For ordinary humans, the extraordinary migration of salmon is difficult to imagine. Take Chinook salmon. Some of these fish swim from the Columbia River up to Canada and beyond, covering up to sixteen miles a day. Calculated as body lengths per second, that would be the equivalent of a human swimming more than 160 miles a day — fast enough to circumnavigate the equator in 150 days. Migrating fish also cover vast distances. In its trans-Pacific migration, a tagged bluefin tuna was found to have covered an amazing twenty-five thousand miles — a distance greater than the Earth’s circumference.

If the mileage clocked by these fish sounds impressive, it is nothing compared to the journeys some of them take after their death. In the case of salmon, it is all because of their pin bones — dozens of tiny bones not connected to the rest of the fish’s skeleton that cannot be dealt with by filleting machines. Pin bones must be extracted by hand using tweezers or small pliers. It is a laborious process that when carried out in North America or Europe is costly. Not in China, though, with its low wages and high productivity.

Here is a typical journey for a Norwegian salmon destined for sale in a supermarket in America or Europe: Once harvested, the fish is frozen and packed into boxes that are loaded onto a small feeder vessel in a Norwegian fishing harbor. From here, the fish sails to Rotterdam or Hamburg, where it will change ships and end up on a large international container vessel bound for China, traveling at a temperature of minus twenty-three degrees Celsius all the way.

Thousands of miles and about a month later, the fish arrives in China, often ending up in Qingdao, a large port city on the tip of the Shandong Peninsula of China’s northeast coast that is home to several hundred fish-processing centers. After being unloaded from the vessel, the “raw material” is trucked to a fish-processing center on an industrial park. At this smart new facility with vast cold storage, the salmon is defrosted and moved out to the factory floor. In a large, neon-lit industrial space are ranks of tables, each with dozens of brightly colored plastic trays on top of them. Standing at the tables, dressed in white coats and caps and wearing latex gloves and cotton masks, are hundreds of factory workers — most of them young women from rural villages. Using nimble fingers and small scalpels, they swiftly skin the salmon, remove its bones, and cut it into the exact portions specified by a Western supermarket chain on the other side of the world. Once the fish is filleted and in pieces, it is refrozen, packed onto a ship, and sent back to Europe or the United States. By the time it reaches the supermarket, our “fresh” salmon may have been traveling for an astonishing two months.