Foul fish or fishy fowl – your market choice
If the author intended to say that in times past the market sold dirty fish, then the error is one of punctuation a misplaced comma, but if the intention was to refer to fowl (cock or hen bird), then the error is one of spelling. In English grammar foul and fowl are called homophones, ie words having the same sound as each other, but having different meaning. Cork will be the European City of Culture in 2005 and this piece of grammatical confusion should be removed before then.
The city has an Irish language facility to promote the use of the native tongue and I have no doubt as to the expertise employed in this area. However, I humbly suggest that future public notices of historical importance, in the English language, are submitted to my office for scrutiny and correction.