About 40% of hundreds of reservoirs in Nagano City, Nagano Prefecture, which are habitat for the endangered Pseudorasbora pumila, have been abandoned and are predicted to rapidly deteriorate in the future. In a survey lasting from 1996–2010, 36 ponds were assessed using eight variables to determine the habitat status of each pond. Of the 36 ponds, 33 were determined to meet the habitat requirements by P. pumila. A total of 29 ponds were confirmed to be inhabited by P. pumila. Presence of P. pumila were reconfirmed in twenty-seven ponds and were newly discovered in two ponds. Ponds where P. pumila could not be captured were found to be significantly deteriorated due to abandonment. Local extinctions of P. pumila are a concern as more ponds with P. pumila habitat are abandoned. In order to efficiently conserve a large number of P. pumila habitat ponds, we established a conservation priority using eight variables. By using these eight variables, we evaluated the importance of each population and the urgency of each pond's management status. With this we devised a conservation priority ranking system from 1st to 9th. Using this conservation priority ranking system can help to efficiently allocate management costs such as the frequency of monitoring surveys and the maintenance and repair of abandoned reservoirs. Because it will be increasingly difficult to resolve the conservation of rare species within the region it is important to build a new pond management system from a long-term perspective. While using the new pond management system, it is important to share knowledge about the relationship between farming and conservation of rare species to a wide range of stakeholders, including not only local residents but also urban dwellers.

The second location where Bembidion nakamurai was discovered and recorded in Kumamoto Prefecture. B. nakamurai had previously been known from only one location in Kagoshima Prefecture. Habitats of B. nakamurai in both localities were investigated and the environmental characteristics of their habitat were also noted.

Numerous individuals of Hydrometra okinawana Drake, 1951 (Hemiptera, Hydrometridae) were collected from a pond surrounded by forest in Nikaho City (southern region of Akita Prefecture) in September 2015 and 2021. Until this finding, the northernmost record of this species was in Miyagi Prefecture, but this report updates that record. This is also the first record of this species in Akita Prefecture.

We collected 17 Coreoperca kawamebari specimens in northern Mie Prefecture, Japan, in 2022. This study is the first record of C. kawamebari in Mie Prefecture. Because C. kawamebari has been introduced in the neighboring prefectures of Mie (Aichi, Gifu, Shiga, Nara, and Wakayama), the C. kawamebari found in Mie Prefecture were also considered to be introduced. Adults and young of the year were collected in the collection surveys. Therefore, there is a high possibility that C. kawamebari is reproducing in the study area.

We report the first record of the domestic invasive species, Coreoperca kawamebari (Perciformes: Sinipercidae), in the Uso River system, Shiga Prefecture, Japan. This species has not been observed in previous studies of fish fauna in this vicinity, thus it was likely introduced recently. We caught mature adults and yearlings, indicating that this species has reproduced in this river system. Based on stomach content analysis, this species feeds on aquatic insects such as midge and mayfly larvae, suggesting possible risk, derived from predation pressure and competition, on the ecosystem of the Uso River system.

In 2022, the introduced species Macropodus ocellatus was collected from the Kiso River system in Gifu Prefecture. Although M. ocellatus has been found in the Kiso River system, there was no description of where it was collected and no referral record identifying it as being in Gifu Prefecture. Therefore, this is the first record of M. ocellatus in Gifu Prefecture and the first record in the Kiso River system in about 60 years. Although the details of the origin of this species in Gifu Prefecture are not known, it has been distributed as a rare fish in Japan and its population has been decreasing. Therefore, it is possible that M. ocellatus was intentionally released by individuals or ornamental fish traders to introduce it to the Kiso River. There is concern that M. ocellatus may spread in the Kiso River system, and therefore, it is necessary to monitor its distribution, expansion and habitat status, and to exterminate it.

Juvenile Fejerverya kawamurai were collected in the paddy fields of Sagamihara City, Kanagawa Prefecture, central Japan on 23 July 2022. This is the first record of the domestic alien species F. kawamurai in the Basin of the Sagamigawa River.

Host species for the glochidia of a freshwater unionid mussel Lanceolaria oxyrhyncha were identified by determining whether the glochidia matured after infecting 5 fish species. The fish were kept in aquarium tanks for 14 days after glochidial infection, and the numbers of glochidia and metamorphosed juveniles that detached from the hosts were counted. Living juveniles detached from Candidia sp. Phoxinus lagouskii steindachneri, Misgurnus anguillicaudatus, Oryzias latipes and Rhinogobius sp. Therefore, these fish were identified as suitable host species for the glochidia. P. lagouskii steindachneri, M. anguillicaudatus and O. latipes were newly identified as host species for L. oxyrhyncha.

Odontobutis potamophila (Günther) is a freshwater fish native to northern Vietnam and eastern China. In Japan, this species was first identified in 2010 in Sugao Swamp in the Tone River system in Ibaraki Prefecture. The distribution of the species is expanding in the Tone River. In this study, an individual of the species was collected in the Edo River, a tributary of the Tone River system. The collected fish would have entered the river via two routes: one by streamflow via the Tone Canal from a known habitat and the other via direct release by someone. Its feeding habit may have a negative impact on native ecosystems. The continuous monitoring and management of this species is necessary during the early stages of its invasion.

“Aquarium medaka” finding their way into natural ecosystems is a concern for causing negative effects on wild medaka populations. One such negative effect could be genetic pollution because they easily intercross with each other. Recently, aquarium medaka was collected from some regions in Japan. We collected medaka from a park’s biotope in Chiba Prefecture and they were identified as aquarium medaka by their morphological characteristics and body color. Most of these medaka had incomplete traits. These would be released with such traits to keep them from breeding with wild populations. The release and expansion of species with dominant traits causes many problems such as genetic pollution and the mediation of infections and parasites. Therefore, public awareness is needed to prevent intentional and unintentional releases of aquarium medaka.

I investigated actual sales of Acheilognathus tabira nakamurae on internet auctions from January 2011 to March 2021 (designated as a "nationally rare species of wild fauna/flora" in February 2020) and evaluated the effect of the "nationally rare species of wild fauna/flora" designation. Of the 723 confirmed sale records, 5.5% were wild caught (WC), 72.9% were captive bred (CB), and 21.6% were unknown. Additionally, the designation of A. tabira nakamurae as a "nationally rare species of wild fauna/flora" has at least ostensibly prevented its sale. Throughout the study period, the proportion of transactions that could be determined as WC were small, and the proportion of alleged CB was relatively large. Therefore, suggesting that the importance of sales restrictions through designation as a "nationally rare species of wild fauna/flora" is not so high for this species. If poaching for the purpose of breeding increases in spite of the catch control regulations, it is necessary to consider the option of shifting the category to "designated class 1 nationally endangered species of wild fauna/flora". In this category only specific operators may engage in the business of a national species or be allowed to engage in commercial transactions of CB as a measure to control poaching.