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Changes in the metabolic profile within the intestine of lenok (Brachymystax lenok) when challenged to acute and lethal heat stress (HS) are studied using no-target HPLC-MS/MS metabonomic analysis. Of 51 differentially expressed metabolites identified in response to HS, 34 occurred in the positive ion mode and 17 in negative ion mode (VIP > 1, P < 0.05). Changes in metabolites (i.e. alpha-D-glucose, stachyose and L-lactate) related to carbohydrate and glycolysis are identified in HS-treated lenok. Fatty acid β-oxidation in HS-treated lenok was inhibited by accumulation of acetyl carnitine, palmitoylcarnitine, carnitine, and erucic acid. Many amino acids (L-tryptophan, D-proline, L-leucine, L-phenylalanine, L-aspartate, L-tyrosine, L-methionine, L-histidine and L-glutamine) decreased to support energy demands in HS-treated lenok. Oxidative damage in HS-treated lenok was indicated by decreased glycerophospholipid metabolites (i.e. glycerophosphocholine, 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphoethanolamine, 1-palmitoyl-sn-glycero-3-phosphocholine, 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine, and 1, 2-dioleoyl-sn-glycero-3-phosphatidylcholine), and increased oxylipin production (12-HETE and 9R, 10S-EpOME). Oxidative stress increased formation of eicosanoids and dicarboxylic acids, overwhelming the mitochondrial β-oxidation pathway, while minor oxidative pathways (omega-oxidation and peroxisomal beta-oxidation) were likely to be activated in HS-treated lenok.

Freshwater whitefishes, Salmonidae Coregoninae, are cold stenothermic fishes of ecological and socio-economic importance in northern hemisphere lakes that are warming in response to climate change. To address the effect of warming waters on coregonine reproduction we experimentally evaluated different embryo incubation temperatures on post-hatching survival, growth, and critical thermal maximum of larval cisco (Coregonus artedi) sampled from lakes Superior and Ontario. Embryos were incubated at water temperatures of 2.0, 4.4, 6.9, and 8.9°C to simulate present and increased winter temperatures, and hatched larvae were reared in a common environment. For both populations, larval survival and critical thermal maximum were negatively related to incubation temperature, and larval growth was positively related to incubation temperature. The magnitude of change across incubation temperatures was greater in the population sampled from Lake Superior than Lake Ontario for all traits examined. The more rapid decrease in survival and critical thermal maximum across incubation temperatures for larval cisco in Lake Superior, compared to those from Lake Ontario, suggests that Lake Superior larvae may possess a more limited ability to acclimate to and cope with increasing winter water temperatures. However, the rapid increase in growth rates across incubation temperatures in Lake Superior larvae suggests they could recover better from hatching at a small length induced by warm winters, as compared to Lake Ontario larvae. Our results suggest propagation and restoration programs may want to consider integrating natural habitat preferences and maximizing phenotypic variability to ensure offspring are set up for success upon stocking.

Repeatedly and recently evolved sympatric morphs exhibiting consistent phenotypic differences provide natural experimental replicates of speciation. Because such morphs are observed frequently in Salmonidae, this clade provides a rare opportunity to uncover the genomic mechanisms underpinning speciation. Such insight is also critical for conserving salmonid diversity, the loss of which could have significant ecological and economic consequences. Our review suggests that genetic differentiation among sympatric morphs is largely nonparallel apart from a few key genes that may be critical for consistently driving morph differentiation. We discuss alternative levels of parallelism likely underlying consistent morph differentiation and identify several factors that may temper this incipient speciation between sympatric morphs, including glacial history and contemporary selective pressures. Our synthesis demonstrates that salmonids are useful for studying speciation and poses additional research questions to be answered by future study of this family. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Live oribatid mites of the family Malaconothridae were found on Salmo spp. parr caught in the rivers of Northwest Russia. The mites were localised in the gill filaments and enclosed in connective tissue capsules. The encapsulation was accompanied by hyperplasia and displacement of the respiratory epithelium. One mite specimen was an adult female, while all the other specimens were protonymphs. The adult female and one protonymph specimen were identified as Tyrphonothrus sp. Other protonymphs could be identified only at the family level. The obtained partial 18S rDNA sequence of one protonymph was 100% identical to that of Tyrphonothrus maior (NCBI accession No. KY922215). This is the first report of living malaconothrid mites encapsulated in fish gills, and the phenomenon may assume parasitic behaviour. However, the nature of the relationship between the mites and the fish requires further investigations.

Proliferative kidney disease (PKD), caused by the myxozoan endoparasite Tetracapsuloides bryosalmonae, is of serious ecological and economical concern to wild and farmed salmonids. Wild salmonid populations have declined due to PKD, primarily in rivers, in Europe and North America. Deep lakes are also important habitats for salmonids, and this work aimed to investigate parasite presence in five deep Norwegian lakes. Kidney samples from three salmonid species from deep lakes were collected and tested using real-time PCR to detect PKD parasite presence. We present the first detection of T. bryosalmonae in European whitefish in Norway for the first time, as well as the first published documentation of the parasite in kidneys of Arctic charr, brown trout and whitefish in four lakes. The observed prevalence of the parasite was higher in populations of brown trout than of Arctic charr and whitefish. The parasite was detected in farmed, but not in wild, charr in one lake. This suggests a possible link with a depth of fish habitat and fewer T. bryosalmonae-infected and PKD-affected fish. Towards a warmer climate, cold hypolimnion in deep lakes may act as a refuge for wild salmonids, while cold deep water may be used to control PKD in farmed salmonids.

The lateral line system and its innervation were examined in the masu salmon Oncorhynchus masou masou. The species has 8 cephalic canals (supraorbital, infraorbital, otic, preopercular, mandibular, postotic, supratemporal, and temporal portion of trunk), 1 trunk canal and 9 superficial neuromast groups (rostral, nostril, preinfraorbital, postocular, cheek and supratemporal groups in the cephalic groups, and predorsal, trunk accessory and caudal fin groups in the trunk groups). The components are generally similar to those in many other teleosts, the lateral line system of O. m. masou is distinctive in having a preinfraorbital superficial neuromast group and lacking infraorbital, mandibular and opercular superficial neuromast groups. The lateral line system of O. m. masou is compared with some other species of Oncorhynchus.

For the first time, we localized the spawning grounds of the white char endemic for the Kamchatka River lower course. We confirmed the significant restriction in gene flow between the sympatric white char and related Dolly Varden, and supposed the ecological mechanisms providing for the chars’ divergence in the riverine system.

Abstract In order to study the distribution of phylogenetic mtDNA lineages of Arctic charr Salvelinus alpinus in their contact zones in the north of East Siberia we analyzed nucleotide sequences of mtDNA control region of charr from 10 Arctic populations in the area from the Yenisei to the Lena. At the Putorana plateau, haplotypes of Atlantic and Siberian subgroups of Eurasian group were recorded, in the Khatanga River basin, haplotypes of Atlantic subgroup, in the Lena River delta, haplotypes of Siberian subgroup and of Bering group were observed. Some Siberian haplotypes found at the Putorana and in the Lena delta, have been earlier registered in other regions of East Siberia. New findings, along with published materials allow to specify the ranges of these three phylogenetic lineages and the margins of their contact zones; they also evidence wide sympatry of Atlantic and Siberian haplotypes in Taimyr water bodies and support close relationship of charr of Siberian subgroup from all main areas of their distribution.

Abstract Changes in the motivational component of rheoreaction (the ratio of rheoreaction types) during starvation in some fish species has been analyzed. The presence of fish motivation to migrate (before starvation) is the major pattern of the future changes in the motivational component of rheoreaction resulting from starvation. All fish of the families Cyprinidae and Salmonidae studied with initially behavior as resident individuals show the same type of response to starvation. Their preference for currentwise movement increases on the 2nd–5th days of starvation, then the preference for movement against the current increases on the 7th–12th days, and the ratio of rheoreaction types approaches the initial one. Juveniles of the Black Sea salmon (Salmo trutta labrax) with a motivation to downstream migration, represent a different response to starvation: the downstream movement of individuals monotonically increased from two days after starvation.

The experimental study yielded new data on changes in the activity of Na+/K+-ATPase and the level of cortisol in juvenile pink salmon Oncorhynchus gorbuscha that left the spawning nests (Olkhovka River, White Sea basin) during their transfer from fresh water to sea water (25‰) and back. The development of tolerance to increased salinity in juvenile pink salmon is accompanied by activation of Na+/K+-ATPase after 1 h and 24 h of maintaining in seawater and by cortisol content increase after 1 h of this exposure, followed by a return to the initial level after 24 h. The results obtained indicate the readiness of juvenile pink salmon to downstream migration into the marine environment immediately after leaving spawning nests. With the subsequent transfer of fish from salt water to freshwater after 24 h, the activity of Na+/K+-ATPase and the content of cortisol in them decrease, which may indicate the plasticity of the osmoregulatory reaction of pink salmon smolts.

Rapids habitats are critical spawning and nursery grounds for multiple Laurentian Great Lakes fishes of ecological importance such as lake sturgeon, walleye, and salmonids. However, river modifications have destroyed important rapids habitat in connecting channels by modifying flow profiles and removing large quantities of cobble and gravel that are preferred spawning substrates of several fish species. The conversion of rapids habitat to slow moving waters has altered fish assemblages and decreased the spawning success of lithophilic species. The St. Marys River is a Great Lakes connecting channel in which the majority of rapids habitat has been lost. However, rapids habitat was restored at the Little Rapids in 2016 to recover important spawning habitat in this river. During the restoration, flow and substrate were recovered to rapids habitat. We sampled the fish community (pre- and post-restoration), focusing on age-0 fishes in order to characterize the response of the fish assemblage to the restoration, particularly for species of importance (e.g. lake whitefish, walleye, Atlantic salmon). Following restoration, we observed a 40% increase in age-0 fish catch per unit effort, increased presence of rare species, and a shift in assemblage structure of age-0 fishes (higher relative abundance of Salmonidae, Cottidae, and Gasterosteidae). We also observed a “transition” period in 2017, in which the assemblage was markedly different from the pre- and post-restoration assemblages and was dominated by Catostomidae. Responses from target species were mixed, with increased Atlantic salmon abundance, first documented presence of walleye and no presence of lake sturgeon or Coregoninae.

Co-infections are common in host-parasite interactions, but studies about their impact on the virulence of parasites/diseases are still scarce. The present study compared mortality induced by a fatal bacterial pathogen, Flavobacterium columnare between brown trout infected with glochidia from the endangered freshwater pearl mussel, Margaritifera margaritifera, and uninfected control fish during the parasitic period and after the parasitic period (i.e. glochidia detached) in a laboratory experiment. We hypothesised that glochidial infection would increase host susceptibility to and/or pathogenicity of the bacterial infection. We found that the highly virulent strain of F. columnare caused an intense disease outbreak, with mortality reaching 100% within 29 h. Opposite to the study hypothesis, both fresh ongoing and past infection (14 months post-infection) with glochidia prolonged the fish host’s survival statistically significantly by 1 h compared to the control fish (two-way ANOVA: fresh-infection, F1, 82 = 7.144, p = 0.009 and post-infection, F1, 51 = 4.227, p = 0.044). Furthermore, fish survival time increased with glochidia abundance (MLR: post-infection, t = 2.103, p = 0.045). The mechanism could be connected to an enhanced non-specific immunity or changed gill structure of the fish, as F. columnare enters the fish body mainly via the gills, which is also the glochidia’s attachment site. The results increase current knowledge about the interactions between freshwater mussels and their (commercially important) fish hosts and fish pathogens and also emphasise the importance of (unknown) ecosystem services (e.g., protection against pathogens) potentially associated with imperilled freshwater mussels.

Hematopoiesis is a mechanism of multifunctional adaptation in vertebrates, including fish. Adaptive capabilities of populations are studied for a species of genus Salvelinus with high ecological plasticity. Char Salvelinus malma is represented in Kamchatka by the anadromous, river, brook, and several lake forms. Peripheral blood cells are investigated for this species juveniles and adults from the Raduga River in the lower Kamchatka River basin. The fish sampled in August 2013 were divided into two groups: sexually mature individuals (10 specimens) and juveniles (10 specimens). The body length (AC) of mature chars (mean ± standard deviation, range in brackets) was 338.90 ± 12.64 (304.0–380.0) mm, the body weight — 437.40 ± 57.74 (235.0–735.0) g, their sex ratio was close to 1 : 1. The length of juvenile chars was 150.50 ± 9.14 (104.0–195.0) mm, the weight — 33.90 ± 6.19 (10.1–68.8) g. Blood was sampled from the caudal vessel of alive fish immediately after catching, the blood smears were dried and fixed with May-Grunwald dye and then stained with azure-eosin. Composition of leukocytes and erythrocytes was determined on the stained blood smears. The blood cells were classified according to Ivanova (1983) and Zhiteneva et al. (1989). Statistical significance of the blood cells composition differences between fish groups was assessed using the Mann-Whitney U-test, after checking for normal distribution of characteristics (Kolmogorov-Smirnov test). The erythroid row of S. malma was represented by proliferating (erythroblasts, basophilic and polychromatophilic normoblasts), maturing (oxyphilic normoblasts) and mature erythrocytes, the leukocyte row — by blast cells, agranulocytes and granulocytes. The juveniles were characterized by intense proliferative processes (great number of immature erythrocytes, large and medium lymphocytes, presence of blast cells) and appearance of poikilocytes; the sexually mature chars were distinguished by greater number of granulocytes, mainly due to stab and segmented neutrophils (p < 0.01). Parasitological analysis showed different infestation of the juvenile and adult chars by pathogenic helminths (Anisakis simplex, Eubothrium salvelini, Neoechinorhynchus salmonis) that influenced on their blood. Broad adaptive capabilities of S. malma hematopoiesis provided by wide morphological and functional diversity of blood cells are concluded that maintains homeostasis of the species. Blood indices for char from the Raduga River can be used to form reference intervals for monitoring physiological state of this species.

The review considers probable ways to overcome the deficiency of eicosapentaenoic and docosahexaenoic acids in the human diet through the rational development of aquaculture. Currently, aquaculture is not a producer, but a consumer of polyunsaturated fatty acids, since it is based on feed, the main components of which are fishmeal and fish oil obtained from commercial catches. It is proposed to transform farmed fish from a consumer to producer of these polyunsaturated fatty acids. The source of production of eicosapentaenoic and docosahexaenoic acids in aquaculture can be their synthesis by fish from short-chain α-linolenic acid contained in the oil of terrestrial agricultural plants. Calculations of the threshold value of the content of eicosapentaenoic and docosahexaenoic acids in feed for salmon fish (Salmonidae) with partial replacement of fish oil with vegetable oil are presented. Another possible way to transform aquaculture into a producer of polyunsaturated fatty acids is to partially replace fishmeal in feed with flour from terrestrial invertebrates. Some species of insects and worms that are promising for aquaculture as objects for the production of feed meal are considered.

The article presents information on the long-term behavior of biological indicators and returns and catches of three species of the Pacific salmon, namely, pink salmon (Oncorhynchus gorbuscha), chum salmon (O. keta), and coho salmon (O. kisutch) for two conditional periods of the end of the 20th century and beginning of the 21st century. A number of changes occurred in the structure of biological indicators during the specified periods of time. There was a synchronous decrease observed in length, body weight, and fecundity in pink salmon, chum salmon, and coho salmon by the end of the second period. Dominant age groups changed in chum salmon and coho salmon, while age of both species increased. Characteristics of the dynamics of pink salmon returns were identified for two major capture fisheries areas, Shelikhov Gulf and Taui Bay. They fluctuated in antiphase along the even- and odd-year lines at the end of the 20th century; odd-year returns were largely recorded at the beginning of the 21st century. Returns have become strong both for even- and odd-year generations since 2015. The chum and coho salmons returns are on the rise. Taui Bay is noted to have lost its commercial importance as the main harvesting area of the pink and chum salmons.

Severe flooding often leads to downstream displacement of aquatic animals. Despite this, many salmonid populations persist in habitats located upstream of tall barriers, such as artificial check dams and/or natural waterfalls, that completely block fishes from returning to the upstream areas after flooding. The evolution of such populations may be affected by spatial sorting due to differential rates of downstream displacement. This study examined whether a morphological trait (increased body depth) that allows individuals to better maintain their position during flooding has evolved in juvenile amago salmon Oncorhynchus masou ishikawae inhabiting above-barrier habitats in two rivers. In both rivers, juveniles collected at the stations with multiple downstream barriers had deeper bodies than those collected at other stations. Similar differences were found in juveniles reared in a common-garden experiment. Field experiments with natural flooding also indicated that deep bodies help juveniles resist downstream displacement. These results consistently suggest that juveniles in some above-barrier habitats have evolved deep bodies to resist downstream displacement due to flooding. Our study is the first to show the evolutionary outcomes of passive spatial sorting during severe climate events.

The structural response and plasticity of the cestode tegument in response to the influence of the host organism is not yet well understood. The main aims of our in vitro study were to analyse the ultrastructural mechanisms and kinetics of tegumental secretion in two cestode species, Dibothriocephalus dendriticus and Ligula interrupta, in response to the influence of fish host blood serum. The incubation of plerocercoids in the culture medium, which contained fish host blood serum, resulted in an increased number of secretory products on the tegumental surface. Our study is the first to experimentally demonstrate the formation of plerocercoid protective layers influenced by the host's internal environment factors. The mechanism of the generation of the protective layer included the following: the intensive formation of organelles in the tegumental cytons and their transfer to the distal cytoplasm of the tegument; increases in extracellular vesicles and vacuoles released on the tegumental surface; arrangement of secretory products and fine-dispersed extracellular matrix in layers; and formation of the protective layer. The structural tegumental response included increases in the glycocalyx layer and structural changes. Our study revealed that the universal mechanism of protective layer formation was intrinsic to different tapeworms. We hypothesize that plerocercoids of cestodes parasitizing fish may use tegumental secretion in the formation of a protective layer and in the release of immunoregulator molecules to evade the host's immune response.

Allowing reproductive individuals to colonize novel habitat or recolonize previously occupied habitat is increasingly being considered as a tool for recovery of depleted populations of anadromous salmon. Successful application of these techniques requires thorough understanding of how adults use the riverscape during colonization to ensure that programs achieve desired outcomes. We examined the movements and habitat use of adult Atlantic Salmon Salmo salar during colonization of novel habitat in an eastern Canadian river using a novel combination of acoustic telemetry, remote sensing, ground surveys, and continuous records of river temperature and discharge. Females moved less than males, regardless of river temperature or discharge, whereas males engaged in more extensive movements except at elevated temperature and discharge. Probability of movement was lower during the summer, coincident with individuals holding in pools during high-heat/low-discharge events. River temperature, discharge, and day of year were influential in predicting whether salmon held in pools, and size was the most important physical characteristic identifying “suitable” holding pools. Observed movement patterns may reflect different evolutionary strategies employed by each sex to maximize reproductive fitness. Because spawning behavior is highly conserved within salmonids, these findings may (1) provide a generalized picture of how Atlantic Salmon use space during colonization of unoccupied habitat and (2) be used to optimize future reintroduction and assisted migration programs.

The thyroid hormones (THs) play an important role in the regulation of the rate of metabolism, affect the growth and function of different systems in the organism. The aim of this study was to assess serum concentration of total triiodothyronine (T3), total thyroxine (T4) as well as T3/T4 ratio in serum from healthy fresh water fish from Salmonidae, Acipenseridae, Cyprinidae, and Clariidae families to determine species-specific reference intervals. Mean concentrations of T3 and T4 levels varied significantly among fish. Finally, the test results show clear differences in the serum concentration of the T3 and T4 and give new insight into the thyroid hormones reference values in some commercial fresh water fish species.

We investigated the cause of skeletal deformities found in brown trout from the Aspromonte mountain area in Reggio Calabria, Italy. Toxicological, histopathological and parasitological analyses were carried out on 14 fish with evident macro-morphological alterations from 2 different locations in the same river, and 4 control fish without morphological alterations from a different river (far from the first river but still within the area under study). Histopathological and radiological observations confirmed severe skeletal deformities in the specimens investigated. Parasitological examinations highlighted the presence of the nematodeCystidicoloides ephemeridarum, found only within the gastrointestinal tract of specimens showing deformities. Moreover, a direct correlation between parasite number and fish size was found. Given the low heavy metal levels and the presence of a massive parasitosis in teleosts showing deformities, we postulate a correlation between skeletal deformities and nematode infestation: the parasites caused a serious vitamin and mineral deficiency in the fish, which led to a dysplastic vertebral column. The low calcium levels found in malformed specimens compared with negative controls effectively confirm this hypothesis.

The rational use of valuable fish species from aquaculture is difficult to implement without knowledge of the state of the genetic structure of local stocks. Different types of DNA markers can be used to achieve the goals of selection and breeding work. The genetic structure of a local stock of rainbow trout (Oncorhynchus mykiss Walbaum, 1792) (Salmoniformes, Salmonidae) farmed in Ukraine was studied using DNA-markers: microsatellite (SSR-markers – simple-sequence repeats-markers) and intermicrosatellite (ISSR – inter-simple sequence repeat). Five fragments of trinucleotide microsatellite motifs with a single anchor nucleotide at the 3'-end were used as a primer for analysis by the ISSR-PCR method. Totally, 85 amplicons were obtained across the five loci, of which 92.9% were polymorphic. The total number of alleles ranged from 10 (marker (ACC)₆G) to 23 (marker (AGC)₆G). The following monomorphic amplicons were determined for the studied local stock of rainbow trout: according to marker (CTC)₆C – 770 and 520 bp bands, for the marker (GAG)₆C – 345, 295 and 260 bp, and for the marker (AGC)₆C – 350 bp. The average number of polymorphic bands per locus was 15.8. The selected ISSR primers had a level of polymorphic information content above the average. The most effective markers for molecular-genetic analysis of rainbow trout were (AGC)₆G and (AGC)₆C according to the percentage of polymorphic bands, marker index, effective multiplex ratio and resolving power. The selected ISSR loci allow the genetic structure of the studied local stock to be characterized using the total and the effective number of alleles per locus (Na and Ne were 1.9 and 1.4, respectively), the Shannon index (average value I was 0.4) and the unbiased expected heterozygosity (mean uHe = 0.3). Microsatellite-based analysis showed features of the genetic structure of the local stock of rainbow trout at six microsatellite loci (OMM 1032, OMM 1077, OMM 1088, Str 15, Str 60, Str 73). Allelic diversity was established and alleles with the highest frequency and most typical for the given stock were identified. The Shannon index and unbiased expected heterozygosity were determined using SSR-markers and were 1.42 and 0.79, respectively. This depicts the complexity of the population structure, a high level of genetic diversity and indicates a high level of heterozygosity of local stock. The “gene pool profile” established as a result of ISSR-PCR in the future will help to differentiate local stocks of rainbow trout in aquaculture of Ukraine. Microsatellite markers provide the ability to determine individual features of genetic variation of local populations and to conduct the management of genetic resources on fish farms.

Adaptive radiation in fishes has been actively investigated over the last decades. Along with numerous well-studied cases of lacustrine radiation, some examples of riverine sympatric divergence have been recently discovered. In contrast to the lakes, the riverine conditions do not provide evident stability in the ecological gradients. Consequently, external factors triggering the radiation, as well as developmental mechanisms underpinning it, remain unclear. Herein, we present the comprehensive study of external and internal drivers of the riverine adaptive divergence of the salmonid fish Salvelinus malma. In the Kamchatka River, north-east Asia, this species splits in the reproductively isolated morphs that drastically differ in ecology and morphology: the benthivorous Dolly Varden (DV) and the piscivorous stone charr (SC). To understand why and how these morphs originated, we performed a series of field and experimental work, including common-garden rearing, comparative ontogenetic, physiological and endocrinological analyses, hormonal 'engineering' of phenotypes and acute toxicological tests. We revealed that the type of spawning ground acts as the decisive factor driving the radiation of S. malma. In contrast to DV spawning in the leaf krummholz zone, SC reproduces in the zone of coniferous forest, which litter has a toxic impact on developing fishes. SC enhances resistance to the toxicants via metabolism acceleration provided by the elevated thyroid hormone expenditure. These physiological changes lead to the multiple heterochronies resulting in a specific morphology and ecology of SC. Salvelinus malma represents a notable example of how the thyroid axis contributes to the generation of diverse phenotypic outcomes underlying the riverine sympatric divergence. Our findings, along with the paleoecology data concerning spruce forest distribution during the Pleistocene, provide an opportunity to reconstruct a scenario of S. malma divergence. Taken together, obtained results with the data of the role of thyroid hormones in the ontogeny and diversification of fishes contribute a resource to consider the thyroid axis as a prime director orchestrating the phenotypic plasticity promoting evolutionary diversification under the changing environmental conditions.

Diversity of trout (genus Salmo) in Croatia is still not well described on several levels, resulting in numerous taxonomic controversies and accumulation of conservation problems, especially in protected areas. The aim of this study was to determine genetic diversity and spatial distribution of trout in Žumberak-Samoborsko gorje Nature Park in Croatia using mitochondrial cytochrome b sequences and to estimate the stability of their populations for conservation. Effective population sizes and migration rates, and intraspecific and intrapopulational genetic diversities were also estimated. Phylogenetic reconstruction revealed three evolutionary independent and genetically distinct lineages, comprising 26 haplotypes. Majority of samples and haplotypes belong to S. labrax, the native species for this region. Even though S. labrax is widespread in the watercourses of the park and is present with moderately high genetic diversity, haplotypes of non-native S. trutta and S. marmoratus were also observed. In addition to the presence of non-native trout species, survival of native trout in this area is also endangered by habitat fragmentation and other anthropogenic pressures, causing conservational concern.

This study compared the repulsive effects of sound playbacks of intermittent 30, 150, 300, 600 and 900 Hz tones on two fish with different auditory capabilities: juvenile chum salmon (Oncorhynchus keta) and common carp (Cyprinus carpio). When 150 and 300 Hz tones were emitted from an underwater speaker, O. keta exhibited a moderate repulse reaction. Conversely, C. carpio exhibited a moderate repulse reaction to a tone with a frequency of 30 Hz, which indicates that a low-frequency component in complex broadband sound may be important for inducing a repulse reaction in cyprinids.

During their different life stages, parasites undergo remarkable morphological, physiological, and behavioral “metamorphoses” to meet the needs of their changing habitats. This is even true for ectoparasites, such as the monogeneans, which typically have a free-swimming larval stage (oncomiracidium) that seeks out and attaches to the external surfaces of fish where they mature. Before any obvious changes occur, there are ultrastructural differences in the oncomiracidium’s outer surface that prepare it for a parasitic existence. The present findings suggest a distinct variation in timing of the switch from oncomiracidia epidermis to the syncytial structure of the adult tegument and so, to date, there are three such categories within the Monogenea: (1) Nuclei of both ciliated cells and interciliary cytoplasm are shed from the surface layer and the epidermis becomes a syncytial layer during the later stages of embryogenesis; (2) nuclei of both ciliated cells and interciliary syncytium remain distinct and the switch occurs later after the oncomiracidia hatch (as in the present study); and (3) the nuclei remain distinct in the ciliated epidermis but those of the interciliary epidermis are lost during embryonic development. Here we describe how the epidermis of the oncomiracidium of Discocotyle sagittata is differentiated into two regions, a ciliated cell layer and an interciliary, syncytial cytoplasm, both of which are nucleated. The interciliary syncytium extends in-between and underneath the ciliated cells and sometimes covers part of their apical surfaces, possibly the start of their shedding process. The presence of membranous whorls and pyknotic nuclei over the surface are indicative of membrane turnover suggesting that the switch in epidermis morphology is already initiated at this stage. The body tegument and associated putative sensory receptors of subadult and adult D. sagittata are similar to those in other monogeneans.

Endangerment of fish habitats worldwide is a global problem. Breeding fish in restocking hatcheries is important for bioconservation of many fishes. Analysis of biochemical and hematological parame...

A complete annotated list of marine, brackish-water, and freshwater ichthyofauna of Sakhalin Island and the adjacent southern part of the Sea of ​​Okhotsk is provided for the first time in the entire history of the study of the fish population. It is based on a critical analysis of the literature data for the last 200 years, collection materials, and the results of our own long-term studies. The list includes 600 species in 4 classes, 44 orders, 17 suborders, 129 families, 50 subfamilies, and 312 genera. It presents both English and Latin (scientific) names, information on the ranges in the World Ocean and distribution within Sakhalin waters, and data on the conservation status, commercial importance, and abundance. For a number of species, the list also provides information on collection specimens, confirming their presence within the studied water area. For all species, the current ranges and taxonomic status are specified according to the new data, if any. The so-called controversial taxa are discussed. The first part provides brief information about the history of the study of the Sakhalin ichthyofauna, the geographical and oceanological characteristics of the study area, as well as the first 118 species of the annotated list belonging to 79 genera, 42 families and 20 orders in 4 classes.

Salmon pancreas disease virus, more commonly known as salmonid alphavirus (SAV), is a single-stranded positive sense RNA virus and the causative agent of pancreas disease and sleeping disease in salmonids. In this study, a unique strain of SAV previously isolated from ballan wrasse was subjected to whole genome sequencing using nanopore sequencing. In order to accurately examine the evolutionary history of this strain in comparison to other SAV strains, a partitioned phylogenetic analysis was performed to account for variation in the rate of evolution for both individual genes and codon positions. Partitioning the genome alignments almost doubled the observed branch lengths in the phylogenetic tree when compared to the more common approach of applying one model of substitution across the genome and significantly increased the statistical fit of the best-fitting models of nucleotide substitution. Based on the genomic data, a valid case can be made for the viral strain examined in this study to be considered a new SAV genotype. In addition, this study adds to a growing number of studies in which SAV has been found to infect non-salmonid fish, and as such we have suggested that the viral species name be amended to the more inclusive ‘piscine alphavirus’.

Selenium (Se) toxicity to fish is primarily manifested via maternal transfer to the eggs, which may result in adverse effects on larval survival and development. The present study assessed the effects of egg Se concentrations derived via maternal transfer on early life-stage development, survival, and growth of Arctic grayling (Thymallus arcticus), a salmonid species not previously assessed for Se sensitivity. Fish gametes were collected from 4 streams in Alaska known to exhibit a range of egg Se concentrations. Eggs were fertilized and reared in the laboratory from hatch through post-swim-up. Larvae were assessed for survival, length, and weight, as well as deformities (skeletal, craniofacial, fin-fold) and edema based on a graduated severity index. Eggs from a total of 47 females were collected, with egg Se concentrations ranging from 3.3 to 33.9 mg kg-1 dry weight. No relationships were observed between larval endpoints evaluated and parent females' egg, muscle, or whole-body Se concentrations. Therefore, Se 10% effective concentrations (EC10s) were defined as the maximum measured Se concentrations: >33.9, >17.6, and >19.7 mg kg-1 dry weight for eggs, muscle, and whole-body tissue, respectively. Collectively, these data indicate that Arctic grayling are relatively insensitive to maternally transferred Se compared to other fish species. Environ Toxicol Chem 2021;40:380-389. © 2020 SETAC.

Background. Biomarker indices (protein, lipid, carbohydrate, mineral, enzymatic, and antioxidant enzymes) are used for the evaluation of health in fish blood. No studies conducted to date have provided standard values of various biomarkers in the blood plasma of Hucho hucho (Linnaeus, 1758). Therefore, we evaluated the physiological status and seasonal variation in metabolic profiles of this species. Significant seasonal changes were observed in all blood biomarkers, with the exception of red blood cells, hemoglobin, and mean corpuscular hemoglobin. Using these data, the physiological status and seasonal variation in the metabolic profiles of H. hucho were evaluated. Generally, the goal of this study was to characterize the variation in the blood biomarkers of huchen between different seasons. Materials and methods. Fish were raised in captivity to obtain a breeding group to repopulate submontane rivers. Blood samples were collected by puncture of the caudal vein in a vacutainer with Li-Heparin to determine the seasonal values of hematological, biochemical parameters, and oxidative stress. Blood was collected from a random sample of 10 huchen in all four seasons. Results. We found significant seasonal variation in several parameters: packed cell volume (PCV), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), total protein (TP), albumin (ALB), γ-globulins (GG), urea (UREA), creatinine (CRN), triglycerides (TG), cholesterol (CHOL), glucose (GLC), calcium (Ca2+), phosphorus (PO43–), iron (Fe3+), sodium (Na+), potassium (K+), alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyl aminotransferase (GGT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), creatine kinase (CK), α-Amylase (α-Amy), lipase (LIP), total bilirubin (TB), superoxide dismutase (SOD), and glutathione peroxidase (GPx). Conclusion. This is the first study to provide standard values of proteins, lipids, carbohydrates, and minerals and the enzyme profile in huchen in all seasons, which may be a benchmark for future investigation that would favor the bioconservation and increase the spread of huchen.

Abstract Morphological analysis of muksun Coregonus muksun of the Khatanga River basin revealed that along with its typical high-density-rakered form, individuals of the low-density-rakered form also live in this region. Analysis of the genetic polymorphism of three marker regions of mitochondrial (ND1 and COI fragments) and nuclear (ITS1) DNA indicates the polyphyletic origin of these forms. The revealed low level of genetic differentiation of muksun and whitefish C. lavaretus, along with the available data on the absence of clear diagnostic species characteristics, suggest that they belong to the same biological species C. lavaretus.

The review assembles chronological data on Black Sea trout (Salmo labrax) from Romanian waters and brings up-to-date information related to the distribution of the species. The information used dates from 1909 to 2020 and includes books, articles, digital databases, field observations, and notes from different research fields such as ichthyology, biogeography, genetics, aquaculture, conservation, and ecology. Global distribution, migration, meristic characters, and aquaculture of the species were analyzed based on the recorded data from the specialty literature. New information related to a possible population of Salmo labrax inside the Carpathian Arch was discussed. In Romanian waters the species is found in the Black Sea, Danube, Danube Delta but the current paper proposes a new hypothesis, namely that resident populations can be found in rivers and lakes adjacent to the Carpathian Arch. The highest migration point of the Black Sea trout in the Danube was recorded near Corabia locality, Olt County, (43°46′25″N- 24°30′12″E). In the Danube Delta, it was caught in all the three branches (Sulina, Sf. Gheorghe and Chilia), and lagoonary complexes such as Razim-Sinoe. Sexually matured females were caught especially in Spring Season while unmatured specimens were caught in all seasons. Even if the species is protected under Romanian legislation, fishermen and anglers should report its presence when caught accidentally.

In 1848, the grayling Thymallus aeliani (Valenciennes) was described from Lake Maggiore, Italy, in the north Adriatic basin. Genetic analyses of the mitochondrial control region showed a unique evolutionary history of grayling inhabiting the rivers of northern Adriatic basin, from the upper reaches of the Po River and its left tributaries in the west to the Soča River in the east, which resulted in the designation of this phylogenetic lineage as Adriatic grayling. Consequently, the name T. aeliani was connected to the Adriatic lineage, re-establishing the validity of this taxon. However, the mitochondrial haplotypes belonging to Adriatic grayling were never compared with the type specimens of T. aeliani, as their whereabouts were unknown. In this study, a neotype for T. aeliani was designated using topotypical specimens stored at the Natural History Museum in Vienna. The neotype (NMW 68027:2 labelled as “Lago Maggiore, Bellotti, 1880”) was designated pursuant to the conditions stipulated in Article 75.3 of the International Code of Zoological Nomenclature. Furthermore, the mitochondrial control region of the neotype was compared to haplotypes of the Adriatic lineage and showed high genetic similarity, which therefore connects the species name T. aeliani to the Adriatic grayling. This crucial step in fixing nomenclatural status of this species is very important for its protection and management.

The morphological variability of nine characters in six samples of Siberian taimen Hucho taimen from the Amur River was studied. The differences in the level of fluctuating asymmetry of fish from different tributaries are small, which indicates the similarity of the conditions of embryonic and early postembryonic development; significant differences between the samples were noted only in six cases. The maximum fluctuations in the coefficient of variation are characteristic for the number of postorbital bones and channels of the seismosensory system on the 1st postorbital bone; the minimum, for the number of soft rays in the pectoral fins and channels of the seismosensory system on the preopercular bones. The largest sum of the variation coefficients values for individual characteristics differs in the sample from the Bikin River; the smallest, the Limuri River. These difference positively correlates with the length and area of ​​the basin of these tributaries. A regular decline in the mean values in the fish sampled at increasing distance from the mouth of the Amur River concerns only the number of postorbital bones. Clustering according to the mean values ​​of the features, revealed that the samples form three clusters: (1) the rivers Bol’shaya Ussurka and Tyrma (2nd order tributaries, the farthest from the Amur mouth), (2) the Limuri River (the least distant from the Amur mouth), 3) the rivers Anyui, Khor and Bikin (geographically close populations). Revealed features may indicate the similarity of the conditions of early development and the likelihood of gene exchange between the last three groups.

In the scope of this study, origin of the two Salmo populations from streams Sapur (a southwestern drainage of Lake Van) and Arpet (an uppermost drainage of Botan River, Tigris catchment) was investigated based on morphologic and molecular data. The occurrence of the any Salmo species in both drainages have never been recorded up to date. The both populations found conspecific and identified as Salmo trutta which translocated from Europe. Besides, both populations were observed as successfully established., Bu çalışma kapsamında, Sapur Çayı (Van Gölü'nün güneybatı drenajı) ve Arpet Çayı'ndan (Botan Nehri Dicle havzasının en üst drenajı) iki Salmo popülasyonunun kökeni morfolojik ve moleküler verilere dayalı olarak araştırılmıştır. Her iki akarsuda da herhangi bir Salmo türünün varlığı günümüze kadar hiç kaydedilmemiştir. Her iki popülasyonun türdeş ve Avrupa’dan taşınmış olan Salmo trutta türüne ait olduğu saptanmıştır. Ayrıca, her iki popülasyonun da başarılı bir şekilde yerleşmiş olduğu görülmüştür.

Caligus rogercresseyi is the dominant sea louse parasite affecting the salmon and trout industry in southern Chile. This parasite has a wide range of native and endemic fish hosts. The Patagonian blenny Eleginops maclovinus, which is parasitized mostly by the caligid species Lepeophtheirus spp. and C. rogercresseyi, is presumably responsible for the transmission of C. rogercresseyi to salmonids. The aim of this study was to characterize the transmission of parasites between different fish species and parasite cohort development under laboratory conditions. Parasite abundances and intensities were quantified. Transmission of parasites from Patagonian blenny to Atlantic salmon Salmo salar was lower (~9%, mainly corresponding to C. rogercresseyi) than from salmon to Patagonian blenny (14.7-26.9%, where only C. rogercresseyi were observed). This suggests that the transmission of C. rogercresseyi from salmon individuals is higher than the transmission from a native fish. Parasite cohorts developed successfully on both fish species, but apparently under different developmental rates. Water temperature, oxygen, and juvenile abundances were the variables that better explained cohort development success and variation in C. rogercresseyi adult abundances over time.

Hematological parameters of fish are useful for diagnosing pathophysiological conditions associated with metabolic perturbations in fish and therefore act as a non-specific biomarker of acute and chronic stress in the natural habitat and in aquaculture. Salmonid fish are of great importance in aquaculture; however, hematological studies of these species are scarce. This study presents the first set of data for the complete hematological profile of brook trout (Salvelinus fontinalis, Salmonidae). In total, seven blood cell types were identified and their characterization, range, size/surface area, and the leukocyte differential count are presented. Large numbers of immature erythrocytes and two subtypes of thrombocytes (round and prolate) were present in blood. Lymphocytes were the dominant leukocytes, followed by segmented neutrophils. Total leukocyte and segmented neutrophil counts were higher in the blood of male than female fish (P

The growth, order of anlage, and features of transitive stages of skeletal elements (cranial bones and serial structures: teeth, gill rakers, fin rays, pterigyophores, vertebrae muscles, predorsalia, and scales) in were studied in pre-larvae, larvae, and fingerlings of the nose char (N1-form), endemic lakustrine-riverine form of the Dolly varden Salvelinus malma complex of the Lake Kronotskoe, reared in the laboratory at a constant temperature. A comparative analysis of the early ontogenesis of sympatric species of nose char and white char of the Lake Kronotskoe evidences on a high similarity in the growth rate and development of the two forms, differing by the body length of free embryos and the larvae coloration.

Fish fraud is a problematic issue for the industry. For it to be properly addressed will require the use of accurate, rapid, and cost-effective tools. In this work, near infrared reflectance spectroscopy (NIRS) was used to predict nutritional values (protein, lipids, and moisture) as well as to discriminate between sources (farmed vs. wild fish) and conditions (fresh or defrosted fish). Samples of five whitefish species—Alaskan pollock (Gadus chalcogrammu), Atlantic cod (G. morhua), European plaice (Pleuronectes platessa), common sole (Solea solea), and turbot (Psetta maxima)—including farmed, wild, fresh, and frozen ones, were scanned by a low-cost handheld near infrared reflectance spectrometer with a spectral range between 900 and 1700 nm. Several machine learning algorithms were explored for both regression and classification tasks, achieving precisions and coefficients of determination higher than 88% and 0.78, respectively. Principal component analysis (PCA) was used to cluster samples according to classes where good linear discriminations were denoted. Loadings from PCA revealed bands at 1150, 1200, and 1400 nm as the most discriminative spectral regions regarding classification of both source and condition, suggesting the absorbance of OH, CH, CH2, and CH3 groups as the most important ones. This study shows the use of NIRS and both linear and non-linear learners as a suitable strategy to address fish fraud and fish QC.

Whole-genome duplication (WGD) is hypothesized to be an important evolutionary mechanism that can facilitate adaptation and speciation. Genomes that exist in states of both diploidy and residual tetraploidy are of particular interest, as mechanisms that maintain the ploidy mosaic after WGD may provide important insights into evolutionary processes. The Salmonidae family exhibits residual tetraploidy, and this, combined with the evolutionary diversity formed after an ancestral autotetraploidization event, makes this group a useful study system. In this study, we generate a novel linkage map for cisco (Coregonus artedi), an economically and culturally important fish in North America and a member of the subfamily Coregoninae, which previously lacked a high-density haploid linkage map. We also conduct comparative genomic analyses to refine our understanding of chromosomal fusion/fission history across salmonids. To facilitate this comparative approach, we use the naming strategy of protokaryotype identifiers (PKs) to associate duplicated chromosomes to their putative ancestral state. The female linkage map for cisco contains 20,292 loci, 3,225 of which are likely within residually tetraploid regions. Comparative genomic analyses revealed that patterns of residual tetrasomy are generally conserved across species, although interspecific variation persists. To determine the broad-scale retention of residual tetrasomy across the salmonids, we analyze sequence similarity of currently available genomes and find evidence of residual tetrasomy in seven of the eight chromosomes that have been previously hypothesized to show this pattern. This interspecific variation in extent of rediploidization may have important implications for understanding salmonid evolutionary histories and informing future conservation efforts.

Temperature is a key environmental parameter affecting both the phenotypes and distributions of organisms, particularly ectotherms. Rapid organismal responses to thermal environmental changes have been described for several ectotherms; however, the underlying molecular mechanisms often remain unclear. Here, we studied whole genome cytosine methylation patterns of European grayling (Thymallus thymallus) embryos from five populations with contemporary adaptations of early life history traits at either 'colder' or 'warmer' spawning grounds. We reared fish embryos in a common garden experiment using two temperatures that resembled the 'colder' and 'warmer' conditions of the natal natural environments. Genome-wide methylation patterns were similar in populations originating from colder thermal origin subpopulations, whereas single nucleotide polymorphisms uncovered from the same data identified strong population structure among isolated populations, but limited structure among interconnected populations. This was surprising because the previously studied gene expression response among populations was mostly plastic, and mainly influenced by the developmental temperature. These findings support the hypothesis of the magnified role of epigenetic mechanisms in modulating plasticity. The abundance of consistently changing methylation loci between two warmer-to-colder thermal origin population pairs suggests that local adaptation has shaped the observed methylation patterns. The dynamic nature of the methylomes was further highlighted by genome-wide and site-specific plastic responses. Our findings support both the presence of a plastic response in a subset of CpG loci, and the evolutionary role of methylation divergence between populations adapting to contrasting thermal environments.

The Lake Huron ecosystem is unique among the Laurentian Great Lakes (USA/Canada) in that its surface area encompasses 3 distinct basins. This ecosystem recently experienced significant ecological restructuring characterized by changes in primary production, species dominance and abundances, and top predator energy dynamics. However, much of the evidence for this restructuring has been largely derived from biomonitoring data obtained from long-term sampling of the lake's Main Basin. We examined polychlorinated biphenyl (PCB) concentrations and the stable isotopes of carbon (δ13 C) and nitrogen (δ15 N) in rainbow smelt (Osmerus mordax), bloater (Coregonus hoyi), and round goby (Neogobius melanostomus) to determine spatial variability in these environmental markers as indicators of the ubiquity of trophic restructuring throughout Lake Huron. Stable isotopes indicated that North Channel fish occupied trophic positions between 0.5 and 1.0 lower relative to Main Basin and Georgian Bay conspecifics, respectively. Sum PCB concentrations for 41 congeners were highest for fish from the Main Basin (27.5 ± 3.0 ng g-1 wet wt) and Georgian Bay (26.3 ± 3.4 ng g-1 wet wt) relative to North Channel (13.6 ± 1.2 ng g-1 wet wt) fish. Discriminant functions analysis demonstrated basin-specific PCB congener profiles with individual species also having distinct profiles dependent on their basin of collection. These bioaccumulation patterns among Lake Huron forage fish mirror those reported for lake trout in this lake and indicate that the degree of food-web ecological restructuring in Lake Huron is not equivalent across the basins. Specifically, basin-specific PCB congener profiles demonstrated that differences among Lake Huron secondary and top predator consumer species are likely dictated by cross-basin differences in zooplankton community ecology and trophodynamics that can regulate the efficiencies of prey energy transfer and PCB congener bioaccumulation patterns in aquatic food webs. Environ Toxicol Chem 2020;39:1712-1723. © 2020 SETAC.

Identifying early gene expression responses to hypoxia (i.e., low dissolved oxygen) as a tool to assess the degree of exposure to this stressor is crucial for salmonids, because they are increasingly exposed to hypoxic stress due to anthropogenic habitat change, e.g., global warming, excessive nutrient loading, and persistent algal blooms. Our goal was to discover and validate gill gene expression biomarkers specific to the hypoxia response in salmonids across multi-stressor conditions. Gill tissue was collected from 24 freshwater juvenile Chinook salmon (Oncorhynchus tshawytscha), held in normoxia [dissolved oxygen (DO) > 8 mg L−1] and hypoxia (DO = 4□5 mg L−1) in 10 and 18°C temperatures for up to six days. RNA-sequencing (RNA-seq) was then used to discover 240 differentially expressed genes between hypoxic and normoxic conditions, but not affected by temperature. The most significantly differentially expressed genes had functional roles in the cell cycle and suppression of cell proliferation associated with hypoxic conditions. The most significant genes (n = 30) were selected for real-time qPCR assay development. These assays demonstrated a strong correlation (r = 0.88; p < 0.001) between the expression values from RNA-seq and the fold changes from qPCR. Further, qPCR of the 30 candidate hypoxia biomarkers was applied to an additional 322 Chinook salmon exposed to hypoxic and normoxic conditions to reveal the top biomarkers to define hypoxic stress. Multivariate analyses revealed that smolt stage, water salinity, and morbidity status were relevant factors to consider with the expression of these genes in relation to hypoxic stress. These hypoxia candidate genes will be put into application screening Chinook salmon to determine the identity of stressors impacting the fish.

Necrosis Pancreatic Infectious Virus does not block 701-STAT1 (α/β) tyrosine in Oncorhynchus mykiss (‎Salmoniformes: ‎Salmonidae). Introduction: Infectious pancreatic necrosis virus (IPNV) is a pathogen important that affects predominantly salmonids. The type I interferon alpha system has a crucial role in the first line of defense against IPNV infection. IFN-I(α) activation triggers the signaling pathway JAK-STAT, binding to their receptors results in the rapid phosphorylation of STATs a critical step for the nuclear translocation to induce the interferon stimulated genes (ISGs). The relationship between infectivity level of IPNV strain and pathway signaling of IFN is yet poorly understood. Objective: our purpose was to investigate if the IFN-I(α) signaling pathway is affected by IPNV strains of different infectivity levels. Methods: We used two IPNV isolated (VR-299 and Sp) to infect RTG-2 cells. Total RNA was isolated using the commercial kit for determine to VP2 expression and ISGs using qRT-PCR. Western Immunoblotting analysis was carried out for determine the 701 STAT1(α/β) phosphorylation into infected cells. Results: Hence, a higher virulence strain is not associated with a greater blocking effect for interferon signaling. Furthermore, the activation of Y701-STAT1 (α/β) was significantly increased in serotype Sp virus infected cells compared with serotype VR-299 virus infected cells, indicating that IPNV inhibits IFN signaling pathway. Conclusions: As concluded, IPNV does not block the phosphorylation of 701-tyrosine STAT1 (α/β) stimulated by IFN-I(α), contrary to other RNA viruses.