Fish Milkshakes

Back in the seventies there was a sketch TV show in Australia called "The Aunty Jack Show". They loved poking fun at the steel city of Wollongong, and strange habits of the residents. The cast produced a song about "Fish milkshakes". Yuk, what could be worse?
Last week, on the way down to Wollongong I stopped at a bottle shop to buy a bottle of Irish Bailey's. Too dear I thought, and looked along the shelf of bottles. One that caught my eye was KilKenny Cream about a third the cost of Baileys, and made in Australia.
There, on the back label in hard-to-read small print, was a list of ingredients: "produced with the aid of egg, milk and fish..."
Fish. What in the name of all that's weird did they use fish for, in a liqueur? Helping me get stewed to the gills?