This came up in another thread not long ago.

'Fiddle' is simply slang for a member of the violin family, including violin, viola, cello and double bass. A double bass was sometimes called a 'bass fiddle', although you don't often hear the term used today. 'Fiddle' on its own normally refers to a violin. The verb 'to fiddle' means to play a fiddle.

I know classical violinists who refer to their 'fiddles', although I suspect this may be frowned upon by certain sections of the classical music world.

So on that basis, I don't think there is a difference.