A strange expression

Today I found myself saying "what's that got to do with the price of eggs?" and then as soon as I did, I realised how bizarre and old-fashioned I sounded. I mean really, who says that?But rather than dwell on my repertoire of Enid Blyton-esque expressions, I started to wonder what does the expression even mean, and where does it come from? I thought it was much more important to sort this out now, rather than, say, work on my honours literature review.

Apparently it's an American expression that originated in the 1920s. Its used to respond to someone who has said something that is perceived to be completely irrelevant and unrelated to the discussion topic. It seems that the "eggs" can be substituted for a whole range of things, including the price of tea in china, butter and fish. I have never heard the expression "whats this got to do with the price of fish" but several websites are adamant it is an Australian expression - supposedly it originates from a comment made by the Queensland Premier in the 1980s, but just because he said it, and its on written record, doesn't automatically equate to it being a national expression used by everyone! Its certainly got nothing to do with my eggs thats for sure.