Salmon is a relatively new ingredient for sushi. Until recently, salmon was never eaten raw or even seen in sushi bars in Japan.
The main reason that salmon made a late debut in the sushi bars in Japan is that a low percentage of them contained parasites, since it dwells in the rivers during some of its life time and therefore it was very risky to serve it.
In the early days of the sushi boom in the US, some sushi chefs in California used to cure the salmon like the regional masu sushi (pressed trout sushi from the northern region of Japan) to kill the possible salmon parasites, however it destroyed the delicate taste and texture of raw salmon, and was not so popular.
Norwegian smoked salmon killed possible parasites in raw fish by cold smoking, but it was not adaptable for sushi, and Japanese cuisine had nothing similar to it.
However, the Ainu culture which live in northern Japan were accustomed to eating raw salmon (luibe) for hundreds of years. By trial and error they discovered that freezing fresh fish in the snow for a few days prevented them from getting stomach aches.
Researchers later found out that the Anisakis parasites that salmon carry are completely killed if they are frozen for 48 hours. Some powerful freezers require only 24 hours. Therefore, food poisoning by consuming fish is very rare now. As a result, salmon is becoming one of the most popular sushi fish in Japan right now.
Often, if an infected fish is eaten, the parasites may be digested with no ill effects. Adequate freezing or cooking fish will kill any parasites that may be present.
The name sake is believed to originate from the verb sakeru or to tear. The salmon was always cooked in Japan until recently and was one of the fishes that tore, or “flaked” easily when cooked. Thus the word sake (abbreviated term for tear) eventually took its place.