Bird species of an artificial wetland in Fukuoka Prefecture, Kyushu Island, Japan were concurrently surveyed by employing the environmental DNA metabarcoding method using gBird and MiBird primer sets, and visual census. While 28 species were observed by the visual census, only four species of the Anatidae family were detected by the metabarcoding method. Although some sequences other than the four Anatidae species were found by the metabarcoding method, it was difficult to distinguish between Mallard and Eastern Spot-billed Duck, or between Falcated Duck and Eurasian Wigeon. In addition, Common Shelduck and Teal were detected by the metabarcoding method only with the MiBird primer set.

We investigated the diet of red swamp crayfish Procambarus clarkii collected in an irrigation canal near Lake Inba-numa using DNA metabarcoding. A total of eight taxon of aquatic and terrestrial invertebrates (Hydroglyphus japonicus, Chironomidae sp.，Aquarius paludum paludum, Armadillidium vulgare, Tetramorium sp., Heterocypris incongruens, Orientogalba ollula，Plumatellidae sp.) were detected, including animals for which predation by this species has not been clearly documented. The detections of the invertebrate DNA may result not only from predation by the crayfish but also from their consumption of carcasses. However, our results suggest the broad dietary range of P. clarkii.

We examined the temporal and spatial variance in the sex ratio of Three-lips Opsariichthys uncirostris uncirostris, a threatened endemic piscivorous cyprinid of Lake Biwa, using 20-years of data, which was collected from individuals captured during the reproductive seasons of 1995 to 2014. The sex ratio varied year by year but was estimated to be stable over the long term with the estimated average sex-ratio being 0.52 : 0.48 (male : female). The sex ratio varied among capture methods. Namely, the male rate exceeded the female rate for sampling by casting nets and gill nets from the shore, while the opposite was true for sampling by nearshore set nets (Eri). The ratio for offshore scoop nets (Okisukui) was equal. We have no data to explain the reason for the annual change in the sex ratio. The variance by capture methods is thought to be derived from the location of each capturing method in the lake. This spatial difference in the sex ratio may indicate the difference in the strategy of upstream migration for the reproduction, e.g., the duration of stay of the males at the reproduction sites is longer than females. The equal sex ratio over the long term concluded in this study is consistent with the previous studies in the 1940s–1960s, and partially corrects the recent snapshot-like findings of male-biased sex ratios, which have been specifically observed near the lakeshore and in the rivers. It is suggested that the continuously decreasing catch of Three-lips is not due to its male-biased sex ratio.

Larvae of endangered gomphid dragonflies were found in the stomach contents of channel catfish Ictalurus punctatus, an invasive alien species, collected in the lower Yodo River, Osaka Prefecture, Japan in 2020–2023. The following dragonfly species were identified: Stylurus annulatus (25 individuals), S. oculatus (6 individuals), Melligomphus viridicostus (2 individuals), Shaogomphus postocularis, Nihonogomphus viridis, and Sieboldius albardae (1 individual each). One of the channel catfish collected in April 2022 fed on 20 larvae of S. annulatus, which is listed as Vulnerable (VU) in the Red List of Japan. Predation pressure from channel catfish may cause a decline in the population of S. annulatus. Ongoing accumulation of information on the feeding habits of channel catfish will reveal its impact on native aquatic organisms, including threatened insect species.

Spawning experimentation of the Tokai fluvial eight-barbel loach Lefua tokaiensis was conducted from May 1st to July 31st in 2022 and 2023 in order to confirm the number of days the loaches spawned and the number of eggs that were laid. In each trial, a pair of loaches was kept in an experimental tank, and the water temperature was raised from 16 to 21°C to induce them to lay eggs. During the trials the number of eggs laid and the total number of eggs were recorded. Five pairs of loaches laid eggs during three trials each year. The spawning period of the loaches ranged from 3 to 54 days, their spawning interval was between 1 to 18 days and the number of spawning days ranged from 2 to 13 days. These results indicate that the Tokai fluvial eight-barbel loach is a multiple-spawning fish. The number of eggs laid per female per day ranged from 1 to 177, and the total number of eggs laid per female during the spawning period ranged from 94 to 207. Pre-spawning behavior was observed where the male chased the female at night. Additionally, most of the spawning occurred at night (96.6%). During spawning the water temperature was 16.2–19.2℃, and the pH was 6.98–8.24.

Pseudovelia esakii Miyamoto, 1959 was collected from rivers in the Agano River system in Niigata Prefecture, Japan. This species has been collected in the middle and lower reaches of rivers and lakes in Honshu, but its distribution in Niigata Prefecture has not been recorded. This report is the first record of this species in Niigata Prefecture. In addition, we summarized data on its habitat from previous studies. Our literature survey showed that P. esakii is mostly found from the margins of lakes and mid-way downstream, indicating that the semiaquatic insect utilizes the land-water ecotone as its primary habitat.

Recently, the distribution of channel catfish, Ictalurus punctatus, an invasive alien species, has been expanding in several water systems in Japan. The species’ first occurrence in the Yahagi River was confirmed in 2005. Since then, a local institute and citizen groups had been worked together to eliminate the species for 10 years. They caught over 100 individuals at Azuri and Koshido dams (Toyota City, Aichi Prefecture, approximately 53 km and 46 km upstream from the river mouth, respectively) in the middle reaches. The number of individuals captured peaked in 2010 and declined in 2011–2014. However, no surveys of the species have been conducted in the river since 2015; therefore, its current status is unknown. In this study, longline surveys were conducted to confirm the species’ presence at Azuri and Koshido dams using the same sampling method as in the past. Four surveys were conducted, once each at both dams in June 2021, once at Azuri dam in October and once at Koshido dam in November. A total of eight channel catfish were captured; three at Azuri dam (total length: 28.0–33.7 cm) and five at Koshido dam (total length: 53.5–73.0 cm). The age of the individuals estimated from body length was 2–6 years for three individuals captured at Azuri dam (i.e., they were born after 2015) and was 6+ years for five individuals captured at Koshido dam (i.e., they were born before 2015). The number of fish caught per hook (i.e., catch per unit effort, or CPUE) was 0.050 at Azuri dam and 0.073 at Koshido dam; the former was the second highest value following 2010 and the latter was the highest ever recorded. These results suggest that the population has recovered in the waters around both dams since 2014, possibly due to the reproduction of individuals that have survived at the time; the current population densities are estimated to be similar to or higher than those during the early 2010’s.

Long-tailed Tits Aegitholos caudatus japonicus is a subspecies, a resident in Hokkaido, Japan. In the winter of 2023–2024, one to six (up to 20) A. c. japonicus were recorded intermittently from 23 December to 16 March in Lake Izunuma-Uchinuma in Miyagi Prefecture, northern Japan. This is the first detailed winter record of A. c. japonicus in Honshu.

A stickleback Pungitius sp., named “Musashi-tomiyo”, is an endemic species that originally ranged across spring-fed streams in the Kanto region, eastern Japan. The species’ population has dramatically decreased due to habitat degradation and water pollution over the past decades. Currently, the last remaining wild population is found only in the upper reaches of the Moto-Arakawa River in Kumagaya, the northern part of Saitama Prefecture. Although the species is protected by prefectural law, the population dynamics have fluctuated largely and abundances estimates outside the preserved area have now declined. Therefore, conservation concerns for the wild population of this species have grown. We surveyed the distribution, relative abundance and habitat conditions of the threatened stickleback in areas outside of preserved habitats. We found that the sticklebacks were abundant in habitats with rich aquatic vegetation cover and a relatively close proximity to an inflow of groundwater. We also found that water temperatures, depths and velocities were stable for the studied period, while invasive red-swamp crayfish Procambarus clarkii was in relatively low density. We concluded that the habitat conditions at this site might be suitable for the survival and reproduction of the stickleback.

The Grey-headed Lapwing is a medium-sized wading bird that is listed as an endangered species in some prefectures and requires conservation measures. While Greyheaded Lapwing utilizes agricultural land, particularly rice fields, for breeding, there are no reports specifically detailing the preferred characteristics of these rice fields. In this study, we obtained knowledge, albeit partial, on the characteristics of the breeding distribution of the Grey-headed Lapwing. We observed a total of 45 active nests of Greyheaded Lapwing in Akita, Iwate, Miyagi, and Shizuoka prefectures, with the main study site around the Hachiro Lagoon Regulating Pond in Akita Prefecture, and discussed their environments. The results suggest that there are two types of breeding patterns: those that breed in lowland rice paddies near rivers and lakes at elevations of 0 m, and those that breed in high-elevation rice paddies unrelated to rivers and lakes. The former type nested at an average distance of 361 m and a maximum distance of less than 900 m from rivers and lakes.

The sharpbelly Hemiculter leucisculus, an invasive species from continental eastern Asia, has successfully established non-indigenous populations in many countries outside its native range. In Japan, the first record of H. leucisculus collected from the Hyakken River in the Asahi River system, Okayama Prefecture was reported in 2017. In this study, we newly collected H. leucisculus from four river systems (the Yoshii River, Sasagase River, Kurashiki River, and Kamo River systems) in Okayama Prefecture. Partial nucleotide sequences of the mitochondrial COI gene of the 10 individuals from the four river systems were consistent with the two haplotypes from the firstly reported population of Okayama Prefecture. Our results indicate that the distribution of H. leucisculus has already expanded to major river systems in the Okayama Plain.