''Cambaroides japonicus'', also known as , is a species of

crayfish Crayfish are freshwater crustaceans belonging to the clade Astacidea, which also contains lobsters. In some locations, they are also known as crawfish, craydids, crawdaddies, crawdads, freshwater lobsters, mountain lobsters, rock lobsters, mu ...

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. They are small in size (6 cm) and grayish in color. Its front claws are much weaker than the American crayfish, which is an invasive species in Japan. The Japanese crayfish needs low temperature and high water purity, so they live in upper streams of rivers or lakes in highland regions. The distribution of Japanese crayfish comprises

Hokkaidō is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The la ...

and northern Tōhoku (the northern area of

Honshū , historically called , is the largest and most populous island of Japan. It is located south of Hokkaidō across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyūshū across the Kanmon Straits. The island separa ...

). The Environmental Agency (now Ministry of Environment) of Japan added it as a vulnerable species (

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

category) to the Red Data List in 2000. It is thought that the causes of its decrease are corruption of water quality and the spread of the

American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

crayfish '' Pacifastacus leniusculus'', which was imported in the 20th century and has steadily proliferated in northern Japan. Some suspect that this American crayfish carries some disease, such as the

crayfish plague Crayfish plague (''Aphanomyces astaci'') is a water mold that infects crayfish, most notably the European ''Astacus'' which dies within a few weeks of being infected. When experimentally tested, species from Australia, New Guinea and Japan were a ...

known in Europe, that eliminates endemic crayfish.

References

{{Taxonbar, from=Q13403251 Cambaridae Freshwater crustaceans of Asia Crustaceans of Japan Crustaceans described in 1841 Endemic fauna of Japan Taxa named by Wilhem de Haan