MEDAKA IN JAPANESE AGRICULTURAL WATER CHANNELS: GENETIC DIVERSITY AND CONSERVATION

Medaka is familiar to Japanese people as a small fish inhabiting paddy fields, agricultural water channels and ponds. This would be a consequence of adaptation of medaka to the agricultural management calendar during the long history of Japanese paddy production. However, medaka has been categorized as lvulnerabler in the Red List of Threatened Wildlife of Japan since 1999. Habitat deterioration due to the recent modernization of paddy fields and agricultural channels is suggested as a likely cause. On the other hand, medaka has a history of more than a century as an excellent experimental model vertebrate like zebrafish, and a draft nucleotide sequence of the whole genome was released in 2007. Such biological information can be successfully applied to the conservation of medaka in paddy fields and channels. We summarize genetic analyses of medaka including our own research to elucidate the effects of the modernization of agricultural water channels to the subpopulation structure of medaka. We also focus on the analytical methods such as PCR-RFLP, RAPD and microsatellite and examples of their use in population structure analyses of various organisms that are much more detailedly examined for conservation purpose than medaka. Conservation efforts of medaka in paddy fields would be most successful if they are harmonized with the paddy production there. Practices to promote production and add values to the products such as lmedaka ricer are mentioned in this context.