Jay Hemdal
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Fish Medic
Euthanasia
Euthanasia is a word derived from two Greek words that roughly translates to “good death”. In other words, euthanasia is the painless killing of an organism. In general usage, there is also the underlying understanding that euthanasia is performed on terminal patients only. This however, is not always the case with aquarium animals. Euthanasia may be performed as a population management tool, or for scientific research. Sometimes the phrase “humane euthanasia” is used, but that is redundant, as the lack of pain means the process is humane.
In this era of quick fixes and immediate gratification, it can be difficult for aquarists to understand that some fish diseases are simply not going to respond to any medication or treatment provided. Some ailing fishes, especially those with chronic diseases, simply cannot be cured and are in fact, slowly dying. Once they reach the point of being “moribund” (not able to feed or swim normally) euthanasia should be considered as a humane alternative to continued unsuccessful treatments.
Do fish feel pain?
Some research has indicated that fish do feel pain, while other studies show that they don’t. The true answer probably lies somewhere in-between; fish do feel an avoidance to adverse stimulus, but it isn’t “conscious pain” as seen in mammals. Termed “Nociception”, this is an animal’s nervous system's response to potentially harmful stimuli. Nociception triggers a variety of physiological and behavioral responses and usually results in a subjective experience of pain in sentient beings. It is less clear how fish and invertebrates receive nociception; is it felt as classical pain, or does it simply create an avoidance response in the animal? Since it is better to err on the side of caution, so euthanasia (painless death) is the most humane option.
Whatever degree of pain or physical discomfort fish experience, it can be argued that allowing chronically ill fish to continue suffering from any major nociception is ethically questionable.
When is euthanasia warranted?
Euthanasia should be considered for a fish if:
1) It has a chronic, untreatable disease (such as tumors, blindness, or starvation)
2) The fish is “moribund” due to severe injury or illness.
3) In some cases, euthanasia is considered necessary for population management reasons. For the sake of argument, let’s say that a population of an endangered species is being managed for conservation purposes, and there is an issue where if the male/female ratio becomes skewed, and increased numbers of one sex (often the males) will disrupt the integrity of the whole population. In that case, it may be best to euthanize the surplus males in order to better preserve the genetic diversity of the entire population.
The American Veterinary Medical Association have their 2020 euthanasia guidelines posted online at https://www.avma.org/KB/Policies/Documents/euthanasia.pdf
Preferred methods for euthanasia
MS-222
Every aquarist should have a plan for specimen euthanasia before they need to employ it. An overdose of buffered Tricaine methane sulfonate (MS-222) is the preferred method for euthanizing fish. Dosing at a rate of greater than 300 mg/l MS-222 along with 300 mg/l sodium bicarbonate is effective for euthanizing fish within 30 minutes. However, MS-222 is expensive, and not readily available in smaller quantities to home aquarists. Removing the fish too soon from the solution may allow it to recover. It is therefore suggested to leave the fish in a small amount of the euthanizing solution, and freeze it for later disposal.
Clove oil (eugenol)
One product that aquarists can buy that is approved by at least some veterinarians and research biologists is clove oil, also called eugenol. A dose of 50 mg/l is usually sufficient in euthanizing fish. This equates to about 0.20 ml of eugenol in one gallon of aquarium water.
Because eugenol does not mix well with water, and because larger volumes are easier for hobbyists to measure out, it can be dosed using the following method:
1) Add 2 ml of eugenol to 100 ml of tank water in a sealed container and shake it vigorously.
2) Add 10 ml of this suspended solution to each gallon of water needed to euthanize the fish.
3) Place the fish in this solution and keep it covered to prevent it from jumping out and to help keep it calm.
4) Wait at least twenty minutes after it stops breathing, and then remove the fish from the solution and freeze it for later disposal.
Other methods
A variety of other methods have been proposed for the euthanasia of fishes, but none are fully accepted by veterinary experts. Still, home aquarists need more common tools to use, so those methods are listed here in roughly descending order of suitability:
Ethanol
Regular alcohol at a dose of 25 ml per liter will cause respiratory collapse and death in fishes within 30 minutes. The trouble is that alcohol is not available in pure form unless it has been “denatured” by the addition of distasteful chemicals such as turpentine. Vodka is about 40% alcohol by volume, so using it 62 ml per liter will give an effective dose.
Decapitation/pithing
Cutting a fish’s spinal cord, right behind the head, is a quick method of euthanasia that is approved for use in food fishes (where the use of chemicals would otherwise make the flesh unfit to eat). The issue is really that the method is distasteful for most people to do, so it is rarely used by aquarists. However, it is quick and effective.
Freezing
Placing the affected fish in a small amount of aquarium water in a sealed container and then placing the container in a freezer is a euthanasia technique used by some people. However, it is slow to work, so it is not considered humane. Its appeal as a method is that the fish is “out of sight” so people feel more detached from the process.
An option of last resort
The animals in your aquariums are completely reliant on you for proper care. It is your responsibility to see to it that their lives in captivity are humane as possible and that all of their needs are met. If you cannot meet their needs, please find someone who is more able. Euthanasia should be considered only for health reasons, not because it is no longer convenient to care for an animal.
Jay
Euthanasia is a word derived from two Greek words that roughly translates to “good death”. In other words, euthanasia is the painless killing of an organism. In general usage, there is also the underlying understanding that euthanasia is performed on terminal patients only. This however, is not always the case with aquarium animals. Euthanasia may be performed as a population management tool, or for scientific research. Sometimes the phrase “humane euthanasia” is used, but that is redundant, as the lack of pain means the process is humane.
In this era of quick fixes and immediate gratification, it can be difficult for aquarists to understand that some fish diseases are simply not going to respond to any medication or treatment provided. Some ailing fishes, especially those with chronic diseases, simply cannot be cured and are in fact, slowly dying. Once they reach the point of being “moribund” (not able to feed or swim normally) euthanasia should be considered as a humane alternative to continued unsuccessful treatments.
Do fish feel pain?
Some research has indicated that fish do feel pain, while other studies show that they don’t. The true answer probably lies somewhere in-between; fish do feel an avoidance to adverse stimulus, but it isn’t “conscious pain” as seen in mammals. Termed “Nociception”, this is an animal’s nervous system's response to potentially harmful stimuli. Nociception triggers a variety of physiological and behavioral responses and usually results in a subjective experience of pain in sentient beings. It is less clear how fish and invertebrates receive nociception; is it felt as classical pain, or does it simply create an avoidance response in the animal? Since it is better to err on the side of caution, so euthanasia (painless death) is the most humane option.
Whatever degree of pain or physical discomfort fish experience, it can be argued that allowing chronically ill fish to continue suffering from any major nociception is ethically questionable.
When is euthanasia warranted?
Euthanasia should be considered for a fish if:
1) It has a chronic, untreatable disease (such as tumors, blindness, or starvation)
2) The fish is “moribund” due to severe injury or illness.
3) In some cases, euthanasia is considered necessary for population management reasons. For the sake of argument, let’s say that a population of an endangered species is being managed for conservation purposes, and there is an issue where if the male/female ratio becomes skewed, and increased numbers of one sex (often the males) will disrupt the integrity of the whole population. In that case, it may be best to euthanize the surplus males in order to better preserve the genetic diversity of the entire population.
The American Veterinary Medical Association have their 2020 euthanasia guidelines posted online at https://www.avma.org/KB/Policies/Documents/euthanasia.pdf
Preferred methods for euthanasia
MS-222
Every aquarist should have a plan for specimen euthanasia before they need to employ it. An overdose of buffered Tricaine methane sulfonate (MS-222) is the preferred method for euthanizing fish. Dosing at a rate of greater than 300 mg/l MS-222 along with 300 mg/l sodium bicarbonate is effective for euthanizing fish within 30 minutes. However, MS-222 is expensive, and not readily available in smaller quantities to home aquarists. Removing the fish too soon from the solution may allow it to recover. It is therefore suggested to leave the fish in a small amount of the euthanizing solution, and freeze it for later disposal.
Clove oil (eugenol)
One product that aquarists can buy that is approved by at least some veterinarians and research biologists is clove oil, also called eugenol. A dose of 50 mg/l is usually sufficient in euthanizing fish. This equates to about 0.20 ml of eugenol in one gallon of aquarium water.
Because eugenol does not mix well with water, and because larger volumes are easier for hobbyists to measure out, it can be dosed using the following method:
1) Add 2 ml of eugenol to 100 ml of tank water in a sealed container and shake it vigorously.
2) Add 10 ml of this suspended solution to each gallon of water needed to euthanize the fish.
3) Place the fish in this solution and keep it covered to prevent it from jumping out and to help keep it calm.
4) Wait at least twenty minutes after it stops breathing, and then remove the fish from the solution and freeze it for later disposal.
Other methods
A variety of other methods have been proposed for the euthanasia of fishes, but none are fully accepted by veterinary experts. Still, home aquarists need more common tools to use, so those methods are listed here in roughly descending order of suitability:
Ethanol
Regular alcohol at a dose of 25 ml per liter will cause respiratory collapse and death in fishes within 30 minutes. The trouble is that alcohol is not available in pure form unless it has been “denatured” by the addition of distasteful chemicals such as turpentine. Vodka is about 40% alcohol by volume, so using it 62 ml per liter will give an effective dose.
Decapitation/pithing
Cutting a fish’s spinal cord, right behind the head, is a quick method of euthanasia that is approved for use in food fishes (where the use of chemicals would otherwise make the flesh unfit to eat). The issue is really that the method is distasteful for most people to do, so it is rarely used by aquarists. However, it is quick and effective.
Freezing
Placing the affected fish in a small amount of aquarium water in a sealed container and then placing the container in a freezer is a euthanasia technique used by some people. However, it is slow to work, so it is not considered humane. Its appeal as a method is that the fish is “out of sight” so people feel more detached from the process.
An option of last resort
The animals in your aquariums are completely reliant on you for proper care. It is your responsibility to see to it that their lives in captivity are humane as possible and that all of their needs are met. If you cannot meet their needs, please find someone who is more able. Euthanasia should be considered only for health reasons, not because it is no longer convenient to care for an animal.
Jay
