Henricia reniossa reniossa was first discovered on the coast of Honshu Island, Japan, extending the southern limit of this subspecies to central Japan. This finding suggests that the distributional range of the two subspecies of Henricia reniossa presumably overlapped. Herein, we describe the morphology of Henricia reniossa reniossa with brief comments regarding its subgeneric classification of Henricia reniossa.

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The intrinsic optimum temperatures (TΦ) for the zoeal stages of five species of the terrestrial hermit crab genera Birgus and Coenobita, namely B. latro, C. brevimanus, C. purpureus, C. rugosus, and C. violascens, were estimated based on the relationship between temperature and the number of developmental days using the nonlinear thermodynamic Sharpe–Schoolfield–Ikemoto model. The results showed that the TΦ estimates (approximately 26 °C) corresponded to the temperatures at which high survival rates were observed for the zoeae, except for C. rugosus, whose TΦ was approximately 24 °C. The low TΦ of C. rugosus when compared to the other species may have been due to the relatively high northern latitude of its distribution and its late breeding season. The optimum temperatures determined for these terrestrial hermit crabs would be useful in understanding and predicting the changes in and northward expansion of their distributions.

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The snow crab Chionoecetes opilio is an important fishery species in Japan, and its morphological abnormality has been reported in many cases. This report represents morphological abnormalities of snow crab based on photographic records. One male individual had a large lateral projection on the propodus of the left second pereiopod. This lateral projection was trapezoidal in shape and had two dactyl-like spines at the top base. These two spines were different in morphology from the movable and fixed fingers of the cheliped and the dactylus of the pereiopod. The other male individual was missing about a half of the fixed finger of the left cheliped, instead having another fixed finger protruding diagonally from just below the missing part.

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The black tiger shrimp Penaeus monodon, a commercially important species in Southeast Asian countries, has been recorded from tropical to temperate regions of the Indo-West Pacific. The northernmost record of the species has been from Tokyo Bay or the Boso Peninsula, central Japan. In this study, we report the occurrence of P. monodon based on 20 juvenile specimens (4.8–28.3 mm in carapace length) collected from the Edokami, Kuji, Naka and Tone River estuaries, and the brackish water Lake Hinuma (35°48'N to 36°49'N, 140°32'E to 140°47'E), all located in Ibaraki Prefecture north of Tokyo Bay and the Boso Peninsula, from September 2021 to November 2023, showing the northward expansion of distributional range of the species. Periods of high water temperature (> 20 ºC) partly associated with warm water intrusion from the Kuroshio from 2021 to 2023 persisted twice as long as the previous 30-year average for the region. Recruitment of P. monodon juveniles to the above estuaries may increase in the near future due to rising water temperatures, although a lack of tolerance to low water temperatures as shown in previous studies suggests that overwintering in coastal waters of Ibaraki Prefecture should be unsuccessful.

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The present study aimed to examine the relationship between stream temperature and the occurrence of amphidromous atyid shrimps as a basis for inferring the impacts of global warming on shrimp populations and communities. We investigated the occurrence of amphidromous atyid shrimps from spring 2017 to summer 2019 in the Banda River, a small stream located at near the southern tip of the Boso Peninsula, Japan. Five amphidromous atyids, including Caridina leucosticta, C. multidentata, C. serratirostris, C. typus, and Paratya compressa, were collected. The number of shrimps collected showed a distinct seasonal variation, being high in summer and low in winter. A positive correlation was found between the stream temperature and the number of shrimps collected. A notable reduction in shrimp occurrence was observed at temperatures below 15°C, particularly for C. typus, followed by C. serratirostris. Additionally, interspecific variability in shrimp occurrence was observed, likely due to interspecific differences in larval performance under changing ocean conditions. Global warming and climate change may affect the overwintering success and larval performance of atyids, potentially altering their population dynamics and community structure.

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We investigated the sex ratio in five amphidromous atyid shrimp species of the genera Caridina and Paratya; namely, C. leucosticta, C. multidentata, C. serratirostris, C. typus and P. compressa. Our surveys revealed slight or significant male-biased sex ratios for Caridina and Paratya species, particularly during the breeding season, except for C. serratirostris, which had a significant female-biased sex ratio. Size-specific sex ratios were observed as male-biased and female-biased for the middle and large size classes, respectively. We discuss the possible causes of biased sex ratios in atyid shrimps.

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We studied the effects of temperature on the reproduction of two atyid shrimp species of the genus Caridina, namely C. multidentata and C. typus, by culturing them at 20, 23 and 26 °C. Females of both species oviposited at all temperatures. Temperature did not affect the hatching rates in C. typus, but the hatching rates in C. multidentata were low at 26 °C. The number of newly hatched larvae from a single female was affected by temperature for both species and decreased with increasing temperatures. The reduction rate in the number of newly hatched larvae from 20 °C to 23 °C and 26 °C was 67 % and 88 % for C. multidentata and 27 % and 29 % for C. typus, respectively. Thus, high-temperature regimes negatively affected the reproductive output of these atyid shrimps.

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A freshwater mussel, Buldowskia shadini, recently confirmed to occur in Japan, has been identified for the first time in the Tohoku region (Tarumizu Dam in southern Miyagi Prefecture). A mussel species morphologically similar to B. shadini was previously observed at this site in 2005, and three individuals collected at this site in 2023 were identified as B. shadini through morphological and genetic analysis. The Tarumizu Dam, completed in 1977, is located in a mountainous area and the watershed is not a habitat for the mussel species that inhabit lentic waters. It was considered possible that B. shadini was accidentally introduced with game fish such as largemouth bass Micropterus nigricans.

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The freshwater prawn Macrobrachium ustulatum (Nobili, 1899) is distributed throughout the western Pacific Ocean and was first identified in Japan in 2015 on Okinawa Island, Ryukyu Islands. Knowledge of its distribution and habitat is lacking due to difficulties in distinguishing it from a morphologically similar sister species, Macrobrachium australe (Guérin-Méneville, 1838). Here we report an adult male specimen of this species collected from the Kawazu-Yatsu River, Izu Peninsula, Japan. This specimen was morphologically intermediate between the two sister species but was consistent with M. ustulatum based on mitochondrial DNA 16S rRNA and nuclear DNA 28S rRNA sequences. This is not only the northernmost record of M. ustulatum, but also the second record from Japan based on a single male specimen, and the first from Honshu.

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Juveniles of the Japanese turban shell Turbo sazae were reared under static and flowing water conditions by feeding cabbage alone for two years. The growth of the reared individuals was comparable to that of reared juveniles fed formulated diets and/or algae and to that of wild juveniles, indicating that the cabbage could be an alternative or supplemental food source for rearing the turban shells. Survival rates were approximately 60 % after one year and decreased to 20 % after two years. Spine formation was not observed in all individuals. Factors involved in the spine formation were discussed.

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The blackfin seabass Lateolabrax latus is distributed in the warm-temperate region of East Asia. On the coasts of Japanese Archipelago, the distribution of this species is mainly south of the Noto Peninsula on the Sea of Japan side and south of Ibaraki Prefecture on the Pacific Ocean side, whereas there have been no collection records from the Pacific Ocean side of the Tohoku region. This paper presents the first record of L. latus from the Pacific side of the Tohoku region. Two juvenile specimens were collected at the seagrass bed in Koyadori Fishing Port, Onagawa Town, Miyagi Prefecture (38.4075°N, 141.5020°E) on 27 March 2023. Based on the morphological characteristics and results of molecular phylogenetic analysis of mitochondrial DNA, the specimens were identified as L. latus. Furthermore, we examined the possibility that the distribution of this species has expanded north of the Tohoku region utilizing the ANEMONE Database. The eDNA of this species was detected, even though in extremely small amounts, at four sites on the Pacific Ocean side of Tohoku and Hokkaido regions, implying expansion of distribution of this species to more northern areas.

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