Kaisendon is a bowl of rice topped with several raw fish. This kaisendon consists raw sea urchin, raw scallop and salmon roe. The salmon row's is actually marinated with soy sauce and sake. Salmon roe is called IKURA in Japanese but it is adopted from Russian word for caviar.
Kaisendon is not considered as a type of sushi due to the rice is not flavored as sushi rice(vinegar & sugar). If the sushi rice is topped with raw fish, the meal is called kaisenchirashi.
The word kaisen means fresh seafood. Don means bowl and chirashi means spread.
Kaisendon is a popular meal in Hokkaido, especially for tourists outside of Hokkaido. In Hakodate city, there is a special street specialized for kaisendon diners. These diners offer several types of kaisendon with dozens of combinations of raw fish. Please check the menu carefully before you order your meal!