Is sushi and sashimi a Japanese invention?

Sushi originated from China.

Sushi is also called 鮨 or 鮓, which appeared in the Chinese dictionary in 4BC. 鮨 means minced fish. 鮓 means the preservation (fermentation) of fish with salt and rice. Eventually the Chinese stopped preserving food with rice and in the Ming dynasty, sushi disappeared from Chinese cuisine.

The word "鮨" first appeared in the Japanese dictionary in 718AD but it had a different meaning. Then in 927AD, the word appeared again in literature and it was used to described the preservation of fish using salt and pressure (ie. placing heavy objects on top of the salted fish). Because this process took too long, people began using soaking the fish in vinegar to instead. Sushi nowadays simply means adding vinegar to rice and serving it with a piece of fish/meat/vegetable.

The sushi we eat now are developed in Japan, with the exception of some of the rolls that are popular in western countries. California roll was "invented" in North America and I am sure those rolls with philly cream cheese were also invented in North America, too.

http://www.asianartmall.com/originsofsushi.htm
according to this source it comes from China.

Originated in the deepest jungles of Africa.

sashimi is japanese.
sushi is american