The population of Yamato salamander, Hynobius vandenburghi, is declining due to habitat loss and predation by alien species. In this study, we revealed the predation on H. vandenburghi by the invasive crayfish Procambarus clarkii in Koka City, Shiga Prefecture, using DNA analysis with direct sequencing of mitochondrial cytochrome b gene. These results suggest a new looming crisis for the H. vandenburghi in Koka City. P. clarkii have been reported in other H. vandenburghi breeding habitats. Further studies will be required to assess the negative effects of P. clarkii on H. vandenburghi.

We captured largemouth bass, an invasive alien species, in 43 floodplain water bodies of the Kiso River using fixed nets for a total of 5 days in September 2023. We identified prey species found in the stomachs of largemouth bass captured from 18 floodplain water bodies. The stomach contents of 27 largemouth bass (mean total length: 138.1±33.9 mm, range: 70.4–194.2 mm) contained 14 fish species, mainly Cyprinidae, as well as shrimp and insects. In addition, 24 largemouth bass, including individuals presumed to be an initial year class, predated fish. The floodplains in river channels serve as spawning and nursery grounds for native fish species. However, as these areas are also rich in small fishes that juvenile largemouth bass can prey on, they may also provide favorable habitats for the growth and development of largemouth bass. Therefore, the negative impacts of largemouth bass on the fish communities in this area are likely to be significant.

Middendorf’s Bean geese (Anser fabalis middendorffii) winter in Katano-kamoike, a Ramsar site in Kaga City, Ishikawa Prefecture, where they forage on rhizomes of Wild rice (Zizania latifolia) and fruits of Water chestnut (Trapa natans var. quadrispinosa). Water chestnut is an annual floating-leaved plant species that germinates in April and grows rapidly after June. The leaves, located at the outer edge of the rosette, rise above the water surface and fully expand by the end of July. Blooming begins in early July and peaks in August, and after local people drain the pond water, the plants deteriorate by the end of August. I collected Water chestnut fruits at the end of August or the beginning of September for nine years, between 2009 and 2022. I recorded the density, size, and dry weight of the fruits, as well as the rosetta density, and investigated the effects of weather conditions on them. Significant negative correlations were found between the density of Water chestnut fruits and rainfall in July. The dry weight of the fruits showed significant positive correlations with the daily average temperature and with the sum of the daily maximum temperature for June to July. The size of Water chestnut fruits had a significant positive correlation with the monthly maximum temperature in June and the sum of temperatures from June to July. Significant negative correlations were observed between the density of rosettas and the monthly minimum temperature in August and the cumulative temperatures for July to August. The number of Middendorf’s Bean geese recorded during autumn and winter had a significant negative correlation with the size of Water chestnut fruits. Based on previous studies and the phenology of Water chestnuts in Katano-kamoike, air temperatures affect the timing of bloom, the timing when rosettas are fully grown, and the rate of starch synthesis in Water chestnuts, which may result in increased fruit density, size, and weight. Precipitation likely affects the density of Water chestnut fruits by inhibiting fruit growth due to rain clouds blocking sunlight. The number of Middendorf’s Bean geese was only negatively correlated with the size of the fruits, which may reflect the geese's preference for smaller-sized Water chestnut fruits. For the conservation of Middendorf’s Bean geese, further studies on the relationship between weather conditions and other food resources, as well as research on suitable food species for wintering Middendorf’s Bean geese, are important.

We collected Tanakia lanceolata and Acheilognathus tabira erythropterus in Hokkaido, Japan, in 2017. This report represents the first record of both species in Hokkaido. Mitochondrial DNA analysis (cytochrome b region) revealed that T. lanceolata was introduced from the Sea of Japan side of the Tohoku region, while A. t. erythropterus was introduced from the Kanto region. Surveys in 2022 and 2023 have collected more than 100 specimens of T. lanceolata and confirmed that they are successfully reproducing using the freshwater mussel Inversiunio jokohamensis as a host.

We morphologically distinguished the native and non-native lineages of Misgurnus anguillicaudatus and investigated the distribution of both lineages in the Yodo River water system in Kyoto Prefecture. Our investigation showed that many native lineages were found outside of the Kyoto Basin. However, the distribution of native lineages within the Kyoto Basin was localized and non-native lineages were widespread. Additionally, an alien species of loach Misgurnus dabryanus was found in the Yodo River water system in Kyoto Prefecture for the first time.

We analyzed the stomach contents of an alien fish species, Korean aucha perch Coreoperca herzi, which has invaded the Oyodo River system in Miyazaki Prefecture, Japan. The analysis showed that aquatic insects were an important food resource for all size classes, with mayflies being particularly important prey. The feeding habits suggest a direct negative effect of predation on aquatic insects, and also competition with native fish species for food resources.

The yellowfin goby Acanthogobius flavimanus inhabits the inner bays and estuaries of Japan and has contributed to both recreational and commercial fisheries. However, recently, the catch has drastically declined and it has become an expensive fish. Although there are detailed reports on the spawning ecology, early development, and morphology of larvae and juveniles of this species, few reports compare annual changes in abundance. In this study, long-term changes in population density were investigated by conducting a fixed-point survey using an angling method with constant effort for 10 years. Throughout 122 surveys conducted between 2009 and 2019, with a total fishing effort of 244 hours, 847 individuals were captured. The monthly catch per unit effort (CPUE, individuals per person per two hours) for this species ranged from 0 to 31, with no interannual variation. On the other hand, the seasonal variation in CPUE was distinct throughout the year, with values remaining near zero from February to May, gradually increasing from June onward, and peaking at high values of 8 to 31 between August and November. For some individuals, age was assessed by observing scale ridges. Scales from fish of 93 mm standard length (SL) had one set of broad and narrow bands, indicating that the fish was in the 0-year old class. Scales from fish of 143 mm SL had two sets of broad and narrow bands, indicating that the fish was 1-year old. It was confirmed that two age classes inhabit the study site. Based on the monthly body length composition, the occurrence patterns of each age class were estimated. For the 0-year age class, individuals measuring approximately 80 mm began to be caught around August. Over time, they continued to grow, reaching approximately 120 mm between October and December. For the 1-year age class, individuals measuring approximately 120–130 mm in August grew to 140–190 mm between October and November. This study demonstrated that scrupulous catch records maintained by recreational anglers are effective for fish monitoring, as they provided insights into the long-term and seasonal variations in CPUE, as well as the occurrence and growth dynamics of year classes.

The reproductive behavior of large Japanese spined loach Cobitis sp. BIWAE type A has never been observed, and little is known about its reproduction. We observed and photographed the approach and embracing behavior, which is part of the reprod-uctive behavior of the large Japanese spined loach, under aquarium conditions on four occasions in 2024: once on April 7 and April 10, and twice on April 12.

We investigated feeding habits of five sympatric anuran species including an endangered species, Pelophylax porosus brevipodus, in the paddy fields of Kyoto Pref. Japan. We analyzed the seasonal change of their feeding habits and its difference among the frog species. During our field research, which occurred every two to three weeks between April to November 2010, we collected 36, 172, 36, 98, and 136 individuals of the following frog species: Dryophytes leopardus, Fejervarya kawamurai, Glandirana rugosa, P. nigromaculatus, and P. porosus brevipodus, respectively. The size of the frogs was smaller after the mid-summer drainage of the paddy fields in late July, called Nakaboshi, than during the pre-drained period. We detected 3770 food items in total, which amounted to 158077 mm3 and 367.3 g. The proportion of individuals with empty stomachs ranged from 0.055 to 0.58 among the frog species. Hemiptera, Hymenoptera, and Collembola had a high food item count in their stomachs while Coleoptera, Dermaptera, Diptera, and Lepidoptera had high total food volume. We calculated the stomach content index (SCI) and index of relative importance (IRI) for the food of each frog species. The findings were generally consistent with previous studies, but the marked tendency of P. porosus brevipodus and F. kawamurai to prey on Collembola in autumn is noteworthy. Since infrastructure development projects for the paddy fields were executed around our study site after this study, this study is the final record of the feeding habits for the five sympatric frog species in traditionally kept paddy field environments.