Question: Wild type axolotl or salamander juvenile

[Tinkibell]

Hi I have a wild type axolotl I have had it for a month and it's back fin has got smaller I have checked the water it's all ok my other axolotls are all ok I did look it up on some other websites and they say it might be an salamander juvenile instead of an axolotl but I'm not sure how to tell

 

[xxianxx]

It's an axolotl

 

[auntiejude]

definitely an axolotl.