This is a piece of folk/protest art symbolizing the demise of the North Atlantic cod fishery in the exhibit On the Water in the Smithsonian's National Museum of American History in Washington, DC. More info from the museum's website:
In 1992, Canada declared a moratorium on cod fishing in its Atlantic coastal waters. Fisherman Dan Murphy of Dunville, Newfoundland, made this cod-in-a-coffin to express his view of the decision and its impact on his livelihood. He sold these coffins at a local flea market.