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Lake trout (Salvelinus namaycush) are an ecologically and economically important piscivore with reported differences in diet and feeding behaviour throughout its range. Eleven stomach content and stable isotope-based metrics were used to describe diets of 349 lake trout between two years (2013 and 2018) and among geographic zones (west, central, east, Kingston basin) in Lake Ontario. Using individual (e.g., volumetric, %V) and aggregate (e.g., index of relative importance, %IRI) diet metrics, we found an overwhelming dominance of alewife (Alosa pseudoharengus) in lake trout diets among some zones in 2013 (%V = 23.3 – 92.7; %IRI = 12.2 – 99.5) and all zones in 2018 (%V = 83.9 – 96.7; %IRI = 96.5 – 100). Round goby (Neogobius melanostomus) and rainbow smelt (Osmerus mordax) were secondary lake trout prey items with relative diet percentages only marginally reflected by spatial and temporal variation in prey abundance (round goby: %V = 1.0 – 33.3, %IRI = 0.1 – 13.2; rainbow smelt: %V = 2.5 – 54.0, %IRI = 0.1 – 54.0). Carbon (δ13C) and nitrogen (δ15N) isotopic niche areas and orientations were similar across all year-zone combinations reinforcing temporal and spatial consistency in lake trout diet. The findings of this study advance the time series in describing Lake Ontario lake trout diets and can be used to complement stock assessments and management decisions associated with carrying capacity for the diverse salmonid community.

The invasive rainbow smelt (Osmerus mordax) was an abundant food source for Lake Winnipeg walleye (Sander vitreus), especially in the north basin of the lake, until the smelt’s collapse in approximately 2013. We quantified changing length-at-age (≈ growth rates) and relative mass (≈ body condition) in Lake Winnipeg walleye caught for a gillnet index data set. Here, walleye showed smaller length-at-age, particularly young fish in the north basin, over time. This approach to assessing growth suggests a constraint in the north basin fish, possibly a nutritional limitation between 2017 and 2018, that was not present in the south. We then analyzed a separate group of walleye (≥452 mm in fork length) sampled in 2017 as part of a large-scale tracking study, which had a similar slope in length-mass relationship to large walleye caught in that year for the gillnet index data. A panel of metabolites in whole blood samples associated with amino acid metabolism and protein turnover was compared. These metabolites revealed elevated essential amino acids in fish caught in the Dauphin River, and suggest that protein degradation may be elevated in north basin walleye. Therefore, based on both growth estimates and metabolites associated with protein balance, we suggest there were spatially distinct separations affecting Lake Winnipeg walleye with decreased nutritional status of walleye in the north basin of Lake Winnipeg being of particular concern.

Arctic rainbow smelt Osmerus dentex is one of the most abundant fish species widely distributed in the NW Pacific and Arctic seas. Studying this species can contribute to understanding the microevolutionary processes of the Arctic fauna in unstable climatic conditions and new habitats. However, little is known about the genetic structure and the mechanisms underlying its population dynamics. Ten microsatellite loci were used to genotype 822 individuals in 20 locations throughout a large part of the species’ range in the Sea of Japan, Sea of Okhotsk, Bering, Kara, and White seas (across more than 11,000 km). O. dentex displayed substantial levels of genetic differentiation (overall FST = 0.067, RST = 0.091) and STRUCTURE identified eight distinct clusters. The significant regional variation was demonstrated in both genetic diversity and population structure, most notably between Arctic and Pacific basins. On a regional scale, contrasting patterns were revealed with limited gene flow between populations of the Arctic region (FST = 0.117) and high gene flow between the Bering Sea (FST = 0.017) or Sea of Okhotsk (FST = 0.031), which were probably associated with differences in larval distribution from the spawning grounds due to different oceanographic conditions of the studied areas. These results demonstrate the effect of local contemporary forces in shaping different patterns of genetic connectivity and diversity within O. dentex.

Hydroacoustic surveys using hull-mounted down-looking transducers are useful for estimating pelagic fish densities; however, this method may miss shallow fish owing to the acoustic surface dead zone and vessel avoidance. Our objective was to compare pelagic fish density estimates acquired by a traditional down-looking acoustic survey to estimates obtained by a new multi-directional-towed sled capable of sampling the entire water column using upward-, sideways-, and downward-aimed transducers simultaneously. We deployed both systems concurrently in the western arm of Lake Superior during a period of stable stratification. We found the two survey approaches provided significantly different estimates of fish density in the upper water column layer (~4–9 m below the lake surface) with the sled up-looking transducer providing 56 times higher densities compared to the traditional ship down-looking method. Densities also varied significantly in the 9–14 m layer where densities were 6.2 times higher in the sled survey. Midwater trawl sampling indicated that cisco (Coregonus artedi) and rainbow smelt (Osmerus mordax) were the predominant species occupying the uppermost 14 m of the water column. The two acoustic approaches provided similar results at water column depths >14 m where rainbow smelt and kiyi (Coregonus kiyi) were predominant. Overall, the sled-based method estimates were, on average, 2.5 times higher for the whole water column. Our findings show that the new sled can reduce bias by better sampling the surface dead zone leading to more accurate estimation of pelagic fish densities for both management and research.

Fishery at the northwestern Okhotsk Sea coast is analyzed for the period from 2000 to 2019. Pacific herring, saffron cod, pacific cod, capelin, flounders (Limanda aspera, Pleuronectes quadrituberculatus and Platichthys stellatus), and smelts (Hypomesus japonicus and Osmerus mordax) are landed in this area. The spawning herring prevails (95.2 %) in the catch. Almost all spawning herring is caught at the coast of Khabarovsky Krai. Taking into account the area of spawning grounds for herring in the lagoons of the coasta, withdrawal of this species could be increased, though actually it was decreased in the last two decades in 1.8 times, and since 2012 the herring fishery is continued in Okhotsk District only. The fishing strategy changed: offshore harvesting with stationary nets transformed to combined using of stationary and casting nets and expanded to the rivers. The catches delivery changed, as well: the herring catches are processed mostly ashore since 2008. Withdrawal of saffron cod fluctuated from 1.9 % to 186.5 % of the total available catch (TAC) volume for this species, with rapid growth in the last 5 years; its main fishing grounds shifted from the waters of Nikolayevsk District to the waters of Tugur-Chumikan District. Landings of smelt grew since 2009, too: annual catches of rainbow smelt increased from 72.2 t, on average, in 2009–2014 to 119.4 t in the last 5 years (up to 90 % of this volume was caught in Tugur-Chumikan District); landing of japanese smelt grows even faster and now exceeds 50 % of TAC. The stock of capelin was exploited weakly, annual catches of this species changed from 0.7 % to 23.3 % of TAC. Stationary and casting nets were the only fishing gears used for the capelin fishery in 2000s, but recently midwater trawls are also used. Catches of flounders had a growth tendency, though they were rather low and never exceeded 50 % of the recommended volumes. Dynamics of the pacific cod landings became positive when fishermen started to use small boats for this fishery, its annual catches increased in 2014–2019 from 69.7 to 84.8 t, the withdrawal rate achieved 9.3 % of TAC. Available fish resources in the northwestern Okhotsk Sea and technical equipment of local enterprises provide strong potential of fishery industry in this area.

Current status of aquatic biological resources in the middle and lower parts of the Amur River basin, including Lake Khanka and the Amursky Liman, is assessed. Generally high abundance of the water organisms is noted, but a downward trend is revealed. In 2015–2019, the total annual catch in the basin by Russian fishermen changed between 15.9–69.6 . 103 t (on average 39.1 . 103 t), with the main portions of pacific salmons (31.9 . 103 t, or 81.6 % of total catch) and smelts (5.5 . 103 t, 14.1 %). After the peak in 2016, the salmons abundance in the Amur has decreased, particularly for summer chum salmon and pink salmon, the number of arctic rainbow smelt Osmerus dentex has decreased gradually in the last 3 years. The stocks of freshwater fish are generally stable, with a slight increase for some species. The program of fisheries research «Amur River Fishes» implemented for 2020–2024 includes intensifying of traditional monitoring of the stocks and their biological state, as well as organization of detailed comprehensive studies for key species. Improvement of data quality on status of the main stocks of pacific salmons, smelts, and freshwater fishes is planned, as the basis for fisheries forecasting. Besides, the program conducts quantitative assessment of the main components of the ecosystem (phyto- and zooplankton, macrozoobenthos, and fish) and their dependence on environmental changes. State of food base for the Amur fish will be evaluated, including the feeding of artificially reproduced juveniles of salmons and sturgeons. Results of these studies will allow to improve approaches to regulation of fishery and to promote development of fishery industry toward organization of effective fishery complex in the Amur River basin.

A mycological examination of the saffron cod Eleginus gracilis (Tilesius, 1810) and the Asiatic smelt Osmerus mordax dentex Steindachner & Kner, 1870, caught in the Amursky Bay (Peter the Great Bay of the Sea of Japan) revealed several species of filamentous fungi. In total, 105 isolates of filamentous fungi were obtained from the skin integument and internal organs (31 isolates from the saffron cod and 74 isolates from the Asiatic smelt). Three species of filamentous fungi were found in the saffron cod: Aspergillus flavus Link, Penicillium brevicompactum Dierckx, and Phialophorophoma sp. Six species of filamentous fungi were found in the Asiatic smelt: Aspergillus wentii Wehmer, Aspergillus sp., Cladosporium cladosporioides (Fresen.) de Vries, Penicillium albidum Sopp., Penicillium nigricans (Bain.) Thom, and Humicola grisea Traaen. All the identified species are anamorphic stages of ascomycetes. In the saffron cod, the organs most frequently invaded by fungi were the gills (three fungal species were found); two species of fungi were found in the muscles and liver and one species each were identified in the skin integument and in gonads. The distribution of fungi in the Asiatic smelt was different: four fungal species were revealed in the skin integument, three species in the gills, two species in muscles, one species in the liver, one species in the gonads, and two species on the fins.

Identification of fish stocks plays an important role in fisheries management, but stock identification often depends on the techniques used and the management goals as much as on actual population structure. Historically, stocks were identified by place of capture, population demography and morphology, but genetic stock identification has become a standard approach. Here, we evaluate the stock structure of rainbow smelt (Osmerus mordax) in three basins of Lake Champlain separated by causeways using genotype data from six microsatellite loci and 26 years of demographic data. No genetic differences among rainbow smelt from the different basins were evident, which suggests that gene flow occurs among basins. However, length, age, and catch-per-unit-effort of rainbow smelt suggests asynchronous population dynamics in the different basins, and thus each basin may hold populations that are at least partially isolated from one another. Consequently, we conclude that while rainbow smelt in Lake Champlain consist of at least three demographic stocks they may form only a single genetic stock. Our results concur with other studies that suggest care should be taken when only a single method of stock identification is used.

Spawning flocks of rainbow smelt Osmerus dentex, in an anadromous migration in the Amur River were represented by individuals of length 15–25 cm at ages 3–5, among which males predominated (1 : 2). Histologic analysis shows that rainbow smelt is an iteroparous species with determinate fecundity, group-synchronous ovary organization and total spawning. Absolute fecundity (AF) varied from 20.9 to 31.2 oocytes per female; relative fecundity (RF) ranged between 679 and 776 oocytes/g of body weight between 2014–2018. AF statistically correlated and increased with length and age; such correlation between RF and length and age parameters did not occur.

Increasing our understanding of invasive species is important because of the negative impacts they can have on the economies and ecosystems of invaded regions. There is growing interest in how environmental variability (e.g. temperature) and stochastic invasion events (e.g. founder effects) affect the genetic composition of populations of invasive species. Rainbow smelt (Osmerus mordax) are a cold-water, planktivorous fish that spread into the Great Lakes basin in the early 1900s. We performed genetic analyses using microsatellites (N = 10) to investigate the influence stochastic invasion events have had on the genetic composition of invasive rainbow smelt populations across a broad geographic range. Genetic analyses were conducted on rainbow smelt populations (N = 30/population) from Lake Ontario, Lake Michigan, Lake Superior, and four inland lakes in Northern Wisconsin. Populations from the Great Lakes were generally less differentiated than inland populations. Additionally, we found evidence of a significant bottleneck in two inland populations and evidence for two distinct genetic strains of rainbow smelt in Lake Ontario. We also performed genetic analyses using microsatellites to determine if a thermally-induced extreme mortality event had an effect on a population of rainbow smelt and found that there was no measurable genetic effect on the population. Overall, this study provides evidence that the genetic structure and diversity of introduced populations can vary significantly, and are likely influenced by factors such as the frequency and magnitude of introductions. Also the resiliency of an invasive species can be high despite a history of bottlenecks and low genetic diversity.

Osmerus dentex Steindachner & Kner, 1870. Arctic Smelt. To 34 cm (13.4 in) TL (Eriksen et al. 2020). White and Barents Seas eastward to Bathurst Inlet, Nunavut, also southward to North Korea, Japan, and Sea of Okhotsk, and in North America to Heceta Head, Oregon (Mecklenburg et al. 2011). Near coast; depth: surface to 194 m (636 ft) (min.: Mecklenburg et al. 2011; max.: NWFSC-FRAM). Also reported from deeper depths (i.e., 290 m, 951 ft, Federov et al. 2003), but deep records may represent fish entering nets nearer the surface than at the maximum depth of the tow. Anadromous. Previously as Osmerus mordax (Mitchill, 1814)., 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 52, DOI: 10.11646/zootaxa.5053.1.1, http://zenodo.org/record/5578008, {"references":["Eriksen, E., Benzik, A. N., Dolgov, A. V., Skjoldal, H. R., Vihtakari, M., Johannesen, E., Prokhorova, T. A., Keulder-Stenvik, F., Prokochuk, I. & Strand, S. (2020) Diet and trophic structure of fishes in the Barents Sea: The Norwegian-Russian program \" Year of stomachs \" 2015 - Establishing a baseline. Progress in Oceanography, 183, 102262 https: // doi. org / 10.1016 / j. pocean. 2019.102262","Mecklenburg, C. W., Moller, P. R. & Steinke, D. (2011) Biodiversity of arctic marine fishes: taxonomy and zoogeography. Marine Biodiversity, 41, 109 - 140. https: // doi. org / 10.1007 / s 12526 - 010 - 0070 - z","Federov, V. V., Chereshnev, I. A., Nazarkin, M. V., Shestakov, A. V. & Volubuev, V. V. (2003) Catalog of Marine and Freshwater Fishes of the Northern Part of the Sea of Okhotsk. Vladivostok, Dolnauka [In Russian]."]}

Understanding trophic interactions is critical for successful resource management. However, studying diet patterns (e.g., spatial and seasonal changes) can require extensive effort. Using individual analyses to interpret patterns may be further complicated by assumptions and limitations of the analytical approach. We investigated and compared predicted adult lake trout (Salvelinus namaycush) diet composition and patterns using stomach content analysis (SCA), fatty acid analysis (FAS), and stable isotope analysis (SIA) individually and simultaneously. The three analyses were conducted for fall-captured fish in Lake Ontario and provided different diet composition estimates; SCA suggested alewife (Alosa pseudoharengus) was dominant by frequency and mass, while FAA and SIA suggested rainbow smelt (Osmerus mordax) contributed the most based on similarity among fatty acid signatures and two-stable isotope (carbon and nitrogen) mixing models, respectively. We hypothesize the disagreement among diet estimates is a result of a seasonal shift in diet variably expressed due to differing extent of time reflected by the diet metric: hours to days for SCA, weeks to months for FAA and several months for SIA. Despite variability in diet composition estimates among methods, similar patterns in lake trout diet were observed among the three diet analyses; the contribution of alewife in lake trout diet was greater for larger individuals and for males compared to females, particularly in the east and northeast regions of the lake where alewife density was relatively low. Thus, the complementary results from the three analyses suggest that length, location, sex, and season all influence lake trout diet. Individually, analyses often failed to identify these patterns in lake trout diet with significance, and some of the patterns have not been observed in previous studies of lake trout diet in Lake Ontario. The thorough description of lake trout diet obtained from a single sampling season demonstrates how simultaneous use of multiple diet analyses may allow investigation of spatial and seasonal diet composition and with reduced sampling effort.

Data on biology, ecology and fishery of asiatic smelt in the Uda River during its spawning migration are analyzed. The spawning begins in May-June in 2–11 km from the river mouth and lasts 3–10 days. Timing of its start varies from May 22 (2014 and 2018) to June 14 (2001), with 24 days difference. The spawning migration begins under the water temperature 6.0оС, during the spawning the temperature varies from 6.2 to 11.9оС. The river flow velocity on the spawning grounds is 1.2–2.6 m/s, the river depth varies from 0.3 to 2.5 m. Age of the spawners is 2–8 years, their length is 11.5–32.0 cm and weight 10.8–275.0 g, males usually prevail in number (63–81 %). Depending on the year-class strength, the fish in age of 3 or 4 years prevail among the spawners. After spawning, females leave the spawning grounds immediately — in that time their occurrence in the catches below the spawning grounds can reach 85 %. Size of the spawners decreases during the migration, for males the decreasing was from 19.0 to 15.0 cm in 2007, from 20.2 to 18.8 cm in 2014, from 19.3 to 16.6 cm in 2015, and from 19.4 to 16.0 cm in 2016, for females — from 21.0 to 18.0 cm in 2007, from 22.1 to 19.6 cm in 2014, from 21.3 to 19.0 cm in 2015, and from 24.5 to 16.1 cm in 2016. Annual increments of the smelt body length are 0.7–7.8 cm, on average 3.9 cm, for the body weight 17.1–39.9 g, on average 32.1 g. The minimum registered size of mature male and female was 11.5 and 13.0 cm, respectively. Percentage of the smelt with non-commercial size during spawning migration was 19.2 % in 2007, 0.4 % in 2014, 15.4 % in 2015, and 28.4 % in 2016. The group linear growth of asiatic smelt could be approximated by Bertalanffy equation: L = 30.5 [1 – e–0.317 (t – 0.533)]. Its body length dependence on weight is described by the equation of simple allometry: W = 0.002 L3.380(determination r 2 = 0.92–0.99). The body weight depends on age as the function: Wt = 2.974t2.136. Individual absolute fecundity of the smelt in the Uda varies from 11300 to 141300 eggs, on average 52500 eggs in 2016 and 50400 eggs in 2007; these values are close to the smelt fecundity in the Ulbeya and Inya rivers. The fecundity variation generally increases with the age: the registered ranges of absolute fecundity (thousand eggs) were, by age groups: 19.1 for 3 years, 53.5 for 4 years, 37.8 for 5 years, 57.5 for 6 years, and 60.3 for 7 years old fish, the ranges of relative fecundity (eggs/g of body weight) were: 864, 537, 565, 501, and 449 eggs/g for the same age groups. The total population fecundity was 32.7. 109eggs in 2016. The individual absolute fecundity has the following dependencies on body length, weight, and age: AF(L) = 0.001 L3.437, AF(W) = 0.650 W0.986, and AF(t) = 1.661 t2.250, respectively. The stock of asiatic smelt in the Uda is represented by migrating fish only. Its fishery was conducted by 8 companies, their total annual landing increased from 10 t in 2012 to 373 t in 2017 and slightly decreased recently: the mean landing for 2013–2019 was 276 t. The spawning biomass of smelt was estimated from 637 to 1734 t, by years, that was about 70 % of the biomass of mature smelt in the Shantar Sea.

Rainbow smelt (Osmerus mordax) is a key planktivore and prey fish in Lake Huron. Given the declining offshore productivity in the lake since the early 2000s, we described the energy content of rainbow smelt in 2017 across five different regions (North Channel, Georgian Bay, Saginaw Bay, northern main basin, southern main basin) where phytoplankton and zooplankton productivity likely varied. To increase contrast across the productivity gradient, rainbow smelt energy content was also estimated from western Lake Erie. Within the North Channel where large fish (≥90 mm, total length) were sampled most frequently, mean energy density (kJ/g wet weight) varied seasonally: 4.29 in April (month of spawning), 3.86 in June, 3.99 in July, and up to 4.35 in September. Energy density of rainbow smelt from higher productivity western Lake Erie was 37% (large fish ≥90 mm) to 60% higher (small fish

We studied the consequences of a nonnative species introduction and changes in temperature on early mortality and recruitment of native rainbow smelt (Osmerus mordax) and nonnative alewife (Alosa pseudoharengus) in Lake Champlain using a simulation model. Distribution patterns of adults and young-of-the-year (YOY) fish were predicted using a model based on observed distribution of different age groups as a function of temperature and light profiles simulated on a daily basis. Mortality rates averaged over the growing season were calculated as a function of fish densities and overlap between adults and YOY. Survival of YOY rainbow smelt and alewife depended on which predator was most abundant. Rainbow smelt YOY mortality rates are highest when rainbow smelt adults are abundant, and alewife YOY mortality rates are highest when alewife adults are abundant, potentially allowing coexistence. August and September mortality rates were higher in the climate change scenario because of increased overlap of adults and YOY of both species. These results indicate that accounting for spatiotemporal fish distribution patterns can be important when forecasting the interacting effects of climate change and aquatic invasive species on fish recruitment.

The complete mitochondrial (mt) genome was sequenced in two individuals of the European smelt Osmerus eperlanus. The genome sequences are 16,608 and 16,609 bp in size, and the gene arrangement, composition, and size are very similar to the other smelt mt genomes previously published. The difference between the two genomes studied is low, 0.05%. The difference is significantly higher (6.95%) between the O. eperlanus genomes studied here and the genome of the congeneric species, O. mordax (HM106493.1) available in GenBank. The distribution of divergence is non-uniform along the genomes. There is a continuous segment (≈2.5 kb) encompassing tRNA-Phe, complete 12S rRNA gene, tRNA-Val, and partial 16S rRNA gene, which demonstrates significantly lower levels of divergence than on average for the whole genome. The 12S rRNA and 16S rRNA genes are frequently used for phylogenetic and molecular taxonomy analyses and could underestimate the level of divergence between osmerid fishes.

The genetic diversity of ten microsatellite loci is examined in samples of Arctic rainbow smelt. The expected heterozygosity estimates vary in the range of 12.6–83.9% (mean 55.3%). The degree of genetic differentiation is statistically significant: θ = 2.8%, 95% CI (1.4–4.9%). The greatest differences are found between datasets of smelt in Eastern and Western Kamchatka. The samples from Lake Nerpich’e demonstrate the maximum estimates of divergence from the other datasets from both the western and eastern coasts.

The invasive rainbow smelt (Osmerus mordax) was an abundant food source for Lake Winnipeg walleye (Sander vitreus), especially in the north basin of the lake, until the smelt’s collapse in approximately 2013. We quantified changing length-at-age (≈ growth rates) and relative mass (≈ body condition) in Lake Winnipeg walleye caught for a gillnet index data set. Here, walleye showed smaller length-at-age, particularly in the north basin with young fish, over time. This approach to assessing growth suggests a constraint in the north basin fish, possibly a nutritional limitation between 2017 and 2018, that was not present in the south. We then analyzed a separate group of walleye (≥452 mm in fork length) sampled in 2017 as part of a large-scale tracking study, which had a similar slope in length-mass relationship to large walleye caught in that year for the gillnet index data. A panel of metabolites associated with amino acid metabolism and protein turnover was compared in whole blood. These metabolites revealed elevated essential amino acids and suggest protein degradation may be elevated in north basin walleye. Therefore, based on both growth estimates and metabolites associated with protein balance, we suggest there were spatially distinct separations affecting Lake Winnipeg walleye with decreased nutritional status of walleye in the north basin of Lake Winnipeg being of particular concern.

A baseline environmental characterization of the northeastern reaches of Bristol Bay, Alaska was conducted using the National Status and Trends’ sediment quality triad approach. The study area was subdivided into 6 strata based on geophysical and hydrodynamic patterns (the upper and lower reaches of Nushagak and Kvichak Bays, Dillingham Harbor and the mouth of the Naknek River). Within each stratum, a stratified random sampling approach was used to select sampling sites for infauna and sediment chemistry. Ambient toxicity was assessed at a subset of sites using two bioassays (Microtox® and sea urchin fertilization and development). Fish species including, starry flounder (Platichthys stellatus) and rainbow smelt (Osmerus mordax) were collected by trawl for body burden analyses for chemical contaminants. Persistent organic pollutant concentrations were low relative to National Oceanic and Atmospheric Administration (NOAA) sediment quality guidelines (SQG). All metal/metalloid concentrations were below NOAA SQGs except for arsenic which was uniformly above the threshold SQG. Benthic communities were relatively sparse at most locations due to harsh physical oceanographic conditions. Significant chemical toxicity was virtually absent except for selected locations with high pore-water ammonia levels associated with fish processing plant waste streams. Contaminant body burdens were very low in the fish tested. The fish were generally healthy and non-contaminated.

Results of parasitological studies of rainbow smelt Osmerus mordax dentex Steindachner et Kner, 1870 at the northern coast of the Okhotsk Sea are presented. Its helminth fauna includes 21 species: Cestoda — 8, Trematoda — 7, Nematoda — 4, and Acanthocephala — 2. Almost all these species (19) were detected in the Shelikhov Bay, with the highest species diversity among 4 investigated sites in the secondary Perevolochny Bay (14 species). Six species of helminthes from the smelt dwelling in the northern Okhotsk Sea are known as dangerous for human or other mammals: Nybelinia surmenicola, Diphyllobothrium dendriticum, Hysterothy­lacium aduncum, Anisakis simplex, Pseudoterranova decipiens , and Corynosoma strumosum . The species diversity of helminthes at the northern coast is comparable with the number of species at the coasts of Kamchatka (16 species: Cestoda — 4, Trematoda — 5, Nematoda — 4, Acanthocephala — 3) and Sakhalin (19 species: Cestoda — 5, Trematoda — 8, Nematoda — 3, Acanthocephala — 3); totally 33 species of helminthes are detected in these three areas. The cestodes Diplocotile olrikii, Bothriocephalus spp., trematodes Bucephaloides iskaensis, Po­docotyle atomom, and P. reflexa and nematodes Ascorophis pacificus infect rainbow smelt at the northern coast of the Okhotsk Sea only. The most epidemically significant species Anisakis simplex is widely distributed in all three areas.

Climate change affects the thermal environment of aquatic organisms. Changes in the thermal environment may affect muscle function in the eurythermal rainbow smelt, Osmerus mordax, and relatively more stenothermal rainbow trout, Oncorhynchus mykiss. Literature suggests that the trout will be more sensitive to changes in environmental temperature, as they experience a more limited range of environmental temperatures. To examine the effects of thermal environment on red muscle function, both the smelt and trout were thermally acclimated to either a warm (12-15°C) or cold (4-5°C) temperature, after which studies of swimming performance and muscle mechanics were performed. The data on swimming performance and maximum muscle shortening velocity in rainbow smelt were previously published. In both species, cold-acclimated (CA) fish swam with a significantly faster maximum aerobic swimming speed than warm-acclimated fish, when tested at a common temperature of 10°C. Similarly, CA smelt and trout had faster red muscle contraction kinetics. However, smelt displayed a greater shift in contractile properties, such as having a significant shift in maximum muscle shortening velocity that was not observed in trout. The smelt red muscle outperformed trout, with twitch and tetanic times of relaxation being significantly faster for CA smelt compared with CA trout, especially when contraction kinetics were tested at 2°C. The smelt shows a greater thermal acclimation response compared with trout, with more robust increases in maximum swimming speed and faster muscle contractile properties. These differences in acclimation response may contribute to understanding how smelt and trout cope with climate change.

A critical analysis of literature data on the distribution, morphology, and phylogeography of the Arctic lamprey (Lethenteron camtschaticum) and five species of marine and anadromous fish such as navaga (Eleginus navaga), pollock (Theragra chalcogramma), rainbow smelt (Osmerus mordax dentex), Pacific herring (Clupea pallasii), and pond smelt (Hypomesus olidus) has been performed. The results show that all these species have colonized Northern European seas, distributing along the Arctic coastline of Eurasia after the glacier retreat. The reasons that the dispersal of these species in the Atlantic Ocean may be impeded (preference for a cold environment, competition, and decrease of the evolutionary potential) are discussed.

The Pacific smelt Osmerus dentex is widely distributed in the North Pacific and Arctic seas and belongs to the species that may shed light on the biogeography and evolutionary history of Arctic marine fauna. O. dentex came into existence in the northwestern Pacific at the Pliocene–Pleistocene border and could widely spread along the Eurasian and North American coasts. We assessed the impact of global climatic and geological changes on the formation of the genetic structure of O. dentex in the Eurasian parts of the species area using a variety of phylogenetic methods and molecular dating. The results were interpreted in conjunction with paleoclimatic evidence. Phylogeographic patterns based on cytb and coI sequences, and RFLP ND3/ND4L/ND4 and A8/A6/COIII/ND3 mtDNA regions for 462 Pacific smelts from 25 Eurasian locations were analyzed. Our results suggest that (1) geographical distribution observed for mtDNA haplotypes resulted from influences of historical range expansions, episodes of long-distance colonization and restricted dispersal; (2) the main refugium was located in the northwestern Pacific and the genetic similarities observed among and within geographical regions probably originated from postglacial recolonization from common sources; (3) an additional small refugium in the White Sea existed in the Late Pleistocene.

Reproduction of external fertilizing vertebrates is typically constrained to either fresh or salt water, not both. For all studied amphibians and fishes, this constraint includes immotile sperm that are activated after ejaculation only by the specific chemistry of the fertilizing medium in which the species evolved (fresh, brackish, or salt water). No amphibians can reproduce in the sea. Although diadromous fishes may migrate between salt and fresh water, they are shackled to their natal environment for spawning in part because of sperm activation. Here, we report for the first time among all documented external fertilizing vertebrates, that in the absence of any external media, sperm are motile at ejaculation in a marine spawning fish (Osmeridae, capelin, Mallotus villosus). To illuminate why, we evaluated sperm behavior at different salinities in M. villosus as well as the related freshwater spawning anadromous rainbow smelt (Osmerus mordax). Surprisingly, sperm performance was superior in fresh water for both species. M. villosus spend their entire life at sea but our results show that their sperm are deactivated by sea water, suggesting a freshwater ancestry. By circumventing constraining water chemistry, we interpret the unique pre‐ejaculatory sperm activation in this species as a novel adaptation that enables fertilization in the marine environment. These findings also contribute to understanding the persistence of anadromy, despite great energetic costs to adult fishes.

Changes in the isotopic composition (δ13 C and δ15 N) in biofilm, macro-invertebrates and resident salmonids were used to characterize temporal dynamics of marine derived nutrients (MDNs) incorporation between stream reaches with and without MDN inputs. Five Atlantic rivers were chosen to represent contrasting MDN subsidies: four rivers with considerable numbers of anadromous fishes; one river with little MDN input. Rainbow smelt Osmerus mordax, alewife Alosa pseudoharengus, sea lamprey Petromyzon marinus and Atlantic salmon Salmo salar, were the primary anadromous species for the sampled rivers. Regardless of the spatial resolution or the pathway of incorporation, annual nutrient pulses from spawning anadromous fishes had a positive effect on isotopic enrichment at all trophic levels (biofilm, 1·2-5·4‰; macro-invertebrates, 0·0-6·8‰; fish, 1·2-2·6‰). Community-wide niche space shifted toward the marine-nutrient source, but the total ecological niche space did not always increase with MDN inputs. The time-integrated marine-nutrient resource contribution to the diet of S. salar parr and brook trout Salvelinus fontinalis ranged between 16·3 and 36·0% during anadromous fish-spawning periods. The high degree of spatio-temporal heterogeneity in marine-nutrient subsidies from anadromous fishes lead to both direct and indirect pathways of MDN incorporation into stream food webs. This suggests that organisms at many trophic levels derive a substantial proportion of their energy from marine resources when present. The current trend of declining anadromous fish populations means fewer nutrient-rich marine subsidies being delivered to rivers, diminishing the ability to sustain elevated riverine productivity.

Dietary niche overlap between invasive rainbow smelt (Osmerus mordax) and the native cisco (Coregonus artedi) of similar size in Lake Winnipeg was examined using stomach content analysis throughout the open water period in 2010 and 2011. Although smelt and cisco were caught together in the North Basin (n = 7 stations), rainbow smelt were exclusively caught in the North Basin (n = 39 stations), whereas cisco were predominantly caught in the South Basin (n = 31 stations). Substantial dietary overlap was evident when found together and apart, illustrating little dietary niche differentiation between the two species in sympatry and allopatry in the lake. Both smelt and cisco appear to shift from copepods in spring to large-bodied cladocerans in summer and fall. Although high dietary overlap suggests that these species have the potential to compete for prey, differential abundance in each basin of Lake Winnipeg suggests possible environmental niche divergence between these two species. Overall, this study provides important baseline information to examine the impact of another recent invasive planktivorous species (e.g. Bythotrephes longimanus, spiny water flea) on the smelt-cisco competition as well as the commercially important piscivorous walleye (Sander vitreus) population in Lake Winnipeg.

The spectral sensitivity and complement of the retinal photoreceptors of the Asiatic smelt from the Sea of Japan were studied by microspectrophotometry and light microscopy. Apart from rods, one type of single cones and one type of unequal double cones were found in major parts of the retina. The dominant type of the cone pattern (mosaic) is a row pattern consisting of various linear arrangements of separate single and double cones. The absorbance maxima of rods and a majority of singe cones and double cones equaled 516, 425 and 514/565 nm, respectively. It has been established that all of the pigments are based on retinal. The findings are compared with data on the osmerid retina from the literature and discussed with respect to the adaptations to light conditions, peculiarities of behavior, and seasonal migrations of smelts.

Most fishes undergo ontogenetic diet shifts, progressing from small to larger prey as they grow. The availability of suitable prey throughout early ontogeny can influence growth, survival and ultimately, year-class strength. Simultaneously, due to their numeric abundance and high mass-specific consumption rates, young fish can serve as influential consumers and thereby affect abundance of various prey. The walleye Sander vitreus population in Saginaw Bay, Lake Huron, recently recovered and is now entirely supported by natural reproduction. Recovery coincided with a dramatic decline of alewife Alosa pseudoharengus, a preferred prey of walleye. Thus, we are uncertain what primary prey now support production of young life stages of this recovered walleye population. To this end, we collected young (larval and later-stage young of year) walleye in Saginaw Bay and characterized their growth, diets and cumulative consumption using bioenergetics models. Young walleye progressed from feeding entirely on zooplankton as larvae in April to feeding almost entirely on fish by September. Based on bioenergetics analyses, fish were the most important prey for young walleye cohorts. Shiners Notropis spp., along with invasive rainbow smelt Osmerus mordax and round goby Neogobius melanostomus, were the primary fish prey. In contrast, yellow perch Perca flavescens, an important prey for adult walleye in Saginaw Bay, were largely absent in young walleye diets. Young walleye growth rates were similar to rates observed in other systems, but lower than growth rates previously observed in Saginaw Bay when alewife were abundant and the density of walleye was low.