User:HirokiTomida/sandbox

Ecology
Medaka is living in the small pond, swallow rivers and rice fields. They can survive in a wide range of water temperature (3℃-42℃), but they prefer a water temperature of 15℃-28℃. Since they eat the juvenile of mesquite and small plankton, they are known for the beneficial organism for humans. They produce 10-20 eggs per birth and they can produce eggs every day in the laboratory condition. They are seasonal breeding animals and usually lay eggs between spring and summer. They prefer to lay eggs around water grass and often prefer living in a rice field; they are known for Japanese rice fish. The egg usually requires 4-10 days to hatch. They have an advanced renal function, which enables them to live in saltwater and brackish water. The average life span of this species in the wild is estimated to be 2years. Yet, in laboratory conditions, they will survive 3-5 years. They live in herds, and they can recognize other fish's face.

Status
Medaka is listed as least concern species by IUCN red list. The justification of this categorization is that this species is living in widespread habitat(755,000 km2) and relatively abundant in the various habitat. Whereas, Medaka is considered endangered species by Ministry of Environment in Japan. Many local communities try to preserve wild Medaka in Japan

Concerns
There are two major conservational concerns about Medaka, habitat degradation and hybridization with domesticated Medaka(Himedaka). Due to modernization of rice field and irrigation canal, the optimal place for Medaka's reproduction is massively decreasing. In addition, recent studies confirmed that Himedaka was introduced into many local regions by artificial release. This will eliminate local genetic adaptation of each sub-population of Medaka. Furthermore, Since Himedaka has vivid orange body color, the hybrid will attract more predators and decrease the total population of Medaka. In 2011, the researchers discovered that almost 15% of wild caught Medaka in Nara had Himedaka specific gene marker. . In addition to these concerns, invasive species like mosquitofish competes with Medaka by sharing same habitat. The study reports over 70% Medaka was injured their tail fins by attack from Mosquitofish. The damage at anal fin will decrease offspring by preventing courtship behavior. Recently, the transgenic line was brought from Taiwan for commercial purpose. This transgenic line was introduced a gene which can express the green fluorescence and make body glowing. Now, this transgenic line was released into the wild and causing genetic pollution .There is no comprehensive study of population size of Medaka. But the genomic analysis of one of Medaka sub-population indicates that their effective population size is around 25000-70000.

Popularity in Japan
Medaka has been popular domesticated pet in Japan since at least 200years ago. Recently, Medaka gained further popularity in Japanese society. Some strains costs over 1million yen(approximately $10,000 in 2019 currency exchange rate) but common line like Himedaka can be purchased by 50yen(50cent in $) per fish .Currently, there are 456 commercial strains are available. Medaka is not only popular for domesticated pet but also widely seen in educational and cultural scene. The elementary school students often raise Medaka in the class in order to learn how to raise live organism and appreciate the life.

Inbreeding lines
Inbreeding strain is helpful and facilitate to conduct genetic research due to reduction of heterozygous sites in the genome. Medaka is relatively easy to establish inbred lines unlike other model species like Zebrafish and mice. Since 1979, the researchers have generated 10 inbred strains. This inbred lines made Medaka one of model species for scientific research by .The researchers also generated 111 inbred lines from single population.

Understanding Sex and Reproduction by Medaka
Medaka reproduce on daily basis, which is optimal trait to study reproduction biology. The researchers study HPG axis activities intensively in this species. Moreover, Medaka is first non-mammal vertebrate species that sex-determination gene(dmy) was identified and their sex is reversible by sex steroid manipulation and they exhibit morphological sexual dimorphism exist between male and female. Furthermore, some methods such as ovariectomy and changing light-dark cycle are developed to study the mechanism of reproduction in Medaka.

Origin of Southern＆ Northern Population
Phylogenetic analysis shows that the southern population was derived from Northern Kyushu area and spread into Honshu island. On the other hand, Northern population was derived from Tango and spread alongside with Japan sea coast. Orizias Latipes is known to have nine sub populations, East Japanese type, East Setouchi type, West Setouchi type, Saninn type, Northern Kyusyu type, Osumi Type, Ariake type, Satuma type and Ryukyu type. These sub-populations are mixed each other due to artificial releasing and decreasing local genetic diversity.