Evaluating a species phylogeny using ddRAD SNPs: Cyto-nuclear discordance and introgression in the salmonid genus Thymallus (Salmonidae).

Hybridization and introgression are very common among freshwater fishes due to the dynamic nature of hydrological landscapes. Cyclic patterns of allopatry and secondary contact provide numerous opportunities for interspecific gene flow, which can lead to discordant paths of evolution for mitochondrial and nuclear genomes. Here, we used double digest restriction-site associated DNA sequencing (ddRADseq) to obtain a genome-wide single nucleotide polymorphism (SNP) dataset comprehensive for allThymallus (Salmonidae)species to infer phylogenetic relationships and evaluate potential recent and historical gene flow among species. The newly obtained nuclear phylogeny was largely concordant with a previously published mitogenome-based topology but revealed a few cyto-nuclear discordances. These incongruencies primarily involved the placement of internal nodes rather than the resolution of species, except for one European species where anthropogenic stock transfers are thought to be responsible for the observed pattern. The analysis of four contact zones where multiple species are found revealed a few cases of mitochondrial capture and limited signals of nuclear introgression. Interestingly, the mechanisms restricting interspecific gene flow might be distinct; while in zones of secondary contact, small-scale physical habitat separation appeared as a limiting factor, biologically based reinforcement mechanisms are presumed to be operative in areas where species presumably evolved in sympatry. Signals of historical introgression were largely congruent with the routes of species dispersal previously inferred from mitogenome data. Overall, the ddRADseq dataset provided a robust phylogenetic reconstruction of the genus Thymallus including new insights into historical hybridization and introgression, opening up new questions concerning their evolutionary history.

Elevated river discharge enhances the immigration of juvenile catadromous and amphidromous fishes into temperate coastal rivers.

Anthropogenic alterations to river flow regimes threaten freshwater biodiversity globally, with potentially disproportionate impacts on species that rely on flow cues to trigger critical life history processes, such as migration for diadromous fishes. This study investigates the influence of river discharge on the abundance of juvenile fish moving into rivers by four temperate catadromous or amphidromous species (common galaxias Galaxias maculatus, spotted galaxias Galaxias truttaceus, climbing galaxias Galaxias brevipinnis and the threatened Australian grayling Prototroctes maraena). Fyke netting or fishway trapping was used to catch juvenile fish moving from estuaries into freshwater in five coastal waterways in south-eastern Australia during the spring migratory period. There was a positive relationship between the probability of high catch rates and mean discharge in September. We also found a positive relationship between discharge and the number of recruits captured 22-30 days later in a flow stressed system. In addition, day-of-year had a strong influence on catch rates, with the peak abundance of juveniles for three species most likely to occur midway through the sampling period (spotted galaxias in October, climbing galaxias in late October and Australian grayling in late October and early November). Our study shows that higher magnitudes of river discharge were associated with increased catches of juvenile catadromous and amphidromous fishes. With a limited supply of environmental water, environmental flows used to enhance immigration of these fishes may be best targeted to maintain small amounts of immigration into freshwater populations in waterways or years when discharges are low and stable. When there are natural, large discharge volumes, relatively large numbers of juvenile fish can be expected to enter coastal waterways and during these times environmental flows may not be required to promote immigration.

Morphological re-description and molecular characterization of Chloromyxum thymalli (Myxosporea: Chloromyxidae) infecting the gall bladder of Hovsgol grayling Thymallus nigrescens.

Chloromyxum thymalli infects the gall bladder of fishes belonging to the genus Thymallus. Here, we provide morphological, histological, and molecular data to complete the original description. Rounded plasmodia measured from 25 to 30 µm in diameter and contain 8 developing spores at most. Spores are typical of the genus Chloromyxum. Mature spores are subspherical, (mean ± SD) 9.05 ± 0.08 µm (range: 7.75-10.03 µm) long, and 8.81 ± 0.09 µm (range: 7.19-10.01 µm) wide. Four pyriform polar capsules are equal in size, 3.4 µm long and 2.7 µm wide on average. Histopathological analysis showed that presporogonic stages were found in the lamina propria under the epithelial cells of the host's gall bladder and destroyed the integrity of the epithelium. The obtained SSU rDNA sequences of C. thymalli did not match any available sequences in GenBank. Phylogenetic analysis showed that C. thymalli forms a sister cluster with C. truttae, with a subclade of Chloromyxum spp. that infect the gall bladder of freshwater teleosts.

Neutral variation does not predict immunogenetic variation in the European grayling (Thymallus thymallus)-implications for management.

Preservation of genetic diversity is critical to successful conservation, and there is increasing demand for the inclusion of ecologically meaningful genetic information in management decisions. Supportive breeding programmes are increasingly implemented to combat declines in many species, yet their effect on adaptive genetic variation is understudied. This is despite the fact that supportive breeding may interfere with natural evolutionary processes. Here, we assessed the performance of neutral and adaptive markers (major histocompatibility complex; MHC) to inform management of European grayling (Thymallus thymallus), which routinely involves supplementation of natural populations with hatchery-reared fish (stocking). This study is the first to characterize MH II DAA and DAB loci in grayling and to investigate immune genetic variation in relation to management practice in this species. High-throughput Illumina sequencing of "introduced," "stocked native" and "non-stocked native" populations revealed significantly higher levels of allelic richness and heterozygosity for MH markers than microsatellites exclusively in non-stocked native populations. Likewise, significantly lower differentiation at the MH II than for microsatellites was apparent when considering non-stocked native populations, but not stocked populations. We developed a simulation model to test the effects of relaxation of selection during the early life stage within captivity. Dependent on the census population size and stocking intensity, there may be long-term effects of stocking on MH II, but not neutral genetic diversity. This is consistent with our empirical results. This study highlights the necessity for considering adaptive genetic variation in conservation decisions and raises concerns about the efficiency of stocking as a management practice.

Make the Most of the Data You've Got: Bayesian Models and a Surrogate Species Approach to Assessing Benefits of Upstream Migration Flows for the Endangered Australian Grayling.

Environmental water managers must make best use of allocations, and adaptive management is one means of improving effectiveness of environmental water delivery. Adaptive management relies on generation of new knowledge from monitoring and evaluation, but it is often difficult to make clear inferences from available monitoring data. Alternative approaches to assessment of flow benefits may offer an improved pathway to adaptive management. We developed Bayesian statistical models to inform adaptive management of the threatened Australian grayling (Prototroctes maraena) in the coastal Thomson River, South-East Victoria Australia. The models assessed the importance of flows in spring and early summer (migration flows) for upstream dispersal and colonization of juveniles of this diadromous species. However, Australian grayling young-of-year were recorded in low numbers, and models provided no indication of the benefit of migration flows. To overcome this limitation, we applied the same models to young-of-year of a surrogate species (tupong-Pseudaphritis urvilli)-a more common diadromous species expected to respond to flow similarly to Australian grayling-and found strong positive responses to migration flows. Our results suggest two complementary approaches to supporting adaptive management of Australian grayling. First, refine monitoring approaches to allow direct measurement of effects of migration flows, a process currently under way. Second, while waiting for improved data, further investigate the use of tupong as a surrogate species. More generally, alternative approaches to assessment can improve knowledge to inform adaptive management, and this can occur while monitoring is being revised to directly target environmental responses of interest.

Development of sperm vitrification protocols for two endangered salmonid species: the Adriatic grayling, Thymallus thymallus, and the marble trout, Salmo marmoratus.

Vitrification was applied to the sperm of two endangered fish species of Soca River basin in Slovenia, the Adriatic grayling (Thymallus thymallus) and marble trout (Salmo marmoratus) following testing different cooling devices and vitrifying media. Sperm was collected, diluted in species-specific non-activating media containing cryoprotectants, and vitrified by plunging directly into liquid nitrogen without pre-cooling. Progressive motility, curvilinear velocity, and straightness of fresh and vitrified-warmed sperm were evaluated with computer-assisted sperm analysis (CASA). Fertilization trials were carried out to test the effectiveness of vitrification in the case of grayling. A protocol utilizing a glucose-based extender, 30% cryoprotectants (15% methanol + 15% propylene glycol), 1:1 dilution ratio, and droplets of 2 µl on a Cryotop as cooling device yielded the highest post-thaw motility values for both Adriatic grayling (7.5 ± 6.5%) and marble trout (26.6 ± 15.8%). Viable embryos were produced by fertilizing eggs with vitrified grayling sperm (hatching 13.1 ± 11.7%, control hatching 73.9 ± 10.4%). The vitrification protocol developed in this study can be utilized in the conservation efforts for the two species as an alternative to slow-rate freezing when working in field conditions or when specific equipment necessary for slow-rate freezing is not available.

Comparative study of proliferative kidney disease in grayling Thymallus thymallus and brown trout Salmo trutta fario: an exposure experiment.

Proliferative kidney disease (PKD) is an emerging disease threatening wild salmonid populations, with the myxozoan parasite Tetracapsuloides bryosalmonae as the causative agent. Species differences in parasite susceptibility and disease-induced mortality seem to exist. The aim of the present study was to compare incidence, pathology and mortality of PKD in grayling Thymallus thymallus and brown trout Salmo trutta under identical semi-natural conditions. Young-of-the-year grayling and brown trout, free of T. bryosalmonae, were jointly exposed in cage compartments in a river in the northeast of Switzerland during 3 summer months. Wild brown trout were caught by electrofishing near the cage, and PKD status was compared with that of caged animals. Cage-exposed grayling showed a PKD incidence of 1%, regardless of whether parasite infection was determined by means of real-time PCR or histopathology/immunohistochemistry. In contrast, PKD incidence of caged brown trout was 77%. This value was not significantly different to PKD prevalence of wild brown trout caught above and below the cage (60 and 91%, respectively). Mortality in grayling was significantly higher compared with that of brown trout (40 versus 23%); however, grayling mortality was not considered to be associated with PKD. Mortality of caged and infected brown trout was significantly higher than mortality of non-infected caged trout. Histopathology indicated an ongoing mostly acute or chronic active infection in brown trout, which survived until the end of exposure. The results suggest that grayling are less susceptible to infection with T. bryosalmonae compared with brown trout under the tested field conditions.

Polychlorinated biphenyls (PCBs) in fish from the Sana River (Bosnia and Herzegovina): A preliminary study on the health risk in sport fishermen.

Fish is the main single source of polychlorinated biphenyls (PCBs) exposure in men. Anecdotal reports suggest high wild fish consumption rates among sport fishermen in Sanski Most area, Bosnia and Herzegovina (BiH). Presence of PCBs in the environment in BiH was previously documented. The main objective of this work was to estimate the magnitude of PCBs exposure and assess the potential health risk in sport fishermen in Sanski Most. The fishing pattern and magnitude of fish consumption were estimated in the questionnaire survey conducted during April 2012 among members (n = 60) of the local sport fishermen association in Sanski Most. Calculated median and high-end (90th percentile) fish consumption rates were 31 g d(-1) and 126 g d(-1), respectively. The PCB concentrations (as Aroclor 1254 equivalents), determined by ELISA immunoassay in 28 fish fillets ranged from undetectable to 208 µg kg(-1). Two different exposure scenarios were used: (a) median exposure, calculated from the median fish consumption rate and median PCB concentrations, and (b) "worst case" scenario, calculated from the high-end fish consumption rate and mean PCB concentrations. The results suggest negligible lifelong cancer and non-cancer risks in case of low to moderate fish consumption rate, but possibly unacceptable risk levels in high-end consumers.

Effect of Total Dissolved Solids on Fertilization and Development of Two Salmonid Species.

Some studies have shown that the early life stages of salmonids are particularly sensitive to elevated concentrations of total dissolved solids (TDS). We evaluated the effect of TDS released in treated effluent into Snap Lake (Northwest Territories, Canada) by the Snap Lake Diamond Mine on two salmonids native to Snap Lake: Salvenius namaycush (lake trout) and Thymallus arcticus (Arctic grayling). Exposures encompassed the embryo-alevin-fry early life stages and extended to 142 days for lake trout and 69 days for Arctic grayling. Such extended testing is uncommon with these two species. Two exposures were conducted with each species, one initiated prior to fertilization, and the other subsequent to fertilization. Fertilization, survival, and growth were not adversely affected for either species by TDS at concentrations >1400 mg/L, with the exception of survival of lake trout, which produced an LC20 of 991 mg/L in one test, and >1484 mg/L in the second test. For the specific TDS composition tested, which was dominated by chloride (45 %-47 %) and calcium (20 %-21 %), the early life stages of these two fish species were relatively insensitive. Although some authors have suggested lower TDS regulatory limits for salmonid early life stages, our study indicates that this is not necessary, at least for these two fish species and for the specific ionic composition tested.

First isolation of hirame rhabdovirus from freshwater fish in Europe.

A rhabdovirus was isolated in cell culture inoculated with tissue material from diseased grayling, Thymallus thymallus (L.), originating from a fish farm affected by a mortality episode in Poland. Diagnostics tests showed that the virus was not related to novirhabdoviruses known in Europe, nor to vesiculovirus-like species, except perch rhabdovirus (PRhV) with which it shared moderate serological relations. However, RT-PCR with PRhV probes gave negative results. To identify the virus, a random-priming sequence-independent single primer amplification was adopted. Surprisingly, two of the obtained sequences exhibited a high identity (>99%) with hirame rhabdovirus (HIRRV), a novirhabdovirus usually found in fish in marine Asiatic countries, for instance Japan, China and Korea. The full-length sequence of the phosphoprotein gene (P) demonstrated a higher identity of the present isolate with HIRRV from China compared with the Korean isolate. An identical viral sequence was also found in brown trout, Salmo trutta trutta L., affected by mortalities in a second farm in the same region, after a likely contamination from the grayling farm. To our knowledge, this is the first report of HIRRV in Europe, and in two hosts from fresh water that have not been described before as susceptible species.

Liver transcriptome and physiological analyses preliminarily revealed the adaptation mechanisms of Amur grayling (Thymallus arcticus grubei, Dybowski, 1869) fry for dietary lipid nutrition.

The Amur grayling (Thymallus arcticus grubei Dybowski, 1869), a species of potentially economic and research value, is renowned for its tender meat, exquisite flavor, and high nutritional contents. This study was conducted to investigate the physiological adaptation mechanisms to dietary lipids in Amur grayling fry (with average initial weight 4.64±0.03 g). This study involved a 56-day feeding trial with diets containing varying lipid levels (9.07%, 12.17%, 15.26%, 18.09%, 21.16%, and 24.07%, designated as GL1 through GL6, respectively) to explore the impact of dietary lipids on growth performance, intestinal digestion, liver antioxidative function, and transcriptomic profiles. Results showed that The group receiving 18% dietary lipid exhibited a markedly higher weight gain rate (WGR) and specific growth rate compared to other groups, alongside a reduced feed conversion ratio (FCR), except in comparison to the 15% lipid group. Activities of lipase in pancreatic secretion and amylase in stomach mucosa peaked in the 18% lipid treatment group, indicating enhanced digestive efficiency. The liver of fish in this group also showed increased activities of antioxidative enzymes and higher levels of glutathione and total antioxidative capacity, along with reduced malondialdehyde content compared to the 9% and 24% lipid treatments. Additionally, serum high-density lipoprotein cholesterol levels were highest in the 18% group. Transcriptomic analysis revealed four significant metabolic pathways affected: Cholesterol metabolism, Fat digestion and absorption, PPAR signaling, and Fatty acid degradation, involving key genes such as Lipase, Lipoprotein lipase, Fatty acid-binding protein, and Carnitine palmitoyltransferase I. These findings suggest that the liver of Amur grayling employs adaptive mechanisms to manage excessive dietary lipids. Quadratic regression analysis determined the optimal dietary lipid levels to be 16.62% and 16.52%, based on WGR and FCR, respectively. The optimal dietary lipid level for juvenile Amur grayling appears to be around 18%, as evidenced by improved growth performance, digestive function, balanced serum lipid profile, and enhanced liver antioxidative capacity. Exceeding this lipid threshold triggers both adaptive and potentially detrimental liver responses.

Effect of temperature on growth, survival, and chronic stress responses of Arctic Grayling juveniles.

Arctic Grayling Thymallus arcticus are Holarctically distributed, with a single native population in the conterminous United States occurring in the Big Hole River, Montana, where water temperatures can fluctuate throughout the year from 8 to 18 °C. A gradual increase in mean water temperature has been reported in this river over the past 20 years due to riparian habitat changes and climate change effects. We hypothesized that exposing Arctic Grayling to higher temperatures would result in lower survival, decreased growth, and increased stress responses. Over a 144-day trial, Arctic Grayling juveniles were subjected to water temperatures ranging from 8-26 °C to measure the effects on growth, survival, gene expression and antioxidant enzyme activity. Fish growth increased with increasing water temperature up to 18 °C, beyond which survival was reduced. Fish did not survive at temperatures above 22 °C. In response to temperatures above 16 °C, a 3-fold and 1.5-fold increase in gene expression was observed for superoxide dismutase (SOD) and glutathione peroxidase (GPx), respectively, but no changes were seen in the ratio of Heat Shock Protein 70 (HSP70) and heat shock protein 90 (HSP90) expression. Enzyme activities of SOD and GPx also rose at temperatures above 16 °C, indicating heightened oxidative stress. Catalase (CAT) gene expression and enzyme activity decreased with rising temperatures, suggesting a preference for the GPx pathway, as GPx could also be providing help with lipid peroxidation. An increase of Thiobarbituric acid reactive substances (TBARS) was also recorded, which corresponded with rising temperatures. Our findings thus underscore the vulnerability of Arctic Grayling to minor changes in water temperature. Further increases in mean water temperature could significantly compromise survival of Arctic Grayling in the Big Hole River.

Fine ultrastructural features of germ cells and spermatozoa during spermatogenesis in the European grayling, Thymallus thymallus (Teleostei, Salmoniformes, Salmonidae).

This study aimed to examine the ultrastructure of spermatogenic stages and mature spermatozoa in the European grayling, Thymallus thymallus. The testes were examined microscopically with a transmission electron microscope to find out details of the structure and morphology of the grayling germ cells, spermatozoa and some somatic cells. The grayling testis has a tubular shape, with cysts or clusters of germ cells within seminiferous lobules. The spermatogenic cells, including spermatogonia, spermatocytes, and spermatids, can be found along seminiferous tubules. There are electron-dense bodies in germ cells from the primary spermatogonia to secondary spermatocyte stages. These undergo mitosis to reach the secondary spermatogonia stage, when they form primary and secondary spermatocytes. Spermatids undergo three different stages of differentiation during spermiogenesis, characterized by the level of chromatin condensation, elimination of cytoplasm, and the occurrence of the flagellum. The midpiece of spermatozoa is short and contains spherical or ovoid mitochondria. The sperm flagellum has an axoneme with nine doublets of peripheral microtubules and two central microtubules. The result of this study is valuable to be used as a standard reference for germ cell development, which is of great importance to get a clear insight into the process of grayling breeding practice.

The genome sequence of the Rock Grayling, Hipparchia semele (Linnaeus, 1758).

We present a genome assembly from an individual female Hipparchia semele (the Rock Grayling; Arthropoda; Insecta; Lepidoptera; Nymphalidae). The genome sequence is 403.4 megabases in span. Most of the assembly is scaffolded into 30 chromosomal pseudomolecules, including the W and Z sex chromosomes. The mitochondrial genome has also been assembled and is 15.22 kilobases in length. Gene annotation of this assembly on Ensembl identified 17,540 protein coding genes.

Phylogeography and Population Genetic Structure of Amur Grayling Thymallus grubii in the Amur Basin.

Amur grayling, Thymallus grubii, is an important economic cold freshwater fish originally found in the Amur basin. Currently, suffering from loss of habitat and shrinking population size, T. grubii is restricted to the mountain river branches of the Amur basin. In order to assess the genetic diversity, population genetic structure and infer the evolutionary history within the species, we analysised the whole mitochondrial DNA control region (CR) of 95 individuals from 10 rivers in China, as well as 12 individuals from Ingoda/Onon and Bureya River throughout its distribution area. A total of 64 variable sites were observed and 45 haplotypes were identified excluding sites with gaps/missing data. Phylogenetic analysis was able to confidently predict two subclade topologies well supported by maximum-parsimony and Bayesian methods. However, basal branching patterns cannot be unambiguously estimated. Haplotypes from the mitochondrial clades displayed local homogeneity, implying a strong population structure within T. grubii. Analysis of molecular variance detected significant differences among the different geographical rivers, suggesting that T. grubii in each river should be managed and conserved separately.

Gonadal steroid fluctuations and reproduction results of European grayling (Thymallus thymallus L.) from broodstock farmed in a recirculation aquaculture system.

The initial experiment of this study was conducted to determine whether sex steroid concentrations varied before, during and after the reproductive season of European grayling (Thymallus thymallus L.) farmed broodstock confined in a recirculation aquaculture system (RAS). The results indicated that the plasma sex steroid (testosterone - T, progesterone - P4 and estradiol - E2) concentrations varied (P < 0.05) during these reproductive periods. There were greater concentrations of T, P4 and E2 before and during the grayling reproductive season indicating there are important functions of these steroid hormones associated with gonadal maturation, gamete production and reproductive behavior during the spawning period. In the second experiment of this study, the effectiveness of European grayling controlled reproduction treatment regimens was analyzed and there were 34.69 % and 68.18 % having ovulations in the 2 and 3-year-old broodfish, respectively. Of the embryos developing to the eyed-egg stage, there were 3.70 % and 6.87 % derived from eggs of 2- and 3-year-old grayling females, respectively. Proportions of embryos developing from the eyed-egg stage to hatching were 38.1 % and 52.1 % from eggs of 2- and 3-year-old grayling females, respectively, when there was culturing in a RAS. The results indicate that with grayling broodfish there is greater efficacy in induction of reproduction when there is imposing of the controlled reproduction treatment regimen on 3- rather than 2-year-old broodfish.

Drawdown flushing in a chain of reservoirs-Effects on grayling populations and implications for sediment management.

We used an information theoretic approach to assess the effects of an ecologically adjusted sediment management scheme on grayling (Thymallus thymallus L. 1758) populations. Additionally to reservoir operation, candidate models included a variety of parameters and processes that may influence grayling populations such as flow, temperature, density dependence, and bird predation. Population parameters analyzed included total densities, young of the year numbers, and larval densities. These analyses were supplemented by a characterization of sediments and sedimentation patterns in the reach. Investigations were carried out in six sites affected by flushing and in one control site. A total of thirteen flushing operations have been undertaken within the study period leading to considerable remobilization of fine sediments and gravel. Due to seasonal and hydrological restrictions, not every flood could be used for flushing. These limitations led to an interrupted management throughout the chain of reservoirs as well as to long time intervals between flushing events with possible effects on spawning habitat quality. None of the investigated population parameters was affected by flushing, and thus, the study generally supports the current reservoir management scheme. Our analyses revealed the magnitude and timing of high water events, temperature, and density-dependent effects, that is, population densities the year before, as the most influential variables for grayling population dynamics in the investigated stretch. The siltation of reservoirs is a significant problem for reservoir storage, flood protection, river deltas, and coastal zones. Its management-which is inevitable to safeguard river deltas and secure flood protection-poses also the challenge to safeguard riverine ecosystems below reservoirs. Based on our experience, we propose a periodic flushing regime in concordance with the hydrograph thereby mimicking the timing, magnitude, frequency, and duration of natural SSC pulses and gravel transport. This flushing regime minimizes adverse downstream environmental impacts and maximizes benefits.

New record of the fish leech Piscicola pojmanskae (Annelida: Hirudinida: Piscicolidae) - DNA barcoding and phylogeny.

The aim of this study was to confirm the taxonomic status of Piscicola pojmanskae Bielecki, 1994 found on Salmonidae fish. The fish leech was identified based on a diligent morphological analysis as well as COI gene sequence (DNA barcoding). The phylogenetic relationship with other piscicolid leeches was analyzed as well. Piscicola pojmanskae was found on various fins of both graylings and the resident form of trouts. The prevalence of infection was 1.63%. In this paper, probable causes of the lack of relation between the number of leeches on the fins and the fish body length as well as the host-searching strategy used by P. pojmanskae are discussed.

Complete mitochondrial genome of the Kamchatka grayling Thymallus mertensii (Salmoniformes, Salmonidae).

The complete mitochondrial genome was sequenced in two individuals of the Kamchatka grayling Thymallus mertensii. The genome sequences are 16 662 bp in size, and the gene arrangement, composition, and size are very similar to the salmonid fish genomes published previously. The low level of sequence divergence (0.92%) detected between the genome of T. mertensii and the GenBank complete mitochondrial genomes of the Arctic grayling T. arcticus (FJ872559) may likely be due to recent divergence of the species and/or historical hybridization and interspecific replacement of mtDNA.

Complete mitochondrial genome of the yellow-spotted grayling Thymallus flavomaculatus (Salmoniformes, Salmonidae).

The complete mitochondrial genome was sequenced in two individuals of yellow-spotted grayling Thymallus flavomaculatus. The genome sequences are 16,659 bp in size, and the gene arrangement, composition and size are very similar to the salmonid fish genomes published previously. The low level of sequence divergence detected between the genome of Th. flavomaculatus and the GenBank complete mitochondrial genomes of the Th. yaluensis (KJ866484) and Th. grubii (KF649073) may likely be due to recent divergence of the species and/or historical hybridization and interspecific replacement of mtDNA.