it’s just one of the little cute expressions that scrooge/the ducks use in some of the comics! very often it’s just ‘ye cats’, but sometimes its the full phrase

it’s a bit like Tintin’s famous “Great Snakes!” exclamation of surprise- they don’t really mean anything specific, but they’re quaint and rather catchy. Two other famous phrases are ‘oh me, oh my!’ and ‘oh my stars and little comets!’, which are reused by the duck comics even now! it’s just a nice little nod to Scrooge’s origins and Carl Barks’ way of writing the character- like a verbal signature.