The rosy bitterling or Tairiku baratanago (''Rhodeus ocellatus'') is a small freshwater

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

belonging to the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Acheilognathidae, the bitterlings. This species occurs in

East Asia East Asia is a geocultural region of Asia. It includes China, Japan, Mongolia, North Korea, South Korea, and Taiwan, plus two special administrative regions of China, Hong Kong and Macau. The economies of Economy of China, China, Economy of Ja ...

from the

Amur River The Amur River () or Heilong River ( zh, s=黑龙江) is a perennial river in Northeast Asia, forming the natural border between the Russian Far East and Northeast China (historically the Outer and Inner Manchuria). The Amur ''proper'' is ...

basin to the

Pearl River The Pearl River (, or ) is an extensive river system in southern China. "Pearl River" is often also used as a catch-all for the watersheds of the Pearl tributaries within Guangdong, specifically the Xi ('west'), Bei ('north'), and Dong ( ...

basin. Females are about long and males are . Their bodies are flat with an argent-colored luster. However, males change to a reddish (sometimes purple) color during the spawning season (March to September) which functions to attract females. This reddish color is similar to the color of a red rose, which is why it is called a rosy bitterling.

Ecology and reproductive system

Rosy bitterlings live in ponds (

reservoirs A reservoir (; ) is an enlarged lake behind a dam, usually built to store fresh water, often doubling for hydroelectric power generation. Reservoirs are created by controlling a watercourse that drains an existing body of water, interrup ...

) where freshwater

mussels Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, whic ...

are abundant. Farm ponds are an important habitat for not only rosy bitterlings, but also mussels and plankton. Freshwater mussels play an important role in rosy bitterling reproduction. The female rosy bitterling has a unique pipe about the same length as its own body, used for laying eggs on a specific spot of mussels. Usually, two or three eggs are laid at once and placed on the gill of the mussel. A male spawns into the gill cavity of the mussels right after a female lays eggs to ensure fertilization. Normally, a female lays eggs repeatedly at 6- to 9-day intervals about 10 times in a season. Eggs grow in the mussels' gills and juveniles stay inside the mussel about 15 to 30 days after fertilization. Eggs hatch after about three days when juveniles are about 2.8 mm long. The body has a unique shape resembling the bud of a

matsutake , ''Tricholoma matsutake'', is a species of choice edible mycorrhizal mushroom that grows in Eurasia and North America. It is prized in Japanese cuisine for its distinct odor. Etymology The common name and specific epithet, ''matsutake'', i ...

mushroom. Juveniles swim out of the mussel from the margin of the excurrent siphon. At this point, juveniles are about 7.5 mm long and about the same shape as adults. Usually, juveniles grow around 40–50 mm within one year, when they become adults. This and '' Rhodeus smithii'', sometimes called the Japanese rosy bitterling, were formerly considered conspecific. In 1942, rosy bitterling were accidentally introduced with grass ('' Ctenopharyngodon idellus'') and silver carp ('' Hypophthalmichthys molitrix'') from mainland

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

. Since the rosy bitterling was introduced, their population has been increasing dramatically all over Japan. Hybridization and subsequent gene introgression has been observed within these species in Kashima and Ogori. Because of these interbreeding events, the number of ''R. smithii'' has dramatically declined all over Japan and now is in danger of extinction. In 1994, ''R. smithii'' was on the

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...

as an

endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching, inv ...

, and now it is

critically endangered An IUCN Red List critically endangered (CR or sometimes CE) species is one that has been categorized by the International Union for Conservation of Nature as facing an extremely high risk of extinction in the wild. As of December 2023, of t ...

References

External links

Genetic markers distinguishing between the two subspecies of the rosy bitterling, ''Rhodeus ocellatus'' (Cyprinidae)
*
Taxonomy summary for ''R. o. ocellatus''IUCN Red List
{{Taxonbar, from=Q703072 Fish of Asia Rhodeus Fish described in 1866