New black on my axoltl ??

[YyzVince]

Hi
I have a 5yr old Leucistic male axoltl who has been healthy until recently. He still eats regularly & seems fine. He has developed some blk on his underbelly (behind rear legs) & on tips of toes. At first I thought it was just natural aging but it seems to be spreading? Does this look like bacterial? Should I do salt baths and/or antibiotic? My vet doesn't know much about axoltls.

 

[EasternRomioi3]

My little girl, who is 3, has had those appear on her slowly over the years. More experienced owners have told me it's natural, it's an age thing.