Abstract To clarify the current status of the Japanese pond turtle, Mauremys japonica, in a lowland marsh (Nakaikemi marsh) in Japan, a capture-recapture study was conducted from 2016 to 2019. This study showed that over 100 turtles aged from one to 14 years (including individuals of undetermined age) have inhabited the lowland marsh. The estimated growth patterns of both the male and female turtles, based on von Bertalanffy growth curves, were similar to those found in river populations, in a previous study. Recently, lowland marshes have not been recognized as an appropriate habitat for the turtle, because a previous study indicated that M. japonica prefer rivers and ponds in foothill environments. However, this study showed that lowland marsh is one of the most important habitats for the growth of this turtle. In the future, to prevent the extirpation of lowland populations of this turtle, long-term monitoring of the population dynamics of M. japonica should be conducted in the Nakaikemi marsh.

Nitella mirabilis Nordstedt ex J. Groves var. inokasiraensis (Kasaki ex R. D. Wood) is an endemic variety in Japan, which is only found in Mitaka, Tokyo Metropolis and Ichikawa, Chiba Prefecture. We report our finding of N. mirabilis var. inokasiraensis from an abandoned paddy field in the mesomountainous region of Boso hills, Chiba Prefecture, as a new locality.

Semi-aquatic warm-temperate annual fern, Ceratopteris gaudichaudii Brongn. var. vulgaris Masuyama et Watano, was collected on October 4, 2019 in a rice paddy where traditional farming practices were used in Matsushima, Miyagi Prefecture, Japan. The collection site (38.4°N) is north of the previous northernmost recorded location in Yamagata (38.1°N) on the Sea of Japan side and in Fukushima (37°N) on the Pacific side. Furthermore, the location in Matsushima is the northernmost range of the genus Ceratopteris in the world. Warmth index near the collection site (87.9) is close to the value in Yamagata (88.1) but considerably lower than in Fukushima (103.1). Characteristics such as the ferns' small size and some sporophytes without fertile leaves, even in early October, indicate the severe conditions of the collecting site for this species. The climatic condition at the collection site may be close to the limit of compensatory progenetic adaptation to a shorter growth period and subsequent dwarfism in the cold climates.

The Japanese white crucian carp, Carassius cuvieri, is a cyprinid fish end- emic to Lake Biwa, central Japan. Due to a drastic decline in the commercial catch, it is listed in the IUCN Red List as an endangered species. Its largest spawning ground was Hayasaki Lagoon, in the northeastern part of the lake. However, the lagoon was drained and converted into agricultural paddies in 1970, which was thought to have decreased the C. cuvieri population greatly. To promote the recovery of native cyprinid fish populations, including species such as Carassius buergeri grandoculis, Gnathopogon caerulescens, and C. cuvieri, the prefectural government developed artificial reed zones along the lake shore. However, it had not been confirmed whether C. cuvieri used these zones as spawning grounds. This study investigated the spawning of C. cuvieri through DNA identification of eggs collected in an artificial reed zone developed between 2002 and 2005, located outside the reclaimed Hayasaki Lagoon. The survey area consisted of Area-A, occupied by willow trees, located farthest offshore; Area-B, dominated by common reed (Phragmites australis); Area-C, an open-water area behind the reed area (partly floating herbaceous islands). These areas were searched for eggs attached to plants near the water surface between 13:00 and 13:40 on 11 May 2018 and the eggs were collected by hand. For each batch of egg samples, GPS data were recorded, and each egg was identified in the laboratory using DNA markers. The identification results were then mapped on a satellite image of the survey area on Google Earth, and the relationship between collection areas and spawning fish species was examined. While no eggs were collected in Area-A, 194 were collected from nine points in Area-B and 174 from seven points in Area-C. From these eggs, 80 and 56 were randomly selected for Areas-B and -C, respectively, and all were identified as belonging to Carassius by PCR using genus-specific primers. These eggs were then identified by PCR using species- specific primers. Of the 127 eggs, 79 (62.2%) were judged as C. cuvieri, and the remainder as either C. buergeri grandoculis or triploid Carassius species. By collecting area, 41.3 and 92.3% of the eggs from Areas-B and -C, respectively, were C. cuvieri; the proportion of C. cuvieri eggs in Area-C was significantly greater than that in Area-B. These results confirmed that C. cuvieri used the artificially developed reed zone studied here as a spawning ground, especially the open water area behind the reed zone.

Larvae of Asynarchus sachalinensis are known from ponds and streams in mountainous areas. Typically, their larval case materials change from plant pieces to sand grains prior to pupation. In this paper, I report on larvae of Asynarchus sachalinensis found in a suburban reservoir at an altitude of 33 m in Miyagi Prefecture. At this location it was observed that larvae did not change larval case material from plant pieces to sand grains.

The availability of the big scaled redfin, Pseudaspius hakonensis and tadpole of Rana japonica as host animals for the glochidia of the unionid mussel, Pronodularia cf. japanensis 3 was investigated. The hosts to which the glochidia were attached in a paddy field ditch were cultured in a tank (6 L, 22.3 ± 0.2 °C) for thirteen days. Glochidia and juveniles that became detached from the hosts were counted daily. Live juveniles appeared from Ps. hakonensis about nine days after glochidia attachment. On the other hand, juveniles did not appear from R. japonica. Ps. hakonensis is thought to be a suitable host, on which over 27% of attached glochidia metamorphosed to juveniles.

Invasion status of an invasive alien species, Micropterus dolomieu, was ex- amined in the main stream and its tributary (Iida River and Lake Kasama) of the Hinuma River system upstream of Lake Hinuma, a Ramser site in Ibaraki Prefecture, eastern Japan. A total of 228 individuals (6.3–295 mm in body length) including adult and larvae of this species were collected at seven sites immediately downstream of the tributary from June to September in both 2019 and 2020. A spawning nest with larvae and an adult was found at one site in the main river in June 2019. These results suggest that Micropterus dolomieu have expanded their distribution by continuing to reproduce within the river system.

We estimated the origins of Nuphar subintegerrima and Nymphaea tetra- gona, ex situ populations cultivated at Meijo University and Nagoya Higashiyama Zoological Park in Nagoya, Aichi Prefecture, Japan. The results of our interview research indicated three possible origins: Nu. subintegerrima and Ny. tetragona from Otama Pond in Yagoto-Urayama, Tenpaku, Nagoya (Origin A, cultivated at Meijo University), Nu. subintegerrima from Tenpakukei Wetland (or a surrounding wetland) in Yagoto-Urayama (Origin B, cultivated at Meijo University), and Nu. subintegerrima from anonymous Wetland in Yagoto-Urayama (Origin C, cultivated at Nagoya Higashiyama Zoological Park). In the results of the specimen research, we found specimens of Nu. subintegerrima and Ny. tetragona from Otama Pond collected during the 1970–1980’s. Consequently, we judged that Origin A represents the Nagoya populations. Wild populations of Nu. subintegerrima and Ny. tetragona were extirpated from Nagoya, therefore the knowledge of the populations origin is important for biodiversity conservation in Nagoya.

Two invasive exotic fish species, largemouth bass Micropterus salmoides and bluegill Lepomis macrochirus were eradicated by drawing down the Terukoshi farm pond, Kurihara, Japan in September, 2018. These two species were absent the following August, but largemouth bass juveniles recurred in June, 2020. Are they offspring of bass that survived the eradication activity or of illegal release after re-impoundment? Aided by various assumptions such as current biomass, brood size, mortality, growth, etc., juvenile biomass on the sampling day, number of nests, parents in 2020 spawning season, the assumed surviving bass were respectively estimated about 7,000, two, two and eight (c.a. 35 cm TL), or if the assumed survivors were young-of-the-year, their number was estimated about 88 at the time of drainage. These numbers of eradication survivors are unlikely because the pond was drained with only a very narrow streak of running water left and quick lime was spread to reduce the chance of survival. In case of illegal release, five to eight adults of about 38–22 cm TL at release eight months before were estimated to be needed in order to realize the juvenile biomass at our sampling. Suspected outlaw angler(s) might have exceptional angling skill to catch a number of basses at a time under the recently difficult angling conditions, or have an illegal bass retention facility to gather enough basses for such a release.

Caridina logemanni is a landlocked freshwater shrimp native to Hong Kong. Between May 2018 and May 2021, 31 individuals were collected from a small stream of the Ara River System on the Kanto Plain, Japan. During the sampling period, four ovigerous females and one juvenile were among the individuals collected, suggesting that this species has established and is reproducing at the survey site. This shrimp species is commonly kept for ornamental purposes, and the morphological charact- eristics of individuals sold in an aquarium shop near the survey site match those of the sampled specimens. Therefore, the origin of the C. logemanni population at the survey site is thought to be the abandonment of ornamental shrimp into the stream. A standard Japanese name is proposed for this species.

Biwia zezera was collected from 2019 to 2020 in the Monobe River system in Kochi Prefecture. This species was recorded from 1972 to 1979 in the Kagamigawa and Monobe River systems in Kochi Prefecture, but little is known about its recent occurrence in Kochi Prefecture, and its presence has not been confirmed by riverine surveys. The distribution of this species in Kochi Prefecture could be due to introduction from Lake Biwa, but further research is needed on the habitat, ecology and genetic analysis of this species in the Monobe River system.

A hybrid strain of the freshwater pearl mussel Sinohyriopsis schlegeli, endemic to Lake Biwa, and the Chinese species S. cummingii is used for pearl farming in Lake Kasumigaura. The strain is highly tolerant of water pollution, and seems to have escaped from aquaculture facilities and become established in the wild. In order to clarify the habitat status of this hybrid strain, we collected wild pearl mussels and compared their morphology to both wild-type S. schlegeli and to hybrids cultured in pearl farms. Wild individuals collected near pearl farms were identified as belonging to the hybrid strain on the basis of their shell morphology and location of collection. Adult hybrids were triangular and had a prominent wing from the posterior slope to the apex, and could be distinguished from the elongate ovate shells of S. schlegeli. Moreover, an analysis of covariance of the body sizes of S. schlegeli and the hybrid strain showed a significant difference in the ratio of shell length to shell height. S. schlegeli was introduced to Lake Kasumigaura in 1936 and initially grew well in the wild. The species was also used in pearl farming beginning in 1963. However, S. schlegeli proved to be vulnerable to water pollution and grew poorly after the 1980s. Hence, the hybrid pearl-mussel strain that is more tolerant of water pollution was developed in 1988. As aquaculture operations using the hybrids expanded in scale, they escaped into the wild. In recent years, mortality of even this hardier strain has been frequently observed; we conclude that present-day Lake Kasumigaura may provide a poor environment for freshwater mussels.