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In Lake Nojiri, the Japanese smelt, Hypomesus nipponensis McAllister, 1963, population has been thought to be maintained by artificial spawning, and stocking efforts as natural spawning in in-flowing streams is unlikely due to the lack of inflowing stream habitat. In this study, novel resident Japanese smelt spawning was observed along the lakeshore in shallow areas with clean gravel and flow. Spawning occurred at night during early March to mid-April and eggs, confirmed on gravel substrate, progressed to the eyed state in 5–6 weeks. Although natural spawning was observed, the ratio of eggs that progressed to the eyed stage was minimal, possibly due to thick algae cover in areas with low flow velocity. Therefore, resident Japanese smelt spawning along the lake shoreline is physically possible and potentially contributes to the overall population in Lake Nojiri, but in-lake spawning alone presumably is not a biologically viable method for population sustainability due to low survival rates and egg density at present. Environmental improvements such as construction of fish ladders to suitable in-flowing spawning habitat, introduction of clean gravel to shorelines, and water level management adjusted to the smelt spawning run would contribute to higher recruitment by natural smelt reproduction, and consequently enhance the smelt production in Lake Nojiri.

Vision plays a crucial role in the life of the vast majority of vertebrate species. The spatial arrangement of retinal ganglion cells has been reported to be related to a species’ visual behavior. There are many studies focusing on the ganglion cell topography in bony fish species. However, there are still large gaps in our knowledge on the subject. We studied the topography of retinal ganglion cells (GCs) in the Japanese smelt Hypomesus nipponensis, a highly visual teleostean fish with a complex life cycle. DAPI labeling was used to visualize cell nuclei in the ganglion cell and inner plexiform layers. The ganglion cell layer was relatively thin (about 6‐8 μm), even in areas of increased cell density (area retinae temporalis), and was normally composed of a single layer of cells. In all retinal regions, rare cells occurred in the inner plexiform layer. Nissl‐stained retinae were used to estimate the proportion of displaced amacrine cells and glia in different retinal regions. In all retinal regions, about 84.5% of cells in the GC layer were found to be ganglion cells. The density of GCs varied across the retina in a regular way. It was minimum (3990 and 2380 cells/mm(2) in the smaller and larger fish, respectively) in the dorsal and ventral periphery. It gradually increased centripetally and reached a maximum of 14,275 and 10,960 cells/mm(2) (in the smaller and larger fish, respectively) in the temporal retina, where a pronounced area retinae temporalis was detected. The total number of GCs varied from 177 × 10(3) (smaller fish) to 212 × 10(3) cells (larger fish). The theoretical anatomical spatial resolution (the anatomical estimate of the upper limit of visual acuity calculated from the density of GCs and eye geometry and expressed in cycles per degree) was minimum in the ventral periphery (smaller fish, 1.46 cpd; larger fish, 1.26 cpd) and maximum in area retinae temporalis (smaller fish, 2.83 cpd; larger fish, 2.75 cpd). The relatively high density of GCs and the presence of area retinae temporalis in the Japanese smelt are consistent with its highly visual behavior. The present findings contribute to our understanding of the factors affecting the topography of retinal ganglion cells and visual acuity in fish.

** Hypomesus nipponensis McAllister, 1963. Wakasagi. To 19.5 cm (7.8 in) SL (Saruwatari et al. 1997). Widespread in Japan, Sakhalin Island and environs (Dyldin and Orlov 2016b); introduced to California lakes in 1959 (Saruwatari et al. 1997), now in Sacramento���San Joaquin Estuary (Aasen et al. 1998). Primarily a brackish-water species; found also in fresh water, commonly from transplants (Saruwatari et al. 1997); depth: shallow waters to 50 m (164 ft) (Kim and Kim 2019)., Published as part of Love, Milton S., Bizzarro, Joseph J., Cornthwaite, Maria, Frable, Benjamin W. & Maslenikov, Katherine P., 2021, Checklist of marine and estuarine fishes from the Alaska-Yukon Border, Beaufort Sea, to Cabo San Lucas, Mexico, pp. 1-285 in Zootaxa 5053 (1) on page 51, DOI: 10.11646/zootaxa.5053.1.1, http://zenodo.org/record/5578008, {"references":["McAllister, D. E. (1963) A revision of the smelt family, Osmeridae. Bulletin of the National Museum of Canada, 191.","Saruwatari, T., Lopez, J. A. & Pietsch, T. W. (1997) A revision of the osmerid genus Hypomesus Gill (Teleostei: Salmoniformes), with the description of a new species from the southern Kuril Islands. Species Diversity, 2, 59 - 82. https: // doi. org / 10.12782 / specdiv. 2.59","Dyldin, Yu. V. & Orlov, A. M. (2016 b) Ichthyofauna of fresh and brackish waters of Sakhalin Island: an annotated list with taxonomic comments: 2. Cyprinidae - Salmonidae families. Journal of Ichthyology, 56, 534 - 555. https: // doi. org / 10.1134 / s 0032945216050040","Aasen, G. A., Sweetnam, D. A. & Lynch, L. M. (1998) Establishment of the wakasagi, Hypomesus nipponensis, in the Sacramento- San Joaquin Estuary. California Fish and Game, 84, 31 - 35.","Kim, S. T. & Kim, A. (2019) The structure of multispecies associated communities of fish at western Sakhalin coast by the results of a trawling assessment survey on R / V Bukhoro in June 2018. Journal of Ichthyology, 59, 707 - 726. https: // doi. org / 10.1134 / s 0032945219050060"]}

The Fukushima Daiichi Nuclear Power Plant accident also contaminates lakes in Japan. Especially in closed lakes, there is a problem of prolonged low-level $$^{137}$$ 137 Cs contamination because the activity concentration of $$^{137}$$ 137 Cs declines sharply immediately after the accident, but then begins to decrease slowly. In this paper, we derived a long-term prediction formula based on the fractional diffusion model (FDM) for the temporal variation in $$^{137}$$ 137 Cs activity concentrations of the water in Lake Onuma on Mt. Akagi, one of the closed lakes, and of pond smelt (Hypomesus nipponensis), a typical fish species inhabiting in the lake. The formula reproduced well the measured $$^{137}$$ 137 Cs activity concentration of the lake water and pond smelt for 5.4 years after the accident. Next, we performed long-term prediction for 10,000 days using this formula and compared it with the prediction results of the two-component decay function model (TDM), which is the most common model. The results suggest that the FDM prediction will lead to a longer period of contamination with low-level $$^{137}$$ 137 Cs than the TDM prediction.

The introduction of non-native fish species is known to have adverse effects on aquatic ecosystems, but their effect on plateau lakes is not well studied. In this study, we examined the effect of the Japanese smelt (Hypomesus nipponensis) invasion on the fish assemblage in Lake Erhai, a subtropical plateau lake in southwestern China. Through cluster analysis and non-metric multidimensional scaling (NMDS), we found a significant fish assemblage shift: the population of sharpbelly (Hemiculter leucisculus) fell by 67% in catch per unit effort (CPUE) from 2.262 to 0.741, topmouth gudgeon (Pseudorasbora parva) fell by 52% from 0.61 to 0.29, and icefish (Neosalanx taihuensis) plummeted by 88% from 0.736 to 0.088. Meanwhile, the numbers for crucian carp (Carassius auratus) improved by almost 185% from 1.82 to 3.36. A Pearson correlation analysis showed that these four species significantly correlated with the invasion of the Japanese smelt: sharpbelly (−0.71), topmouth gudgeon (−0.71), icefish (−0.62), and crucian carp (0.81). This study documented the expansion of invasive fish and their effects on native species over time, thus providing a case study of invasive fish as well as a theoretical basis for further research into interspecies interactions.

We report the draft genome sequence of Deefgea sp. strain CFH1-16, isolated from the intestine of a Hypomesus nipponensis collected from the Republic of Korea. The genome sequence was assembled into two contigs with 48.2% G+C content. This genome data could improve our understanding of adaptation in the fish intestine., Reported here is the draft genome sequence of Deefgea sp. strain CFH1-16, isolated from the intestine of a Hypomesus nipponensis fish collected from the Republic of Korea. The genome sequence was assembled into two contigs with 48.2% G+C content. These genome data could improve our understanding of adaptation in the fish intestine.

Pond smelt (Hypomesus nipponensis) is a cold-freshwater fish species as a winter economic resource of aquaculture in South Korea. Due to its high susceptibility to abnormal water temperature from global warming, a large number of smelt die in hot summer. Here, we present the first draft genome of H. nipponensis and transcriptomic changes in molecular mechanisms or intracellular responses under heat stress. We combined Illumina and PacBio sequencing technologies to generate the draft genome of H. nipponensis. Based on the reference genome, we conducted transcriptome analysis of liver and muscle tissues under normal (NT, 5°C) versus warm (HT, 23°C) conditions, to identify heat stress-induced genes and gene categories. We observed a total of 1,987 contigs, with N50 of 0.46 Mbp with a largest contig (3.03 Mbp) in the assembled genome. A total number of 20,644 protein coding genes were predicted, and 19,224 genes were functionally annotated: 15,955 genes for Gene Ontology (GO) terms; and 11,560 genes for KEGG Orthology (KO). We conducted the lost and gained genes analysis compared with three species that human, zebrafish and salmon. In the lost genes analysis, we detected smelt lost 4,461 (22.16%), 2,825 (10.62%), and 1,499 (3.09%) genes compare with above three species, respectively. In the gained genes analysis, we observed smelt gain 1,133 (5.49%), 1,670 (8.09%), and 229 (1.11%) genes compare with above species, respectively. From transcriptome analysis, a total of 297 and 331 differentially expressed genes (DEGs) with False discovery rate (FDR) < 0.05 were identified in the liver and muscle tissues, respectively. Gene enrichment analysis of DEGs indicates that up-regulated genes were significantly enriched for lipid biosynthetic process (GO:0008610, P < 0.001) and regulation of apoptotic process (GO:0042981, P < 0.01), and down-regulated genes by immune responses such as myeloid cell differentiation (GO:0030099, P < 0.001) in the liver under heat stress. In muscle tissue, up-regulated genes were enriched for hypoxia (GO:0001666, P < 0.05), transcription regulator activity (GO:0140110, P < 0.001) and calcium-release channel activity (GO:0015278, P < 0.01), and down-regulated genes for nicotinamide nucleotide biosynthetic process (GO:0019359, P < 0.01). The results of KEGG pathway analysis were similar to that of gene enrichment analysis. The draft genome and transcriptomic of H. nipponensis will be used as a useful genetic resource for functional and evolutionary studies. Our findings will improve understanding of the molecular mechanisms and heat responses and will be useful for predicting survival of the smelt and its closely related species under global warming.

The Fukushima Dai-ichi Nuclear Power Plant accident on 11 March 2011 released large amounts of radiocesium (134Cs and 137Cs) and contaminated the environment of Gunma Prefecture in eastern Japan. Concentrations of 640 Bq kg−1-wet radiocesium were found in wakasagi (Hypomesus nipponensis) in Lake Onuma on Mt. Akagi in Gunma Prefecture in August 2011. To elucidate the effect of body size on radiocesium levels in the Lake Onuma ecosystem, we determined age, body weight class, and radiocesium concentrations in wakasagi from 2012 to 2019. Furthermore, we estimated the effective ecological half-life of 137Cs using 137Cs concentration survey data and decay function models. A body size effect was found for the 137Cs concentration of wakasagi from 2012 to 2015, i.e., the 137Cs concentration increased with increased body weight. Conversely, no body size effect was found from 2016 to 2019. This may be due to the 137Cs concentration of the lake water stabilizing after May 2014, and wakasagi being a small plankton-feeding fish. The decay of the 137Cs concentration in wakasagi at age 0+ consisted of fast- and slow-term components, and the 137Cs concentration decay rate was greatly reduced. Although the radiocesium contamination level of wakasagi inhabiting Lake Onuma has decreased, contamination has continued and monitoring studies should be continued.

The Fukushima Daiichi Nuclear Power Plant accident on March 11, 2011 released substantial amounts of radiocesium (134Cs and 137Cs) and contaminated the environment across eastern Japan. In this study, we aimed to elucidate the temporal dynamics of 137Cs in the aquatic ecosystem of Lake Onuma, Mt. Akagi. We estimated the effective ecological half-life of 137Cs in fish and lake water, using 137Cs concentration survey data collected from 2011 to 2019, and single- and two-component decay function models (SDM and TDM, respectively). TDMs provided a good fit for 137Cs concentration decline processes in wakasagi (Hypomesus nipponensis), pale chub (Zacco platypus), and lake water. We concluded that 137Cs concentrations approached a state of dynamic equilibrium between these aquatic organisms (wakasagi and pale chub) and the lake water. However, SDMs better predicted decline processes in 137Cs concentrations in charr (Salvelinus leucomaenis), Japanese dace (Tribolodon hakonensis), and western waterweed (Elodea nuttallii). The 137Cs mass balance in Lake Onuma suggests that 137Cs may be eluted from the lake bottom sediments. In summary, 137Cs contamination levels in Lake Onuma have significantly decreased, but monitoring surveys should continue to further our understanding of the processes underlying this reduction.

Introductions or alien species invasions will induce changes in aquatic ecosystems but are rarely reported in Chinese highland lakes. The Japanese smelt (Hypomesus nipponensis) invaded and has become a dominant fish species in Lake Erhai, a highland lake in southwestern China, since 2016. Here, we engineered Ecopath models for two different periods, 2008–2009 (preinvasion) and 2016–2018 (postinvasion), in Lake Erhai to model ecosystem impacts from the Japanese smelt invasion. In the dynamic Ecosim model based on the 2016–2018 Ecopath model, we ran three 50-year scenarios to simulate the potential effects of Japanese smelts on the system. Our results showed competition between invasive and native species as well as changes in trophic structures, highlighting the impacts of the invasive species over time. The lake ecosystem additionally experienced significant degradation after invasion, mainly reflected in several related indicators, such as total biomass/total system throughput (TB/TST), total primary production/total biomass (TPP/TB), total primary production/total respiration (TPP/TR), Finn's mean path length (FML), Finn's cycling index (FCI) and the Connectance Index (CI). The simulation results indicated that the relative biomass of icefish (Neosalanx taihuensis), bighead carp (Hypophthalmichthys nobilis), sharpbelly (Hemiculter leucisculus), and zooplankton were significantly affected by increasing the strength of the top-down control of the Japanese smelt on its prey. It is also important to do ecological regulation of planktivorous fishes in the studied Lake Erhai, especially the Japanese smelt.

Freshwater smelt (Hypomesus nipponensis) is a planktivorous fish found in the river of South Korea, Japan, China, and Russia. Because of its specific characteristics living in the cold temperature, this species is economically valuable in the various countries that held winter festival. The body size of the smelt is too small, so people consumed raw smelt during the winter festival sometimes. However, the microbial studies of smelt are nonexistent. Here, we characterized and compared the bacterial communities in the gut and skin of freshwater smelts. We amplified, sequenced, and analyzed the V4 regions of bacterial 16S rRNA genes from freshwater smelts. The microbial diversity in the skin (375 OTUs) was much greater than that in the gut (250 OTUs). At the phylum level, Proteobacteria (gut: 51.5%; skin: 52.9%), Firmicutes (gut: 30.6%; skin: 25.4%), Bacteroidetes (gut: 7.7%; skin: 14.7%), and Actinobacteria (gut: 5.2%; skin: 3.8%) were predominant in both organs. At the genus level, Sphingomonas (gut: 24.9%; skin: 4.4%, P

Understanding ecosystem dynamics of radionuclides is necessary to ensure effective management for food safety. The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident on March 11, 2011 released large amounts of radiocesium (134Cs and 137Cs) and contaminated the environment across eastern Japan. In this study, we aimed to elucidate the temporal dynamics of 137Cs in the aquatic ecosystem of Lake Onuma on Mt. Akagi. The effective ecological half-life (Teff) of 137Cs in fishes, western waterweed (Elodea nuttallii), seston (phytoplankton and zooplankton), and lake water was estimated using survey data of 137Cs concentration collected from 2011 to 2016, and single- and two-component decay function models (SDM and TDM, respectively). The decay processes of 137Cs concentrations in wakasagi (Hypomesus nipponensis), pale chub (Zacco platypus), phytoplankton, and total 137Cs concentrations of the water column (WC) in the lake were well suited by the TDMs. The Teff in the fast component of the TDMs in these samples ranged from 0.49 to 0.74years. The Teff in the slow component of the TDMs could converge towards the physical half-life of 137Cs. Nearly five and a half years after the FDNPP accident, we concluded that 137Cs concentrations approached a state of dynamic equilibrium between some aquatic organisms (wakasagi, pale chub, and phytoplankton) and the environment (lake water). However, the decay processes of 137Cs concentrations in Japanese dace (Tribolodon hakonensis), western waterweed, zooplankton, and particulate- and dissolved-forms in the WC were better predicted for the SDM. The total 137Cs concentrations in inflowing river and spring waters were one to two orders of magnitude lower than lake water under normal flow conditions. However, particulate 137Cs contamination level in the river water was high after heavy rains. Overall, 137Cs contamination levels have significantly decreased in Lake Onuma, but monitoring surveys should be continued for further understanding of the reduction processes.

Two threatened osmerid species native to the San Francisco Estuary (SFE)—Delta Smelt (Hypomesus transpacificus) and Longfin Smelt (Spirinchus thaleichthys)—are subject to broad human influence, including significant habitat alteration and the presence of the introduced osmerid, Wakasagi (Hypomesus nipponensis). The identification of these closely related species and their hybrids is difficult in field collected specimens which are subject to damage through handling and may be difficult to identify morphologically, especially when young. In addition, it is known that these three species hybridize, but the extent and effect of hybridization is difficult to quantify and monitor. We developed assays for 24 species-specific single nucleotide polymorphisms (SNPs) that identify whether a sample is a pure species (Delta Smelt, Longfin Smelt, or Wakasagi), a first generation (F₁) hybrid, or a backcross. We used this SNP panel to genetically identify wild osmerids collected in Yolo Bypass from 2010 to 2016 and detected nine Delta Smelt×Wakasagi F₁ hybrids and two Wakasagi×(Delta Smelt×Wakasagi) backcross hybrids; all assayed hybrids had Wakasagi as the maternal parent. The backcrossing into Wakasagi suggests that hybridization may only occur in one direction and thus preclude introgression to Delta Smelt. We also found substantial morphological field misidentifications (32.7%) in the Yolo Bypass samples resulting in more Wakasagi and fewer Delta Smelt than previously recorded when based on morphology. The SNP panel described in this study constitutes a valuable resource for monitoring hybridization in the SFE and assigning species identifications with accuracy and efficiency.

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident has resulted in the contamination of the environment in Gunma Prefecture with radioisotope cesium (radio-Cs, 134Cs and 137Cs). Concentrations of radio-Cs >500Bqkg-1 were found in wakasagi (Hypomesus nipponensis) in Lake Onuma at the top of Mount (Mt.) Akagi in August 2011. To explain the mechanism of this contamination, monitoring studies have been conducted around Lake Onuma by measuring radio-Cs concentrations in samples of fish, aquatic plants, plankton, lake water, lake sediments, and surrounding soil. The leachability of radio-Cs was evaluated using sequential extraction by Tessier et al. The total concentration of radio-Cs in Lake Onuma ecosystems decreased gradually with time. In the brown forest soil, radio-Cs concentrations of 2000 to 6000Bqkg-1 were detected. The abundance ratio of the easy-elution form (exchangeable and carbonate forms) in the samples was

We carried out the diet study of the little tern on the sandy islet in inland Andong Lake, Korea, during the beeding season (April to July 2018). To identify its diet and examine the importance of the main prey species as a food resource, we set two remote-control video cameras with 4K-resolution on the islet. One thousand two hundred seventy-five still images that the tern had prey in its bill were identified at the species level and measured on a monitor. Then, they were classified to five length-categories and compared among months and breeding stages. Freshwater fishes dominated the diet (100%; eleven species overall), where the landlocked pond smelt Hypomesus nipponensis (80.8%) and largemouth bass Micropterus salmoides (13.7%) were the primary and next essential prey species, respectively. The average prey item length was 51.04 ± 20.89 mm and significantly differed among months and breeding stages (P < 0.001, respectively). 50–75 mm prey length category was the most frequent in the diet (42.2%). In April and May, larger fish >50 mm constituted the greater part of their diet (93.1%, 66.3%, respectively), whereas the diet in June and July consisted of smaller fishes P < 0.001): 1–25 mm and 50–75 mm were overrepresented and underrepresented, respectively, at the chicks in the nest stage. On the other hand, 50–75 mm was preferred for the pre-laying and incubation stages. In terms of the survival condition of pond smelts, the before- and after water surface temperatures of the day when terns flew away showed a significant difference (P = 0.004), where a threshold looks like between 29.11°C and 30.04°C. These results support the prey abundance hypothesis that, when cold-water pond smelts might wholly swim down into the deeper lake in the hot summer, the terns might also leave their colony for another foraging place with higher prey availability.

To determine the food habits of salt marsh fishes, the gut contents of 28 species, caught from a salt marsh in Lake Hinuma, Ibaraki Prefecture, central Japan, were investigated. Ontogenetic changes in diet were apparent in six species, including several of commercial importance (e.g., Acanthopagrus schlegelii and Hypomesus nipponensis). Smaller juveniles of such species fed mostly on planktonic copepods, with other prey items, including mysids, gammaridean amphipods and chironomid larvae, forming greater proportions in the diet of larger individuals. A cluster analysis based on dietary overlaps indicated that the salt marsh fish assemblage consisted of seven feeding guilds (small benthic and epiphytic crustacean, zooplankton, aquatic insect, polychaete, plant, terrestrial insect and detritus feeders). Among these, the first two guilds were the most abundantly represented in terms of species number, suggesting that small benthic and epiphytic crustaceans (e.g., mysids and gammaridean amphipods) and zooplankton (e.g., calanoid and cyclopoid copepods) were important food resources for the fish assemblage at the study site.

Production of fish communities is evaluated for 15 types of estuaries in Primorye on the data collected in 80 surveys (860 seine stations) conducted in 2002-2015. The bulk of the production in all cases is formed by semi-anadromous species ( Liza haematocheilus , Tribolodon spp., Hypomesus nipponensis and others). In polyhaline estuaries ( EP ), a significant part of the production is formed by resident marine species (mainly by Eleginus gracilis , Liopsetta pinnifasciata , Pholis nebulosa ) and southern migrants ( Mugil cephalus , Konosirus punctatus , Hyporhamphus sajori , Strongylura anastomella ). In mesohaline ( EM ) and oligohaline ( EO ) estuaries, the portions of marine residents and southern migrants are minimal, but the portion of freshwater species ( Gobio macrocephalus , Carassius gibelio , Phoxinus spp., Rhodeus sericeus , Acanthorhodeus spp., etc.) is heightened. Seasonal dynamics of the production is distinguished by the maximum in July-September. Mean fish biomass in May-October (vegetation season) varies in the range 143-1463 mgС/m 2 , mean annual production - from 174 to 4267 mgС/m 2 , and mean P/B -ratio - from 0.2 to 3.2. Previously (in 2007) much higher annual production was registered in the Artemovka River estuary - 9356 mgС/m 2 , but such high value was formed only once by juveniles of L. haematocheilus belonged to highly abundant year-class hatched in 2006. Both production and P/B are the lowest in the waterbodies with salinity close to the barrier values (5-8 ‰ for a - horohalinicum and 22-26 ‰ for b - horohalinicum) that is usual for the types EM and EP ; this lowering is caused by osmotic regulation for freshwater and marine fish, respectively, in particular their juveniles with low tolerance to salinity changes. That’s why EM estuaries have lower abundance of juveniles relative to adult fish and therefore the lower production. In general, patterns of fish production in the estuaries of Primorye are similar to production of well investigated estuaries in the moderate, subtropical and tropical zones. The values of fish production in the estuaries of Primorye are comparable with the production in mesotrophic and eutrophic lakes of north-western Russia; being significantly lower than the production in large floodplain rivers but higher than the production in small rivers. Fish production for seas, including Japan Sea (0.20 gС/m 2 ) or its northwestern part - Peter the Great Bay (0.28 gС/m 2 ), is significantly lower.

Radionuclide ((131)I, (134)Cs, and (137)Cs) concentrations of monitored freshwater fish species collected from different habitats (rivers, lakes, and culture ponds) in Fukushima Prefecture during March 2011-December 2014 (total 16 species, n = 2692) were analyzed to present a detailed description of radionuclide contamination after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, and to elucidate species-specific spatiotemporal declining trends of (137)Cs concentration for their respective habitats. Low concentrations of (131)I (≤24 Bq kg(-1)-wet) were detected from only 11 samples collected during March-June 2011, demonstrating that (131)I transferred to freshwater fish were not intense. In river and lake fishes, a more gradual decrease and higher radiocesium ((134)Cs, (137)Cs) concentrations were observed than in culture pond fishes, which strongly implied that radiocesium in freshwater fish species was mainly bioaccumulated through the food web in the wild. During 2011-2014, percentages above the Japanese regulatory limit of 100 Bq kg(-1)-wet for radiocesium in river and lake fish (14.0% and 39.6%, respectively) were higher than in monitored marine fish (9.9%), indicating longer-term contamination of freshwater fish species, especially in lakes. Higher radiocesium concentrations (maximum 18.7 kBq kg(-1)-wet in Oncorhynchus masou) were found in the northwestern areas from the FDNPP with higher deposition. However, radiocesium contamination levels were regarded as 1-2 orders of magnitude less than those after the Chernobyl accident. Lagged increase of (137)Cs concentration and longer ecological half-lives (Teco: 1.2-2.6 y in the central part of Fukushima Prefecture) were observed in carnivorous salmonids (O. masou, Salvelinus leucomaenis), whereas a rapid increase and decrease of (137)Cs concentration and shorter Teco (0.99 and 0.69 y) were found in herbivorous and planktivorous osmerids (Plecoglossus altivelis, Hypomesus nipponensis) with younger age at maturity. Comparison of Teco among salmonids, osmerids, and cyprinids suggests that, in addition to the fish feeding habits and life-cycles, hydraulic conditions in rivers and lakes (e.g., turnover time), which are expected to affect radiocesium concentration in prey items, are an important factor affecting the (137)Cs decreasing rate of freshwater fish.

The dietary utilization of cyanobacterial carbon by fish communities is poorly understood. We examined the transfer of cyanobacterial carbon to fish in a eutrophic lake using fatty acid biomarkers and measuring the stable carbon isotope ratios of fatty acid and bulk nitrogen. We collected five species of fish (Hypomesus nipponensis, Carassius sp., Cyprinus carpio, Tridentiger brevispinis, and Gymnogobius castaneus) as well as the seston from June to November 2016 from Lake Hachiro, Japan. Cyanobacterial blooms were observed from August to October. From June to August, cyanobacterial fatty acid biomarkers (18:2ω6 and 18:3ω3) accounted for only 1.4–4.3% of total fatty acids in these fish species, indicating a low contribution of cyanobacteria to fish diets during this period. However, the contribution of the cyanobacterial fatty acid biomarkers in these fish species increased sharply in September (10.5–17.1%), except in second-year H. nipponensis. In September, the stable carbon isotope ratios of 18:3ω3 in these fish species were almost equivalent to those in the seston, which was primarily composed of cyanobacteria. The trophic positions of the collected fish species ranged from 1.6 to 3.4, based on their stable nitrogen isotope values, indicating that some fish ingested cyanobacteria directly, while others acquired cyanobacteria indirectly, through the food chain. These findings indicate that cyanobacterial carbon is transferred up the food chain in eutrophic lake ecosystems with cyanobacterial blooms.

According to the reference data in GenBank, the complete mitochondrial genome KP281293.1 presumably belongs to Hypomesus olidus from China. The phylogenetic analysis based on the Cytb and CoI genes...

The Japanese pond smelt (Hypomesus nipponensis) stock has been observed to fluctuate quite rigorously over the years with sustained periods of low catch in Lake Kasumigaura and Kitaura of the Ibaraki prefecture, Japan which would adversely affect the socioeconomic livelihood of the local fishermen and fisheries industry. This study was aimed at determining the factors affecting the stock fluctuation of the pond smelt through the different years in the two lakes. Through exploratory analysis it was found that the pond smelt had significant relationship with total phosphorus (TP) level in both lakes. The global mean land and ocean temperature index (LOTI) was also found to be indirectly related to the pond smelt stock in lake Kasumigaura and Kitaura at the latitude band of 24°N to 90°N (l). Both TP and LOTI had inverse relationship with pond smelt trajectory in both lakes. For both Lake Kasumigaura and Kitaura, TP for the individual lakes and LOTI (l) were used as independent variables using generalized linear model and response surface methods for modeling the stock dynamics of the pond smelt in the two lakes. Model selection was based on significant parameter estimates (p < 0.05), Akaikes Information Criterion and R2 values. Phosphorus loading is an indication of increasing anthropogenic activities in the surrounding area having negative impact on the pond smelt population. When management decisions are being made regarding pond smelt fishery and sustainability plans in the Ibaraki prefecture, the effects of TP and LOTI should be taken into account. Future research needs to be directed towards deeper understanding the mechanisms by which TP and LOTI affect pond smelt population in Lake Kasumigaura and Kitaura for more effective management.

We estimated the population size of the pond smelt Hypomesus nipponensis at the beginning of the fishing season in Lake Kasumigaura and Lake Kitaura, Japan using two DeLury methods and cohort analysis. A growth curve was estimated on the basis of monthly standard length. The relationship between standard length and weight was utilized for calculating the mean weight on the survey day in a particular month. Total monthly catches in Lake Kasumigaura and Lake Kitaura were calculated using partial monthly pond smelt catch obtained from processing plants located near the lakes between July and December. The total monthly catch was calculated from the total monthly catch weight and the monthly mean weight. The number of boats operating each month, compiled by the Kasumigaura-Kitaura Fisheries Office of Ibaraki Prefecture, was also employed. The estimated initial population sizes were compared with the population level index (PLI) estimated from survey data before the start of the fishing season. No significant differences were detected among the initial population sizes estimated by DeLury method, cohort analysis and PLI. The estimates ranged from 7.4 million to 410 million in Lake Kasumigaura, and from 7.7 million to 44 million in Lake Kitaura.

To evaluate the influences of the Fukushima nuclear accident in 2011 on lake sediments and fish and to understand the difference in their contamination levels, data on radiocesium concentrations ( 137 Cs and 134 Cs) were analyzed for sediments and 18 fish species (including one freshwater prawn) taken from 15 lakes in northeastern Japan. Temporal trends in radiocesium concentrations (referenced to radioactivity on 15 Mar 2011) were not clear during 2011–2013 except in a few species of fish. There was a decrease among topmouth gudgeon ( Pseudorasbora parva), icefish (Salangichthys microdon), and pond smelt (Hypomesus nipponensis) but an increase among channel catfish (Ictalurus punctatus) and kokanee (Oncorhynchus nerka). Significant positive correlations between lake-averaged radiocesium concentrations of sediments and fish were observed for most fish species. The partition coefficients (PCs), defined as fish concentration divided by sediment concentration on a dry weight basis, clustered mostly in the range of 0.3–3 ([Bq/kg-dry]/[Bq/kg-dry]) and were high in large-sized types (e.g., channel catfish and brown trout [ Salmo trutta]) but low in small-sized types (e.g., topmouth gudgeon and icefish). After normalization, the PCs of the respective lakes were analyzed together with lake characteristics related to water exchange and lake dimensions, water quality, and sediments and were found to be high in the lakes with high water retention time and vice versa, suggesting prolonged contact and equilibration between the water and the sediments. Finally, the efficacy and potential problems of using the PCs between sediments and fish are discussed.

The aim of this study was to investigate differences in δ13C and δ15N of pond smelt (Hypomesus nipponensis) collected from three brackish lagoons, which have different characteristics, the principal one being the presence or absence of a weir located near the mouth of the outlet channel. The presence or absence of a weir is reflected in a difference in salinity among the study lakes. We found a general pattern of lower pond smelt δ13C values in Lake Mae with lower salinity and higher pond smelt δ13C values in Lake Hwajinpo and Lake Youngrang (lagoons with higher salinity). Pond smelt δ13C values showed little variation among the three lagoons related to pond smelt length, but likely reflected the availability of freshwater prey in Lake Mae. Among the lagoons, we found that pond smelt δ15N values were lower in Lake Hwajinpo compared with pond smelt δ15N values in Lake Youngrang and Lake Mae. This pattern likely shows a difference in anthropogenic nitrogen (N) loading among the lagoons. The results...

The potential invasiveness of 28 freshwater fishes in northern Kyushu Island, Japan, was evaluated using the Fish Invasiveness Scoring Kit (FISK). The five co-authors scored the level of invasiveness for each species and calculated the total FISK scores; the maximum and minimum scores were then eliminated, and the mean of the remaining three scores was used as the final score for each species. The mean scores ranged from 11.0 (Hypomesus nipponensis) to 31.0 (Cyprinus carpio). The receiver operating characteristic curve indicated that the threshold value between fishes that present a high risk of invasion and the other species were 19.8.

The life histories of the pond smelt Hypomesus nipponensis collected from Japanese fresh waters and brackish (sea) waters were studied by examining the strontium (Sr) and calcium (Ca) concentrations in their otoliths. The Sr:Ca ratios in the otoliths changed with the salinity of the habitat. The pond smelt living in a freshwater environment showed consistently low Sr:Ca ratios throughout the otolith, averaging 1·2-1·3 x 10 -3 . These samples were identified as a standard freshwater type. In contrast, fish collected from the intertidal zone showed higher otolith Sr:Ca ratios than those in the standard freshwater type, and the ratios fluctuated along the growth phase. In addition to the two representative life-history types of H. nipponensis, i. e. freshwater and anadromous life-history types, other pond smelts were found to have an estuarine resident life history-type with no freshwater phase, indicating that the pond smelt has a flexible migration strategy with a high degree of behavioural plasticity and an ability to utilize the full range of salinity in its life history.

The polymerase chain reaction (PCR) was used to amplify a segment of the mitochondrial DNA coding for NADH-dehydrogenase subunits ND5/ND6 in five smelt species (family Osmeridae). Amplified DNA was screened for restriction fragment length polymorphism (RFLP). Nucleotide sequence divergence of mitochondrial DNA between species ranges from 11.9 (between Hypomesus nipponensis and H. japonicus) to 24.7% (between Osmerus mordax dentex and Mallotus villosus catervarius). The genetic divergence between populations of H. nipponensis, H. japonicus, and Osmerus mordax dentex was 0.32, 0.08 to 0.15, and 0.025%, respectively. The absence of common haplotypes enables differentiation of closely related smelt species and, therefore, can be used for solving current problems in the taxonomy and biogeography of this family.

Neutrophils of vertebrates undergo respiratory burst activity (RBA) as a defense mechanism against bacterial infections. We report here that ayu ( Plecoglossus altivelis ) have unusually high RBAs even when they are in a healthy condition. Kidney and blood leukocytes were obtained from ayu, rainbow trout ( Oncorhynchus mykiss ), carp ( Cyprinus carpio ), eel ( Anguilla japonica ), and pond smelt ( Hypomesus nipponensis ). Neutrophil RBA was measured by flow cytometry using dihydrorhodamine after stimulation with phorbol myristate acetate. The amount of RBA of neutrophils from both blood and kidney was significantly higher in ayu than in the other species (e.g. the fluorescence intensity of ayu blood neutrophils was about 3–7 times higher than that from trout and carp, and that of ayu kidney neutrophils was 2–19 times higher than that of rainbow trout, carp, eel, and pond smelt). This unique character of ayu neutrophils was invariable even at different ages, locations, and sex-maturation stages.

The echinorhynchid acanthocephalan Acanthocephalus sp. was collected and described from four species of fishes (rainbow trout Oncorhynchus mykiss, Sakhalin huchen Hucho perryi, Japanese pond smelt Hypomesus nipponensis, and threespine stickleback Gasterosteus aculeatus) from a lake system, the Tsugaru-Jūniko Lakes, in Aomori Prefecture, northern Japan. In rainbow trout, the prevalence and intensity of infection markedly differed between lakes, and the fish were most frequently and most heavily infected in the lakes with a dense population of the isopod intermediate host Asellus hilgendorfi. In isopods, the prevalence of acanthocephalan larvae increased in the late winter and reached its highest level in March or April. In rainbow trout, male worms were abundant from winter to spring, and female worms were immature during these seasons. Gravid females were abundant in summer and autumn. These findings indicate that Acanthocephalus sp. is an annual species and its recruitment from the intermediate host to the fish occurs mainly in winter and spring.

(2001). The interaction between lacustrine sockeye salmon (Oncorhynchus nerka) and pond smelt (Hypomesus nipponensis) in relation to the decline of zooplankton biomass in Lake Toya, northern Japan. SIL Proceedings, 1922-2010: Vol. 27, No. 7, pp. 3881-3885.