Do you know that Salmon sushi did not originate from Japan? It was invented by Norwegian. And actually, domestic species of “salmon” in Japan cannot be eaten raw.
This orange colored flesh fish is called “Syake” in Japanese and looks very similar to salmon. Many people including Japanese think that salmon is the English name for Syake. They are in fact biologically related but not synonym. The local species in Japan are mainly Shirosyake(white syake) and Ginsyake(silver syake) and both are eaten cooked. Another way of differentiate salmon and syake is if the fish swam up the river back to its birthplace to breed. Syake does.
The main reason, as far as i know, Syake needs to be cooked is due to fresh water parasite problem as they make the journey up the river. While salmons from Norway commonly Atlantic salmon are farmed in sea water under controlled environment, thus could be eaten raw.
Traditionally Syake will be aged with salt, in fact most Syake in supermarkets here are salted, then grill on fire. Paring it with rice and miso soup make one of the most iconic Japanese breakfast. Many Japanese apartment have a small drawer type oven under the stove called fish grill. Quite particular about it huh.
Another interesting thing i find about syake is the way it is sliced. As it is mostly cooked with fish grill, it is sliced thin in contrast to how salmon for pan grilling is sliced. Pan grilled Salmon is commonly sliced with width so the skin side could sit comfortably on the pan sizzling towards crispiness.
Back in Mexico i used to buy a whole salmon and slice it myself to desired width and things were a lot easier. Today, I had to hold my syake with chopsticks up right in place over hot pan for the crispy skin. FOR THE CRISPY SKIN.