I actually remember shipping fish on CIE. In the days before fish farming, my grandfather regularly caught salmon on the River Bonet in Leitrim - valuable fish which were much in demand in the capital. Up until 57 it travelled to Dublin via SLNC- the railcar stopped at Lisgorman to collect, and it was weighed on the scales at Dromahair station to ensure the best weight was recorded. From 57 to c1980 it travelled by road to the railhead, wrapped in sacking and reeds, and was carried in the guards van of the Sligo Mail. I well recall one such trip, racing over the mountain to Sligo to catch the train. I suspect that much fish traffic was of similar nature.