According to Executive Sushi Chef Kazunari Araki, sushi is not originally Japanese.
He says the combination of rice and fish began in the 3rd century along the Mekong River in Southeast Asia. It was cleaned, gutted and finally covered in a salt and rice mixture for several months in order to preserve it. When the fish was ready for consumption, the rice would be thrown away as it would have become too salty to eat.
By the 12th century, this process had spread to China, and subsequently Japan, where it was called narezushi. According to Araki, things changed in the 16th century, vinegar replaced salt, which was key to the development of sushi. This also led to the name sushi—which translates to “vinegared rice”.