Glochidium larvae of the freshwater unionid mussel, which parasitize the fish, can be widely dispersed as the fish migrate. Under captive conditions, the glochidium larvae obtained from Beringiana beringiana were allowed to infect the euryhaline Japanese rice fish (Oryzias latipes) and the salinity tolerance of the larvae was investigated. The fishes were kept in three saline environments (static freshwater environment at 0 psu, fluctuating environment from 0 to 22 psu, and fluctuating environment from 0 to 33 psu), and the number of glochidia and metamorphosed juveniles detached from the host fishes was counted for 15 days. Live juveniles detached from O. latipes were observed in all saline environments, indicating that glochidia of B. beringiana can survive on the host at high salinities, supporting the connectivity among geographically distant mussel populations at the larval stage with diadromous fish species via brackish water or the sea.

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The deep-sea jellynose fish Guentherus katoi (Ateleopodidae) has rarely been studied since its description in 2008. We performed the morphological and histological analyses on the ovary and free pelvic fin rays (PFRs) of a female specimen (625.6 mm total length) caught in the Goto Islands, Japan. Histological analysis of the ovary revealed six stages of oocyte development, ranging from oogonia to migratory nucleus stage oocytes. The coexistence of multiple oocyte stages indicates that G. katoi may be a multiple spawner. Despite the low gonadosomatic index (0.35 %), the presence of migratory nucleus stage oocytes indicated that this female was close to spawning conditions. Immunohistochemical analysis revealed cell proliferation in oogonial nuclei and granulosa cells. The first PFR had a previously undescribed ventral longitudinal groove (~700 μm deep, 1.05 cm long) with central lepidotrichia surrounded by connective tissue, and no sensory receptor cell was observed. These findings provide new insights into the reproductive biology and appendage morphology of this rare deep-sea species.

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Through observations of captive individuals, this study confirmed that Makassaritanais itoi (Ishimaru, 1985) is a protogynous hermaphrodite and dwells in tubes. Seven of ten isolated females changed sex and three did not, implying that M. itoi may consist of hermaphrodites and gonochoristic females, as has been suggested for other protogynous hermaphroditic tanaidaceans.

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The freshwater jellyfish Craspedacusta sowerbii is a small cnidarian belonging to the class Hydrozoa, inhabiting ponds and dam reservoirs. Like other hydrozoans, this species exhibits both an asexual polyp stage and a sexual free-swimming medusa stage. During the asexual stage, minuscule motile "frustules" develop into polyps, leading to enhanced clonal propagation. In contrast, the sexual stage involves the release of eggs and sperm by males and females, resulting in the formation of fertilized eggs. Craspedacusta sowerbii exhibits sporadic appearances and is rarely observed continuously in the same location over consecutive years. Even during mass occurrences, it is often the case that only one sex (either male or female) is present within the same site, leaving much of its ecology still shrouded in mystery. In September 2024, our team discovered C. sowerbii for the first time at Yanase Dam in Shikokuchuo City, Ehime Prefecture, Japan. Through sexual identification and molecular phylogenetic analysis, we identified that these individuals comprised at least two distinct male and female populations.

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Rice paddy ecosystems are regarded as alternative wetlands in Japan. The diversity of aquatic insects living in wetlands is supported by a combination of temporary water bodies, such as paddy fields, and permanent water bodies, such as agricultural ditches and ponds. Permanent water bodies remaining water during the winter also function as their overwintering sites. Clarifying the overwintering ecology of aquatic insects in rice paddy ecosystems is important for conservation strategy for declining aquatic insect populations in Japan. In this study, we recorded aquatic insects (Hemiptera and Coleoptera) with body lengths ›5 mm overwintering in agricultural ditches and ponds in rice terraces of Hyogo Prefecture, Japan. In addition, by comparing the number of species that appeared from spring to fall (active season), their life cycles and overwintering ecology were discussed. Overwintering surveys were conducted in December 2021 and 2022 with dredging in ditches and sweeping with D-frame nets in ponds. Active season surveys were conducted monthly from May to October 2023, with sweeping methods in ditches, paddy fields, and ponds. The results showed that 11 species (6 Hemiptera and 5 Coleoptera) were found in overwintering surveys. Of them, 7 species were found as either adults or larvae/nymphs in paddy fields during the active season, consistent with life cycle patterns reported in previous studies, while Eretes griseus was found only in the winter season at ponds, and Ranatra unicolor was found only in ponds. Because Kirkaldyia deyrolli, Hydaticus grammicus, and Gerridae were not found in overwintering surveys, it is guessed they overwinter on land. Ponds and agricultural ditches serve as important overwintering sites for aquatic insects, and periodic dredging for keeping water was considered effective for conservation.

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Information on zooplankton abundance is essential to evaluate the health of marine ecosystems, but zooplankton remain poorly studied in many regions. This study describes seasonal changes and community composition of zooplankton on the coast of Sado Island, in the Sea of Japan, which has unique geographic features. Zooplankton diversity and environmental parameters were surveyed monthly from April 2022 to March 2023 on the coast of Sado Island. The zooplankton community comprised 113 morphologically distinguished operational taxonomic units (OTUs). Zooplankton diversity was maximal in late winter whereas abundance peaked in early spring. Small harpacticoid copepods, copepod nauplii, and meroplankton (bivalves and fish larvae) were dominant throughout the year. Cyclopoid nauplii and bivalve larvae (veliger spp.) were more abundant in spring and summer, whereas small harpacticoid copepods were abundant in autumn and winter. Radiolarians and foraminifera were also found in summer and autumn along the coast. Moreover, several polychaetes were abundant in summer and winter. Distinct seasonal changes in zooplankton community composition and abundance were observed at Sado Island, which provide general information of zooplankton in the central Sea of Japan.

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Cymothoid isopods are fish-parasitic crustaceans, with 47 genera and 391 species recorded worldwide. In this study, we collected fishes to investigate the cymothoid fauna at four localities in Japan: Sakihama (Muroto City, Kochi Prefecture), Kashiwajima Island (Otsuki Town, Kochi Prefecture), Sakurajima Island (Kagoshima City, Kagoshima Prefecture), and Yakushima Island (Yakushima Town, Kagoshima Prefecture). A total of 526 fish specimens belonging to 65 genera and 83 species were examined for cymothoid isopod prevalence. Parasites were found in only three species: Diodon holocanthus from Kashiwajima Island, Chilomycterus reticulatus, and Prionurus scalprum from Yakushima Island. Five individuals of Cymothoa pulchrum were collected from the buccal cavities of C. reticulatus and D. holocanthus, and one individual of Anilocra prionuri was obtained from the body surface of P. scalprum. This study constitutes the first record of C. pulchrum and A. prionuri from Yakushima Island. Given the generally low prevalence of cymothoids, a combination of different sampling methods and continuous data accumulation is needed to elucidate host-parasite relationships.

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In recent study, the identification of the species distributed in Japan previously reported as “Medaeops granulosus” has been changed to M. japonicus. This study clarified that the “M. granulosus” from the Okinawa Islands of the Central Ryukyus is not M. japonicus but true M. granulosus. The distinguishing character of these two species are also discussed.

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Research on the spawning season of Takifugu alboplumbeus has been conducted in various regions, however no studies have been conducted on this species in Osaka Bay. This study aims to investigate the maturation of T. alboplumbeus in the estuarine area of Onosato River, located in the southern part of Osaka Bay, and to provide insights into their life history. In this study, the spawning season was considered to be from April to June, based on changes in the gonadosomatic index (GSI). In addition, hepatosomatic index decreases during the spawning season and recovers after spawning, suggesting that it is related to maturity. The minimum standard length to attain sexual maturity in this species was 72.7 mm (GSI: 10.5 %) for male and 87.7 mm (GSI: 15.4 %) for female.

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Two specimens of Diadema setosum (Leske, 1778) were collected from Onahama Port, Tatsumi-cho, Onahama, Iwaki, Fukushima Prefecture, Japan, on August 15, 2024. This represents the first record of diadematid sea urchin in Fukushima Prefecture and also appears to be the northernmost record of the species. In this report, the external morphology of D. setosum was described in detail based on the collected specimens. Diadema setosum is a tropical to subtropical species distributed in the Indo-West Pacific Ocean. Therefore, continuous research is needed to determine whether the occurrence of these tropical-subtropical animals is due to long-term seawater temperature increase or a temporary effect of warm currents.

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Thirty-four exon-primed intron-crossing PCR (EPIC-PCR) primer pairs for amplifying ribosomal protein gene introns were tested using eight individuals from four Thunnus tuna species. Only two pairs failed to amplify fragments for all individuals. Whenever amplicons were observed, no apparent fragment length difference was observed between species. Possible allelic variation due to fragment length polymorphism was observed at 13 loci.

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Although the Pacific coast of Honshu Island, Japan, is a temperate zone, tropical aquatic species have been known to occur in this area because of the influence of the Kuroshio Current. The distributional records of the southern species provide interesting information for studying the expansion of their distributional ranges owing to climate change. In the present study, we report the first records of two tropical palaemonid shrimp species, Macrobrachium grandimanus and M. lepidactyloides, from Honshu Island, Japan, with molecular identification using mitochondrial 16S rDNA sequences. These records update the northern limits of the two species.

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Laboratory culture experiments have been conducted to investigate larval development in cone snails of the genus Conus, primarily focusing on Hawaiian species. As a foundation for studying the larval biology of Japanese Conus species, the present study examined captive spawning in C. fulmen and C. pulicarius. Conus fulmen was cultured in aquariums at 24, 26, and 28 °C, and C. pulicarius at 23 and 26 °C. Spawning occurred at 24 °C for C. fulmen and at 26 °C for C. pulicarius, with both species producing egg capsules containing viable eggs.

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Mitochondrial cytochrome b (cytb) gene sequences were obtained from the invasive tubeworm Ficopomatus enigmaticus (Annelida: Serpulidae) collected at Yagura-Ryokuchi, Osaka Bay, Japan. Two lineages, Clades 1 and 2 sensu Styan et al. (2017), previously reported sympatrically in specimens collected from Australia, California, the Mediterranean, and Japan (Tama River, Tokyo), were detected. This result provides an additional case supporting the sympatric distribution of the two lineages of F. enigmaticus.

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The whirligig beetle, Gyrinus curtus Motschulsky, 1866, is an aquatic insect endemic to Japan, inhabiting standing or slow-flowing waters from Hokkaido to Kyushu, and has been listed as an endangered species due to habitat degradation since the 1960s. The only reliable record of this species in Saitama Prefecture is based on incidentally obtained specimens from puddles in Kumagaya City, where no reliable habitat has been found. This survey revealed that the whirligig beetle inhabits the endangered sticklebacks “Musashi-tomiyo” habitat in Motoarakawa River, designated as a natural monument of the prefecture. The habitat of G. curtus originates from a spring and is stable in water quantity and temperature. This characteristic is similar to the environment in Fukushima Prefecture, where this beetle and different sticklebacks from “Musashi-tomiyo” are also found. In other words, both species (G. curtus and sticklebacks) are presumed to prefer similar environments.

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To improve our understanding of optimal feeding conditions for larval culture in terrestrial hermit crabs, we investigated larval survival and developmental duration to the megalopal stage in Coenobita cavipes. Larvae were reared under three feeding regimes: Artemia only (AR), rotifers only (RO), and a mixture of Artemia and rotifers (AR + RO), all of which are commonly used prey in the culture of decapod crustacean larvae. Although larval survival tended to be higher in the AR + RO group, feeding regime had no significant effect on survival rates. However, developmental duration to the megalopal stage varied among groups, with larvae in the AR + RO group exhibiting significantly shorter developmental times than those in the other groups. These results suggest that a mixed diet of Artemia and rotifers is an effective feeding regime for culturing C. cavipes larvae and may enhance larval survival and development in terrestrial hermit crabs under laboratory conditions.

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A juvenile spiny lobster (50.6 mm in body length, 20.6 mm in carapace length) was collected off Usujiri (41°93'N, 140°96'E), Hakodate, Japan, November 2023. Morphological analysis and DNA barcoding using mitochondrial 16S rDNA sequence unambiguously indicated this juvenile to be the Japanese spiny lobster Panulirus japonicus. This is the second report of this species from Hokkaido, but the first with species identification by DNA analysis.

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An adult mussel Buldowskia iwakawai, was collected from Hokkaido in Northern Japan and reared in an aquarium tank. The glochidia released from this individual were used to investigate the fish host under captive condition. Fifteen fish species were used as host candidates. The fishes were kept in tanks for 6–14 days after glochidial infection, and the number of glochidia and metamorphosed juveniles detached from each fish species were counted. Nine fish species (Acheilognathus tabira nakamurae, Pungtungia herzi, Pseudorasbora parva, Gnathopogon caerulescens, Coreoperca kawamebari, Acanthogobius flavimanus, Sicyopterus japonicus, Gymnogobius petschiliensis and Rhinogobius flumines) were identified as new hosts for the glochidia of B. iwakawai in captivity.

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シラウオ（Salangichthys microdon）は河口域、海跡湖、潟湖などの汽水域に主に生息する汽水魚である。防潮水門によって淡水化された複数の海跡湖には陸封個体群が出現し、地域漁業の対象となっているが、淡水域での本種の生態に関する知見は少ない。本研究では淡水域における産卵期の本種成魚の生息環境特性を明らかにするため、2017年と2018年の早春に、淡水湖の北浦の沿岸帯（水深約0.5–1 m）で小型地曳網による採集調査を実施したところ、2017年に368個体（体長58–80 mm）、2018年に196個体（体長59–88 mm）が採集された。それらの大半が雄であり、産卵場周辺への集群が示唆された。成魚の個体数密度を目的変数、各環境変量（水温、溶存酸素量、濁度、水深、波高、底質の中央粒径、ヨシ帯の有無）を説明変数として一般化線形混合モデル解析を実施したところ、成魚は水深と波高がより大きく底質の中央粒径が125–500　µmの場所で多いことが示された。したがって、淡水湖の沿岸帯では波浪の影響が及ぶ砂地が本種成魚の重要な生息場所の一つとなっていると考えられた。本種の自然再生産の維持を図るために、そのような環境を保全していくことが望まれる。

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A single female specimen of a rare euryplacid crab species, Trissoplax dentata (Stimpson, 1858), was collected from a muddy tidal flat on Okinawa Island, Ryukyu Islands, Japan. Although this species has previously been recorded based on specimens from several localities in Japan, morphological information on those specimens has not been provided. This species is distinguished from the congener, T. tuberosa Castro and Ng, 2010, by the presence of an inner tooth and a median lobe on each suborbital border, and a tomentum on the dorsodistal regions of the cheliped carpi, and the absence of conical tubercles on the outer surfaces of the chelae. This study is the first to present the morphological features of a Japanese specimen.

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Floating behavior of the freshwater snail Semisulcospira libertina was observed under controlled conditions in experimental tanks. Individuals were categorized by size into three groups based on shell width: juveniles (1–3 mm), semi-adults (3–6 mm), and adults (˃6 mm). Seven individuals from each size group were placed in small cylindrical containers (300 mL volume) at an average temperature of 12.4 °C. Observations were conducted every 2 to 14 hours over a period of 5 to 7 days. The proportion of individuals exhibiting floating behavior was recorded for each size group. Snails from all size categories demonstrated this behavior, in which they floated upside down while adhering to the water surface. Juveniles displayed the highest frequency of floating, followed by semi-adults and adults. This floating behavior was easily disrupted by mild external stimuli. This behavior may facilitate short-term dispersal in natural environments, which could potentially aid in the expansion of the species distribution.

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Altogether nine crab species of five families from Japanese waters, viz., four species of the Parthenopidae, one species of the Portunidae, one species of the Xanthidae, one species of the Trapeziidae, and two species of the Pilumnidae, are recorded largely based on the specimens in the Nagai Collection of the Wakayama Prefectural Museum of Natural History. Most of them are rather rare in Japanese waters, and some of them are remarkably variable in the form and tuberculation of the carapace and chelipeds. Latopilumnus tubicolus Türkay & Schuhmacher, 1985 of the family Pilumnidae is considered to be synonymous with L. tuberculosus (Garth & Kim, 1983). Planopilumnus minabensis Sakai, 1969 and P. pygmaeus Takeda, 1977 of the Pilumnidae, both of which are currently referred to the genus Vellumnus Ng, 2010, are also reduced to junior synonyms of V. labyrinthicus (Miers, 1884).

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To understand the pelagic community of zooplankton near the offshore island, an investigation was conducted on Sado Island, in the Sea of Japan with two commonly used plankton nets (mesh size: 100 and 335 μm). Zooplankton were surveyed from the sea surface at two offshore sampling stations using a research vessel in late spring 2023. The zooplankton community comprised 34 morphologically distinguished operational taxonomic units (OTUs). Zooplankton collected from the two sampling stations contained mainly copepods, radiolarians, cladocerans, larvaceans, and crustacean nauplii. Some meroplankton were observed only at the station closer to shore, whereas many others were observed at both stations. Large zooplankton, such as calanoid and cyclopoid copepods, chaetognaths, meroplanktonic fish larvae and radiolarians were collected with the larger-mesh plankton net whereas small zooplankton, such as harpacticoid copepods, cyclopoid nauplii and molluscans were collected with the smaller-mesh plankton net. This study describes the zooplankton community near Sado Island, and it will be useful for understanding and predicting changes in plankton distribution in the Sea of Japan.

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We report the first record of the paranthurid isopod Paranthura japonica Richardson, 1909 from Okinawa, Japan, based on two specimens. The specimens were morphologically identified as P. japonica in having (1) the rostrum shorter than the anterolateral lobes, (2) the contiguous ommatidia, (3) the pereonite 6 shorter than the pereonite 5, (4) the pleonites 1–5 fused dorsally, (5) the oval telson with short simple setae on the apical tip, (6) the uropodal exopod being sinuate on the dorsodistal margin, and (7) the uropodal endopod with the length almost same as the width. We determined partial nucleotide sequences of the cytochrome c oxidase subunit I (COI) gene from the specimens. Their COI sequences differed from that of a P. japonica individual collected from the type locality, Muroran, Hokkaido, Japan, by 0.31 to 1.70 % (Kimura 2-parameter distance). This is the first molecularly supported evidence that P. japonica has a broad distribution spanning more than 2000 km.

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An adult specimen of a freshwater shrimp belonging to the genus Paratya was collected from the Omoto River in Iwate Prefecture, northeast Japan. Based on the number of rostral spines on the carapace and the number of spinules on the dactyls of the third and fifth pereiopods, this individual was identified as Paratya compressa. Records of this species in the Tohoku region are limited; however, recent changes in the Kuroshio and Tsushima Currents are believed to have facilitated the northward expansion of warm-water aquatic organisms. In fact, similar northward occurrences of other southern aquatic species have been reported along the Pacific coast of the Tohoku region. These findings suggest that P. compressa may also be expanding its distribution range in response to changes in ocean currents. Continuous monitoring of distributional shifts in warm-water species, with consideration of climate change and oceanographic dynamics, is essential for predicting and understanding future ecosystem fluctuations.

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This study reports the first record of the non-native freshwater fish Coreoperca kawamebari in Nagano Prefecture, based on a specimen collected from a pond within the Tenryu River system. Stomach content analysis revealed that the fish primarily preys on aquatic insects and crustaceans. Among the identified prey items, Chironomidae larvae, Amphipoda sp., and Polycentropodidae larvae were particularly frequent. Given the presence of rare aquatic insect species in the pond, there is concern that predation by C. kawamebari may have a negative impact on the local aquatic insect community.

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Gonad color of old sea urchins is known to be inferior to that of young ones. Thus, the age of sea urchins should be considered when trying to improve the gonad quality of sea urchins in aquaculture settings. In this study, using the number of rings on the rotula of Aristotle's lantern, we estimated the ages of individual sea urchins collected at two sites in the Seto Inland Sea. Based on the estimated ages and test diameters, we drew the growth curves of both populations. The youngest and oldest individuals in both populations are 1 and 12–13 years old, respectively. All ages in-betweens were detected, suggesting that new individuals were recruited annually. The growth curves obtained in this study will be useful for the assessment of the sea urchin ages collected from a habitat where macroalgal flora is still maintained in the Seto Inland Sea.

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Ryusendo Cave, a renowned cave in Japan, is located within Akka limestone area, where is hydrologically connected to several surface rivers and underflow water through dynamic exchanges. This study conducted a sediment sampling survey in Shizu River, adjacent to Ryusendo Cave, identifying six crustacean species across three classes, four orders, and five families. Two of these might be species that previously recorded in Ryusendo Cave, suggesting ecological connectivity between the cave and the adjacent river ecosystem. However, ecological surveys of the Ryusendo, Ryusen-shindo and Akka Caves – popular show caves subject to heavy human traffic and potential anthropogenic disturbances – remain limited. Ongoing and comprehensive monitoring is recommended to elucidate and conserve these interconnected ecosystems.

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To elucidate larval life history traits of the cone snail Conus fulmen, we conducted three culture experiments using artificial seawater. In experiment 1, larvae were fed Tetraselmis sp. and Chaetoceros calcitrans at three different densities. Early veliger mortality was high, likely due to low initial larval quality, but two larvae exhibited typical Conus development and survived without metamorphosis for 110 days. In experiment 2, 27-day-old larvae—possibly competent to metamorphose—were exposed to tiles potentially coated with biofilm from the adult culture tank, but no metamorphosis occurred. In experiment 3, salinity was reduced from 34 ppt by 3 ppt every three days starting 21 days after hatching. Larvae began velum resorption at 19 ppt; however, mortality sharply increased at 16 ppt, and metamorphosed juveniles retained partial velum. Hawaiian Conus larvae are known to undergo rapid metamorphosis in response to biofilms present in natural seawater. Our findings suggest that reduced salinity in inshore environments may serve as a cue for metamorphosis in C. fulmen, but it is unlikely to function as the primary inducer. Further laboratory studies using seawater from natural habitats are needed to clarify the environmental factors—such as biofilms and salinity levels—that initiate metamorphosis in this species.

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A large megalopa was collected from the floating seaweed at the mouth of Ago Bay. Morphological and DNA barcoding analysis using 16S rDNA sequence revealed that the megalopa is Percnon guinotae Crosnier, 1965. This is the second record of the megalopa of P. guinotae and the first from Japan.

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The xanthid crab Atergatis floridus is toxic, containing paralytic shellfish toxins at levels lethal to humans. To predict the species’ potential distribution, it is essential to understand the environmental factors that influence survival and development throughout its life cycle. This study investigated the effects of temperature—one of the most critical environmental variables for decapod embryos—on the survival and development of A. floridus embryos. Specimens were collected from Ishigakijima Island (~24°N) and Tateyama on the Boso Peninsula (~35°N), Japan. Embryos from three broods at Ishigakijima Island and one brood at Tateyama were individually cultured at five temperatures (16, 20, 24, 28, and 32 °C) until hatching. No embryos hatched at 16 °C, consistent with the lower developmental threshold temperature (14.0–14.8 °C) estimated using heat summation theory. Hatching occurred at temperatures ≥ 20 °C, with the highest success at 24–28 °C, and similar thermal adaptations were observed between localities. These findings provide insight into the reproductive season and the geographic regions suitable for larval production in A. floridus based on embryonic temperature tolerance.

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The diet and morphology of juvenile yellow goosefish (Lophius litulon) collected by bottom trawl surveys were analyzed. The size distribution of the juveniles collected (39.5–87.7 mm standard length; SL, n = 46) overlapped with that of pelagic juveniles reported in a previous study. Prey items were exclusively dominated by demersal fish. Allometric relationships of the head length and head width to the SL showed inflection points, shifting from positive to negative allometry at 44.6 mm and 48.2 mm SL, respectively. The positive allometry of the head size may enable the juveniles to swallow larger prey items such as demersal fish. The head size of juveniles larger than the inflection points and most of the other examined traits tended to show negative allometry, indicating a growth strategy that favors somatic growth rather than further enlargement of prey size or swimming ability. Based on the allometric growth and previous studies on feeding habits of juveniles, the transition from the pelagic to the demersal phase appears to be completed by ca. 50 mm SL.

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We determined the complete mitochondrial DNA sequences of the Japanese endemic subspecies Yamato-charr (Salvelinus leucomaenis japonicus) collected from two separate rivers in central Japan: Kiso and Oi rivers. The sequences were 16,655 bp and 16,654 bp, respectively. Molecular phylogenetic and dating analyses suggest that the Kiso River population descends from the oldest lineage in the Central Japanese region and has been isolated in cold, mountainous refugia for up to 600,000 years.

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The common freshwater shrimp Palaemon paucidens is recognized as a species complex comprising three genetically distinct types, referred to as A, B, and C. The B type is further subdivided into two subtypes, B-I and B-II, with B-I being described as the new species P. septemtrionalis. In this study, we designed a PCR primer pair based on the nucleotide sequence of the cDNA encoding the insulin-like androgenic gland hormone (IAG) of P. paucidens. PCR products were cloned and the nucleotide sequences from A, B (including both B-I and B-II subtypes), and C types were determined. The PCR products encompassed the entire exon 1, the complete intron 1, and partial exon 2. Phylogenetic analysis revealed two largely divergent clades, designated as IAG1 and IAG2 paralogs. Substantial nucleotide sequence differences were observed among the three types in IAG1 and between B and C types in IAG2. Notably, no IAG2 was detected in A type samples, and no apparent difference was observed between the B-I and B-II subtypes in either paralog.

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In August 2025, two species of flagtails, Kuhlia marginata (Cuvier, 1829) and Kuhlia rupestris (Lacepède, 1802) were collected from the mouth of Kamo-gawa River on Hachijo-jima Island, Izu Islands, Tokyo Metropolis, Japan. Although both species have wide ranges of distributions through the Indo-Pacific, no verifiable records have been known in the Izu Islands. Thus, the present specimens represent the first confirmed records of each species in the region. As the two species of Kuhlia are catadromous fish, their presence on Hachijo-jima Island, located on the path of the Kuroshio Current, is likely due to the natural dispersal of larvae from the south. However, given the scarcity and instability of inland freshwater habitats on Hachijo-jima Island, it may be difficult for K. marginata and K. rupestris to establish stable populations.

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The Pelagiidae family is a diverse group of jellyfish that vary greatly in morphology and ecology. Members of this family are found worldwide except in the polar regions. While some species pose a public health concern due to their ability to cause stinging injuries and impact fisheries, Pelagiidae jellyfish are also popular aquarium animals. Artemia nauplii are often used to raise jellyfish, but Pelagiidae jellyfish require other jellyfish and fish meat. Although Asian moon jellyfish (Aurelia coerulea) can be used as feed, propagating and maintaining a stable supply present numerous challenges. At the Shimoda Floating Aquarium in Japan, we fed horse mackerel (Trachurus japonicus) meat to Pelagiidae jellyfish, which sometimes caused digestive issues. We have been working on developing and testing alternative jellyfish feed. This report introduces a method for preparing the new feed and presents results from feeding it to three Pelagiidae species (Chrysaora pacifica, Chrysaora helvora, and Sanderia malayensis).

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The olfactory apparatus along with the gustatory system are the key networks approaching the chemicals present in aquatic environments. Among these two, olfaction employs its interpretative cellular framework for detection and interaction and convey decisive signals to the brain for necessary behavioral vis-à-vis physiological processes. The structural variation in shape, size and number of lamellae on the olfactory organ, as well as the distribution pattern of sensory cells together with non-sensory zones, characterize ecological niche of teleost. Additionally, the intricate cellular architecture of olfactory epithelium explains the regions of procurement of chemical signals through discrete neuronal cells. Keeping eye on teleost, the current study investigated about the anatomy, structural and cellular characterization of olfactory organ of Indian Major Carp Labeo rohita with the help of light, fluorescence and electron microscopy. The present study finds L. rohita olfactory organ as an oval structure consisting an intricate neuro-cellular organization. The findings highlight three morphologically distinct olfactory neurons. Furthermore, Immunolabelling of with Gα subtypes reveals distribution of functionally peculiar olfactory neurons and corresponding axonal projection to olfactory bulb regions. Thus, this study bridges the gap of existing knowledge on detailed neuroanatomical and functional magnitudes of teleost olfactory organ. This detailed information will pave new path for future investigations on its chemosensory mannerism.

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Over the past five years, Aquamarine Fukushima has conducted deep-sea surveys off the coast of Rausu, Hokkaido, Japan. During these surveys, two species of aegid isopods were collected. In the present study, we report the first discovery of these two species in an attaching state, along with the identification of their host fishes. We also describe observations made from the time of collection to the detachment of the isopods from their hosts. Additionally, we provide an overview of the husbandry records of cold-water isopods maintained at Aquamarine Fukushima to date.

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The habitat of the Japanese Silhouette Goby Silhouettea dotui was confirmed from the tidal flat at the mouth of the Ohura River, Minami-satsuma, Satsuma Peninsula, Kagoshima Prefecture, Kyushu, Japan. The species was originally described from Ariake Bay (western part of Kyushu) and has been recorded from Japan (Aomori Prefecture to Kagoshima mainland) and Taiwan. In Kagoshima Prefecture, the species was previously known only from Fukiage-hama beach in the western part of the Satsuma Peninsula, Kagoshima mainland. Therefore, the Ohura River mouth is the second recognized habitat for the species in the Kagoshima Prefecture, as well as being the southernmost distribution record in Japanese waters. The species was the most abundant species in the lower intertidal zone to the adjacent subtidal zone between May and early June, while the species did not appear in other seasons. On 9 June 2024, radial structures created by shallow grooves radiating outwards were found, with one leaf shallowly embedded in the center of each structure. The maximum diameter of the structure was ca. 30 cm. A total of 664 eggs at similar developmental stage were observed in one nest. One leaf (with eggs on the underside) and an adult male were collected together from one groove structure. In other cases, one leaf (without eggs) and one adult male and female were collected together from each structure. These results suggest that Silhouette dotui lays their eggs on the underside of a structure shallowly embedded in the sandy sediment and makes the radial groove structure around their spawning nest before spawning.

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This study conducted DNA barcoding based on the mitochondrial DNA (mtDNA) COI sequences for all seven known species of the family Mesoveliidae (Hemiptera) recorded in Japan. Additionally, molecular phylogenetic analyses were performed using these COI sequences. The results revealed that Japanese species are broadly divided into three major lineages. Each of the seven morphologically identified species was clearly distinguished genetically within this region. However, further genetic differentiation was observed within populations of Mesovelia horvathi and Nagisavelia hikarui, indicating the presence of genetically distinct groups within these species.

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The ovigerous female of Latreutes mucronatus (Stimpson, 1860) was collected from Korangi Creek Karachi, Pakistan, and retained in the laboratory. The larvae hatched after 2 days and survived within 3 days at room temperature 27–30 °C in filtered seawater with a salinity of 35–37 ppt and a pH of 7.6–7.8. In order to feed the larvae, Artemia nauplii were used. Two zoeal stages are described, illustrated, and compared with those of the larvae of its congener that are known from previous studies.

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The red-clawed crab Chiromantes haematocheir is a semi-terrestrial species in the family Sesarmidae distributed from Aomori Prefecture to Ryukyu Islands in Japan. It inhabits forest edges near coasts and estuaries, residing in burrows on slopes, embankments, and reed beds along coastal forest edges adjacent to aquatic environments. However, the population has declined significantly due to coastal and riverbank development, including concrete landfilling and road construction that disrupts access to larval release areas. Conservation efforts, such as biotope creation and habitat evaluation using C. haematocheir as an indicator, have been initiated. Studies in urban environments show that it prefers artificial water channels along forest edges while avoiding flat, bare land. This study investigates the habitat conditions around Lake Kamo, a brackish lake on Sado Island, Niigata Prefecture, utilized by C. haematocheir for burrows. A high density of burrows was observed on the grounds of Kisaki Shrine near Lake Kamo, predominantly around the bases of living and dead trees rather than near buildings or stone monuments. Tree species within the shrine grounds were identified, and burrows were counted around each. Chiromantes haematocheir showed a preference for Japanese eurya, Eurya japonica var. japonica, likely due to its shrub-like growth habit with horizontally spreading branches and leaves that provide shelter from bird predation. This study provides the first evidence of tree species preferences in C. haematocheir nesting sites. Future research in other regions could inform innovative coastal park designs and construction plans that incorporate tree species utilization as an indicator for suitable nesting environments.

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The fauna of marine heterobranch sea slugs including Pleurobranchida, Doridida, Nudibranchia, and Aplysiida was investigated at the two sites in Hitachinaka, Ibaraki Prefecture, Japan on January, February, June and August 2024. A total of 16 species in 10 families were collected in this survey. Among them, eight species in six families are newly recorded from Ibaraki Prefecture. These findings represent the baseline data for future studies on the species diversity and distributions of heterobranch sea slugs in the prefecture.

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In this study, we collected an individual of the loach (Misgurnus anguillicaudatus) from the Nakahara River of the Asahi River system in Okayama City, Okayama Prefecture. Genetic analysis of the mitochondrial cytochrome b (cyt-b) gene of this individual revealed a haplotype identical to that of the Chinese lineage. This haplotype has previously been reported only in Hofu City, Yamaguchi Prefecture, western Japan. The number of branched soft rays in the dorsal fin was 7. The ratio of the length from the posterior edge of the anal fin base to the base of the caudal fin, relative to the length from the insertion point of the pelvic fin to the anterior edge of the anal fin base was 1.0. These morphological characteristics were consistent with those of the Chinese lineage. Our study provides the first specimen-based record of the Chinese lineage of M. anguillicaudatus in Okayama City. Misgurnus anguillicaudatus has been designated as Near Threatened on the Red Lists of both the Ministry of the Environment of Japan and Okayama Prefecture, and our finding may provide important information for conserving the native lineages of M. anguillicaudatus in Okayama Prefecture.

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