Medaka or ricefishes, adrianichthyids of the order Beloniformes have been believed a single species by its superficial body shape for more than 160 years, since 1846 when “Fauna Japonica” had published by Temminck and Schlegel. In the 1980s, allozyme studies have shown that Japanese wild population of Medaka, could be divided into two genetic groups, the Northern and the Southern populations. Oryzias latipes（Temminck and Schlegel, 1846）was originally described as Poecilia latipes from Siebold’s collection now at the NCB Naturalis. However, considering the lectotype and paralectotypes of O. latipes, it is showed that O. latipes is only identical with the Southern population in the body shape. The Southern population is found in freshwaters the Pacific coast of eastern, western and southern Japan. Oryzias sakaizumii Asai, Senou and Hosoya, 2011, it has been generally regarded as the genetic variation, the Northern population distributed in the northern coast of the Sea of Japan, within a single species O. latipes. However, the Northern and Southern populations parapatrically coexist the same river drainage, which is the distributional boundary zone for these populations. Both have also been reported to exhibit different schooling behaviors. This implies the ecological diversification between both populations. In addition, frequencies of mitochondrial cytochrome b gene mitotype there have been showed an establishment of reproductive isolation. Furthermore, this species is distinguished from O. latipes by having some diagnostic characters such as notched dorsal-fin or melanophore network, confirming that the Northern population is a distinct species, O. sakaizumii. Therefore, it should be recognized that the Northern and the Southern populations differentiate in a specific level.

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The 4 morphological criteria for a new species of Japanese medaka, “Oryzias sakaizumii” proposed by Asai et al.（2011） were examined in males of 75 closed colonies derived from wild populations caught in the Japan islands and maintained for longer than 30 years in laboratory. Males of 14 colonies from the Northern population medaka （“O. sakaizumii” ） were identified only by one criterion: “dense network of melanophores along each scale margin on body side” , and it was impossible to distinguish the males of the Northern populations from those of the Southern population（O. latipes） by the other 3 criteria. In addition, it has been known that hybrid populations between the Southern and the Northern populations are present in Tajima-Tango area in wild, providing the evidence for crossing of the two medaka populations in Japan in this area. In this report, the author concludes that the Southern and the Northern populations of Japanese medaka are the same species and the Northern population is a geographical subspecies of O. latipes）, since both populations have crossed naturally and the confirmed morphological difference between them is slight, not giving a clear implication that these populations have differentiated into separate species.

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Allozyme studies demonstrated that wild medaka consist of four genetically distinct groups: the Northern Population from the Sea of Japan coast of eastern Japan, the Southern Population from the Pacific coast of eastern Japan and from western Japan, the East Korean Population from eastern and southern Korea, and the China-West Korean Population from China and western Korea. The boundaries separating the geographic distributions of these four groups are clear, and major divergences among groups were observed. Nucleotide sequences of the complete cytochrome b gene clarified the phylogenetic relationships among four groups. The phylogenetic tree based on cytochrome b nucleotide sequences indicated Japanese three major clades（A, B and C） . The geographic distribution of mitotypes in clades A and B was fully concordant with the Northern and Southern Populations defined by allozymes, while mitotypes in clade C were found only in the Kanto district. For Korean and Chinese medaka, phylogenetic trees indicated two major clades, D and E, which were different from the Japanese clades（A, B and C）. The geographic distribution of the mitotypes in clades D and E was consistent with the China-West Korean Population and the East Korean Population, respectively, as defined by allozymic analyses. Subsequently, the China-West Korean Population was described as a new subspecies O. latipes sinensis by morphological differences in 1989, and recently, the Northern Population as a new species O. sakaizumii. Here I propose “O. latipes complex”, a species complex including four distinct species, O. latipes（Southern Population） , O. sakaizumii（Northern Population） , O. sinensis（China-West Korean Population）, and Oryzias sp.（East Korean Population）, as the name corresponding to traditional “O. latipes”（the medaka or Japanese medaka）

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　Shellfish and fish samples were collected at Rayong, Thailand a month and four months after an oil spill in 2013. Their polycyclic aromatic hydrocarbons（PAHs）and alkylated PAHs（alkPAHs）concentrations were analyzed due to their toxicity. While Σall PAHs concentrations in shellfish were almost lower than 200 ng/g except for Stn.1 at Samet Island, where they ranged from 28900 to 134000 ng/g. The diagnostic ratios of PAHs suggest that the sources of these PAHs in aquatic organisms were petrogenic. Σ PAH concentrations in fish and squid caught by set-net ranged from 3.74 to 5.31 ng/g. Benzo（a）pyrene, a carcinogenic PAH, was detected in oyster collected at Stn.1 ranging from 43.1 to 63.9 ng/g, which is a higher level than permitted by EU criteria. However, their levels were much less than the criteria in shellfish and fish from other stations.

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It is important to assess the recovery potential of algal population after the temporal pesticide exposure in natural aquatic environment. In this study, we investigated the temporal variability of delayed fluorescence（DF）of chlorophyll as the indicator of algal physiological state during the exposure period and the subsequent recovery period. The tested substance was 3,5-dichlorophenol（DCP）and the test species were a green alga Pseudokirchneriella subcapitata and a diatom Navicula pelliculosa. After the 72-h DCP exposure period, algal cells were inoculated into a clean medium and then the algal growth was monitored for around 10-d. The DF intensity per biomass（DF/biomass） decreased with increasing DCP concentration during the exposure period. In the recovery period, algal growth rate recovered with the recovery of DF/biomass. The values of DF/biomass were well-correlated with the algal growth rates, and the correlations during the exposure and the recovery periods showed similar pattern. This indicates the potential use of DF/biomass as the indicator of population recovery status.

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Running laboratory toxicity tests is costly and time consuming, and therefore extrapolations based on the limited toxicological information are necessary in performing the ecological risk assessment/management of chemical substances. Two widely-used extrapolation methods are the use of assessment factors（AF）as adopted in, for example, the Japanese chemical substances control law, and the other is the application of species sensitivity distribution（SSD）. In this study, we theoretically investigated the performance of two extrapolation methods by comparing predicted no effect concentrations（PNECs）derived by the methods. For the comparison, two criteria were adopted. One criterion considers that an extrapolation method which derives a PNEC smaller than the hazardous concentration for 5% of species（HC5）with higher possibility is better. Another criterion considers that an extrapolation method which sets a PNEC closer to the HC5 is better. The AF method adopted by the chemical substances control law was superior under the first criterion but was inferior under the second criterion. Our results show that there is no unique assessment method that always defeat the others, and thereby suggests that a better strategy may be required to compile the merits of existing extrapolation methods depending on data and goal of protection in risk assessments.

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