Oh my, I do not know what that is.
Did you cycle their tank ahead of time before putting them into the tank? Do you own any kits to test water quality. Without a fully cycled tank, you could very easily injure (or worse) your axolotl. The test kits are important to check water quality. If ammonia is too high, skin burns will occur. If nitrites are too high, it thins their blood too much or something, I don't quite understand what that one does but it is bad. And then there's nitrates, too many of them limits the axolotl's ability to breathe. It like, deprives them of oxygen, I think. I am not great with the scientific/medical stuff.
Have any other photos of your little guy? How about a photo of the whole tank too. Might see something. Although your little guy doesn't appear to be taking the defensive posture. If the water quality is terrible, they may throw their gills forward and act defensively, or they my try to flee by swimming around all crazy.
I don't know if I can help, I'm new to this too.