Euthanasia for Amphibians
By Edward Kowalski
Those who care for animals are sometimes faced with the decision to end an animal's suffering. Several methods of humane euthanasia are readily available, specifically Orajel®, clove oil, and ethyl alcohol. Other methods may require a veterinarian.
How to decide if an animal should be euthanized
You need to evaluate the animal. Some basic questions that you need to ask yourself in these situations. Is the animal likely to recover? Is the animal injured so it is likely to be in pain? Is the pain likely to be severe (e.g., a scrape compared to severe trauma such as a body cavity torn open)? Will trying to heal the animal cause it to suffer due to the extent of the injury? Is the animal feeding? Can it digest food? Will force feeding cause the animal too much pain?
These are some guidelines to consider. Basically, evaluate the quality of the animal's life and decide based on that. The other thing to consider is if the animal has a severe infectious disease that is incurable (such as mycobacteria infections). That would also possibly be a candidate for euthanasia.
Unacceptable Methods of Euthanasia for Amphibians
Freezing. Freezing is only acceptable if the amphibian is small (<40 grams), is already anesthetized, and the freezing is immediate (such as immersion into liquid nitrogen). However, refrigerator freezers are too slow and are considered unacceptable. Additionally many arctic, near arctic, and montane species can tolerate freezing for over 48 hours, making this especially ineffective for these species.
Trauma. Due to the ability of many amphibians and reptiles to tolerate severe traumatic injury, trauma is unacceptable as a method of euthanasia, unless the cranium and brain are destroyed on the first blow.
Carbon dioxide. CO2 is an accepted method for humane euthanasia for birds and mammals. However as reptiles and amphibians can survive under severe oxygen debt it is not acceptable for use in these animals.
Humane Methods of Euthanasia for Amphibians
Several methods of euthanasia are accepted by the National Research Council on Pain and Distress in Laboratory Animals and/or American Veterinary Medicine Association.
Tricaine methanesulfonate (MS-222). Overdose at 200 mg/kg of body weight injected into the body cavity. MS-222 is available from pet supply companies in some countries under trade names such as Tricaine-S® or Finquel®. It can also be applied as a bath, but the pH of the solution must be tested and buffered, as it may be acidic enough to be a strong irritant. To avoid the possibility that the animal will re-awaken after removal from the bath, once fully sedated the amphibian can be placed for 30 minutes in a 40% ethyl alcohol bath to ensure it does not recover.
Ethyl alcohol. By sedation in a bath of 5% ethyl alcohol (ethanol) followed by immersion into a stronger bath after the amphibian has been anesthetized. A medium sized newt (12 cm; 5 in) may take 20 minutes or more to become unresponsive using this method. Bear in mind that the use of ethyl alcohol as an amphibian anaesthetic is not backed by primary literature, although some amphibian experts recommend it's use for euthanasia. The method is not sanctioned by AMVA.
Home recipe for 5% ethyl alcohol:
175 ml (3/4 Cup) water
25 ml (2 Tablespoons) of 80-proof (40%) vodka
Pentobarbitol. At 100 mg/kg injected into the body cavity.
Pithing. Anesthetized amphibians can be pithed.
Benzocaine. Orajel® (and other painkillers containing benzocaine*) can rapidly anesthetize and euthanize amphibians. This method has not yet been accepted by the National Research Council on Pain and Distress in Laboratory Animals, probably due to how recently the publications involving these products have come out. Products containing either 7.5% or 20% benzocaine have been shown to be effective in the euthanasia of amphibians. The original descriptions of this procedure had the gel containing the benzocaine applied to the head of the amphibian, however it has been shown that it may be more effective if applied to the ventral (belly) surface of the animal. A 5-mm drop applied to the ventral surface of a Eurycea quadridigitata resulted in relaxation and death in less than one minute (Chen and Combs, 1999).
*Note about benzocaine products: Choose a product that does not contain large amounts of alcohol. The alcohol in these preparations is usually denatured alcohol, which is an irritant and will cause a pain response in the animal. In general, this means you should use a gel or paste, not a liquid preparation. Read labels carefully, including the "inactive ingredients".
Clove oil (eugenol). Clove oil is accepted by the AMVA as an agent for euthanizing fish, and it has been assessed as an anaesthetic for amphibians. It is available for sale at some pet shops, in drug stores as a remedy for oral pain, and as an aromatic oil. It is mixed with water at 25 mg/kg. This can be approximated by shaking several drops of oil in 1 liter (1 quart) of water, then applying to the animal. The animal will generally not respond with any indication of pain. The length of time until full loss of consciousness depends on the size of the animal, and may be anywhere from 1 minute to 30 minutes. To avoid the possibility that the animal will re-awaken after removal from the bath, once fully sedated, the amphibian can be placed for 30 minutes in a 40% ethyl alcohol bath to ensure it does not reawaken.
References
Chen, MH and Combs, CA. 1999. An alternative anesthesia for amphibians: ventral application of benzocaine. Herpetol. Rev. 30(1):34.
Kaiser H and Green DM. 2001. Keeping the frogs still: Orajel is a safe anesthetic in amphibian photography. Herpetol. Rev. 32(2):93-4.
Mitchell, MA, et al. 2009. Evaluating the Clinical and Cardiopulmonary Effects of Clove Oil and Propofol in Tiger Salamanders (Ambystoma tigrinum). Journal of Exotic Pet Medicine 18:1, January 2009: pp 50-56.
Wright KM and Whitaker BR. 2001. Amphibian Medicine and Captive Husbandry. Malabar: Krieger Publishing Company.
American Veterinary Medicine Association guidelines are available from
https://www.avma.org/resources-tools/avma-policies/avma-guidelines-euthanasia-animals.
Article posted 2005. Revised August 2011 (adding clove oil and updated AMVA link). Revised November 2011 (to add details regarding alcohol and clove oil).