Marginal areas in small to medium streams are important as spawning and nursery habitat for freshwater fish, and then there have been concerns about negative effects of covering stream banks with concrete revetments on freshwater fish. It has been reported that water-column fish were negatively influenced by the covering, but little reported for benthic fish. Streamside vegetation can alter substrates, likely relating to benthic fish, from those that prefer sand or mud to those that prefer gravel. Thus, the effects of the covering may differ depending on the life type and species composition of freshwater fish. We examined fish assemblages in reaches with three types of both stream edges: stream water ran along concrete revetments (CC), a concrete revetment and a sand bank (CS), and sand banks (SS). The study reaches were located in small to medium streams which join to the midstream and downstream of the Ibi and Nagara Rivers, and species composition may differ depending on longitudinal positions. Species richness and individuals of the water-column fish were lower in CC than in SS, whereas individuals of the benthic fish preferring gravel were highest in CC. Species composition in CC differed from that in CS and SS in the streams joining to downstream but not in those to midstream. Thus, effects of the covering depended on the life type of freshwater fish and the longitudinal position. The community structures, represented by the species richness, individuals and species composition, in the reaches along a concrete revetment and a sand bank (CS) tended to be similar to those in the reaches along sand banks (SS), suggesting that installation of concrete revetments limited to one-sided bank may mitigate the impact on fish assemblages in small to medium streams.

The purpose of this study is to clarify the effect of anthropogenic load via groundwater on the appearance of Sphagnum subnitens var. nitidum hummock. In August 2014, in the Yufutsu mires in Hokkaido, a loaded area with upland fields and a control area were established. Next, we investigated the hydrochemical environments of groundwater, and analyzed the relationship between the appearance of S. subnitens and the environmental variables. The precipitation contribution ratios of Ca^2＋, Mg^2＋, and K^＋ in the groundwater of the loaded area were lower than the control area, indicating the anthropogenic load of these ions. In non-metric multidimensional scaling (nMDS), the S. subnitens community distribution showed a negative relationship with pH, concentrations of minerals (Na^＋, Ca^2＋, Mg^2＋, K^＋, and Cl^－) and inorganic nitrogen (IN). Logistic regression analysis showed that the appearance of S. subnitens was negatively related to pH, minerals, IN, competitive species, and water level, which was in generally good agreement with nMDS. The estimated ranges of appearance of S. subnitens were pH≦6.5, Na^＋≦7.8 mg L^－1, K^＋≦2.6 mg L^－1, Mg^2＋≦3.0 mg L^－1, Ca^2＋≦13.9 mg L^－1, Cl^－≦6.6 mg L^－1, IN≦0.4 mg L^－1, water level≦＋3.2 cm, and competitive species≦103.9 % in coverage. Some of S. subnitens also appeared in the higher outside the range of appearance, suggesting that the water quality inside the hummock is different from that of groundwater. As a result of path analysis, the effect of each variable on the appearance of S. subnitens was higher in the direct effect than in the indirect effect through the exclusion by competitive species. Therefore, it is important to maintain the hydrochemical environments within the range of the occurrence and to control competitive species in order to conserve S. subnitens.

While social demands for understanding the current status of biodiversity and for its conservation are increasing, biodiversity in river ecosystems may be decreasing rapidly. The importance of setting targets and goals when restoring and rehabilitating ecosystems has been pointed out, and one effective method is to use information on past species distributions. Then, we identified a list of "lost species" of freshwater fishes that have never been found since 1990, although they were recorded in 1978, by organizing the National Survey on Natural Environment conducted in 1978 and the ongoing census as the National Census on River Environments since 1990. We compared the results of the two surveys in 102 of the 109 class A river systems and found that native fishes recorded in 1978 but not collected since 1990 were two species, Pungitius sp. (Musashitomiyo) and Aphyocypris chinensis (Hinamoroko). In 39 river systems, all the native species recorded in the National Survey on Natural Environment were collected in the National Census on River Environments. However, for 63 river systems, one to ten species/species groups were not collected, and these species in each river system were listed as a list of "lost species". This list contained various species, such as diadromous and peripheral as well as pure freshwater fishes, including also many common species not listed in the national Red Lists. The species listed on our "lost species list" are not necessarily extinct, but should be endangered. Therefore, in each river system, confirmation of the presence/absence of the listed species and implementing conservation measures for them are needed before they become locally extinct. In addition, it will be possible to set clear targets and goals for the restoration and rehabilitation of river ecosystems based on information on the habitat and life history of these fish species.

Few studies have investigated the response of estuarine ecosystems to high dam removal with embankment heights exceeding 15 m. Focusing on the Arase dam removal project in the Kuma River system, we surveyed the intertidal zones in the Kuma and Mae River estuaries between 2011 (before the removal) and 2018 (after the removal) to assess the changes in sediment conditions and benthic fauna. A total of 14 surveys were conducted in the fall and spring, with a total of 178 sites, of which 138 sites were used for the analysis. Coarse-graining was observed in the spring of 2012 and 2014, which may have been associated with the permanent gate opening of the Arase Dam in 2010 and the flush in 2011. The results of the benthos community analysis indicated that the changes in the fauna at each site were not based on the specific survey period or season. Therefore, it is possible that the dam removal had no significant impact on the estuarine benthic community. However, the number of infaunal species in both estuaries increased from the fall of 2012 to approximately 2014. During the same period, the occurrence of the mud and ghost shrimps increased, as were the number of symbiotic species that inhabit these shrimp burrows. The coarse-graining of the sediment in the intertidal zones may have expanded the habitat of these species, which are commonly found at sand and sandy mud flats. Since the relationship between the observed changes in the benthos community and the Arase Dam removal has not been fully verified, the dynamics of sediment transportation during the removal should be further evaluated.

Ayu (Plecoglossus altivelis), the most important fish in Japan as a food item, as an export, etc., is used not only as a food item but also as a target of recreational fishing. Stocks of P. altivelis have been affected by releases from fishing cooperatives and fisheries research institutes, but many rivers have maintained their resources naturally through production. Plecoglossus altivelis feed on algae in the riverbed, which increases the levels of certain organisms such as cyanobacteria and benthos. This species of fish is strongly associated with the algal and benthic fauna in rivers, occupying an important position in the ecosystem. Therefore, the conservation of the spawning ground environment of P. altivelis and maintenance of its resources are important for the preservation of the river ecosystem and environment. It is generally well known that alewives spawn on gravel bottoms in middle and lower river rapids in late fall. However, because ayu is a widely distributed species and its spawning tendencies differ from river to river, greatly increasing the amount of information available, data regarding the spawning behavior of ayu have not been sufficiently organized and comprehensively examined. Therefore, we reviewed the spawning grounds of ayu fishes with the aim of summarizing this information and creating guidelines that contribute to the conservation of the river environment. In this study, we comprehensively collected literature on studies that describe the spawning of alewives published between 1895 and 2019, extracting and organizing the physical conditions of their spawning environments from a total of 339 articles. Most of these references used data from natural river spawning grounds, but examples of experiments in artificial rivers and data from artificially created sites were also included. The physical conditions were extracted and organized as follows: spawning season, spawning ground velocity, water depth, riverbed material, penetration (riverbed softness), and egg burial depth. These data provided an overview of the general physical conditions of P. altivelis spawning grounds. Based on combining these five physical conditions, physiological information of P. altivelis, and physical consideration of riverbed environment, we have clarified that the place used by P. altivelis as a spawning habitat is rapid with soft and unstable gravelbed. In addition, the place is defined as "temporary spawning habitat" that is temporarily formed in the river depending on the flood disturbance.

We investigated upstream migration of ayu Plecoglossus altivelis, by attaching PIT tags to 300 wild individuals captured at Naga Dam, approximately 30 kilometers away from the river mouth of Miya River, Mie Prefecture, Japan. The tagged individuals were released on 25 April, 2018, and their upstream migrations were recorded by using a PIT tag reader set up at a fish way in Takihara Dam, located in the lower reach of a tributary, Ouchiyama River, flowing into the middle reach of Miya River. During 3 May to 5 July, 2018, a total of 24 individuals （8 % for the tagged individuals） were recorded by the recorder. The earliest ascending was observed 8 days after releasing, while the latest was observed 71 days later. A generalized additive model revealed that the ascending of ayu was positively related to the water level of Miya River and the amount of water taken from Takihara Dam. These findings suggest that most of the upstream migrants pass by the junction of Ouchiyama River and the mainstream of Miya River, and stray into an upstream pool located directly beneath of Misedani Dam which fragments Miya River for electricity generation. Since no fish way is constructed in Misedani Dam, most stock of ayu seem to have not been utilized as fisheries resources. Artificial transfer to the upper stream of Miya River and/or Ouchiyama River may be beneficial to utilize the stock. Leading the fish up to Ouchiyama River may also be profitable.

The importance of biodiversity conservation in paddy field ecosystems is widely recognised, as is the importance of maintaining a water body in the paddy field throughout the year. This study monitors the ascending and descending of a fish community in a fish-retreat ditch constructed in a paddy field near the sea in Kunitomi District, Obama, Fukui Prefecture, Japan. The fish-retreat ditch is not only a spawning ground but also an overwintering ground for Misgurnus anguillicaudatus and Cobitis sp. BIWAE type A (pure freshwater fish). The fish-retreat ditch will be not only a growing ground but also an overwintering ground for Tribolodon hakonensis, Gymnogobius urotaenia (amphidromous fish) and Acanthogobius flavimanus (brackish water / marine fish). It is considered that the fish-retreat ditch, which has less environmental changes than rivers, drainage canals and oceans, has become a cradle for many fish.

Considering conservation measures for Lefua echigonia populations inhabiting planned areas of the development project in valley-bottom paddy fields in two river basins of midwestern Aichi Prefecture in Japan, the genetic diversity was analyzed for seven sites in this region and one site in another region using their mitochondrial DNA (mtDNA) D-loop and microsatellite DNA. All specimens were found to have the same sequence among seven sites, and they belonged to the previously known populations identified in the Tokai region. Microsatellite analysis revealed that each site was genetically coherent for each river basin, and there was a difference in the degree of genetic divergence between the two river basins in the same water system based on the calculated genetic differentiation (F_ST) and STRUCTURE analysis. One site affected by the project and another neighboring site had very low genetic diversity and middle-range genetic divergence was observed between them. However, it was due to fragmentation and miniaturization of the habitat caused by the paddy field development, and these two sites were identified as belonging to the same genetic group. Therefore, it is considered effective to ensure habitat and genetic exchange by treating both sites as one.

In Toyooka City, Hyogo Prefecture, fallow-field biotopes (hereinafter FFB) have been produced by flooding fallow fields throughout the year to maintain habitats for various aquatic plants and animals, including feeding habitats for the oriental stork Ciconia boyciana. In this study, specifically, we clarified the poorly understood habitat status of Odonata larvae, aquatic Hemiptera, aquatic Coleoptera, and frogs at the FFB. The effects of the FFB on the conservation of local aquatic animal communities were also evaluated by comparing habitat statuses in the FFB with those in the surrounding paddy fields and multitopes (i.e., earth ditches laid alongside the paddy fields). Results showed that many Odonata larvae inhabiting an irrigation pond were found in the FFB, while several peaks in the annual polyploidy of Odonata taxa were also observed. For many species of aquatic Coleoptera, larvae were less abundant in the FFB than in the surrounding paddy fields and side ditches; however, the number of adult taxa increased rapidly after August. In addition, the regal pond cruiser Epophthalmia elegans elegans, water stick-insect Ranatra chinensis, and diving beetle Eretes griseus were captured in the deep waterbody of the FFB in autumn. These results suggest that the FFB serves as a refuge and habitat in the nonbreeding season, and as a wintering site for a variety of aquatic insects; however, its function as a breeding site may not be as important as that of the paddy fields and multitopes, especially for aquatic Coleoptera. Nevertheless, the FFB is an important breeding site for some aquatic animals including the Japanese brown frog Rana japonica and annual polyphagous Odonata taxa. Overall, this study suggests that the coexistence of various water bodies, such as temporary paddy fields and side ditches, with year-round flooded biotopes effectively conserves the diversity of aquatic insects and frogs in the study region.

Margaritifera laevis, an endangered species of freshwater bivalves, inhabit the upper reaches of rivers. The survey site for this study was a small river, with about 1-4 m width in a river basin dotted with springs in inland Iwate prefecture. Four survey points were established, spanning about 6.5 km. For this study, diurnal increases in Cl^－ and Na^＋ concentrations were observed during winter in the survey area upstream of the target river. The maximum value during the study period was 453 mg Cl^－ L^－1. Concentrations exceeding 283 mg Cl^－ L^－1, equivalent to EC 100 mS m^－1, were recorded 12 times in 2018 and 7 times in 2019, which suggests that sodium chloride, an anti-freezing agent, adhered to car bodies and subsequently flowed into the river from a car wash near a highway interchange upstream of the study area. Based on results of transplant surveys conducted over a two-year period at three locations (upstream, midstream, and downstream of the study river), almost no growth of the M. laevis was observed in the upstream area near the car wash. However, annual growth in the middle and downstream study areas was around 1.5 mm, which was less than earlier findings of 3-5 mm. Further investigations must elucidate factors affecting this species' habitat.