It's not an easy subject to discuss but when you have animals you have to tackle it.
First method : Clove essential oil. During an incurable disease, you may wish to euthanize your axolotl or fish to avoid letting it suffer needlessly. Choosing to euthanize an animal is a difficult decision to make, but if you feel that it is better to end the life of your axolotl, then it is possible to perform this act ethically and safely. You just need to get in a pharmacy, or organic store, essential oil of clove (or clove), which contains on average between 60 and 95% eugenol, an active substance with anesthetic power (product on sale free). In large doses, axolotl will overdose anesthetic causing death. The recommended dose for euthanasia is 20 drops (1 mL) of clove essential oil per liter of water. In practice: In a tank of suitable volume, pour the necessary quantity of water from your aquarium; Pour in the clove oil (1 mL / L). You can possibly facilitate the dispersion of the oil, by pre-diluting it in 5 times its volume of hot water; Stir the water / oil mixture well with a kitchen whisk for at least 5 minutes; Transfer your axolotl to be euthanized in this tank, then place a lid on top; Soon your axolotl will lose its balance, become unconscious, and stop breathing; Leave your axolotl in this euthanasia tank for at least 30 minutes after complete cessation of respiratory movements.
Second method: For this kind of act, it is best to consult a veterinarian. In this case, veterinarians recommend the use of benzocaine (delivery only on veterinary prescription see https://www.vetofish.com ) .
Remember that the axolotl feels pain and fear. Certainly not like a mammal, but it still has primary feelings and emotions. It is possible to kill a fish or axolotl without making it suffer. But it doesn't just happen. To type it violently or to put it in the freezer is NOT TO BE! (The clove has been known for many years in the aquarist environment, 22 years ago it was already common, so why use barbaric methods?) Because unless you cut its brain, axolotl or fish will not die immediately. In the event of failure his suffering would be intolerable. For the freezer, we tend to think that the cold will gently "put to sleep" the axolotl. He will fall asleep, of course, but in pain, his body crippled with lesions caused by the frost. Because crystals will very quickly form in his blood system, (unlike the slight drop suffered in a refrigerator and which just plunges him into a lethargic state) So yes you don't see it, far from the eyes, far from the heart. But it's still very cruel. Ditto, scalding axolotl or fish and other ideas of this type are to be forgotten at all costs. When to throw him alive in the toilet and flush ...:? IN SHORT. TO EUTHANASIZE YOUR AXOLOTL / FISH, the only technique recognized as "euthanasia" (gentle and painless death) is the clove technique . Here is a second method still with cloves, I unfortunately had to use it twice about fifteen years ago when we did not use the essential oil of cloves.