The present study examined the preference in water depth for egg deposition of female, orangered variety medaka Oryzias latipes in order to obtain basic information for conservation of wild medaka. Substrates for egg deposition were set at various depths in experimental aquaria and male and female medaka were kept in the aquaria for seven days to observe spawning. The number of eggs and the egg deposition depth were recorded every day. The female medaka deposited eggs on the substrates at various depths but notably a significantly large number of eggs were deposited at shallow depths. These results indicate that female medaka gives a preference to shallow water depths for egg deposition.

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Occurrence of Neocaridina sp. has recently been reported in several places in eastern part of Japan. In order to know the impact of this introduced species on a native freshwater shrimp, Paratya improvisa, which occurs in similar habitats, we examined the distribution of N. sp. and P. improvisa in the Tsurumi River in 2014 and from 2016 to 2017. In riverine habitats, N. sp. occurred at almost all sites of examination. P. improvisa co-occurred at only two sites in 2014, and disappeared by 2016. In small ponds, N. sp. and P. improvisa co-occurred at one site and P. improvisa occurred at three sites in 2014. By 2017, N. sp. replaced P. improvisa at two sites and P. improvisa occurred only at two sites. We found that where two species co-occurred in almost the same number, N. sp. replaced P. improvisa within two to three years. It is thus important to prevent introduction of N. sp. into pond habitats where P. improvisa occurs by raising public awareness of the risky consequence of releasing non-native shrimps.

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The present study was conducted in two fumarole areas in eastern part of Hokkaido, northern Japan, to address a lack of knowledge about volcanic gas action that constrains the progress of succession. The number of species increased in proportion to the distance from fumaroles to adjacent forest zones. Indicator species were extracted using TWINSPAN. The indicator species were different between two topographically different study sites. This finding suggests that the sulfuric acid concentration in the soil varies depending not only on the distance from fumaroles but also on the elevation and this affects the plant distribution.

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