Hello Scott and list,
You didn’t say where your layout was set, which might have some bearing on the cars used, as Garth suggested.
Despite not being able to hold temperatures at 0˚F or below, ice refrigerator cars would have been the dominant type of car used for frozen fish in 1950. Mechanicals were rather rare. The frozen food industry asked for any refrigerator cars they could get with extra thick insulation, because for a long time the issue was largely seen to be a matter of not enough insulation instead of insufficient refrigerant. The available number of such heavily insulated cars never seemed to match the needs of shippers, so it seems that quite a number of frozen foods loads must have gotten shipped in ordinary fan cars, much to the displeasure of the consignees, depending on the product.
“Frozen” was a bit of judgement call in the industry, with a differing bodies recommending different temperatures for different foods and with different amounts of “softening” being acceptable during transit. As Tony noted, it was frozen concentrated orange juice (FCOJ) that began to bring about the change to mechanical refrigerators. To taste right FCOJ had to be kept at temperatures below 0˚F. Other frozen foods were a bit more tolerant to variations in temperature, but FCOJ and fish were among those that were not. Money talks, though, and with a 37,740 percent increase in FCOJ sales between 1945 and 1952, the product and its temperature needs was worthy of attention from carriers, especially when the producers were displeased and were shifting loads to trucks in droves.
FGE ordered 11 mechanical refrigerators in 1948, predominantly because of the growth in FCOJ originating in Florida after 1945. They used these 11 cars to try out 9 different mechanical cooling systems. In the period between 1948 and 1950 FGE ordered 165 mechanical cars. They still were a tiny fraction of the cars “suitable” (according to the frozen food industry) for frozen foods. Sources differ on that number, but in either case the number of mechanicals was less than 1% of cars deemed “suitable” for frozen foods in 1953. By 1953 FGE had 175 mechanicals in service, all but 12 of them dedicated to frozen food shipping.
Things didn’t begin to change all that much until around 1955. Not only had trucks begun to dominate frozen food traffic by this time, but in 1955 the railroad industry began for the first time to publicly acknowledge the insufficiency of ice and salt for frozen food shipment. By the end of 1955 a reported 2,100 mechanical refrigerators had been brought into service nationwide.
In terms of frozen fish movements, the industry tends to lump them in under a general category of “seafood” and in 1950 the ICC didn’t appear to treat frozen fish any different than fresh in its stats, so it’s a little hard to extract an exact number of frozen fish movements. ICC records for 1950 show that a total of 8,763 carloads of "Seafood NOS" (fresh and frozen) were originated and terminated, or 190,303 tons. In 1950 there were 66,500 tons of frozen seafood “produced” by the frozen food industry, of which about 30% moved by truck in 1950, leaving 46,500 tons of frozen seafood for railroads and other modes—not really a huge amount when divided by 365 and split into carloads.
There’s been mention a couple of times in this thread about fish sticks. These were introduced in 1953 by General Foods/Birds Eye; something invented to deal with the fact that mechanized trawler ships were netting fish and freezing them at sea into giant blocks. As fish doesn’t thaw and refreeze well, the processors cut these fish blocks into “portions” and “sticks,” breaded them, and then sought to create a market for them, primarily through institutional sales (schools, etc.). Although packaging was a changing subject itself, fish in the late 1940s and early 1950s was more often sold in fiberboard boxes and was often pre-filleted so as to avoid any air pockets inside the cut of fish that might introduce bacteria. Trays, as we now tend to associate with frozen meals, were around by 1950, but didn’t really begin to achieve their icon position in American dining until the mid-1950s.
I would recommend seeing if your local library has (or can get you) back issues of a frozen food trade periodical called “Quick Frozen Foods” from your year of interest. Not only will it give you a good breakdown of what was on the minds of that industry at the time, the issues often contain useful statistics and news items. The editors of that time were hyper-aware of the insufficiency of their transportation solutions so there frequent articles about railroad developments. Don’t overlook the ads as well, since these also give great insights into the industry that are useful for modeling.
All the best,