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Blackening of the extremities (Uncommon disease), necrosis.
On depigmented or albino axolotls, this results in a blackening of the ends of the legs (we are not talking here of their small claws but of the whole hand or leg), or of the mouth, the cesspool, etc ... more advanced stage, the disease causes disintegration of the fingertips. The bones appear, then dissolve. On a black animal, I think we will only see the fingers that disappear. The evolution is very slow.
Quite simple treatment: It is enough to put a general anti-bacterial of aquarist trade in the water, by respecting the doses. In my case, I used Temerol. An animal just touched at the fingertips healed in a few days. A much more seriously affected animal (legs, muzzle, cesspool) recovered after a period of treatment.

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