Note that Japan already traded with the Nordics quite extensively, including some more traditional fish options, and the parasite-free salmon was promoted on top of a well-established trade that Norway wanted to expand with a fish they produced in abundance.
That also makes sense from a tech standpoint. Ocean salmon aren’t safe for sushi, they have have too many parasites. You need to either catch them from the river they spawn in before they get to the ocean for the first time, or from a lake, which iirc Japan didnt have any lakes with salmon populations. (Harvesting from streams at scale is also a bad idea, because they wont have had a chance to breed so youre going to be killing off a portion of the population)
Even then its dicey; for raw, you really want farmed salmon, that are bred in a tank, with no parasites in the water.
So it wasnt until global shipping and really the rise of factory farmed fish, that safe enough populations of salmon existed.
Japanese salmon nigiri weren’t a thing until the 1980’s when Norway launched a trade push to open up a new market there.
Note that Japan already traded with the Nordics quite extensively, including some more traditional fish options, and the parasite-free salmon was promoted on top of a well-established trade that Norway wanted to expand with a fish they produced in abundance.
That also makes sense from a tech standpoint. Ocean salmon aren’t safe for sushi, they have have too many parasites. You need to either catch them from the river they spawn in before they get to the ocean for the first time, or from a lake, which iirc Japan didnt have any lakes with salmon populations. (Harvesting from streams at scale is also a bad idea, because they wont have had a chance to breed so youre going to be killing off a portion of the population)
Even then its dicey; for raw, you really want farmed salmon, that are bred in a tank, with no parasites in the water.
So it wasnt until global shipping and really the rise of factory farmed fish, that safe enough populations of salmon existed.
Modern flash freezing also keeps the quality high while killing the parasites.
Afaik salmon are farmed in large cages in the sea (fjords)