Fish can be eaten raw or cooked. Raw fish has been eaten in Japan for centuries. Japan has always fed its population from the sea and its rice fields. Putting a slice of fish on top of a portion of vinegar rice was a logical and tasty combination.
Potatoes were discovered in Peru and carried back to Europe in the 1500s by the Spanish conquistadors. Potatoes were eaten baked or boiled Nowadays they are mostly fried and called French fries.