What a dull thread. All that I get out of it, so far, is that men like to snigger about prostitutes, and that nobody's done any really solid research on the origins of this song.
A couple of factual points: seafood was a standard food in Dublin until the city grew to the size where sewage outflow destroyed the safe cockle and mussel beds; Dublin Bay Prawns and Clontarf Oysters were famous.
And the song sounds to me (not that I'm any kind of scientific researcher myself) like a typical children's play rhyme for skipping or ball-hopping - the rhythm and the short and basic number of verses.