The Tokyo bitterling (''Tanakia tanago'') is a

temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

of the carp family (

Cyprinidae Cyprinidae is a family of freshwater fish commonly called the carp or minnow family. It includes the carps, the true minnows, and relatives like the barbs and barbels. Cyprinidae is the largest and most diverse fish family and the largest verte ...

). Taxonomically, it belongs to the subfamily

Acheilognathinae The bitterling-like cyprinids form the cyprinid subfamily Acheilognathinae. This subfamily contains four genera, although the Khanka spiny bitterling is often placed in ''Acheilognathus'', and at least 71 described species to date. Over half of th ...

. The species was first described as ''Rhodeus tanago'' by

Shigeho Tanaka was a Japanese ichthyologist and professor of zoology at the Imperial University of Tokyo. He published numerous works on fishes and sharks and co-authored a book on Japanese fish with famous American scientist David Starr Jordan. Publications J ...

in 1909. It is widely known as ''Tanakia tanago'',''Tanakia tanago''. Catalog of Fishes. California Academy of Sciences
. 27 August 2014. accessed 4 Oct 2014 although a 2014 study suggests it is genetically distinct from other ''

Tanakia ''Tanakia'' is a genus of cyprinid fish, consisting of five species that occurs in Eastern Asia. The type species is the '' Tanakia limbata''. Genus is named for Shigeho Tanaka (1878-1974), “accomplished” ichthyologist of the Imperial Unive ...

'' species, and warrants placement it the monotypic genus ''Pseudorhodeus''.

Distribution

In the wild, this fish is found only on the

Kantō Plain The is the largest plain in Japan, and is located in the Kantō region of central Honshū. The total area of 17,000 km2 covers more than half of the region extending over Tokyo, Saitama Prefecture, Kanagawa Prefecture, Chiba Prefecture, ...

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 ...

, an area near the capital city, Tokyo. The fish was formerly abundant in small streams, but its habitat has been overrun by people and pollution.

Threats

There is a real risk that it could become extinct in the wild. It also suffers from competition from the related but more aggressive

rosy bitterling The rosy bitterling or Tairiku baratanago (''Rhodeus ocellatus'') is a small freshwater fish belonging to the family Cyprinidae (carp), native to East Asia from the Amur River basin to the Pearl River basin. Females are about long and males ar ...

. Bitterlings lay their eggs in

freshwater mussel Freshwater bivalves are one kind of freshwater mollusc, along with freshwater snails. They are bivalves that live in fresh water as opposed to salt water, which is the main habitat type for bivalves. The majority of species of bivalve molluscs ...

shells. The Tokyo bitterling lays its eggs in only one type of mussel shell, limiting its chances of successful breeding. To help protect the fish, it has been declared a "national monument" by the

Japanese government The Government of Japan consists of legislative, executive and judiciary branches and is based on popular sovereignty. The Government runs under the framework established by the Constitution of Japan, adopted in 1947. It is a unitary state, c ...

, and this gives it special protection.

References

Tanakia Natural monuments of Japan Freshwater fish of Japan Endemic fauna of Japan Fish described in 1909 Taxa named by Shigeho Tanaka {{Acheilognathinae-stub