I have to disagree; freezing them in any way is still inhumane.
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. 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 a liter/quart of water, then applying to the animal. 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.
Many vets have no clue about frogs and their needs. Hopefully this helps for future references
