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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.

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.

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.

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.

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.

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.

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.

SUMMARY: The objective of this study was to reveal the spawning grounds and reproductive characteristics of anadromous and resident pond smelt, Hypomesus nipponensis, coexisting in Lake Ogawara. Life history styles of females shedding in spawning grounds in the lake and its inflowing rivers were differentiated by otolith increment analysis. Size, dry weight, and water content of mature oocytes and fecundity of fish were compared between resident and anadromous fish. Both anadromous and resident fish spawned in the lake. In contrast, no resident fish were found in any of the inflowing rivers, where only anadromous fish spawned. Regression of fecundity against standard length was discontinuous with an inflection point at 63.8 mm, which is the body size that differentiates large anadromous spawning groups from small resident spawning groups. Mean oocyte diameters were not significantly different between resident and anadromous fish. The eggs of resident fish had significantly more water content and a significantly lower dry weight than those of anadromous fish. These differences might influence the growth and developmental processes of progeny.

SUMMARY: Growth formulae of two forms of pond smelt Hypomesus nipponensis in Lake Kasumigaura were estimated using frequency distribution of body length, and the relationship between water temperature. Their growth was studied based on specimens collected by fisheries during the period from June 1992 to February 1998. The growth parameters of von Bertalanffy, Gompertz, and Logistic models and their modified models in which the growth rate changes with one or two cycles per year were calculated by the non-linear weighted least squares method. On the basis of the AIC (Akaike’s Information Criterion) values, the modified models in which the growth rate changes with two cycles per year were selected as the best-fitting models for both forms. These formulae represent biological characteristics of the pond smelt in Lake Kasumigaura, i.e. the growth is superior in spring and autumn but inferior in summer and winter. The growth patterns of both forms were similar, but the large form showed a more superior growth rate than the small form from June to July. As for the relationship between the growth and water temperature, until the middle of September the growth was inferior as the cumulative water temperature increased, after which the small form grew to about 82 mm and the large form grew to about 108 mm without any influence from water temperature.

In California’s Sacramento-San Joaquin estuary, environmental protection and habitat restoration efforts directed at a threatened native osmerid, the delta smelt (Hypomesus transpacificus), are complicated by the presence of a morphologically similar non-native congener, the wakasagi (H. nipponensis), transported to the estuary from upstream reservoirs. In order to better define delta smelt critical habitat and to evaluate the potential for habitat overlap by these two species, we compared the tolerances of the two species to temperature, salinity, and water velocity, environmental factors that vary spatially and temporally within the estuary. For fishes acclimated to 17°C and fresh water (0 ppt), we measured critical thermal maxima and minima, chronic upper salinity tolerance limits, and critical swimming velocities. Wakasagi had higher critical thermal maxima (29.1°C vs. 25.4°C for delta smelt), lower critical thermal minima (2.3°C vs. 7.5°C for delta smelt), higher upper salinity tolerances (26.8 ppt vs. 19.1 ppt for delta smelt), and swam faster (for 6–6.9 cm SL fish, 43.3 cm s–1 vs. 28.2 cm s–1 for delta smelt) than delta smelt. This suggests that the wide seasonal and year-to-year fluctuations in temperature, salinity, and flow typical in the estuary would not exclude wakasagi, although their eggs and larvae may be less tolerant. With respect to these factors, the native delta smelt may be at a physiological disadvantage, particularly in habitats with suboptimal environmental conditions, and may be excluded from shallow-water habitat restoration sites, which are characterized by poor circulation, low flows, and more environmentally extreme conditions. The low abundance of wakasagi in the estuary recorded to date may indicate that factors other than temperature, salinity, and flow determine wakasagi distribution.

We characterized 24 polymorphic tetranucleotide microsatellite loci for delta smelt (Hypomesus transpacificus ) endemic to the San Francisco Bay Estuary, California, USA. Screening of samples (n = 30) yielded two to 26 alleles per locus with observed levels of heterozygosity ranging from 0.17 to 1.0. Only one locus deviated from Hardy–Weinberg equilibrium, suggesting these individuals originate from a single panmictic population. Linkage disequilibrium was found in two pairs of loci after excluding the locus out of Hardy–Weinberg equilibrium. Twenty-two primer pairs crossamplified in wakasagi smelt ( Hypomesus nipponensis), and 15 primer pairs cross-amplified in longfin smelt (Spirinchus thaleichthys).

A lot of reports of antifreeze protein (AFP) from fish have been published, but no report has mentioned of commercialized mid-latitude fresh water fish which producing AFP in its body fluid. We found that the AFP in the body fluid of Japanese smelt (Hypomesus nipponensis) from mid-latitude fresh water was purified and characterized. The N-terminal amino acid sequence of the Japanese smelt AFP was 75.0% identical to Type II AFP from herring. Results of EDTA treatment and ruthenium red staining suggested that the Japanese smelt AFP had at least one Ca2+-binding domain. Interestingly, the antifreeze activity of the Japanese smelt AFP did not completely disappear when Ca2+ ions were removed. The molecular mass of the Japanese smelt AFP was calculated to be 16,756.8 by the TOF-mass analysis. The Open reading flame of the gene coding for the Japanese smelt AFP was 444 bp long and was 85.0% identical with the entire herring AFP gene. The cDNA and amino acid sequence of the Japanese smelt AFP were the same length as those of herring AFP.

The fishes of smelt genus Hypomesus lives in fresh water,brackish water and coastal seas,distributes in the Northern Hemisphere.Now,the Japanese smelt H.nipponensis and the pond smelt H.olidus are the common species and mainly distributed in the northeast region in China.Their bodies are small with silvery white.The life span of the fishes is short and theirs age of sexual maturity is above 1 year and they dies after spawning.They have strong adaptability and have been transplanted widely in China as the important commercial fishes.However,it is strange that there still exist disputation so far on which species of Hypomesus ever been transplanted widely in China.In this study,transplanted Hypomesus collected from seven places locating in Heilongjiang,Xinjiang and Yunnan province are identified using CO I gene,which is a popular DNA barcoding for species identification in the world.Comparative analysis showed that CO I gene sequence from all above collected somelts shared more than 99% similarity with that from H.nipponensis,which was published on the webs of GenBank and DNA barcoding Center.Genetic distance within each group and pairwise distance between transplanted smelt and H.nipponensis both ranged from 0.1% to 0.3%,and were rather smaller than those genetic distances between transplanted smelt and other species of Hypomesus(all more than 10%).The topology of each final tree further revealed that all individuals of transplanted smelt and H.nipponensis formed a strong monophyletic group.Taken together,these results all showed that the transplanted smelt were Japanese smelt H.nipponensis.In addition,even the genetic differentiation in transplanted smelt populations was not significant(P = 0.066 47 0.05),six populations of transplant Japanese smelt endured somewhat selection pressure of environment based on Tajima's D value.Median-joining haplotype network for Hypomesus 7 transplanted populations can not tell us too much about their genetic relation and the transplant routes.Cross-transplanted or/and multi-transplanted might be the reason.

Two species of smelt (Osmeridae), Hypomesus transpacificus and Spirinchus thaleichthys, found in the Sacramento-San Joaquin estuary recently have declined in abundance, and H. transpacificus has been threatened by the introduction of nonnative Hypomesus nipponensis. We conducted an allozyme analysis of five species of smelt found in California to determine whether the threatened populations are distinct genetically and to evaluate the possibility of introgression of foreign alleles in H. transpacificus. Native H. transpacificus and introduced H. nipponensis differed genetically (Nei's D = 0.883) and were allelically distinct at 13 of 22 loci. Hypomesus transpacificus is more similar genetically to the native marine species, Hypomesus pretiosus (Nei's D = 0.400) than to H. nipponensis, strongly supporting the interpretation that H. transpacificus and H. nipponensis are distinct species. Populations of S. thaleichthys from Washington and the Sacramento-San Joaquin delta are similar genetically (Nei's D = 0.005). However, gene frequencies among these two populations of S. thaleichthys differed significantly, suggesting that current gene flow between them is restricted. This result, combined with geographic isolation suggests that the delta population of S. thaleichthys warrants management as an isolated and genetically distinct entity.