| Co-Investigator(Kenkyū-buntansha) |
NADEE Nivesh Technical Officer, Ecological Research Department, Thailand Institute of Scienti, 生態学部門(タイ国), 研究員
MAGTOON Wichian Associate Professor, Faculty of Science, Srinakharinwirot University, Thailand, 理学部(タイ国), 副教授
TAKATA Keisuke Research Associate, Faculty of Science, Shinshu University, 理学部, 助手 (90197096)
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| Budget Amount *help |
¥7,200,000 (Direct Cost: ¥7,200,000)
Fiscal Year 1990: ¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 1989: ¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 1988: ¥2,800,000 (Direct Cost: ¥2,800,000)
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| Research Abstract |
We have surveyed 36 localities and confirmed four specie of ricefishes inhabit in Thailand. Oryzias melastigma (McClelland) and O. javanicus (Bleeker) are distributed in the South Region along the coastal areas of the Andaman Sea. Two species are closely related by morphological, karyotypical and allozymic characteristics. Both species inhabit together in several localities, but no heterozygote was detected by morphological, karyotypic and isozyme studies. Thus, these two species seem to be sympatric and are isolated reproductively.
The Thai medaka, O. minutillus, is a small ricefish and is distributed in the North, Central, South, Southeast, and a part of the Northeast Regions. Populations from the South and the Northeast have 2n, 42 acrocentric chromosomes and NORs are located at the telomeric regions of an acrocentric pair (2n=42, NF=42, NORs-A). This karyotype is also found populations from Yunnan, China, and seems to be basic for O. minutillus (Ashida & Uwa, 1987 ; Uwa et al., 1988
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Populations from the North, Central and Southeast Regions are characteristic by having NORs-chromosomes of submetacentric type and NF is 44 in common, although their chromosome number decrease less than 42 according to the increase of large metacentric chromosomes. Karyotypes of the Southeast populations seem to be more basic than those of the North and Central populations, since the former have no or only one pair of large metacentrics, while the latter have four to seven pairs.
Isozyme analyses revealed that O. minutillus can be divided geographically into three genetic groups : the Northeast, Central and South Groups. The Central Group include populations from the North, Central and Southeast Regions. Genetic differences among these three groups are more than 0.083 in genetic distance, while those within each group is less than 0.027. No remarkable difference was detected genetically between the Southeast populations and the North and Central ones subdivided by karyotypic study. No morphological nor morphometric difference was detected among populations in Thailand, China and Myanmer.
Oryzias mekongensis is another small ricefish found from Yang Talat, Northeastern Thailand (Uwa and Magtoon, 1986). Karyotype study revealed that this species is a member of the biarmed chromosome group of Oryzias and seems to be more basic than the other members which are distributed widely in eastern Asia. Oryzias mekongensis inhabits in the Northeast Region ; the drainage area of a tributary of the Mekong. However, this species seems to be distributed widely in the basins of the Mekong and its tributaries from Thailand and Laos to Kampuchea and Vietnam. Father surveys must be conducted widely in these areas to reveal the species differentiation of this species. Less
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