Euthanasia for Amphibians
By Edward Kowalski
Those who care for animals are sometimes faced with the decision to end an animal's suffering. Two methods of humane euthanasia are readily available, specifically ethyl alcohol and OrajelŪ. 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.
Tricaine methanesulfonate (MS-222). Overdose at 200 mg/kg of body weight injected into the body cavity.
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.
Home recipe for 5% ethyl alcohol:
175 ml (3/4 Cup) water
25 ml (2 Tablespoons) 80-proof (40%) vodka
Pentobarbitol. At 100 mg/kg injected into the body cavity.
Pithing. Anesthetized amphibians can be pithed.
Benzocaine. OrajelŪ (and other painkillers containing benzocaine*) appear to 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 (this may actually be most effective in anurans, which have pelvic patches, rather than caudates). 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. The chemicals used as denaturants can be irritants. In general, this means you should use a gel or paste, not a liquid preparation. Read labels carefully, including the "inactive ingredients".
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.
Wright KM and Whitaker BR. 2001. Amphibian Medicine and Captive Husbandry. Malabar: Krieger Publishing Company.