User:HirokiTomida/Japanese rice fish

Conservation status of Medaka
Medaka is categorized to be endangered species by ministry of environment in Japan. 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 decreased. In addition, recent studies confirmed that Himedaka was introduced into many local regions by artificial release. This will leads 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 conflicts with Medaka by sharing same habitat. The study reports over 70% Medaka was injured their tail fin by attack from Mosquitofish. The damage at anal fin will decrease fertility rate. There is no comprehensive study of population size of Medaka. But the genetic analysis of one sub-population of Medaka indicates that their effective population size is around 25000-70000.

Inbreeding lines
Medaka is relatively easy to establish inbred lines. Since 1979, the researchers generated 10 inbred strains. This inbred lines make genetic research easier .The researchers also plan to generate 200 inbred lines from single population.

Understanding Sex and Reproduction by Medaka
Medaka is first non-mammal vertebrate species that sex-determination gene(dmy) was identified and their sex is reversible by sex steroid manipulation. Moreover, the characteristics of Medaka that reproduce daily basis is optimal trait to study reproductive biology and sexual dimorphism and some tools such as ovariectomy and changing light-dark cycle. Since Medaka produce eggs everyday, it is also desirable to measure HPG axis activities.

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.