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Objective: To support the declining wild population of Delta Smelt, a conservation hatchery has expanded its mission from maintaining a backup population as insurance against extinction to also producing fish for release into the wild. The substantially higher production demands require a balance between producing large numbers of fish while adhering to conservation genetic principles that maximize retention of effective population size (Ne) and thus overall diversity. Methods: We performed spawning experiments at the hatchery to evaluate the genetic consequences of two spawning strategies: (1) a pooled strategy where we fertilized premixed eggs from three dams with premixed milt from three sires and (2) a partial-factorial strategy where eggs from three dams were mixed and then apportioned among three containers, each container then receiving milt from one sire. We used genetic parentage analysis of larval offspring to determine the reproductive success of spawners in 10 replicate crosses of each strategy. Result: The contributions of parents to offspring were more even in partial-factorial crosses and consequently resulted in higher Ne (average Ne = 5.50 ± 0.38; expected Ne = 6.0), suggesting its potential for maintaining genetic diversity over time. In contrast, our pooled spawning experiment produced lower and more variable Ne values (average Ne = 3.86 ± 1.30), demonstrating that this more efficient method of production entails high costs in terms of long-term genetic management. Treating our experiments as hypothetical pools of fish for release, we combined the Ne values for pooled or partial-factorial crosses to calculate the effective size of a release population (NeR). Unequal family sizes reduced NeR for our pooled experiment to half of the expected value, whereas the partial-factorial experiment NeR was 88% of the expected value. Conclusion: We discuss the benefits and risks of each method and how these can be considered when designing a spawning strategy for Delta Smelt supplementation.

Accurate species identification is critical to monitoring programs because mis-identifications can lead to incorrect assessments of population status and trends. In the San Francisco Estuary, efforts to monitor the imperiled osmerid Delta Smelt (Hypomesus transpacificus) using morphology can be challenging because of the presence of the similar-looking non-native osmerid Wakasagi (Hypomesus nipponensis). In 2017, the US Fish and Wildlife Service’s field office in Lodi implemented a two-stage verification process for Wakasagi to help prevent Delta Smelt from being mis-identified as Wakasagi. Under this process, Wakasagi are initially identified in the field, independently identified a second time by an experienced staff member in the laboratory, then stored on-site where they can be made available for future studies. Using the recently developed Specific High-sensitivity Enzymatic Reporter un-LOCKing (SHERLOCK) assay for Wakasagi, we evaluated how well verification protocols performed by genetically identifying a subset of Wakasagi collected during routine sampling between 2017 and 2021. Through this study, we found that the protocols have served as an effective quality control measure for over 4 years and across multiple surveys. With the development of field-deployable genetics tools such as SHERLOCK, genetic identification will likely play an increasingly important role in ecological monitoring. We expect that hybrid approaches that combine morphological identifications by trained field crew with application of field-based genetic tools may offer an effective and efficient approach to ensuring data accuracy in the future.

Migration is a complex phenotypic trait with some species containing migratory and nonmigratory individuals. Such life history variation may be attributed in part to plasticity, epigenetics, or genetics. Although considered semianadromous, recent studies using otolith geochemistry have revealed life history variation within the critically endangered Delta Smelt. Broadly categorizable as migratory or freshwater residents, we examined Restriction site Associated DNA sequencing data to test for a relationship between genetic variation and migratory behaviors. As previously shown, we found no evidence for neutral population genetic structure within Delta Smelt; however, we found significant evidence for associations between genetic variants and life history phenotypes. Furthermore, discriminant analysis of principal components, hierarchical clustering, and machine learning resulted in accurate assignment of fish into the freshwater resident or migratory classes based on their genotypes. These results suggest the presence of adaptive genetic variants relating to life history variation within a panmictic population. Mechanisms that may lead to this observation are genotype dependent habitat choice and spatially variable selection, both of which could operate each generation and are not exclusive. Given that the population of cultured Delta Smelt are being used as a refugial population for conservation, as a supply for wild population supplementation, and currently represent the majority of all living individuals of this species, we recommend that the hatchery management strategy consider the frequencies of life history-associated alleles and how to maintain this important aspect of Delta Smelt biological variation while under captive propagation.

The rapid decline of longfin smelt Spirinchus thaleichthys, a threatened euryhaline forage fish in California, is a serious concern for scientists and resource managers. To recover and conserve this species, a captive culture program was initiated, focusing on the collection, captive rearing and breeding of wild broodstock, and the rearing of their offspring. Although progress has been made in the collection of broodstock and the production and culturing of larvae, no studies have evaluated the rearing of juvenile life stages in captivity. The present study examines methodological considerations for culturing F1 juvenile longfin smelt, specifically, the first efforts toward weaning juveniles to a dry commercial pellet feed. Cultured juvenile longfin smelt were fed live Artemia only or co-fed Artemia and dry feed for 62 days, and the effects of feed type on juvenile survival, growth, body condition, and fatty acid profiles were examined. No significant differences were observed between feeding treatments, despite an 80% reduction in Artemia in the co-feeding treatment. Furthermore, examination of fish stomach contents at the end of the trial confirmed the transition to dry feed. This is the first study to indicate successful feeding by longfin smelt on dry commercial pellets, and suggests that juvenile longfin smelt can be fully weaned onto dry feeds. Results of this study are critical for closing the lifecycle of longfin smelt in captivity and developing a successful conservation culture program for this imperiled species.

Objective: The Fraser River in British Columbia, Canada, historically supported productive Indigenous, recreational, and commercial fisheries for Eulachon Thaleichthys pacificus. Although Eulachon spend most of their lives in the marine environment, they spawn in freshwater and it is hypothesized that habitat degradation in the Fraser River has contributed to population decline. A greater understanding of Eulachon life history strategies is necessary to develop species recovery strategies. The purpose of this study was to provide insight into population demographics, migration timing, residence time, travel speed and distance, and movement patterns of Eulachon traveling in the Fraser River by conducting index netting and acoustic telemetry. Methods: In total, 244 Eulachon were acoustically tagged at the mouth of the Fraser River, and their movements were monitored using acoustic receivers in the lowermost 70 km of the Fraser River and in the Pitt River (a tributary to the Fraser River) over a 2‐year period. Result: Tagged Eulachon displayed heterogeneous movement behaviors and a protracted migration period between February and May. Eulachon index gill netting revealed three discrete migration groups matching traditional ecological knowledge from Indigenous knowledge holders. There were shifts in population demographics, with sex ratios changing from predominately males to females throughout the migration. Residence time within the estuarine salt wedge and river was short. Upstream travel speeds varied significantly between sexes and slowed as fish traveled upstream. Conclusion: Overall, Eulachon travel speeds, travel distances, and residence times, along with size and sex effects, provided insights into movement patterns. These results will increase our understanding of sex‐specific risks related to instream disturbance, harvest, and predation and will inform management decisions regarding protection of critical habitats. The observed patterns highlight the need for stock assessment methods to consider all discrete migration groups and will assist in prioritizing species recovery efforts. Impact statementThis research increased our understanding of Eulachon ecology by providing insight into migratory movement patterns and population dynamics in the Fraser River, which will assist habitat management decisions and aid future recovery efforts. [ABSTRACT FROM AUTHOR]

Based on research 1995–2020, abundant and potentially commercial fish in Russian watersof the Chukchi Sea have been identified. In total, 72 species were recorded in trawl catches, 16 species from six families were abundant, among which smelts (Osmeridae), salmons (Salmonidae), and herrings (Clupeidae) accounted for an average of 1.5, 0.2, and 0.1% of the total commercial marine fish biomass, respectively. For the species of the analyzed families, the size-age and weight characteristics, features of linear and weight growth, timing, scale and conditions of spawning were considered. The biological indicators of fish from the Chukchi and Bering seas and other water bodies were compared. Saffron cod Eleginus gracilis, Arctic rainbow smelt Osmerus mordax dentex, Pacific cod Gadus macrocephalus, Greenland halibut Reinhardtius hippoglossoides, and some species of sculpins were represented mainly by juveniles and immature individuals, older fish appeared in climatically warm years. Walleye pollock Gadus chalcogrammus, Pacific salmons, Alaska plaice Pleuronectes quadrituberculatus, and starry flounder Platichthys stellatus were characterized by the presence of older individuals. In polar cod Boreogadus saida, Bering flounder Hippoglossoides robustus, yellowfin sole Limanda aspera, Sakhalin sole L. sakhalinensis, longhead dab L. proboscidea, Pacific herring Clupea pallasii, Pacific capelin Mallotus villosus catervarius, and warty sculpin Myoxocephalus verrucosus smaller body sizes were recorded for the specimens caught at the Chukchi Sea shelf comparing to those from the Bering Sea. [ABSTRACT FROM AUTHOR]

Migration is a complex phenotypic trait with some species containing migratory and nonmigratory individuals. Such life history variation may be attributed in part to plasticity, epigenetics, or genetics. Although considered semianadromous, recent studies using otolith geochemistry have revealed life history variation within the critically endangered Delta Smelt. Broadly categorizable as migratory or freshwater residents, we examined Restriction site Associated DNA sequencing data to test for a relationship between genetic variation and migratory behaviors. As previously shown, we found no evidence for neutral population genetic structure within Delta Smelt; however, we found significant evidence for associations between genetic variants and life history phenotypes. Furthermore, discriminant analysis of principal components, hierarchical clustering, and machine learning resulted in accurate assignment of fish into the freshwater resident or migratory classes based on their genotypes. These results suggest the presence of adaptive genetic variants relating to life history variation within a panmictic population. Mechanisms that may lead to this observation are genotype dependent habitat choice and spatially variable selection, both of which could operate each generation and are not exclusive. Given that the population of cultured Delta Smelt are being used as a refugial population for conservation, as a supply for wild population supplementation, and currently represent the majority of all living individuals of this species, we recommend that the hatchery management strategy consider the frequencies of life history-associated alleles and how to maintain this important aspect of Delta Smelt biological variation while under captive propagation. [ABSTRACT FROM AUTHOR]

The rapid decline of longfin smelt Spirinchus thaleichthys, a threatened euryhaline forage fish in California, is a serious concern for scientists and resource managers. To recover and conserve this species, a captive culture program was initiated, focusing on the collection, captive rearing and breeding of wild broodstock, and the rearing of their offspring. Although progress has been made in the collection of broodstock and the production and culturing of larvae, no studies have evaluated the rearing of juvenile life stages in captivity. The present study examines methodological considerations for culturing F1 juvenile longfin smelt, specifically, the first efforts toward weaning juveniles to a dry commercial pellet feed. Cultured juvenile longfin smelt were fed live Artemia only or co-fed Artemia and dry feed for 62 days, and the effects of feed type on juvenile survival, growth, body condition, and fatty acid profiles were examined. No significant differences were observed between feeding treatments, despite an 80% reduction in Artemia in the co-feeding treatment. Furthermore, examination of fish stomach contents at the end of the trial confirmed the transition to dry feed. This is the first study to indicate successful feeding by longfin smelt on dry commercial pellets, and suggests that juvenile longfin smelt can be fully weaned onto dry feeds. Results of this study are critical for closing the lifecycle of longfin smelt in captivity and developing a successful conservation culture program for this imperiled species.

While there is substantial information about the upstream migration of commercially and recreationally important fishes, relatively little is known about the upstream migration of small-bodied species, particularly through estuaries. In the San Francisco Estuary, there is a major need to understand the behavior of delta smelt Hypomesus transpacificus, a small pelagic fish listed under the state and federal endangered species acts. The spawning migration period may be critical as upstream movements can result in entrainment in water diversions. In general, delta smelt live in the low-salinity zone of the estuary and migrate upstream for spawning. During the fall pre-migration period, delta smelt remain primarily within the low-salinity zone in the western Sacramento–San Joaquin Delta and Suisun Bay. There were no significant upstream shifts of fish into fresher water during late fall, suggesting that delta smelt do not show pre-migration staging behavior. Following winter “first flush” flow events that appear to trigger migration, upstream movement rates are relatively rapid, averaging 3.6 km/d, a finding consistent with results from particle-tracking simulations, laboratory studies, and other fishes. Like some other native fishes, delta smelt apparently “hold” in upstream areas following migration; most do not spawn immediately. Overall, delta smelt fit the pattern of a diadromous species that is a seasonal reproductive migrant. Emerging data suggest that there is variability in the migration behavior of delta smelt, a pattern contrary to the reigning viewpoint that all smelt migrate in winter.

Abstract 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.

This study examines the relationships and origin of a population of smelt (genus Hypomesus) that was recently found in the Barents Sea at a significant distance from the western boundary of its geographic range. Genetic analysis clearly identified this species as pond smelt H. olidus and showed its phylogenetic closeness and shared demographic history with H. olidus from the basin of the Bering Sea. Genetic differentiation indices suggest long isolation of populations of the Pacific and Barents Sea basins. The statistical estimates of historical demographic events, coupled with the paleographic data for the Arctic areas of Russia, show that certain populations of H. olidus might have survived in glacial refugia of the Polar Ural region. H. olidus might have passed repeatedly through a bottleneck in past glacial refugia, as well as in the recent time because of the harsh Arctic conditions. [ABSTRACT FROM AUTHOR]

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 of the smelt genus Hypomesus suggests that the Chinese specimen belongs to Hypomesus nipponensis. The difference in the studied region of mitogenome is low, 0.6%, which is in agreement with the values of intraspecific divergence for the smelts. The use of the sequence KP281293.1 as a marker for H. olidus will not help in improving the understanding of the taxonomic relationships gained from previous morphological studies and is phylogenetically misleading.

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 complete mitochondrial genome was sequenced in two individuals of the Arctic rainbow smelt Osmerus dentex. The genome sequences are 16,615 and 16,616 bp in size, and the gene arrangement, composition, and size are very similar to the other smelt mitochondrial genomes published previously. The difference between the two O. dentex genomes studied is 0.25%, that is, 5.0 times higher in comparison with close species, the European smelt O. eperlanus studied previously. The level of mitochondrial genome divergence between O. dentex and close osmerid fishes, O. eperlanus, and O. mordax is high enough (6.86–7.54%) to consider all of them as separate biological species.

The complete mitochondrial genome was sequenced in two individuals of the surf smelt Hypomesus japonicus. The genome sequences are 16,762 and 16,771 bp in size, and the gene arrangement, composition, and size are very similar to the other smelt mitochondrial genomes published previously. The difference between two H. japonicus genomes studied is 0.37%, which is noticeably higher in comparison with other osmerid fishes. The level of sequence divergence between H. japonicus and related osmerids belonging to genera Hypomeus, Osmerus, and Mallotus varies within a very narrow range (12.31–13.72%) indicating poor phylogenetic resolution of this complex fish group.

Pond smelt Hypomesus olidus is a small-sized economic species of freshwater fish with delicious meat and high output. In this study, the complete mitochondrial genome of H. olidus sequenced to be 16,786 bp in length, including 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs and a control region. The overall base composition of H. olidus is 24.3% for A, 27.3% for T, 29.2% for C and 19.2% for G, with a slight A + T bias. The mitogenome sequence data may provide useful information to the population genetics analysis of H. olidus and the elucidation of evolutionary mechanisms in Hypomesus fish.

Biological features of the four common fish species, giant grenadier Albatrossia pectoralis (Macrouridae), Pacific herring Clupea pallasii (Clupeidae), Pacific rainbow smelt Osmerus mordax dentex, and Pacific capelin Mallotus villosus catervarius (Osmeridae), were studied under the 20-year dataset (1995−2015). These species inhabit the northwestern Bering Sea in the summer-autumn period and form the schoolings in the Olyutorsky-Navarin region. The size-age parameters of the fish caught by different sampling gear, as well as the peculiarities of the body length and body weight dynamics, spawning periods, spawning range, and conditions, were analyzed. The largest specimens of giant grenadier, Pacific herring, and Pacific rainbow smelt were observed in the catches performed by the bottom setline and the gill nets; the smallest fish were found in the trawl catches. The body length and body weight of Pacific herring were larger in the pelagic trawls compared to the bottom trawls; an opposite pattern was observed for the Pacific capelin. The abundant year-class in the species with short life cycle (capelin and herring) is well tracked on the longterm plots of the fish body size; this is accompanied by the decrease of their biological parameters. Herring stock covers large growing grounds; smaller body size was observed for the herring grazing in the coastal waters; young specimens dominate here. [ABSTRACT FROM AUTHOR]

The capelin, Mallotus villosus (Osmeriformes, Osmeridae), is an ecological and commercial key component of the sub-arctic ichthyofauna. Here, we provide the first cytogenetic information on the species based on both conventional karyotyping and chromosomal mapping of 45S and 5S ribosomal genes through fluorescence in situ hybridization (FISH). The capelin genome displayed a diploid number of 54 with the karyotypic formula 26m/sm+28st/a and a fundamental number (FN) = 80. Both classes of ribosomal genes appeared to be spread out to multiple chromosomal locations, i.e. the 45S and 5S rDNA clusters were detected on six and seven chromosome pairs, respectively. A linked chromosomal organization of the major and minor ribosomal genes classes has been visualized in most of the rDNAs chromosomal locations. A comparative analysis of the available cytogenetic data for the family Osmeridae reveals diploid numbers higher than 48 and high fundamental numbers. This suggests that a rearranged karyotype is a shared feature within this family.

Ted Sommer, Francine Mejia, Matt Nobriga, Fred Feyrer, and Lenny Grimaldodoi: http://dx.doi.org/10.15447/sfews.2014v9iss2art2While there is substantial information about the upstream migration of commercially and recreationally important fishes, relatively little is known about the upstream migration of small-bodied species, particularly through estuaries. In the San Francisco Estuary, there is a major need to understand the behavior of delta smelt Hypomesus transpacificus, a small pelagic fish listed under the state and federal endangered species acts. The spawning migration period may be critical as upstream movements can result in entrainment in water diversions. In general, delta smelt live in the low-salinity zone of the estuary and migrate upstream for spawning. During the fall pre-migration period, delta smelt remain primarily within the low-salinity zone in the western Sacramento–San Joaquin Delta and Suisun Bay. There were no significant upstream shifts of fish into fresher water during late fall, suggesting that delta smelt do not show pre-migration staging behavior. Following winter “first flush” flow events that appear to trigger migration, upstream movement rates are relatively rapid, averaging 3.6 km/d, a finding consistent with results from particle-tracking simulations, laboratory studies, and other fishes. Like some other native fishes, delta smelt apparently “hold” in upstream areas following migration; most do not spawn immediately. Overall, delta smelt fit the pattern of a diadromous species that is a seasonal reproductive migrant. Emerging data suggest that there is variability in the migration behavior of delta smelt, a pattern contrary to the reigning viewpoint that all smelt migrate in winter.

Surf smelt Hypomesus pretiosus are an important part of the Salish Sea food web and obligate beach spawners, yet little is known about the spatiotemporal distribution of spawning and beach characteristics related to spawning success. We counted smelt eggs at 51 sites around Camano Island, Puget Sound, Washington every 2 weeks for 1 year and at 13 of those 51 sites each month in the following year. At each site, we measured beach characteristics hypothesized to affect spawning habitat suitability as measured by egg abundance and mortality. Eggs were collected at 45 sites and pooled by month for analyses. Few sites ( N = 10, 19.6 %) contributed 87 % of total eggs and 89 % of all live eggs collected. Mean total egg counts at sites were higher ( p < 0.019) in Jul-Sep (1,790.7, SE = 829.5) than in Jan-Mar (26.1, SE = 10.2). Principal component and regression analyses suggested that aspect, fetch, solar radiation, and beach temperature predicted egg abundance but not mortality. Because a small proportion of sites appear to support most spawning activity, a conclusion consistent with year 2 egg counts, impacts to relatively few beaches could greatly affect surf smelt production. [ABSTRACT FROM AUTHOR]

Capelin in the Barents Sea are primarily harvested in a terminal fishery that targets maturing individuals. Theory predicts that, in a semelparous population (i.e., one in which reproduction is seasonal, synchronous, and followed by parental mortality), an unselective, terminal fishery (i.e., one in which most of the fish that are not caught will not have a new spawning opportunity) does not generate strong selection for changed age and size at maturation. The probabilistic maturation reaction norm (PMRN) method was applied to test this prediction and to detect possible temporal changes in length at maturation of Barents Sea capelin between 1978 and 2008. Maturation reaction norms suggest that maturation is age-independent in capelin, but that males require a larger size to attain the same maturation probability as females. No temporal trends in length at maturation could be detected, thus confirming the theoretical prediction. Furthermore, none of the candidate environmental variables tested to explain the temporal variability in length at maturation (water temperature and capelin biomass) consistently showed a significant correlation with the PMRN midpoints. [ABSTRACT FROM PUBLISHER]

Abstract: Relationships among the species of Northern Hemisphere smelts (family Osmeridae) have long been debated in the fish systematics literature. Eight independent studies based on morphological characters failed to reach any consensus on osmerid interrelationships. We reconstruct the osmerid phylogeny based on DNA sequence data from three mitochondrial (cytb, 16S, 12S) and three nuclear (ITS2, S71, RAG1) gene regions from multiple individuals of the 14 species in 6 genera, using the Japanese ayu (Plecoglossus altivelis) as the outgroup. Analyses with different combinations of nuclear and mitochondrial datasets yielded a generally well-resolved phylogeny of the genera that conflicts with previous hypotheses of osmerid interrelationships, and Shimodaira–Hasegawa tests suggest our topology with the current molecular dataset is significantly better than earlier reconstructions. In addition, mapping 114 morphological characters used in previous studies onto our phylogeny shows widespread homoplasy, which is likely the source of the systematic disagreement produced in earlier works. [Copyright &y& Elsevier]

We characterized 24 polymorphic tetranucleotide microsatellite loci for delta smelt ( Hypomesus transpacificus) endemic to the San Francisco Bay Estuary, CA, 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 cross-amplified in wakasagi smelt ( Hypomesus nipponensis), and 15 primer pairs cross-amplified in longfin smelt ( Spirinchus thaleichthys). [ABSTRACT FROM AUTHOR]

Suggestions that anadromy predominates in northern high latitudes because boreal marine seas have high primary productivity are questioned. Instead, post-Pleistocene invasion of far northern fresh waters, which became inhabitable as Pleistocene temperatures ameliorated, via coastal seas, is suggested as a primary cause for northern distributions of widely anadromous fish families. Also, cold temperature preferences may be implicated in determining the ranges of these families, as well as the inhospitability of far northern fresh waters and the lack of ecosystem space to support the huge populations of boreal anadromous fishes. Moreover, there are significant numbers of tropical anadromous fish species. [ABSTRACT FROM AUTHOR]

Aim We address questions about trans-Pacific distributions of marine organisms and the North Pacific Ocean as a centre of marine biodiversity through a phylogenetic and biogeographical study of a pan-Pacific genus of Northern Hemisphere smelts ( Hypomesus, Pisces: Osmeridae). Location North Pacific Ocean. Methods Relationships of the five species of Hypomesus from throughout the North Pacific were reconstructed through maximum likelihood and Bayesian phylogenetic analyses of sequence data from two mitochondrial (cyt b, 16S) and three nuclear (ITS2, S71, RAG1) gene regions of five to 25 individuals per species, totalling 3588 characters. The resulting phylogenies were used to test hypotheses of species relationships and geographical origins using both dispersal-based and maximum likelihood methods for inferring ancestral areas (lagrange). Cyt b sequence divergence and a Bayesian approach (beast) were used to estimate the timeframe of Hypomesus evolution, which was compared with work on similarly distributed taxa. Results Hypothesized trans-Pacific Ocean relationships based on lateral line scale counts were not supported by the phylogeny, suggesting parallel evolution of this phenotype, although we found one such relationship between the western H. japonicus and the two eastern Pacific species ( H. pretiosus and H. transpacificus). Dispersalist approaches rejected an early proposal of a double-compression vicariant mechanism as well as an eastern Pacific origin. Results from thelagrange analysis suggested a more widespread ancestor, although also supporting a role for the western Pacific. Divergence estimates suggested that most splits between species occurred in the mid-Miocene, and the most recent speciation event, between the eastern Pacific species, occurred in the Pliocene to early Pleistocene. Main conclusions Our molecular data indicate that the character historically used to define relationships within Hypomesus, lateral line scale count, does not reflect ancestry within the genus. Biogeographical reconstructions suggest an important role for the western North Pacific in the diversification of Hypomesus. While uncertainty remains over the date of origin for this genus, estimates place the divergences during periods of climatic cooling that have been important in generating diversity in a number of similarly distributed organisms. Additional comparative data will provide further insight into the relative importance of the western region in generating diversity in the North Pacific Ocean. [ABSTRACT FROM AUTHOR]

Abstract: In many teleost species, the photoreceptive pineal organ harbors the circadian clock that regulates melatonin release in the pineal organ itself. However, the pineal organ of three salmonids (rainbow trout Oncorhynchus mykiss, masu salmon Oncorhynchus masou, and sockeye salmon Oncorhynchus nerka) did not exhibit circadian rhythms in melatonin release when maintained under constant darkness (DD) in vitro, suggesting that the pineal organs of all salmonids lack the circadian regulation of melatonin production. To test this hypothesis, the pineal organ of seven salmonids (common whitefish Coregonus lavaretus, grayling Thymallus thymallus, Japanese huchen Hucho perryi, Japanese charr Salvelius leucomaenis pluvius, brook trout Salvelius fontinalis, brown trout Salmo trutta and chum salmon Oncorhynchus keta) and closely related osmerids (ayu Plecoglossus altivelis altivelis and Japanese smelt Hypomesus nipponensis) were individually maintained in flow-through culture at 15°C under several light conditions. Under light–dark cycles, the pineal organ of all species showed a rhythmic melatonin release with high rates during the dark phase. Under DD, the osmerid pineal organs exhibited circadian rhythms in melatonin release with high rates only during the subjective-night but the salmonid pineal organs constantly released melatonin at high rates. Under constant light, melatonin release was suppressed in all species. The pineal organ of rainbow trout maintained at different temperature (15, 20 or 25°C) under DD released melatonin with high rates but the amount of melatonin released was temperature-sensitive (highest at 20°C). Thus, melatonin release from the pineal organ of osmerids is regulated by both light and circadian clock but the circadian regulation is lacking in salmonids. These results indicate that ancestral salmonids lost the circadian regulation of melatonin production after the divergence from osmerid teleosts. [Copyright &y& Elsevier]

Abstract The outer retina of the smelt Osmerus eperlanus , a visually orientated plankton feeder, of Lake Hiidenvesi (Finland), was examined using both light and transmission electron microscopy. Apart from rods, six morphologically different cone photoreceptor types were identified: short single cones, long single cones, unequal/equal double cones and triple cones (triangular and linear variety). Additionally, in the dorsal region, multiple cone arrangements consisting of up to five members occur. Long single cones and triple cones were observed only sporadically throughout the retina. The incidence of short single cones as a regular element of the cone mosaic is restricted to the ventrotemporal area. The dominant pattern in the Osmerus retina is a pure or a twisted row pattern occurring in all regions. Ventrotemporally, however, square patterns were found as well. The highest cone densities occur in the peripheral ventrotemporal retina. These results indicate that the ventrotemporal region plays an important role in the vision of the smelt. The findings are discussed with respect to the photic habitat conditions and behavioural ecology of the smelt in Lake Hiidenvesi. [ABSTRACT FROM AUTHOR]

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 of the smelt genus Hypomesus suggests that the Chinese specimen belongs to Hypomesus nipponensis. The difference in the studied region of mitogenome is low, 0.6%, which is in agreement with the values of intraspecific divergence for the smelts. The use of the sequence KP281293.1 as a marker for H. olidus will not help in improving the understanding of the taxonomic relationships gained from previous morphological studies and is phylogenetically misleading. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome was sequenced in two individuals of the surf smelt Hypomesus japonicus. The genome sequences are 16,762 and 16,771 bp in size, and the gene arrangement, composition, and size are very similar to the other smelt mitochondrial genomes published previously. The difference between two H. japonicus genomes studied is 0.37%, which is noticeably higher in comparison with other osmerid fishes. The level of sequence divergence between H. japonicus and related osmerids belonging to genera Hypomeus, Osmerus, and Mallotus varies within a very narrow range (12.31-13.72%) indicating poor phylogenetic resolution of this complex fish group. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome was sequenced in two individuals of the Arctic rainbow smelt Osmerus dentex. The genome sequences are 16,615 and 16,616 bp in size, and the gene arrangement, composition, and size are very similar to the other smelt mitochondrial genomes published previously. The difference between the two O. dentex genomes studied is 0.25%, that is, 5.0 times higher in comparison with close species, the European smelt O. eperlanus studied previously. The level of mitochondrial genome divergence between O. dentex and close osmerid fishes, O. eperlanus, and O. mordax is high enough (6.86-7.54%) to consider all of them as separate biological species. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The decline of eulachon spawning runs over the past decade has enhanced the need for management units that reflect the genetic structure of the species. We report the development of 14 novel, highly polymorphic di- and tetranucleotide loci for use in population studies. In a survey of over 200 individuals from two rivers from the Pacific NW, observed heterozygosities of the loci ranged from 0.54 to 0.95 and an average of 23 alleles per locus were resolved. All 14 microsatellite markers were in Hardy–Weinberg equilibrium. [ABSTRACT FROM AUTHOR]

Pond smeltHypomesus olidusis a small-sized economic species of freshwater fish with delicious meat and high output. In this study, the complete mitochondrial genome ofH. olidussequenced to be 16,786 bp in length, including 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs and a control region. The overall base composition ofH. olidusis 24.3% for A, 27.3% for T, 29.2% for C and 19.2% for G, with a slight A + T bias. The mitogenome sequence data may provide useful information to the population genetics analysis ofH. olidusand the elucidation of evolutionary mechanisms inHypomesusfish. [ABSTRACT FROM PUBLISHER]