Japan's seas and rivers contain around 3000 species of fish . The waters around the Ryukyu Islands are home to subtropical anemone fish, parrot fish, wrass and spiny lobster as well as numerous species of shark, turtle and whale. The ocean south of Shikoku and Honshu teems with life, from loggerhead turtles and butterfly fish to dugongs and porpoises, while the colder waters washing around Hokkaido bring with them some of the larger whale species - humpback, grey and blue whale - from the Bering Sea and north Pacific.

Ocean currents play a crucial role in this diversity. Warm water flowing round Taiwan and up through the Ryukyu island chain splits into two upon reaching the island of Kyushu. The branch flowing north into the Sea of Japan, between Japan and China, is known as the Tsushima-shio, while the Kuro-shio or "Black current" follows the more easterly route. Bearing down from the north, hitting Hokkaido's northern and eastern shores, comes the cold, nutrient-rich Oya-shio or Kuril current. Where it meets the Kuro-shio off northeastern Honshu, abundant plankton and the mingling of cold- and warm-water species create one of the richest fishing grounds in the entire world.

The United Nations Food and Agriculture Organization estimates that Japan consumes thirty percent of the world's fresh fish. To offset problems caused by over-fishing , the Japanese fishing fleet has been cut by a quarter in recent years. This has not, however, stopped the import of fish into Japan from other Southeast Asian countries which, for their own economic reasons, are less concerned about protecting fish stocks.