Some heavyweight baggage cars and express boxcars were equipped with fish racks. This was essentially a slotted floor with a drain pan underneath to direct away the water from the melted ice. The fresh fish was packed in boxes or totes, surrounded by crushed ice. I don’t specifically know how the crushed ice was periodically replenished en route.
I found a few pictures by doing a Google Image search using “baggage car fish racks”. Also diagrams in the GN Passenger Car diagrams which can sometimes be located online.
