nothing, it is very peaceful and humane.
    • Don't make the mistake of thinking that if you initially put more in it will act quicker - it will only freak the fish out - it has to be done gradually so the fish doesn't notice the change in the water.
    • The whole procedure should take anywhere from 30 minutes to an hour. You will know when the fish is completely dead because there will be absolutely no movement of the gills. If after an hour the fishes gills are still moving you could add a couple more drops of clove oil. Sometimes it does depend on the size of the fish to how many drops of clove oil are needed.
    • Properly dispose of the deceased fish and wash treatment container thoroughly with soap and water.

    And this video from @Duke4Life shows how to use Clove Oil to euthanize an injured wrasse.

    I want to thank one of the most knowledgeable ladies I know for the clove oil write-up; and both of these fine gentleman for their very informative videos, although I realize they were difficult to make. :(
    Last edited: Jun 29, 2018

  2. revhtree

    revhtree Owner Administrator Staff Member Team R2R R2R Supporter Photo of the Month Award R2R Excellence Award Partner Member 2018 Article Contributor Build Thread Contributor

    May 8, 2006
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    Thank you for the comprehensive thread!
    kschweer and Humblefish like this.
  3. kangadrew

    kangadrew Active Member R2R Supporter R2R Excellence Award

    Sep 11, 2015
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    Man, let me tell you something - euthanizing a fish is the hardest thing to do. I had a puffer for a little over a year, little figure 8 puffer. He had a 10 gallon to himself on my desk, and I kept the tank on a wheeled stand so after I was done he could be next to my bed when I went to sleep - he was awesome to watch swimming right before I fell asleep, he would never fall asleep until after I had either. Well, one day he started swimming funny and getting red sores on him. I had no clue what it was, still don't, but he never got better after two weeks, only worse. Eventually, I had to use some clove oil on him because I didn't want to see him suffer anymore. Having to kill your pet is the worst thing I have ever had to endure, and I had to watch someone get run over before.

    If you're going to euthanize your fish, please please PLEASE do it correctly, be sure to make it quick and as painless as possible. Thanks Humblefish for the thread, hopefully this helps people out
    kschweer and Humblefish like this.
  4. James Rutherford

    James Rutherford Member

    Oct 20, 2012
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    Frisco, Texas
    I had read that euthanizing a fish was also humanly done by using a container and putting the fish and container in the freezer. The slow lowering of the temperature was like the proverbial frog in the boiling water. The fish doesn't seem to notice the cooling of the water as it slowly dies.

    I agree it is very sad to lose a fish.

  5. Prolude006

    Prolude006 Member Partner Member 2018

    May 16, 2016
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    Freezing the fish is the best way to euthanize them. Clove oil actually suffocates them slowly. Honestly in the end the nervous system on a fish is only reactionary, it doesn't "feel" pain in the same way we do.
    Proper disposal is a must, by fire is the best way to avoid introducing anything into the local ecosystem.
    tcoyle and James Rutherford like this.
  6. WilRams

    WilRams Well-Known Member R2R Supporter

    Dec 12, 2014
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    Owings Mills, MD
    From my freshwater days I have always used a combination method. I let them go belly up in clove oil then into the freezer.
  7. Viper99ACR

    Viper99ACR Member

    Apr 19, 2016
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    Great post. I have a friend who bought some joculators that didn't do very well during shipping (over 30 hrs due to delays). They were laying on their side breathing hard and he thought about euthanizing them, but thankfully he didn't. He found them the next morning swimming normally. Tough little fish.
  8. Paul B

    Paul B Valuable Member R2R Supporter Reef Spotlight Award Reef Tank 365 Article Contributor Build Thread Contributor

    Nov 3, 2010
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    Long Island NY
    I myself use the freezer method. Fish being cold blooded keep slowing down until they stop.
  9. Mirya

    Mirya Active Member

    Dec 12, 2013
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    Raleigh, NC
    The American Veterinary Medical Association has a document discussing euthanasia methods. Link is here: The discussion of fish starts on page 67. The AVMA does not consider slow freezing (i.e. putting your fish in a dish of water into the freezer) an acceptable euthanasia method unless the fish is anesthetized. However, rapid freezing is considered humane for small fish. For rapid freezing, the AVMA suggests:

    "It is acceptable for zebrafish (D rerio) to be euthanized by rapid chilling (2° to 4°C) until loss of orientation and operculum movements and subsequent holding times in ice-chilled water, specific to finfish size and age. Zebrafish adults (approx 3.8 cm long) can be rapidly killed (10 to 20 seconds) by immersion in 2° to 4°C (36° to 39°F) water. Adult zebrafish should be exposed for a minimum of 10 minutes and fry 4 to 7 dpf for at least 20 minutes following loss of operculum movement.

    Until further research is conducted, rapid chilling is acceptable with conditions for other small-bodied, similarly sized tropical and subtropical stenothermic species. Species-specific thermal tolerance and body size will determine the appropriateness and effectiveness of rapid chilling for euthanasia of finfish. Finfish size is important because the rate of heat loss via thermal conduction from a body is proportional to its surface area. Based on these 2 factors, it has been suggested that rapid chilling in water associated with an ice slurry is a suitable killing method for small tropical and subtropical finfish species 3.8 cm in length (tip of the snout to the posterior end of the last vertebra) or smaller, having lower lethal temperatures above 4°C.

    To ensure optimal hypothermal shock (ie, rapid killing), transfer of finfish into ice water must be completed as quickly as possible. This means rapid transitions from acclimatization temperature to 2° to 4°C must be achieved. This can be accomplished by using minimal water volume to transfer finfish (ie, using a net to place finfish in chilled water). In addition, finfish should not be in direct contact with the ice in the water; rather a depression should be formed in the ice slurry to expose the entire surface of the finfish to the chilled water. Full contact with cold water ensures optimal exposure and rapid chilling of the finfish. Water temperature must not exceed 2° to 4°C. Well-insulated containers, such as coolers, will assist in maintaining the ice slurry and a probe thermometer can be used to confirm water temperature.

    This method of euthanasia is not appropriate for temperate, cool, or cold-water–tolerant finfish, such as carp, koi, goldfish, or other species that can survive at 4°C and below. It is appropriate for zebrafish and other small-bodied (3.8-cm-long or smaller) tropical and subtropical stenothermic finfish, for which the lower lethal temperature range is above 4°C. This method can also be acceptable for small to medium-sized (2.8- to 13.5-cm-long) Australian river gizzard shad, as long as secondary euthanasia methods are applied after finfish are rendered nonresponsive. However, because of surface-to-volume considerations, use of this method is not appropriate in other medium to large-bodied finfish until data regarding its applicability to euthanasia for those species become available."
    melypr1985 likes this.

    MUSBFRANK Active Member

    Dec 17, 2011
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    Something to think about, I've always used the freezer.
  11. CindyKz

    CindyKz Well-Known Member

    Apr 3, 2017
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    The major active ingredient in clove oil is eugenol, which has anesthetic properties. Both of these organizations list it as appropriate for use in fish euthanasia, though the Canadian Council recommends following the clove oil with another means.

    The one time I had to euthanize a fish (my blue spotted jawfish) I used the clove oil. It was quick and seemed peaceful. :'(

    Thanks to the article author and especially those who made the videos. That must have been really difficult. Your efforts to educate us all really are appreciated.
    sanchoy and Humblefish like this.
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