Almost every morning, a blue-and-white truck pulls up to Union Oyster House near Faneuil Hall to drop off small coolers brimming with cod fillets packed on ice.
Cod is king at Boston’s oldest restaurant — where more than 7,000 diners a year order New England’s most fabled fresh catch.

Comments
If the restaurants did their own cleaned and cut the whole fish this would not be a problem (or at least requested the skin be kept on). The chefs would be able to recognize the species right away. Since most fish is some shade of white it is indeed difficult to determine which fish they actually have. I think restaurants need to stop out sourcing this. It really does not take that much time or skill to clean a fish (yes i was a chef in my former life ) The following are picture of Atlantic Cod: http://mistralseafoods.com/sites/mistralseafoods.com/files/page-images/atlantic-cod_0.jpg Pacific Cod http://apps.acesag.auburn.edu/mediamax/pdata/1935-m.jpg Grouper. There are many verities but do not look at like a Cod: http://www.arkive.org/brown-marbled-grouper/epinephelus-fuscoguttatus/
"Others say regulators could require suppliers and restaurants to identify where fish are from. Supermarkets must label the country of origin, but restaurants are not required to."
And I presume supermarkets get their information on the origin of the fish they sell from the same place the restaurants do, their suppliers.
It's not like Stop & Shop has its own fishing fleet.
Your cheap fish, Boston.
What did the blind man say as he walked past the fish market?