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Temperature is a key driver in determining species distribution and abundance across climatic and geographical gradients. This occurs through direct physiological effects of temperature on performance, but may also result from temperature effects on species interactions.In the current study we experimentally test for temperature‐dependent competition between juvenile anadromous Atlantic salmon and brown trout and evaluate the role of temperature in shaping the relative abundance of these species across 88 Norwegian rivers.When the two species were reared in allopatry their somatic growth rates were similar across a range of temperatures (4–16°C).When reared in sympatry, the growth of salmon was greatly reduced at the coldest temperature relative to when reared in allopatry, whereas this was not the case for trout. The effect of interspecific competition on growth was more similar for the two species at warmer temperatures. Thus, interspecific competition effects were strongly asymmetric only at the lowest temperature, with trout outcompeting salmon.The results from the experiment were reflected in qualitative patterns of relative abundance of salmon and trout in natural populations, which shifted from being trout dominated in rivers with low summer temperatures to being salmon dominated in warmer rivers.These results provide an empirical example of how temperature effects on the relative abundance of species can only be understood in light of information about temperature‐dependent species interactions. [ABSTRACT FROM AUTHOR]

The high plasticity, or the ability to differentiate into various cell types, and capacity to become both gametes of early-stage germ cells (eGCs) allows them to be used for the long-term storage and recovery of genetic information. In this study, species-specific protocols (isolation period, enzymatic separation solution, incubation period, appropriate cryoprotectant, and cryopreservation protocol) were established for the isolation and long-term preservation of Black Sea trout eGCs. In addition, the difference between the application of cryopreservation to the whole gonad tissue and to the enzymatically separated cells has been shown in terms of viability and the number of cells obtained. According to the cell count made from the histological sections of the testicular tissue throughout the year, the period with the highest concentration of eGCs in the tissue is between May and June. To identify the optimal enzymatic dissociation solution, we subjected testicular tissues to digestion using various combinations of trypsin (T) and collagenase (C) (0.3-0.5% T and 0.1-0.3% C). Our findings revealed that the 0.3% C provided the highest yield of viable cells (90.9%). We cryopreserved the enzymatically dissociated cells (EDCs) using six different cryoprotectants (Dimethyl sulfoxide, Glycerol, and CryoSOfree™, in both L-15 and phosphate-buffered saline -- PBS mediums). Additionally, whole tissue exclusively with CryoSOfree™. After storing the samples at -152 °C for two years, the group of EDCs cryopreserved in L15+Glycerol exhibited the highest viability at 93.3%. Meanwhile, the whole tissue group yielded the greatest number of cells per ml after thawing, with a count of 33 210 000 cells. When considering both the viability (91.11%) and the number of cells obtained (33 210 000 cells/ml), the whole tissue cryopreservation group outperformed all the other methods. [ABSTRACT FROM AUTHOR]

Rainbow trout (Oncorhynchus mykiss) is one of the world's most widely farmed cold-water economic fish. It is also the primary cold-water fish species in China. Since the 1960s, the rainbow trout germplasm has been introduced from North Korea, the United States, Denmark, and other countries, and a systematic study has been carried out on germplasm preservation, identification, breeding, and variety breeding. Compared with rainbow trout diploid, the triploid has the advantages of a high feed conversion rate, fast growth rate, and good meat quality. Moreover, the triploid gonadal hypoplasia can mitigate risks associated with high mortality and meat quality decline during spawning and avert the ecological risk of invasive alien species caused by breeding escape. Therefore, breeding triploid rainbow trout has more significant market and ecological benefits. As diploid and triploid rainbow trout are very similar in terms of morphology, it is difficult to distinguish the ploidy of rainbow trout by morphology alone. Currently, DNA content analysis by flow cytometry is the main method used to identify the ploidy of rainbow trout, but this method necessitates the collection of fish blood or tissue samples, and the body length of the fish to collect the blood must be at least 5 cm. Additionally, these sampling operations may harm the fish. This method also involves a delicate operation, complicated technical process, and expensive consumables, thus, the popularization and application of triploid identification of rainbow trout are greatly restricted. Considering the limitations of the technical test for the ploidy of rainbow trout, a minimally invasive and economical method with only a small amount of sampling is needed to identify and analyze the ploidy of rainbow trout in batches. Microsatellite markers (SSR markers) are simple repeated sequences widely distributed in eukaryotic genomes and have been widely used in ploidy and pedigree analyses of fish. The advantages of microsatellite (SSR) analysis include high reproducibility, low sample requirements, and rapid population genetic analysis. In order to achieve the use of a minimally invasive method to collect samples for trout ploidy identification, this study analyzed 153 SSR markers using PCR amplification and electrophoresis separation technology. Among them, 139 SSR markers could be successfully amplified in diploid and triploid, and 132 SSR markers were screened for polymorphism. Finally, seven markers showed high variability in triploid. By verifying 52 reference samples with a known ploidy level and 48 samples with an unknown ploidy level, three SSR markers (SSR1054, SSR1056, and SSR1468) were further screened to distinguish the ploidy level. Moreover, three pairs of primer sequences with good stability were redesigned according to the three marker sequences for ploidy analysis application. When SSR markers were selected for ploidy identification, amplification sites with high variability were preferred because they greatly improve the efficiency of SSR-assisted ploidy identification. Differentiation of the variability of amplification sites mainly considers the number of alleles expressed and the relative frequency of these alleles. Furthermore, having clear map bands that are easy to observe and analyze is an important criterion for screening high-quality specific SSR markers. Statistical clear map bands can correctly judge the allelic configuration at each locus, thus, determining the ploidy level of rainbow trout. However, when the number of microsatellite DNA alleles shown in the electrophoretic map was less than the maximum number of alleles that may occur at the ploidy level of the polyploid species, it was difficult to accurately judge the ploidy by direct observation of the number of alleles. In diploid individuals, highly heterozygous SSR amplifies at most two alleles at a given site. Similarly, three and four alleles can be observed in triploid and tetraploid individuals, respectively. However, in some rare cases, the actual number of alleles cannot be correctly determined by looking directly at the number of alleles. For example, individuals with unknown ploidy show multiple possible genotypes for two alleles, which can occur with both diploids (AB) and triploids (AAB or ABB). Therefore, this study combined the analysis results of multiple specific SSR markers to improve the accuracy of ploidy detection. In addition, this study found three specific labeling bands that can assist in the differentiation of diploid and triploid rainbow trout, namely, SSR1054-305bp, SSR1056-463bp, and SSR1468-363bp. These three specific markers will greatly improve the accuracy of using SSR markers to identify triploid rainbow trout. Microsatellite null alleles are another potential limitation in SSR ploidy identification, which can be eliminated or avoided by changing the binding site of primers and flanking sequences due to the failure of normal gene amplification due to mutations in SSR lateral sequences. Although the results of this study cannot eliminate the presence of null alleles in future samples, the present experimental data suggest that the frequency of null alleles is so low that their impact on polyploid identification is minimal. SSR markers screened in this study solve the existing problems of a complex technical process and expensive consumables in the identification of rainbow trout ploidy, providing a minimally invasive, economical, reliable, and batch-operable molecular method and contributing to the study of the genetic diversity of rainbow trout with different ploidy.

When investigating potential causes of apparent declines in European brown trout angling catch rates over recent decades, fisheries management procedures are rarely considered. Using a 20‐year dataset of brown trout stocking and angling catch rates, we found a significant decline in brown trout angling catch rates in streams of East Bohemia, Czechia, were well predicted by a reduction in the number of brown trout stocked at catchable size (i.e. age‐3+). Increased stocking of smaller sized brown trout, and recent sporadic efforts to stock large brown trout, had no effect on catch rates. Our findings suggest that brown trout catch rates were related to ‘put‐and‐take’ stocking, in which non‐native rainbow trout gradually replaced brown trout in both stocking and catches. Our study stresses the importance of considering historical fisheries management, a sometimes‐neglected factor, when studying angling catches of economically important species. [ABSTRACT FROM AUTHOR]

[Display omitted] • Scenario simulations with coordinated production reduced mean salmon lice abundance. • The salmon lice problem increased in the second year of the production cycle. • Only strategies with less fish in open cages in spring resulted in low impact on wild fish. • Low impact was achieved by stocking larger fish, implying earlier slaughtering. Parasitic salmon lice (Lepeophtheirus salmonis) are a constraint to the sustainable growth of salmonids in open net pens, and this issue has caused production to level off in recent years in the most aquaculture-intensive areas of Norway. The maximum allowed biomass at a regional level is regulated by using the so-called "traffic light" system, where salmon louse-induced mortality of migrating wild salmon post-smolts is evaluated against set targets. As a case study, we have investigated how a specific aquaculture-intensive area can reduce its louse levels sufficiently to achieve a low impact on wild salmon. Analyses of the output from a virtual post-smolt model that uses data on the reported number of salmon lice in fish farms as key input data and estimates the salmon louse-induced mortality of wild out-migrating Atlantic salmon post-smolts, suggested that female louse abundance on the local farms must be halved in spring to reach the goal implied by the traffic light system. The outcome of a modelling scenario simulating a proposed new plan for coordinated production and fallowing proved beneficial, with an overall reduction in louse infestations and treatment efforts. The interannual variability in louse abundance in spring, however, increased for this scenario, implying unacceptably high louse abundance when many farms were in their second production year. We then combined the scenario with coordinated production with other louse control measures. Only measures that reduced the density of farmed salmonids in open cages in the study area resulted in reductions in salmon louse infestations to acceptable levels. This could be achieved either by stocking with larger fish to reduce exposure time or by reducing fish numbers, e.g. by producing in closed units. [ABSTRACT FROM AUTHOR]

Many ecosystems have been dramatically affected by non-native species, but not all such species have strong deleterious effects. American shad, Alosa sapidissima, a fish species native to the Atlantic coast of North America, was transplanted to the Pacific coast in the late nineteenth century and quickly colonized many US rivers. Their increased abundance in the Columbia River coincided with declines in native anadromous Pacific salmon and trout, and adult American shad now greatly outnumber returning salmonids. This paper reviews evidence for possible ecological interactions between salmon and American shad across their life histories and habitats. Despite the great abundance of American shad and their apparent overlap in use of Columbia River mainstem habitats, harmful effects on salmon are neither clear from empirical studies nor from ecological principles. Rather, the life histories and habitat use patterns tend to separate spawning adult salmon and their offspring from American shad in space and time. Currently available evidence indicates that this separation results in weak, neutral, uncertain, or offsetting effects on salmon (i.e., a mix of positive and negative interactions). Given the limited research on shad in Pacific ecosystems, several lines of investigation are warranted to advance understanding of their ecology and scope for interactions with native fishes and to support a clearer scientific basis for management decisions regarding American shad. [ABSTRACT FROM AUTHOR]

Predation can play an important role in structuring ecological communities, and predator–prey dynamics can be altered following the introduction of new species. An unauthorized introduction of redside shiner (Richardsonius balteatus) into reservoirs in the Upper Skagit River, Washington, USA created concern that a consequent shift in predator–prey dynamics in the reservoirs could reduce recruitment and production of native salmonids in the basin. We estimated predation mortality in Ross Lake on nonnative redside shiner and juvenile native salmonids to evaluate the potential role of predation in regulating these populations and limiting survival of native species of concern. We used bioenergetics modelling and stable isotope analysis combined with directed field measurements of growth, seasonal diet and thermal experience of piscivorous salmonids to quantify their consumption demand on prey fishes to evaluate the relative magnitude of predation mortality on invasive redside shiners and native salmonids. While redside shiner are the dominant prey fish species in Ross Lake, the modest biomass of native salmonids consumed could translate into substantial mortality, the magnitude of which depended on the timing and size at which prey fishes were eaten. This information provides important context for how nonnative species may indirectly impact native species through shared predation (apparent competition) and can inform conservation decisions surrounding nonnative species control, sustainability of native salmonids and introductions of anadromous fishes. [ABSTRACT FROM AUTHOR]

The relationships between body size and density of salmonids in natural streams have been well studied, and density‐dependent growth (somatic growth) is interpreted as the principal mechanism responsible for the relationship. Moreover, the body size–density relationship is known to vary over ontogeny. However, the relationship has been studied mostly by experimental procedures (e.g. stocking fish into streams), and knowledge about the relationship in natural populations (e.g. no human‐induced input of fish) is still inadequate. In this study, we compared the relationships between body size and density of young‐of‐the‐year (YOY) masu salmon, Oncorhynchus masou, between different ontogenetic stages, that is, fry (spring) and juveniles (autumn). We used the monitoring data of YOY body sizes and densities across three study sites collected from Horokashubuto stream in Hokkaido, northern Japan, from 2014 to 2022. In the juvenile stage, YOY body size correlated negatively with increasing density. This pattern is typical of the density dependence of salmonid growth demonstrated in many previous studies. In the fry stage, however, YOY body size correlated positively with increasing density. This study suggested that the patterns of density dependence vary as functions of the ontogenetic stages of salmonids. [ABSTRACT FROM AUTHOR]

Aim: Paleohydrological dynamics are well‐documented for European river systems, promoting shifting phases of isolation and connectivity of their aquatic fauna. These conditions coupled with high rates of hybridisation found in freshwater fishes may introduce considerable complexity and potential mito‐nuclear discordance of phylogenetic patterns. We evaluate this hypothesis using the first large‐scale analysis of nuclear SNPs in European species of grayling (Thymallus) compared to mtDNA data with the aim of reassessing the evolutionary history of this group of rheophilic fishes. Location: Freshwater systems in Europe. Methods: Based on mitochondrial (mitogenomes, control region) and nuclear (ddRADseq) data, we applied population‐genetic, phylogenetic, and biogeographic tools to evaluate lineage diversity in the context of paleohydrological alterations. Results: The results corroborated previously recognised high levels of lineage diversity, but revealed several cases of mito‐nuclear discordance and signals of both historical (natural) and human‐mediated introgression among major inter‐ and intraspecific lineages of Thymallus in Europe. A time‐calibrated phylogeny and ancestral area estimation, based on nuclear SNP data, supported a late Pliocene diversification of the genus in Europe and suggested an early colonisation of the Black Sea basin with subsequent dispersal into Central and Western Europe. Main Conclusions: The genetic structure of Thymallus in Europe recovered by nuclear SNPs contrasts considerably with that supported by mtDNA. Several instances of mito‐nuclear discordance underscore frequent contact of allopatric lineages in a dynamic paleohydrological landscape and reveal the weakness of basing both taxonomic and conservation decisions on inferences based on mtDNA alone. The Danube and Rhine drainages were inferred as important zones of contact between divergent phylogeographic lineages. Additionally, our data cast doubt on the genetic integrity of the endangered T. aeliani. Its divergence from T. thymallus, using nuclear SNPs, appears minimal as samples of T. aeliani group within Danubian lineages, despite carrying highly divergent reciprocally monophyletic mtDNA. [ABSTRACT FROM AUTHOR]

Purpose. The purpose of the presented review is to analyse the spread of the red mark syndrome (RMS) in rainbow trout (Oncorhynchus mykiss Walbaum, 1792) from countries neighbouring Ukraine and summarise the ways and mechanisms of the spread of this disease in order to prevent the potential spread of this disease in specialized farms in Ukraine. Findings. The article provides data on the spread of red mark syndrome in rainbow trout from Europe, and methods of its prevention at fish farms. Special attention is paid to the spread of the disease in countries neighbouring Ukraine, which causes concern about the possible penetration of the pathogen into the territory of Ukraine. Geographic proximity to countries with confirmed RMS outbreaks, as well as the presence of developed aquaculture, in particular rainbow trout farming, increase the risk of introducing this disease. The cause-and-effect relationship of RMS is still unknown. A midichlorine-like organism (MLO) is considered the most likely causative agent, as all other possible agents lack sufficient evidence to associate them with RMS. Future studies should focus on confirming the causal relationship of MLO with RMS and developing prevention strategies. The latent period of the disease is an important aspect that needs to be studied in detail. The use of new highly sensitive methods, such as polymerase chain reaction (PCR), will allow more accurate control of the dynamics of infection and determine the optimal time frame for taking fish samples for the purpose of isolating the pathogen. The hypothesis of the host's hypersensitivity reaction to MLO as one of the reasons for the development of RMS requires further investigation. Understanding the factors that contribute to the development of RMS and efforts to isolate MLO are important for the development of targeted solutions to control the disease. Strategies may focus on helping to build up the host's natural immunity against RMS, thereby avoiding the use of antibiotics. The risk of developing RMS in fish is thought to be multifactorial, with certain farming practices and environmental factors making some fish populations more susceptible to the condition. The role of water, eggs, environment, invertebrates and parasites as possible vectors of MLO requires additional research. Collection of up-to-date data on the incidence of RMS is important for a more accurate determination of its economic impact on trout aquaculture. Disease surveillance and broader data on the prevalence of RMS in Europe and the world should be implemented by conducting large-scale studies combining data from different institutions. This will increase the level of biosecurity and help develop effective risk management strategies, which will contribute to maintaining the stability of aquaculture in Ukraine. The potential economic consequences of RMS can be significant for Ukraine. Despite the low mortality, treatment and management costs can significantly affect the economics of aquaculture by increasing production costs. It is important to implement biosecurity measures, including control of live fish imports, regulation of aquaculture systems and increased biosecurity on farms. It is also necessary to conduct a study to assess the potential economic impact of RMS on the industry, which will help to develop effective risk management strategies and maintain the stability of aquaculture in Ukraine. Practical Value. Monitoring of salmon diseases in fish farming enterprises of Ukraine will allow determining the ecological niches of these pathogens and establish the potential risks of epizootics, primarily in the conditions of aquaculture. [ABSTRACT FROM AUTHOR]

The use of barriers in freshwater systems to mitigate invasions, known as isolation management, has been increasingly implemented as a protection strategy for native fish. Barriers are crucial for securing vulnerable populations, but much remains to be learnt about the drivers of success and the implications of deliberate fragmentation.In Aotearoa‐New Zealand, henceforth Aotearoa, native non‐migratory galaxiid (NMG) fishes are characterized by a disproportionate number of threatened species with introduced salmonids (trout) identified as a key driver of NMG declines.We conducted a qualitative review of barriers protecting NMG in Aotearoa, illustrating varying outcomes and current knowledge gaps with case studies. Barrier types ranged from natural bedrock waterfalls, shallow velocity chutes and drying reaches to deliberately engineered structures (known commonly as exclusion barriers). Barriers were typically located in headwater streams or spring systems. NMG species secured by fragmentation often have high conservation value and barriers are essential for their protection.Despite the critical role of these barriers, the isolated NMG populations above them are at risk of stochastic extirpation, invasion, or re‐invasion. Exclusion barriers may restrict access to habitat for native migratory fish species and can sometimes alter or remove ideal mesohabitat from protected populations.Overall, when using exclusion barriers, managers must assess extinction risk for individual populations by isolation or invasion, balancing benefits and consequences. However, these assessments are frequently based on incomplete data and hindered by lack of general understanding of the underpinning processes. Despite well‐documented benefits to NMG population survival, key knowledge gaps such as long‐term viability of isolated populations, combinations of physical barrier parameters conferring exclusion under all flow regimes and extent of habitat loss to other native species still exist. [ABSTRACT FROM AUTHOR]

Aquaculture supplies the world food market with a significant amount of valuable protein. Highly productive aquaculture fishes can be derived by utilizing genome-editing methods, and the main problem is to choose a target gene to obtain the desirable phenotype. This paper presents a review of the studies of genome editing for genes controlling body development, growth, pigmentation and sex determination in five key aquaculture Salmonidae and Cyprinidae species, such as rainbow trout (Onchorhynchus mykiss), Atlantic salmon (Salmo salar), common carp (Cyprinus carpio), goldfish (Carassius auratus), Gibel carp (Carassius gibelio) and the model fish zebrafish (Danio rerio). Among the genes studied, the most applicable for aquaculture are mstnba, pomc, and acvr2, the knockout of which leads to enhanced muscle growth; runx2b, mutants of which do not form bones in myoseptae; lepr, whose lack of function makes fish fast-growing; fads2, Δ6abc/5Mt, and Δ6bcMt, affecting the composition of fatty acids in fish meat; dnd mettl3, and wnt4a, mutants of which are sterile; and disease-susceptibility genes prmt7, gab3, gcJAM-A, and cxcr3.2. Schemes for obtaining common carp populations consisting of only large females are promising for use in aquaculture. The immobilized and uncolored zebrafish line is of interest for laboratory use. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are among the most endangered ecosystems worldwide. While numerous taxa are on the verge of extinction as a result of global changes and direct or indirect anthropogenic activity, genomic and transcriptomic resources represent a key tool for comprehending species' adaptability and serve as the foundation for conservation initiatives. The Loire grayling, Thymallus ligericus, is a freshwater European salmonid endemic to the upper Loire River basin. The species is comprised of fragmented populations that are dispersed over a small area and it has been identified as a vulnerable species. Here, we provide a multi-tissue de novo transcriptome assembly of T. ligericus. The completeness and integrity of the transcriptome were assessed before and after redundancy removal with lineage-specific libraries from Eukaryota, Metazoa, Vertebrata, and Actinopterygii. Relative gene expression was assessed for each of the analyzed tissues, using the de novo assembled transcriptome and a genome-based analysis using the available T. thymallus genome as a reference. The final assembly, with a contig N50 of 1221 and Benchmarking Universal Single-Copy Orthologs (BUSCO) scores above 94%, is made accessible along with structural and functional annotations and relative gene expression of the five tissues (NCBI SRA and FigShare databases). This is the first transcriptomic resource for this species, which provides a foundation for future research on this and other salmonid species that are increasingly exposed to environmental stressors. [ABSTRACT FROM AUTHOR]

This study investigates the effect of large woody debris (LWD) on the abundance of juvenile Atlantic salmon (Salmo salar, L.) and anadromous brown trout (Salmo trutta, L.) in semi‐alluvial side channels of the river Aurlandselva (Norway) using point electrofishing and microhabitat mapping. Not the presence of LWD, but stream bed shelter availability and the distance to spawning grounds affected the fish abundance (fish/point), independent of other habitat components. LWD showed only an effect on fish abundance when in interaction with other habitat components. This discrepancy can be explained by the availability of cavities in the shelter‐rich coarse substrate which provide sufficient cover and territory for juvenile fish at the given carrying capacity of river Aurlandselva. Whilst LWD may be most effective to provide shelter in lowland streams (bed slope <0.005), maintaining or restoring shelter‐rich coarse substrates should be considered a key priority in steeper salmonid rivers and associated semi‐fluvial streams. [ABSTRACT FROM AUTHOR]

We review and draw distinctions between positions held by various federal agencies, tribal agencies, and civil society organizations to identify distinct stakeholder scenarios for salmonid recovery in the Columbia River Basin. We view the Columbia River Basin through a resilience lens from the point of view of the resident endangered salmonid populations. Using the resilience concept of multiple stable states we describe a stability landscape for the basin as a social–ecological system. We use a shared stability landscape as a common locus for mapping and comparing multiple scenarios representing distinct stakeholder perspectives of pathways towards salmon recovery. We found that the potential of using this approach goes well beyond the specifics of the Columbia River Basin. [ABSTRACT FROM AUTHOR]

The pink salmon Oncorhynchus gorbuscha (Teleostei, Salmonidae) is a North Pacific species. It arrived in Northern Europe through freshwater migration each odd year since 2017, creating management issues. In this study, we sequenced a complete mitochondrial genome for a pink salmon caught in the Bresle River (France) with a museum voucher. The sequence is 16,695 bp in length and is similar to previous mitog)enomes published within this genus. Length heteroplasmy on the control region for this species was detected, as described in previous molecular studies. We tested several primers commonly used for metabarcoding studies on four markers (12S, 16S, COI and Cytb), and all allow the discrimination of this species. This mitogenome is a reference for molecular identification, for instance in like environmental DNA studies. [ABSTRACT FROM AUTHOR]

The diversity of functional feeding anatomy is particularly impressive in fishes and correlates with various interspecific ecological specializations. Intraspecific polymorphism can manifest in divergent feeding morphology and ecology, often along a benthic–pelagic axis. Arctic charr (Salvelinus alpinus) is a freshwater salmonid known for morphological variation and sympatric polymorphism and in Lake Þingvallavatn, Iceland, four morphs of charr coexist that differ in preferred prey, behaviour, habitat use, and external feeding morphology. We studied variation in six upper and lower jaw bones in adults of these four morphs using geometric morphometrics and univariate statistics. We tested for allometric differences in bone size and shape among morphs, morph effects on bone size and shape, and divergence along the benthic-pelagic axis. We also examined the degree of integration between bone pairs. We found differences in bone size between pelagic and benthic morphs for two bones (dentary and premaxilla). There was clear bone shape divergence along a benthic–pelagic axis in four bones (dentary, articular-angular, premaxilla and maxilla), as well as allometric shape differences between morphs in the dentary. Notably for the dentary, morph explained more shape variation than bone size. Comparatively, benthic morphs possess a compact and taller dentary, with shorter dentary palate, consistent with visible (but less prominent) differences in external morphology. As these morphs emerged in the last 10,000 years, these results indicate rapid functional evolution of specific feeding structures in arctic charr. This sets the stage for studies of the genetics and development of rapid and parallel craniofacial evolution. [ABSTRACT FROM AUTHOR]

Salmo ekmekciae, new species, is described from the Köprüçay River, a drainage of Mediterranean Sea. It is distinguished from Salmo species in adjacent water by having 9–10 parr marks on flank; 11–13 scale rows between end of base of adipose-fin and lateral line; 22–24 gill rakers on first gill arch; a shorter distance between adipose-fin and caudal-fin base; a slenderer caudal peduncle; and a slenderer body at adipose-fin origin. According to the Bayesian, and maximum likelihood analyses, Salmo ekmekciae cyt b gene resulted in coherent trees supported by high bootstrap values. [ABSTRACT FROM AUTHOR]

Reintroduction is an important tool for the recovery of imperiled species. For threatened Pacific salmonids (Oncorhynchus spp.) species, hatchery‐origin (HOR) individuals from a nearby source are often used to reestablish populations in vacant, historically occupied habitat. However, this approach is challenged by the relatively low reproductive success that HOR Pacific salmonids experience when they spawn in the wild, relative to their natural‐origin (NOR) counterparts. In this study, we used genetic parentage analysis to compare the reproductive success of three groups of adult Chinook salmon (Oncorhynchus tshawytscha) reintroduced above Cougar Dam on the South Fork McKenzie River, Oregon: HOR Chinook salmon from an integrated stock; first‐generation, wild‐born descendants (hereafter F1s) of Chinook salmon produced at the same hatchery; and NOR Chinook salmon that are presumed to have been produced below the dam, on the mainstem McKenzie River, or elsewhere and volitionally entered a trap below Cougar Dam. We found that F1s produced nearly as many adult offspring as NORs, and 1.8‐fold more adult offspring than HORs. This result suggests that, for the South Fork McKenzie reintroduction program, a single generation in the wild increases fitness for the descendants of HOR Chinook salmon. Although these results are encouraging, care must be taken before extrapolating our results to other systems. [ABSTRACT FROM AUTHOR]

Freshwater megafish species, such as sturgeons, salmonids, carps, and catfishes, have a maximum reported weight ≥30 kg. Due to their charisma and economic value, they have been widely introduced outside of their native ranges. Here, we provide a comprehensive overview of the introduction of freshwater megafish and an assessment of their environmental impacts. Of the 134 extant freshwater megafish species, 46% have been introduced to new environments, and of these, 69% have established self‐sustaining alien populations. These introductions affect 59% of the world's main basins, with the USA and western Europe being particular hotspots of megafish introductions. The common carp (Cyprinus carpio) is the most widely introduced species. Using the Environmental Impact Classification for Alien Taxa (EICAT and EICAT+) frameworks, we assessed the severity and type of negative and positive impacts posed by alien megafish on native species. Alien megafish caused negative impacts through nine different mechanisms, with predation being the most frequently reported mechanism, followed by herbivory and competition. Moreover, 58% of the alien megafish species with sufficient data to evaluate the severity of their impacts caused declining populations of native species, or worse, extirpations of native species populations. The positive environmental impacts of alien megafish were far less frequently documented. They include biotic interactions that benefit native species, and the provision of trophic resources or habitats. Widely introduced or extensively studied species are more likely to have documented severe impacts on native species. There is a clear trade‐off between the economic benefits associated with megafish introductions and the severe adverse impacts they have on native biodiversity. Our study highlights the need for comprehensive risk assessments to evaluate the potential environmental impacts of megafish. More research and long‐term monitoring schemes are required to inform management actions to protect biodiversity, particularly in the Global South. [ABSTRACT FROM AUTHOR]

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Hydropeaking mitigation based on down‐ramping thresholds is crucial to avoid stranding of fish and ensure sustainable hydropower production. However, the risk of stranding is influenced by several biotic and abiotic factors that interact with the ramping rate, including river morphology and baseflow magnitude. Also, at the river bar scale, the lateral or horizontal down‐ramping velocity may be of even greater importance than the vertical one as the prior integrates bar morphology. This study investigates the connection between ecologically relevant hydraulic parameters (vertical and lateral ramping velocity, dewatered river bar width) and the stranding of young‐of‐the‐year European grayling (Thymallus thymallus) due to down‐ramping, based on field observations of stranded fish at the hydropeaked Drava River in Austria combined with hydrodynamic–numerical modelling. We also examine the interplay between baseflow conditions and river topography in the dewatered areas. Stranding observations in spring and summer found a median rate of 90 individuals per 100 m, ranging from 50 to 500 fish per 100 m shoreline. Stranding rates were three times higher at night than during the day. Our data revealed a positive relationship between stranded fish and down‐ramping hydraulics, with higher intensity resulting in more stranded fish. This association was stronger for the lateral than the vertical ramping velocity, presumably because the former accounts for bar morphology, suggesting that the lateral dewatering velocity is a better indicator to assess fish stranding at the bar scale than the vertical velocity. We also found a negative relationship between the extent of the dewatered area and baseflow magnitude, indicating that the stranding risk is higher during down‐ramping at low flow conditions. [ABSTRACT FROM AUTHOR]

Many river ecosystems in the boreal zone have faced remarkable changes due to intensive human activities, including land‐use changes in the catchments and channelization. Recently, restoration efforts have increased, hoping to restore a more natural hydromorphology. We studied the community structure of benthic macroinvertebrates (zoobenthos) in seven rivers in Eastern Finland, using samples that covered pre‐ and post‐restoration periods, to examine how environmental metrics relate to the zoobenthos community structure, and the fatty acid (FA) composition and content of Ephemeroptera, Plecoptera, and Trichoptera nymphs and larvae. We also analyzed the FA composition and content of land‐locked salmon (Salmo salar m. sebago) in three of the rivers and brown trout (Salmo trutta) in two of the rivers. Zoobenthos communities differed significantly among most of the rivers: 24% of the differences between the zoobenthos communities were driven by water quality parameters related to the loading of terrestrial organic matter (water color, pH, and iron concentration). Temporal changes in zoobenthos communities could not be fully attributed to restorations. The FA composition of zoobenthos was mostly explained by phylogenetic origin (47%). However, especially mayfly Heptagenia sulphurea (Ephemeroptera: Heptageniidae) had variable FA composition and content among the rivers suggesting an environmental quality indicator role for this species. FA composition and content of salmonids were mostly size‐dependent (24%), but river identity also influenced their FA composition (22%). Our results indicate that water quality affects the availability of essential FAs for consumers by altering the zoobenthos community structure and their FA composition and content. [ABSTRACT FROM AUTHOR]

Every year, ulcerative dermal necrosis (UDN) affects salmonids that spend most of their lives in the sea during their migration to the rivers of northern Poland to spawn. The clinical form of the disease manifests itself in ulcerative skin lesions, which lead to significant weakening of the fish and, in most cases, result in their death. This study was carried out on samples taken from sea trout in the Słupia River in northern Poland. In order to identify the pathogen, experiments on the transmission of the disease were carried out, and additional histopathological, microbiological and electron microscopic examinations were performed. As a result of these studies, it was possible to experimentally transfer the disease from sick to healthy fish. The results indicate a complex etiology of the disease (lack of a clearly defined pathogen), in which the change in the environment from salty to freshwater triggers the related changes in skin physiology, which are the main causes of increased susceptibility to the development of the disease. [ABSTRACT FROM AUTHOR]

A study was conducted in fish processing facilities to investigate the microbial composition, microbial metabolic potential, and distribution of antibiotic resistance genes. Whole metagenomic sequencing was used to analyze microbial communities from different processing rooms, operators and fish products. Taxonomic analyses identified the genera Pseudomonas and Psychrobacter as the most prevalent bacteria. A Principal Component Analysis revealed a distinct separation between fish product and environmental samples, as well as differences between fish product samples from companies processing either Gadidae or Salmonidae fish. Some particular bacterial genera and species were associated with specific processing rooms and operators. Metabolic analysis of metagenome assembled genomes demonstrated variations in microbiota metabolic profiles of microbiota across rooms and fish products. The study also examined the presence of antibiotic-resistance genes in fish processing environments, contributing to the understanding of microbial dynamics, metabolic potential, and implications for fish spoilage.

Adaptive radiations represent some of the most remarkable explosions of diversification across the tree of life. However, the constraints to rapid diversification and how they are sometimes overcome, particularly the relative roles of genetic architecture and hybridization, remain unclear. Here, we address these questions in the Alpine whitefish radiation, using a whole-genome dataset that includes multiple individuals of each of the 22 species belonging to six ecologically distinct ecomorph classes across several lake-systems. We reveal that repeated ecological and morphological diversification along a common environmental axis is associated with both genome-wide allele frequency shifts and a specific, larger effect, locus, associated with the gene edar. Additionally, we highlight the possible role of introgression between species from different lake-systems in facilitating the evolution and persistence of species with unique trait combinations and ecology. These results highlight the importance of both genome architecture and secondary contact with hybridization in fuelling adaptive radiation.

In this study, the biochemical composition of wild and farm origin grayling eggs was compared, first, to evaluate the composition of fatty acids and protein content in grayling eggs for the first time, and second, to discover differences in biochemical composition between wild and farm origin eggs which is affected by broodstock feed. Farm origin grayling females were fed commercial trout starter feed, while wild origin females were feeding on food present in their natural environment. Fatty acid composition, protein content and colour were determined. Based on a principle component analysis (PCA) of the biochemical profile, farm and wild origin grayling eggs were clearly separated. Wild origin grayling eggs contained higher amount of SFA, but lower MUFA and PUFA than farm origin eggs. A considerable difference between wild and farm origin grayling eggs was observed also in essential fatty acids: C22:6 n-3 (DHA), C20:5 n-3 (EPA) and C20:4 n-6 (ARA), resulting in higher EPA/ARA and DHA/EPA ratio in farm origin eggs compared to wild origin eggs. Wild origin grayling eggs were characterised by higher protein content and were more intensely red-coloured than farm origin eggs, which were almost colourless. It could be concluded that the biochemical composition of farm origin eggs significantly differs from wild origin grayling eggs, which might have an influence on the embryonic development and hatching success of farm origin grayling. Therefore, the diet that has the greatest effect on egg composition needs to be optimised to meet the needs of the grayling broodstock and to improve the breeding efficiency of farm raised graylings.

In variable environments, repeatable phenotypic differences between individuals provide the variation required for natural selection. The pace-of-life syndrome (POLS) provides a conceptual framework linking individual physiology and life histories to behaviour, where rapidly growing individuals demonstrate higher rates of resting or "standard" metabolic rate (SMR). If differences in SMR are consistent between fast- and slow-growing individuals, these differences may be important to capture in bioenergetic relationships used to describe their growth, energy acquisition, and allocation. We compared growth rates and SMR between a domesticated and wild strain of rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)) using intermittent flow respirometry. Though mass-scaling exponents were similar between strains, mass-scaling coefficients of SMR for fast-growing rainbow trout were 1.25 times higher than those for slower growing fish. These observed differences in mass-scaling coefficients between fast- and slow-growing rainbow trout were consistent with data extracted from several other studies. Bioenergetic estimates of consumption for domestic strain fish increased as the difference in SMR and wild strain fish increased, and increased as activity level increased. Our results indicate patterns of SMR consistent with POLS, and suggest that strain-specific SMR equations may be important for applications to active populations (i.e., field observations). [ABSTRACT FROM AUTHOR]

Many headwaters across temperate North America have uniform mid‐succession riparian forests recovering from historic land clearing. These young riparian stands contrast with late‐succession forests, which have complex structural characteristics including canopy gaps. Canopy gaps provide structural diversity that can be important for terrestrial species, and they are also hypothesized to be important features for aquatic environments. The light patches below gaps create productivity hotspots in streams and therefore create potential for increased stream apex predator abundances through bottom‐up food web drivers. However, increasing light may also affect stream temperature, a consideration for coldwater fish (salmonids). We established an experimental before‐after control‐impact study to explicitly assess how creating canopy gaps in the riparian forest affects the abundance and biomass of coastal cutthroat trout (Oncorhynchus clarkii clarkii) and Pacific giant salamanders (Dicamptodon tenebrosus) in paired reference and treatment reaches at five replicate streams. Gaps were designed to resemble those in old‐growth forests in the treatment reach of each system although wood was explicitly left out of the stream. At four of five sites, we found small and generally consistent positive responses in adult cutthroat trout and total vertebrate biomass to localized increases in light but only 2 years after treatment. Results suggest that opening riparian canopies adjacent to streams via gaps is a viable tool to enhance structural complexity of riparian forests without negatively impacting stream vertebrates; however, a single gap alone had small effects on aquatic vertebrates. More or larger gaps would likely be needed to notably enhance aquatic apex predators. [ABSTRACT FROM AUTHOR]

The taxonomic status of native trout species of the Marmara and Aegean Sea drainages is evaluated and three species, Salmo duhani, S. coruhensis and S. brunoi sp. nov. , are recognized. Salmo brunoi, a new species, is described from the Nilüfer River, a tributary of the Susurluk River. It is distinguished by a general brownish body color in life; few black spots (fewer than 60) on the body, generally scattered on the back and the upper part of the flank, rarely in the median part; few (fewer than 40) and small (smaller than pupil) red spots on the body, scattered on the median part and lower half of the flank; a number of black and red spots not increasing with size in both sexes; a long adipose fin (adipose-fin height 8–9% SL); a short distance between adipose-fin and caudal-fin (12–14% SL); and a short anal fin (anal-fin height 12–15% SL). Salmo brunoi sp. nov. is separated from the rest of the Marmara and Aegean trouts of Anatolia based on genome-wide distributed 187.385 unlinked SNP markers. According to the best of the authors' knowledge, whole genome data is used for the first time here to characterize a new species of trout. [ABSTRACT FROM AUTHOR]

Documenting the diet of organisms that have been introduced and naturalised outside their native range is a fundamental component of understanding their trophic interrelations in the receiving environment, and for developing holistic management practices for introduced species' predation impacts in an ecosystem. We describe two accounts of terrestrial reptiles in the diet of an introduced fish, rainbow trout Oncorhynchus mykiss in southern NSW, Australia. Our observations from the Southern Hemisphere together with recently published records from the Northern Hemisphere (e.g. USA, France and Italy) represent the presence of reptiles in the diet of O. mykiss across a broad geographical range and highlight a potential additional consideration of introduced salmonids and their impacts on terrestrial species. [ABSTRACT FROM AUTHOR]

Pink salmon, Oncorhynchus gorbuscha (Walbaum, 1792), a native of the North Pacific Ocean, is an invasive fish species rapidly expanding in the North Atlantic, the adjacent waters of the Arctic Ocean, and rivers in their watersheds. We investigated the species composition of parasites and the structure of parasite communities of the introduced pink salmon in Kandalaksha Bay of the White Sea in 2021. The parasites were identified using morphological and genetic methods. A total of 14 parasite species were recorded. The core species of the parasitic fauna of the introduced pink salmon in the Kandalaksha Bay were Clistobothrium sp., ʽDiphyllobothriumʼ spp., Scolex polymorphus Rudolphi, 1819 (plerocercoids), Brachyphallus crenatus (Rudolphi, 1802), Derogenes varicus (Müller, 1784), Lecithaster salmonis Yamaguti, 1934 (adults), Anisakis simplex (Rudolphi, 1809) sensu stricto (juvenile III), and Hysterothylacium aduncum (Rudolphi, 1802) (juveniles III and IV). We provided the first evidence that the Pacific genetic lineage of A. simplex sensu stricto occurs in European marine waters. In 2021, there was a noticeable increase in the mean abundance of the third-stage juveniles of Anisakis in the White Sea pink salmon compared to the period of 1990s-early 2000s. We conclude that the pink salmon occupies the same trophic niche in the new region of its introduction as in the native range. [ABSTRACT FROM AUTHOR]

Sichuan taimen (Hucho bleekeri Salmonidae) populations are declining, and the status of remnant populations in the Qinling Mountains is poorly known. In this study, eDNA and creel netting were used to estimate the distributions of Sichuan taimen in two upper tributaries of the Hanjiang River. A qPCR assay was applied to detect the eDNA of H. bleekeri, and the presence of Sichuan taimen in the Taibai River, but not in the Xushui River, was confirmed. Sampling during summer achieved a relatively higher detection rate. The utility of eDNA techniques for detecting low-density Sichuan taimen was demonstrated in intricate stream ecosystems. The eDNA method can increase the efficiency of the management of endangered freshwater species, such as Sichuan taimen, by providing reliable distribution data. [ABSTRACT FROM AUTHOR]

Brackish water ecosystems often have high primary production, intermediate salinities, and fluctuating physical conditions and therefore provide challenging environments for many of their inhabitants. This is especially true of the Baltic Sea, which is a large body of brackish water under strong anthropogenic influence. One freshwater species that is able to cope under these conditions in the northern Baltic Sea is the vendace (Coregonus albula), a small salmonid fish. Here, we review the current knowledge of its ecology and fishery in this brackish water environment. The literature shows that, by competing for resources with other planktivores and being an important prey for a range of larger species, C. albula plays a notable role in the northern Baltic Sea ecosystem. It also sustains significant fisheries in the coastal waters of Sweden and Finland. We identify the need to better understand these C. albula populations in terms of the predator–prey interactions, distributions of anadromous and sea spawning populations and other putative (eco)morphs, extent of gene exchange between the populations, and effects of climate change on their future. In this regard, we recommend strengthening C. albula‐related research and management efforts by improved collaboration and coordination between research institutions, other governmental agencies, and fishers, as well as by harmonization of fishery policies across national borders. [ABSTRACT FROM AUTHOR]

In this study, the biochemical composition of wild and farm origin grayling eggs was compared, first, to evaluate the composition of fatty acids and protein content in grayling eggs for the first time, and second, to discover differences in biochemical composition between wild and farm origin eggs which is affected by broodstock feed. Farm origin grayling females were fed commercial trout starter feed, while wild origin females were feeding on food present in their natural environment. Fatty acid composition, protein content and colour were determined. Based on a principle component analysis (PCA) of the biochemical profile, farm and wild origin grayling eggs were clearly separated. Wild origin grayling eggs contained higher amount of SFA, but lower MUFA and PUFA than farm origin eggs. A considerable difference between wild and farm origin grayling eggs was observed also in essential fatty acids: C22:6 n-3 (DHA), C20:5 n-3 (EPA) and C20:4 n-6 (ARA), resulting in higher EPA/ARA and DHA/EPA ratio in farm origin eggs compared to wild origin eggs. Wild origin grayling eggs were characterised by higher protein content and were more intensely red-coloured than farm origin eggs, which were almost colourless. It could be concluded that the biochemical composition of farm origin eggs significantly differs from wild origin grayling eggs, which might have an influence on the embryonic development and hatching success of farm origin grayling. Therefore, the diet that has the greatest effect on egg composition needs to be optimised to meet the needs of the grayling broodstock and to improve the breeding efficiency of farm raised graylings. Biochemical composition of grayling eggs differs significantly between the two lifestyles (wild and farm origin). Differences in the proportion of essential fatty acids: DHA, EPA and ARA. Suboptimal EPA/ARA and DHA/EPA ratios in farm origin eggs. [ABSTRACT FROM AUTHOR]

The rainbow trout Oncorhynchus mykiss is non-indigenous species for Europe, with numerous records for occurrence, spawning and self-sustaining populations across the continent. The species has been found in surface water bodies in Bulgaria but naturally-reproducing have not been yet detected. In 2020, 2021 and 2022, we observed spawning behaviour of mature fish in the Ogosta River, downstream of Ogosta Reservoir, north-western Bulgaria. In order to verify whether the rainbow trout reproduces naturally in Bulgaria, complete process of spawning was tracked. Through the winter-spring period of 2022, fish material was sampled from the trout redds and identified via DNA analysis. The results showed that rainbow trout reproduce successfully in the sampled river stretch. Vital specimens at stages of egg and fry development were found through the whole period, from February to April. The registered water temperature and recent flow management occurred as beneficial for the periods of rainbow trout spawning, egg development as well as fry emergence. [ABSTRACT FROM AUTHOR]

Juvenile salmonids often experience high mortality rates during migration and bird predation is a common source of mortality. Research suggests that hatchery‐reared salmonids are more prone to predation than wild salmonids, and that Atlantic salmon (Salmo salar) experience lower predation than Sea trout (Salmo trutta), yet telemetry studies have displayed equivocal results. Here, using a large data set on passive integrated transponder (PIT) tagged hatchery‐reared and wild juveniles of Atlantic salmon and Sea trout (25,769 individuals) we investigate predation probability by piscivorous birds (mainly Great Cormorants Phalarocorax carbo) on salmonids originating from River Dalälven in Sweden. Bird colonies and roosting sites were scanned annually (2019–2021), and the temporal dynamics of bird predation on salmonids released in 2017–2021 was assessed. Hatchery‐reared trout was clearly most susceptible to cormorant predation (0.31, 90% credibility interval [CRI] = 0.14–0.53), followed by wild trout (0.19, 90% CRI = 0.08–0.37), hatchery‐reared salmon (0.13, 90% CRI = 0.07–0.23), and wild salmon (0.08, 90% CRI = 0.04–0.14), in subsequent order. This order in predation probability was consistent across all studied tag‐ and release‐years, suggesting that the opportunistic foraging of cormorants affects the overall survival of juvenile salmonids, but that the inherent predation risk between different salmonid types differs systematically. [ABSTRACT FROM AUTHOR]

Anadromous salmonids exhibit partial migration, where some individuals within a population migrate down to the ocean through complex interactions between body size and photoperiod. This study aimed to integrate the ontogenetic and seasonal patterns of smoltification, a series of changes for future marine life, in a strain of masu salmon (Oncorhynchus masou). Spring smoltification, as evidenced by the activation of gill Na+,K+-ATPase (NKA), was induced during winter under an advanced photoperiod. In addition, juveniles showed an additional peak in gill NKA activity in August regardless of the photoperiod. When juvenile masu salmon were subjected to feeding manipulations during the first spring/summer, only fish exceeding a fork length of 12 cm exhibited an increased gill NKA activity. We tested whether size-driven smoltification required a long-day period by exposing juveniles to a constant short-day length (9-h light and 15-h dark) from January to November. Juveniles under short-day conditions exceeded 12 cm in June but showed no signs of smoltification. Thus, masu salmon undergo photoperiod-limited, size-driven smoltification during the first summer and size-limited, photoperiod-driven smoltification the following spring. The findings of the present study provide a framework for further elucidation of the physiological mechanisms underlying partial migration in salmonids. [ABSTRACT FROM AUTHOR]

Insufficient knowledge about the occurrence and spread of non‐native fish in mountain regions has impeded effective management strategies worldwide. To address this gap, this study analysed over 1300 electrofishing surveys across 650 sites, encompassing a vast 7400 km2 area in the Eastern Alps. The primary objectives were to quantify the occurrence of non‐native species and predict their spread in different river types. Furthermore, the study estimated population sizes and biomass trends for over 150 sites that were surveyed multiple times between 2000 and 2020. Out of the 42 fish species in the study region, 11 were identified as non‐native. Notably, two invasive species of Union concern, Lepomis gibbosus and Pseudorasbora parva, increased their population sizes by 8% and 9% per year, over the past decades, supposedly supported by increasing water temperatures. Among the non‐native species relevant for recreational fishing, Oncorhynchus mykiss populations showed a significant increase of approximately 7% per year, Salmo trutta populations remained stable, and Salvelinus fontinalis populations experienced a notable decline of approximately 7.4% per year. These varying population trends may be attributed to disparities in stocking intensities, with S. fontinalis receiving minimal stocking compared to the other species. This study revealed that non‐native and invasive fish species are a relevant part of fish communities in mountain rivers. Non‐salmonid non‐natives thrive in warm rivers at lower elevations, whereas salmonid non‐natives consolidate in steeper habitats. Because rising temperatures in mountain rivers will accelerate the spread and growth of these species, this first quantification of the current extent will improve fish management strategies in mountainous areas. [ABSTRACT FROM AUTHOR]

This is a preliminary and exploratory study of cranial variation in European populations of grayling. We investigated the correspondence between size/shape variation of the dorsal (DC), ventral (VC) and occipital (OC) cranium and phylogenetic relationships (inferred from mitochondrial control region - mtDNA CR and microsatellite DNA data) of six grayling populations: three from Balkan phylogenetic clade and two from Caspian phylogenetic clade of the European grayling ThymaHus thymallus and one population of the Adriatic grayling Thymallus aeliani, which until recently was considered the Adriatic phylogenetic clade of T. thymallus. Significant size and shape differences were found between populations in all three cranial views. However, significant size-related shape variation (allometry) was found for DC and VC, but not for OC. The size variation of each cranial view does not contain phylogenetic signal, but size variation of OC is consistent with genetic variation inferred from microsatellite DNA. Regarding shape variation, a significant phylogenetic signal was detected only for OC, and only the shape variation of OC is consistent with the genetic variation inferred from the mtDNA CR. Moreover, the Adriatic grayling T. aeliani (Soca population) was clearly separated from the three T. thymallus populations of the Balkan phylogenetic clade and the two T. thymallus populations of the Caspian phylogenetic clade only at the level of OC. Thus, our results suggest that different cranial regions differ in allometry, reflect phylo(genetic) relationships differently, and exhibit differences in ecophenotypic plasticity, with OC seeming best suited to represent the phylogenetic relationships of the grayling populations studied. [ABSTRACT FROM AUTHOR]

In many freshwater ecosystems, carbon dioxide (CO2) is increasing. Unknown are the risks that high CO2 poses for freshwater organisms, especially fish. The objective of this study was to determine how CO2 may influence the growth rate, metabolic rate, feeding rate, and volitional behaviour of young-of-year Arctic charr (Salvelinus alpinus (Linnaeus, 1758)), brook charr (Salvelinus fontinalis (Mitchill, 1814)), and rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)). For this study, fish stayed in control (1100 microatmospheres (µatm)) or elevated (5236 µatm) CO2 levels for 15 days. During this time, metabolic rate and behavioural tests were conducted on alternating days for each treatment. Weight and length of each fish were taken on days 0, 7, and 15. There was no evidence that elevated CO2 affected the growth rate, feeding rate, or behaviour in any of these species. The standard metabolic rate in Arctic charr differed based on CO2 exposure. Therefore, salmonids can withstand short periods of elevated CO2 under these conditions. By comparing closely related species, the implications of this work are more ecologically relevant and will also help industry quantify the effects of high CO2 on young salmonids. [ABSTRACT FROM AUTHOR]

During summer, native anadromous Arctic char (Salvelinus alpinus) and the alien species pink salmon (Oncorhynchus gorbuscha) now coexist in marine environments in Svalbard, following the introduction of the latter in the Barents Region. To investigate potential dietary competition between these two salmonid species, stomach contents from Arctic char (n = 301) and pink salmon (n = 28) were sampled from different areas within the archipelago. The most important prey in terms of biomass for both salmonid species were amphipods; Themisto libellula (B = 26.0%) for Arctic char and Onisimus litoralis (B = 35.0%) for pink salmon. Pianka's niche overlap revealed that dietary overlap between the two species was moderately high (Oobs = 0.59); both species had strong associations with intertidal invertebrates in areas where direct comparisons were possible (Kongsfjorden/Krossfjorden). However, both salmonid species did also eat some fish, with Arctic char consuming more offshore pelagic fish, while the small number of fish eaten by pink salmon were primarily coastal demersal fish species. Arctic char was a more generalist feeder, while pink salmon was more of a dietary specialist. Furthermore, the diet composition of the Arctic char consisted of 32.9% Atlantic prey while the pink salmon, surprisingly, ate only Arctic species, likely due to their tightly coastal feeding habits. Even though the sample size for pink salmon was low, this study contributes new insights into salmonid diets in Svalbard and the potential for introduced species to compete with native Arctic endemics, particularly in the expected warmer Arctic of the future. [ABSTRACT FROM AUTHOR]

Fish often spawn eggs with ovarian fluids that have been hypothesized to support the sperm of some males over others (cryptic female choice). Alternatively, sperm reactions to ovarian fluids could reveal male strategies. We used wild‐caught lake char (Salvelinus umbla) to experimentally test whether sperm react differently to the presence of ovarian fluid, and whether any differential sperm reaction could be predicted by male breeding coloration, male inbreeding coefficients (based of 4150 SNPs) or the kinship coefficients between males and females. Male coloration was positively linked to body size and current health (based on lymphocytosis and thrombocytosis) but was a poor predictor of inbreeding or kinship coefficients. We found that sperm of more colourful males were faster in diluted ovarian fluids than in water only, while sperm of paler males were faster in water than in ovarian fluids. We then let equal numbers of sperm compete for fertilizations in the presence or absence of ovarian fluids and genetically assigned 1464 embryos (from 70 experimental trials) to their fathers. The presence of ovarian fluids significantly increased the success of the more colourful competitors. Sperm of less inbred competitors were more successful when tested in water only than in diluted ovarian fluids. The kinship coefficients had no significant effects on sperm traits or fertilization success in the presence of ovarian fluids, although parallel stress tests on embryos had revealed that females would profit more from mating with least related males rather than most coloured ones. We conclude that sperm of more colourful males are best adapted to ovarian fluids, and that the observed reaction norms suggest male strategies rather than cryptic female choice. [ABSTRACT FROM AUTHOR]

Anthropogenic activities and their influences on aquatic systems is an important topic, especially considering the growing interest in using the earth's resources in a sustainable way. One of those anthropogenic activities is the introduction of renewable technologies into the aquatic environment such as instream turbines. Environmental studies around those technologies are often still ongoing due to their novelty. During the spring of 2018, juvenile individuals of two salmonid species, Atlantic salmon and brown trout were released upstream a vertical axis instream turbine in the river Dal (Dalälven) in eastern Sweden. The aim of this study was to investigate the swimming behavior of the salmonids around a small‐scale prototype vertical axis instream turbine. The swimming pattern and the possible response of avoiding the vertical axis instream turbine were documented with a multi beam sonar. A control area, next to the turbine, was used as reference. No consistent results were shown for trout as they were passing the control area with a statistically high variation, and specimens were rarely observed in proximity of the turbine, neither if the turbine was operating nor at stand still. Salmon clearly avoided the operating turbine, but did not avoid the turbine when it was at stand still, and was often observed swimming straight through the turbine area. These findings indicate that operating this type of instream turbine in a river affects the swimming behavior of Atlantic salmon but is unlikely to affect its migration paths. For brown trout, the statistical results are inconclusive, although data indicate a response of avoiding the turbine. The species are in little risk to suffer physical harm as no fish entered the rotating turbine, despite very turbid water conditions. [ABSTRACT FROM AUTHOR]

In Salmonidae, infections with the parasite Tetracapsuloides bryosalmonae may lead to a temperature‐dependent proliferative disease of the kidney (PKD). Trout that survive infection and recover become resistant to the disease. The use of this approach to improve brown trout (Salmo trutta) stocking success was tested in three PKD‐affected streams in southern Germany. Fish were treated using local spores of the parasite and kept at low temperatures (14°C) to not develop the disease. Controls were similarly kept but not treated with spores. Independent of time of stocking (winter or spring), recapture rates for both control and parasite‐treated stocked trout were very low (<1%). However, recaptured parasite‐treated trout exhibited lower parasite prevalence than control and wild‐caught trout. [ABSTRACT FROM AUTHOR]

Salmo caspius Kessler, 1877 is one of the most commercially important species of Salmonidae in the southern basin of the Caspian Sea. The occurrence of its wild populations has undergone sever reduction during the last years. In spite of the yearly restocking activity, still no progress on the recovery of its wild population has been observed. Hence, the present study was done in order to assess the efficiency of the current restocking activity in the southern Caspian basin in term of genetic diversity. DNA extracts of 32 S. caspius from four different groups were screened using 62621 genome-wide single nucleotide polymorphisms (SNP). The overal genetic diversity and Fst values were 0.18 and 0.08, respectively. Considering the observed admixture pattern and the positive values for inbreeding coeficient it seems that S. caspius suffers from its small effective population size. In order to obtain the maximum performance, alonside with expanding the size of brood stocks, rehabilitation of the habitats and spawning rivers of this nationally endangered species is of great importance. [ABSTRACT FROM AUTHOR]

Here, I review thermal influences on metabolic rates and aerobic scope; growth; adult body size; and reproductive and behavioural traits, such as tendency and timing of the migration of salmonid fishes. A thermal window bounded by the upper and lower incipient lethal temperatures (UILT and LILT) determines where salmonids can survive. For most salmonids, LILT is close to 0 and UILT is between 20 and 30 °C. UILT and LILT are influenced by the acclimation temperature. Thermal tolerance is affected by fish size and ambient oxygen content, which decreases with increasing temperature. Standard metabolic rate (SMR), the energy required to maintain essential functions, increases with temperature, whereas maximum metabolic rate (MMR) increases with temperature until reaching a peak (pejus). Then, it decreases gradually to zero, i.e., the upper critical limit (TCrit). Aerobic scope (AS = MMR-SMR) reaches its maximum at the pejus temperature. Metabolic rates and aerobic scope can be modified by temperatures that the fish experiences during embryogenesis and possibly also as larvae and young fry. At maximum feeding, maximum growth increases to a point at or below the pejus temperature. The optimum temperature for growth decreases with reduced food intake and increased body size. As for metabolic rate, the growth rate is influenced by the temperature during embryonic development. In a warmer climate, adult body size is expected to decrease chiefly because of a younger age at maturity. Parental fish retained at a higher temperature during maturation produce larger eggs, and this change in egg size may also be transferred to next-generation offspring. Furthermore, embryogenesis in warmer water leads to larger gonad and egg sizes at maturity. Water temperature influences locomotion, foraging and migratory activity. In a warmer climate, juveniles migrate to the sea earlier in spring. In addition, higher embryo temperature leads to delayed return of adult salmon from the ocean. Thus, temperature affects life history traits of salmonid fishes, partly as a direct effect on metabolic rates and food consumption and partly induced as a phenotypically plastic effect. The phenotypically plastic response may preadapt offspring to perform better in the expected future thermal environment. [ABSTRACT FROM AUTHOR]

Chinook salmon (Oncorhynchus tshawytscha, Salmonidae) are foundational to social‐ecological systems of the Northeast Pacific Rim and exhibit a rich diversity of life histories including in their adult migration timing, age at critical life‐history transitions and marine feeding distributions. In recent decades Chinook have experienced declines across much of their native range; however, changes in productivity and abundance have rarely been evaluated in relation to life‐history variation. To understand trends in Chinook salmon production, and how they are related to life history, we compiled time series data from the Fraser River to the Sacramento River on total run size (pre‐fishery abundance) and escapement (post‐fishery spawner abundance) and fit time series models to estimate trends across this bioregion. Our analysis revealed that most Chinook populations are declining, with negative trends in escapement (57 of 79) and total run (16 of 23) size. Trends were most acutely negative for interior spring Chinook in the Fraser, Columbia and Snake Rivers and most populations in California. Summer and fall Chinook had mixed trends, with several summer and fall upriver bright populations in the interior Columbia and Fraser exhibiting increases in abundance from the 1990s to 2019. Our research reveals widespread declines of this important species, but local complexity in trends that are mediated by population‐level life history, migratory behaviours and watershed‐scale restoration actions. Understanding linkages between life histories and resilience should inform rebuilding efforts for Chinook salmon and highlight the need to conserve intraspecific biodiversity. [ABSTRACT FROM AUTHOR]

Atlantic salmon Salmo salar supports highly valuable commercial and recreational fisheries in Europe, but its stocks are currently overexploited and threatened by climate change. Its southernmost populations (in northern Spain) play a key role in conserving the species' original genetic diversity, which is endangered due to decades-long (1970s to 1990s) massive stocking with non-native stocks. Their decline is well documented, but the effect of stock transfer and conservation efforts is unclear. Nine microsatellite loci were amplified from archival samples (scales from 1958–1959) from eight Spanish rivers to analyse the species' natural genetic dynamics before its decline started. Allelic richness was high in the historical populations (the 1950s) and above most contemporary estimates. Private alleles were found in most rivers, indicating high local uniqueness and relative isolation among river basins. Some alleles are regional markers since they are rare or absent from contemporary northern European populations. Effective population size suggested good conservation status, with higher values than those estimated for contemporary populations. Strong population structure and genetic differentiation between rivers were found, with limited gene flow, restricted to geographically close populations. Our estimates of historical genetic diversity and structure from southernmost salmon populations are a powerful benchmark to guide conservation programs. [ABSTRACT FROM AUTHOR]