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Classical methods for estimating the abundance of fish populations are often both expensive, time-consuming and destructive. Analyses of the environmental DNA (eDNA) present in water samples could alleviate such constraints. Here, we developed protocols to detect and quantify brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus) populations by applying the droplet digital PCR (ddPCR) method to eDNA molecules extracted from water samples collected in 28 Swedish mountain lakes. Overall, contemporary fish CPUE (catch per unit effort) estimates from standardized survey gill nettings were not correlated to eDNA concentrations for either of the species. In addition, the measured environmental variables (e.g. dissolved organic carbon concentrations, temperature, and pH) appear to not influence water eDNA concentrations of the studied fish species. Detection probabilities via eDNA analysis showed moderate success (less than 70% for both species) while the presence of eDNA from Arctic char (in six lakes) and brown trout (in one lake) was also indicated in lakes where the species were not detected with the gillnetting method. Such findings highlight the limits of one or both methods to reliably detect fish species presence in natural systems. Additional analysis showed that the filtration of water samples through 1.2 μm glass fiber filters and 0.45 μm mixed cellulose ester filters was more efficient in recovering DNA than using 0.22 μm enclosed polyethersulfone filters, probably due to differential efficiencies of DNA extraction. Altogether, this work showed the potentials and limits of the approach for the detection and the quantification of fish abundance in natural systems while providing new insights in the application of the ddPCR method applied to environmental DNA. [ABSTRACT FROM AUTHOR]

To identify the pathogens causing saprolegniosis among farmed fish in Nova Scotia, 172 infected tissues and 23 water samples were collected from six species of teleosts: Atlantic salmon (Salmo salar), brown trout (Salmo trutta), Arctic charr (Salvelinus alpinus), brook trout (Salvelinus fontinalis), striped bass (Morone saxatilis) and rainbow trout (Oncorhynchus mykiss) at nine facilities over a 600 km range. Following laboratory culture, 132 isolates were recovered. Six species of oomycetes were identified from analysis of the internal transcribed spacer (ITS) sequence of the nrDNA: Saprolegnia parasitica, Saprolegnia ferax, Saprolegnia diclina, Saprolegnia aenigmatica, Saprolegnia torulosa, Saprolegnia sp. and Pythiopsis cymosa. Further phylogenetic analyses of the ITS and cytochrome c oxidase subunit 1 (Cox1) regions revealed four strains of Saprolegnia parasitica (named here as S1, S2, S3 and S4), of which S1 and S2 were common (37% and 42% of the isolates), and two strains of S. ferax. Among S. parasitica, S2 and S3 are more closely related to each other than to S1 based on the phylogenetic analyses and predicted RNA secondary structure of the ITS region. Sexual structures with a similar morphology were formed by S1 and S3 in vitro, but were not formed by S2. [ABSTRACT FROM AUTHOR]

It is hypothesized that in diadromous fish, migrations may occur because of differences in the availability of food in marine and freshwater habitats. The benefits of migration to sea may be increased growth opportunities and reproductive output, while the costs may be increased mortality and increased energy use. Here we examine mortality rates of anadromous Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) in fresh water and at sea over a 25-year period to test these hypotheses. Daily mortality rates were 5–15 times higher at sea than in fresh water, with highest rates for first-time migrants, inferring a clear trade-off between increased mass gain and mortality risk during the sea migration. Descending smolts were caught in a trap at the outlet of the river, individually tagged, and thereafter recorded each time they passed through the trap on their annual migration between the river and the sea. Brown trout females seemed to benefit to a higher degree from migrating to sea than did female Arctic char, probably because of the higher growth rate at sea, and hence higher reproductive output. [ABSTRACT FROM AUTHOR]

Climate change has been identified as a global threat to Arctic char Salvelinus alpinus L. populations. Bayesian statistical models were used to identify important physical and ecological factors explaining Arctic char presence and persistence in Irish lakes. Maximum lake depth and the presence of mixed fish communities (i.e. including non‐salmonid fish species) were the most important drivers of Arctic char presence. There was a 75% probability that an Irish lake would contain Arctic char when maximum depth exceeded 40 m, if only a salmonid community was present. However, the required depth increased to 57 m when a mixed fish community (e.g. pike, perch or roach) was present. Similar variables explained char persistence, with surviving Arctic char populations being more likely in lakes with greater maximum depth and fewer non‐salmonid fish species. Tested temperature covariates were not important in explaining Arctic char presence or persistence in Irish lakes. A risk analysis was undertaken to identify which Arctic char lakes are vulnerable to colonisation by thermally plastic mixed fish communities due to flooding. Results indicated that 32 out of 45 lakes were not at any risk from the colonisation of thermally plastic mixed fish communities and 13 lakes had some level of risk. [ABSTRACT FROM AUTHOR]

High levels of organochlorine contaminants (OCs) have been found in arctic char (Salvelinus alpinus) from Lake Ellasjøen, Bjørnøya (Norwegian Arctic). The aim of the present study was to investigate the potential genotoxic effect of environmental organochlorine contaminant exposure in arctic char from Ellasjøen compared with arctic char from the low‐contaminated Lake Laksvatn nearby. Blood was analyzed using agarose gel electrophoresis and image data analysis to quantify the fraction of total DNA that migrated into the gel (DNA‐FTM) as a relative measure of DNA double‐strand breaks (DSBs). Analysis by GC‐MS of muscle samples showed an average 43 times higher concentration of ΣOCs in arctic char from Ellasjøen (n = 18) compared with Laksvatn char (n = 21). Char from Lake Ellasjøen had a much higher frequency of DSBs, as measured by DNA‐FTM, than char from Lake Laksvatn. Principal component analysis and multiple linear regressions show that there was a significant positive relationship between DSBs and levels of organochlorine contaminants in the char. In addition, DSBs were less frequent in reproductively mature char than in immature char. The results suggest that organochlorine contaminants are genotoxic to arctic char. Environ Toxicol Chem 2019;38:2405–2413. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC [ABSTRACT FROM AUTHOR]

Anadromous Arctic charr Salvelinus alpinus and sea trout Salmo trutta are commonly found in marine, estuarine and freshwater habitats across the Northern Hemisphere. The marine phase varies between populations but often involves summer foraging in nearshore waters while spawning and overwintering occur in freshwater. The dependence of anadromous salmonids on nearshore habitats makes them vulnerable to increased industrial activity, such as aquaculture developments, that may increase the risk of salmon lice Lepeophtheirus salmonis, infection. Lice infection in wild salmonids depends on farmed fish density but can also be correlated to environmental factors, including foraging ecology. In the current paper we examine niche use and trophic variation of co-occurring Arctic charr and sea trout in northwest Iceland, using stomach contents and stable isotope values of δ13C, δ15N and δ34S. We then test if these factors correlated to salmon lice infection. The salmonid species differed in niche use, for example, in time of marine foraging, with Arctic charr having a longer marine phase than was expected, and in the level of piscivory between both species. Moreover, we show that both environmental factors and individual trophic use are related to salmon lice infection in sea trout. This information may be useful in evaluating the risk and spatial management of sea farming. [ABSTRACT FROM AUTHOR]

Alternative ecotypes of diverse animal taxa exhibit distinct, habitat-specific phenotypes. Rainbow trout (Oncorhynchus mykiss), a salmonid fish, exhibits stream-resident (fluvial), lake-migrant (adfluvial) and ocean-migrant (anadromous) ecotypes throughout its range. We investigated the coloration, and morphology associated with swimming performance of wild, native non-anadromous rainbow trout in connected stream and lake habitats of a south-west Alaskan watershed to assess if they exhibited phenotypic diversity consistent with the presence of alternative fluvial and adfluvial ecotypes. Colour differences among rainbow trout of different size classes and habitats (stream or lake) indicated ecotype-specific pathways, diverging at the same point in ontogeny and resulting in different terminal coloration patterns. Specifically, lake-caught fish exhibited distinct silvering of the body, whereas stream-caught fish displayed banded coloration when small and bronze colour when larger. The morphology of lake-caught rainbow trout also differed from that of stream-caught fish in features associated with swimming performance, and they exhibited both shared and unique morphological patterns compared to sympatric Salvelinus species in those habitats [Dolly Varden (S. malma) in streams, and Arctic char (S. alpinus) in the lake]. Greater morphological variation within stream- than lake-caught rainbow trout, and their limited overlap in morphology, suggested population-specific partial migration. This study highlights the intraspecific diversity of migratory behaviour and how conservation of particular phenotypes depends on managing both for genotypes and for habitats. [ABSTRACT FROM AUTHOR]

Few ecotoxicological studies exist on the accumulation and effects of rare earth elements (REEs) in fish, particularly on Arctic species. In southwest Greenland, there are currently several advanced exploration REE mining projects. The aim of this study was to investigate accumulation of REEs in native fish species. Juvenile arctic chars, Salvelinus alpinus , were pulse-exposed to cerium (Ce), lanthanum (La) and yttrium (Y) using an in-situ flow-through system over a period of 15 days. Results showed that the arctic char accumulated most REEs in the gills > liver > muscle. We also demonstrated the ability of the arctic char to rapidly excrete the REEs throughout the experiment, where levels of post exposure accumulation also declined throughout the period. These results demonstrate the importance of further studies on accumulation of REE in the arctic char native to the site of future mining operations. Long-term exposure will most likely result in accumulation of REEs in arctic char, and the effects and accumulation patterns of this should be explored further. Unlabelled Image • There is an increasing interest in exploration and exploitation of REE resources in Greenland. • This paper is a study of bioaccumulation patterns in juvenile arctic char pulse-exposed to REEs 5 times over 15 days. • ICP-MS analysis of gill, liver and muscles show how the arctic char accumulated REEs in the short periods of exposure. • The analysis also reveals that the arctic char can excrete the REEs rapidly post exposure. • These results demonstrate the importance of further studies on REE accumulation in arctic char in Greenland. [ABSTRACT FROM AUTHOR]

Ecological opportunity is considered a crucial factor for adaptive radiation. Here, we combine genetic, morphological and ecological data to assess species and ecomorphological diversity of Artic charr in six lakes of a catchment in southernmost Greenland, where only charr and stickleback occur. Because the diversity of habitats and resources increases with lake size, we predict a positive association between lake size and the extent of ecomorphological diversity. The largest lake of the catchment harbours the largest Arctic charr assemblage known today. It consists of six genetically differentiated species belonging to five ecomorphs (anadromous, littoral benthic, profundal dwarf, planktivorous, piscivorous), of which the latter comprises two ecomorphologically extremely similar species. Lakes of intermediate size contain two ecomorphologically and genetically distinct species. Small lakes harbour one genetically homogeneous, yet sometimes ecomorphologically variable population. Supporting our prediction, lake size is positively correlated with the extent of ecomorphological specialization towards profundal, pelagic and piscivorous lifestyle. Furthermore, assemblage-wide morphospace increases sharply when more than one genetic cluster is present. Our data suggest that ecological opportunity and speciation jointly determine phenotypic expansion in this charr radiation. [ABSTRACT FROM AUTHOR]

The availability of diverse ecological niches can promote adaptation of trophic specializations and related traits, as has been repeatedly observed in evolutionary radiations of freshwater fish. The role of genetics, environment, and history in ecologically driven divergence and adaptation, can be studied on adaptive radiations or populations showing ecological polymorphism. Salmonids, especially the Salvelinus genus, are renowned for both phenotypic diversity and polymorphism. Arctic charr (Salvelinus alpinus) invaded Icelandic streams during the glacial retreat (about 10,000 years ago) and exhibits many instances of sympatric polymorphism. Particularly, well studied are the four morphs in Lake Þingvallavatn in Iceland. The small benthic (SB), large benthic (LB), planktivorous (PL), and piscivorous (PI) charr differ in many regards, including size, form, and life history traits. To investigate relatedness and genomic differentiation between morphs, we identified variable sites from RNA‐sequencing data from three of those morphs and verified 22 variants in population samples. The data reveal genetic differences between the morphs, with the two benthic morphs being more similar and the PL‐charr more genetically different. The markers with high differentiation map to all linkage groups, suggesting ancient and pervasive genetic separation of these three morphs. Furthermore, GO analyses suggest differences in collagen metabolism, odontogenesis, and sensory systems between PL‐charr and the benthic morphs. Genotyping in population samples from all four morphs confirms the genetic separation and indicates that the PI‐charr are less genetically distinct than the other three morphs. The genetic separation of the other three morphs indicates certain degree of reproductive isolation. The extent of gene flow between the morphs and the nature of reproductive barriers between them remain to be elucidated. [ABSTRACT FROM AUTHOR]

Catchment-scale variation between lake habitats has the potential to simultaneously influence the trophic niche and parasite community of fish hosts. In this study, we investigated the trophic niche and parasite community of sympatric Arctic charr and brown trout populations from two inter-connected southern Norwegian lakes at different altitudes. Arctic charr and brown trout occupied profundal and littoral habitats in each lake, respectively, whereas brown trout replaced Arctic charr in pelagic habitats of the lower altitude lake. Distinct between-lake differences in diet and parasite community composition were noted for brown trout; however, both fish species showed highly overlapping trophically transmitted parasite communities regardless of the habitats each species used. Our results suggest that environmental differences over relatively limited geographical distances have the potential to influence fish habitat use and parasite community structure. [ABSTRACT FROM AUTHOR]

Parallelism in trophic niches of polymorphic populations of Arctic charr was investigated in two similar subarctic lakes, Tårnvatn and Skøvatn, in northern Norway. Analysis of eleven microsatellite loci confirmed, respectively, the existence of three and two genetically differentiated morphs. Three methods were used to describe their trophic niches: habitat choice and stomach contents for the recent feeding behaviour, and trophically transmitted parasites and stable isotopes (δ13C and δ15N) as proxies for the longer term trophic niche differences. The results showed a distinct segregation in trophic resource utilization of the different morphs. Tårnvatn has three morphs: a littoral omnivorous (LO), a small-sized profundal benthivorous (PB), and a large-sized profundal piscivorous (PP). In contrast, a novel Arctic charr morph was discovered in Skøvatn: a small-sized profundal zooplanktivorous-morph (PZ), which when compared to the sympatric LO-morph, had distinct stable isotope values and a contrasting parasite community. A parallelism in habitat choice and external morphology was found among the small-sized, deep-water morphs and between the upper-water, omnivorous LO-morphs in both lakes. There was a no parallel pattern in diet choice between the PB- and the PZ-morphs. These findings show how evolution can produce diverse outcomes, even among systems with apparently similar environmental and ecological conditions. [ABSTRACT FROM AUTHOR]

Niche diversification of polymorphic Arctic charr can be altered by multiple anthropogenic stressors. The opossum-shrimp (Mysis relicta) was introduced to compensate for reduced food resources for fish following hydropower operations in Lake Limingen, central Norway. Based on habitat use, stomach contents, stable isotopes (δ13C, δ15N) and trophically transmitted parasites, the zooplanktivorous upper water-column dwelling 'normal' morph was clearly trophically separated from two sympatric deep-water morphs (the 'dwarf' and the 'grey') that became more abundant with depth (> 30 m). Mysis dominated (50–60%) charr diets in deeper waters (> 30 m), irrespective of morph. Mysis and/or zooplankton prey groups caused high dietary overlap (> 54%) between the 'dwarf' morph and the two other 'normal' and 'grey' morphs. After excluding Mysis, the dietary overlap dropped to 34% between the two profundal morphs, as the 'dwarf' fed largely on deep-water zoobenthos (39%), while the 'grey' morph fed on fish (59%). The time-integrated trophic niche tracers (trophically transmitted parasites and stable isotopes) demonstrated only partial dietary segregation between the two deep-water morphs. The high importance of Mysis in Arctic charr diets may have reduced the ancestral niche segregation between the deep-water morphs and thereby increased their resource competition and potential risk of hybridization. [ABSTRACT FROM AUTHOR]

Anadromous Arctic charr, Salvelinus alpinus, migrate back to freshwater in late summer to spawn and/or overwinter. While seasonal movement patterns during the freshwater residency period are generally understood, specifics of the short temporal activity patterns remain poorly characterized. This study used temperature and accelerometer sensing telemetry to describe the diel activity patterns of 21 overwintering anadromous Arctic charr in a lake in southern Labrador, Canada. Tagged individuals displayed diurnal activity patterns throughout the overwinter residency period marked by greater activity during the day than at night and distinctive peaks of activity at the beginning and the end of each daylight period. Diurnal patterns were interpreted as driven by prey and light availability in the upper water column because of known linkages between light and foraging efficiency. Movement activity also increased as a function of temperature during the spawning and ice breakup periods, but not during winter when increased movement activity was correlated with colder temperatures. No association was found between movement activity and body size over the size range (36.0–48.5 cm) of fish studied. Our data suggest a complex set of behavioural determinants of overwinter activity, among which temperature and foraging are the most significant. [ABSTRACT FROM AUTHOR]

The divergence of reproductive strategies is an important development toward intraspecific diversification. We describe contrasting spawning patterns of parapatric and sympatric Arctic charr forms in two interconnected lakes Kiryalta-3 and Kiryalta-4 in Transbaikalia for comparison to charr reproduction in nine more lakes of this region. In each Kiryalta lake, two charr forms (small and large) differing in growth and diet are present, in Kiryalta-3 they are morphologically more distinct than in Kiryalta-4. In Kiryalta-3, the spawning of the small form was recorded in autumn and spring suggesting two subpopulations; spawning time of the large form is unknown. In Kiryalta-4, both forms spawn in autumn. Overall, reproductive patterns of Transbaikalian charr vary greatly in spawning time, duration, location, depth, and bottom substrate. Different populations and sympatric forms spawn in early or late autumn, spring, summer, or during more than one season, including the littoral or profundal zone, over rocks or silt, and from 1–2 weeks to at least 7 months. Peak spawning time difference between sympatric forms can reach up to 5 months, and is correlated with morphological and genetic differences. Diversification of reproductive strategies largely contributed to the emergence of exceptionally high diversity of Transbaikalian charr. [ABSTRACT FROM AUTHOR]

The trophic ecology of piscivorous Arctic charr (Salvelinus alpinus (L.); charr) in the food webs of large subarctic lakes is not well understood. We assessed charr diets, parasites, growth, maturity, and stable isotope ratios in Fennoscandian subarctic lakes dominated by monomorphic or polymorphic whitefish (Coregonus lavaretus (L.)) populations. Charr density was low in all lakes, except in profundal habitats. Charr shifted to piscivory at small size (16–25 cm total length) and consumed a range of prey-fish sizes (2–25 cm). Cannibalism was observed in a few individuals from one monomorphic whitefish lake. Charr matured at 37–51 cm (5–8 years old), grew to 52–74 cm maximum observed length and 47–83 cm asymptotic length. Charr increased total area of convex hull and core stable isotopic diversity area of the fish community by 51–98% and 44–51% in monomorphic whitefish lakes, but only 8–11% and 7–10% in polymorphic whitefish lakes. The difference was due to increasing food-chain length in monomorphic whitefish lakes, whereas reliance on littoral carbon did not change. Charr were the top piscivores in monomorphic whitefish lakes, but played a less important role in polymorphic whitefish lakes, which contained a more diverse predator fauna. [ABSTRACT FROM AUTHOR]

Trophically transmitted parasites are known to impair fish growth in experimental studies, but this is not well documented in natural populations. For Arctic charr [Salvelinus alpinus (L.)], individual growth is positively correlated with food consumption. However, increased food consumption will increase the exposure to trophically transmitted parasites. Using a correlative approach, we explore the association between parasite abundance and the individual growth of Arctic charr from five lakes within the same watercourse. The studied parasite species differ in their life cycles and cost to the host. We predicted a positive association between parasite abundance and fish growth for parasites of low pathogenicity reflecting high consumption rates, and a negative association at higher parasite abundances for more costly parasites. We found no direct negative associations between parasite abundance and fish growth. The relationship between parasite abundance and growth was linearly positive for the low costly Crepidostomum sp. and concave for the more costly Eubothrium salvelini. In natural fish populations, the negative effects of parasites on fish growth might be outweighed by the energy assimilated from feeding on the intermediate host. However, experimental studies with varying food consumption regimes are needed to determine the mechanisms underlying our observations. [ABSTRACT FROM AUTHOR]

Insights from long-term subsistence fisheries data can improve our understanding of the population-specific responses of Arctic charr, Salvelinus alpinus, to environmental conditions. In this study, associations were found between temporal environmental variation and Arctic charr length- and weight-based growth using data from fish captured in the Hornaday River fishery. Overall, spring precipitation and summer air temperature appear to be the most important environmental influences on Arctic charr probably because of their respective impacts on the opportunities for acquiring surplus energy for growth. A pattern of decreasing age-related importance of temperature and increasing age-related importance of precipitation suggested that the coupling between growth and environmental effects varied by life-period. The changing prominence of each variable seems to result from the shift in apportioning energy for increases in length to increases in weight, likely as a result of the onset of maturation. The linkage of population characteristics to environmental conditions provides a baseline reference against which future data may be compared to determine the significance of any observed changes in population characteristics as a result of continuing ecological change in the north. [ABSTRACT FROM AUTHOR]

The Arctic charr Salvelinus alpinus populations of Windermere, England's largest natural lake in the Lake District of north-west England, have been studied since the 1940s. However, the species' cultural importance has a much longer history and these populations have been fished since 1223. As early as 1660, Arctic charr were exploited in a high-profile commercial net fishery and greatly enjoyed by locals and in a 'potted' form by wealthier members of UK society. However, overfishing led to substantially decreased catches and commercial netting was stopped in 1921. Local fishing for Arctic charr persists to the present as a small recreational plumb-line fishery using artificial lures. These fishing activities and resulting catches have long held great cultural interest for the local community and visiting national and international tourists. The cultural importance of the Arctic charr populations of Windermere has recently been the subject of national media interest that culminated in a 2017 documentary film highlighting environmental issues facing the Arctic charr and also celebrating the role of this iconic species in the cultural life of Windermere. In addition, international recognition of the Arctic charr populations of Windermere also contributed to the Lake District becoming a UNESCO World Heritage Site in 2017. [ABSTRACT FROM AUTHOR]

Parasite distribution patterns in lotic catchments are driven by the combined influences of unidirectional water flow and the mobility of the most mobile host. However, the importance of such drivers in catchments dominated by lentic habitats are poorly understood. We examined parasite populations of Arctic charr Salvelinus alpinus from a series of linear-connected lakes in northern Norway to assess the generality of lotic-derived catchment-scale parasite assemblage patterns. Our results demonstrated that the abundance of most parasite taxa increased from the upper to lower catchment. Allogenic taxa (piscivorous birds as final host) were present throughout the entire catchment, whereas their autogenic counterparts (charr as final hosts) demonstrated restricted distributions, thus supporting the theory that the mobility of the most mobile host determines taxa-specific parasite distribution patterns. Overall, catchment-wide parasite abundance and distribution patterns in this lentic-dominated system were in accordance with those reported for lotic systems. Additionally, our study highlighted that upper catchment regions may be inadequate reservoirs to facilitate recolonization of parasite communities in the event of downstream environmental perturbations. [ABSTRACT FROM AUTHOR]

The article offers information on the occurrence of nodular gill disease in farmed brown trout. Topics discussed include information on the Nodular gill disease (NGD) as an emerging ectoparasitic condition by amoebae causing significant mortality in some species of salmonids farmed in freshwater environment; Nodular gill disease caused by different species of amoebae; and the role of NGD in highly intensive farming systems in production losses.

Summary: Growing interest of Arctic char (Salvelinus alpinus) aquaculture in Europe, and the fact that it can easily hybridize with brook trout (Salvelinus fontinalis) resulting in fertile progeny, led us to investigate fish from the farmed stocks. Chromosomes of sampled Arctic char were examined using conventional and molecular cytogenetic (FISH) techniques in order to determine possible contamination of genomic elements of brook trout. Investigated fish possessed karyotypes composed of 80–82 chromosomes and up to three chromosome fragments. Using staining methods and FISH approach enabled identification of the brook trout chromosomes in the eight out of twenty‐two examined Arctic char. Specific location of AT‐, GC‐ positive and NOR sites observed on chromosomes as well as chromosome fragments in the karyotypes of several individuals points on past chromosomal rearrangements in fish from examined broodstock. Based on our results, it may be assumed that individuals with the brook trout genomic elements, although phenotypically identified as Arctic chars, were hybrids. Our results highlights that special care should be taken to protect gene pools of brook trout and Arctic char in farms where both species are cultured. [ABSTRACT FROM AUTHOR]

Despite PCBs being banned since the 1980's, some European peri-alpine lakes, and consequently their fish populations, are still contaminated by these xenobiotics. We investigated the relative contribution of physiological and trophic factors that could be implicated in fish PCB bioaccumulation in Lake Bourget (France), one of the most contaminated in Europe, by collecting Arctic char (n = 55) and European whitefish (n = 89) from 2013 to 2016. Concentrations of 7 indicator PCBs were 9–168 ng.g w.w−1 in whitefish and 90–701 ng.g w.w−1 in Arctic char. The fish trophic positions calculated from δ 15N values were positively correlated with PCB concentrations (r2 = 0.45; p < 0.001). A biomagnification model relying on TP and lipid content of fish was then designed, and it confirmed this result. A Bayesian mixing model based on δ 13C and δ 15N values was used to estimate the relative contribution of preys in the fish diet, which explained a significant proportion of the biomagnification model residuals (i.e., 17%). Zooplankton consumption was negatively correlated with PCB concentrations, whereas consumption of chironomids enhanced the PCB burden in fish. Correction of the biomagnification model for individual diets of fish increased the correlation between the predicted and measured fish PCB contents (R2 = 0.71; p < 0.001), highlighting the importance of fish feeding habits in the bioaccumulation process. Unlabelled Image • Lipid content and trophic position explained most of fish PCB contamination • A Bayesian mixing model based on δ 13C and δ 15N was used to estimate the relative contribution of preys in the fish diet • A biomagnification model compared measured and predicted PCB concentration in fish and showed good agreement (r2 adj = 0.64) • Contribution of preys in the model improved the correlation, showing the importance of feeding habits in PCB burden in fish [ABSTRACT FROM AUTHOR]

Limited knowledge exists about the residing microbiome in gamete-related samples in fish. A potential effect between the seminal microbiome composition and sperm quality traits has been previously suggested in humans and livestock. Using a metabarcoding approach, we aimed to gain insights into the structure of the residing prokaryotes and microbial eukaryotes in ovarian fluid (n = 10) and milt (n = 84) from farmed Arctic charr - a species with highly variable reproductive success in captivity. In addition, sperm quality traits were recorded on the sampled males to investigate potential associations with the residing seminal microbiome. Higher microbial diversity was found in the ovarian fluid compared to the milt habitat. Even though the residing microbiome showed distinct differences between the two habitats, substantial overlap was observed, with >70% of the milt core microbiome being found in the ovarian fluid habitat. Statistically significant associations were found between the Shannon diversity index and sperm motility-related traits. Additionally, a fungal operational taxonomic unit (OTU) potentially belonging to the Leotiomycetes class was associated with sperm concentration and motility. Overall, our study documents the microbiome structure of gamete-related samples from Arctic charr. Even though some associations were obtained between sperm quality parameters and either microbiome diversity or with a fungal OTU, follow-up studies on a larger scale with more tank replicates are needed to confirm the robustness and causality of these relationships. • First report of the residing microbiome structure in gamete-related samples on fish • Associations were found between the Shannon diversity index and sperm motility-related traits. • A fungal operational taxonomic unit was associated with sperm concentration and motility. [ABSTRACT FROM AUTHOR]

Infectious salmon anaemia virus detected by RT-qPCR in Norwegian farmed rainbow trout, Oncorhynchus mykiss (Walbaum, 1792) Expression of the infectious salmon anemia virus receptor on Atlantic salmon endothelial cells correlates with the cell tropism of the virus. Keywords: infectious salmon anaemia virus; isavirus; persistence; rainbow trout EN infectious salmon anaemia virus isavirus persistence rainbow trout 479 481 3 03/11/21 20210401 NES 210401 Infectious salmon anaemia (ISA), caused by infectious salmon anaemia virus (ISAV), is a notifiable infection of farmed Atlantic salmon, I Salmo salar i L. The disease is characterized by severe anaemia, infection of the circulatory system, bleeding and variable cumulative mortality. [Extracted from the article]

Disease outbreaks are limiting factors for an ethical and economically sustainable aquaculture industry. The first point of contact between a pathogen and a host occurs in the mucus, which covers the epithelial surfaces of the skin, gills and gastrointestinal tract. Increased knowledge on host-pathogen interactions at these primary barriers may contribute to development of disease prevention strategies. The mucus layer is built of highly glycosylated mucins, and mucin glycosylation differs between these epithelial sites. We have previously shown that A. salmonicida binds to Atlantic salmon mucins. Here we demonstrate binding of four additional bacteria, A. hydrophila, V. harveyi, M. viscosa and Y. ruckeri, to mucins from Atlantic salmon and Arctic char. No specific binding could be observed for V. salmonicida to any of the mucin groups. Mucin binding avidity was highest for A. hydrophila and A. salmonicida, followed by V. harveyi, M. viscosa and Y. ruckeri in decreasing order. Four of the pathogens showed highest binding to either gills or intestinal mucins, whereas none of the pathogens had preference for binding to skin mucins. Fluid velocity enhanced binding of intestinal mucins to A. hydrophila and A. salmonicida at 1.5 and 2 cm/s, whereas a velocity of 2 cm/s for skin mucins increased binding of A. salmonicida and decreased binding of A. hydrophila. Binding avidity, specificity and the effect of fluid velocity on binding thus differ between salmonid pathogens and with mucin origin. The results are in line with a model where the short skin mucin glycans contribute to contact with pathogens whereas pathogen binding to mucins with complex glycans aid the removal of pathogens from internal epithelial surfaces. [ABSTRACT FROM AUTHOR]

Abstract Biodensity is a major factor affecting the production and welfare of farmed fishes. Arctic charr (Salvelinus alpinus) (average mass 176.9 ± 3.9 g) were held at biodensities of 30, 60, 90, 120, and 150 kg/m3 (4 replicates per treatment) during a 91 day study which examined key growth, stress physiology, and welfare parameters. During experimentation fish were fed to near satiety, and a random subsample of 20 fish (5 per replicate tank) were collected from each treatment every 21 days. Biodensity was found to have no significant effect on mortality rates or physical fin damage. Growth rates were lower in charr reared at the highest biodensities (120, and 150 kg/m3), while feed efficiency was negatively affected at both the highest (120, and 150 kg/m3) and lowest (30 kg/m3) biodensities. Plasma cortisol indicated that Arctic charr are more stressed at lower biodensities, but was not correlated with growth or feed efficiency measures. The results support an optimal biodensity range for charr culture between 60 and 90 kg/m3 to optimize production and welfare. Highlights • The purpose of this study was to provide an estimation of an optimal biodensity for Arctic charr aquaculture, with emphasis on production performance and welfare. High intensity aquaculture operations rely upon high biodensities which may compromise the welfare of the animals being farmed (Browman et al., 2018 ; Moccia, 2013). Thus, there are two drivers at play in determining an optimal biodensity with respect to the economics of fish growth and production performance, and the ethics associated with welfare consideration. Ultimately, the determination of an optimal biodensity for Arctic charr aquaculture must be the result of the careful consideration of these two approaches. • Biodensity had no effect on mortality, plasma glucose or fin damage (caudal and dorsal). However the combination of reduced growth rates (i.e. lower TGC's) observed at the high densities (120, and 150 kg/m3) and reduced feed efficiency (0.56–0.83) at the extremes (30, 120, and 150 kg/m3) suggest a density between 60 and 90 kg/m3 for optimal economic gains. The morphometric data presented here also provide additional considerations for the choice of stocking density in terms of the potential commercial productivity for Arctic charr. • Alternatively, the results of the welfare analyses show evidence of reduced stress (as assessed by circulating levels of plasma cortisol) at higher biodensities, with fish stocked at 150 kg/m3 exhibiting the lowest levels of all treatments. • These two approaches provide slightly different result on which to base a suggestion of an optimal biodensity. The economics approach suggests stocking at densities >30 kg/m3 and <90 kg/m3 for the benefit of producing product of similar quality while improving feed efficiency and growth. However, stocking at higher densities (150 kg/m3) resulted in reduced stress which is associated with the welfare status of farmed animals (Turnbull et al., 2008). Therefore, using a combination of an economics and ethics based approach, the suggested biodensity for Arctic charr aquaculture is somewhere in the range of 60–90 kg/m3 (actuals 65.1–99.0 kg/m3). Within this range, Arctic charr exhibited optimal feed efficiency and growth while maintaining cortisol levels below the 10 ng/mL which is a nominal threshold of cortisol implied for stressed salmonids (Pickering and Pottinger, 1989). [ABSTRACT FROM AUTHOR]

Given the importance of anadromous Northern Dolly Varden as a consumption staple for northern residents and the climate- and development-related impacts on total mercury (THg) concentrations, temporal changes in northern Dolly Varden THg concentrations were assessed between historical (1986–1988) and contemporary (2011–2013) periods from two rivers in the north-western Canadian Arctic. In the Rat River, mean THg changed from 79 ± 42 ng/g ww in 1986–1988 to 109 ± 44 ng/g ww in 2011–2013, while in the Firth River, THg changed from 126 ± 45 ng/g ww in 1986–1988 to 178 ± 47 ng/g ww in 2011–2012. Length adjusted values indicated increases in the Firth River were driven by the increased size of fish, but increases in the Rat River were not. After factoring in size, δ13C and δ15N, [THg] was found to be most influenced over time by fish size, but also significantly modified by temporal period and foodweb position. Relationships between log[THg] versus fork-length and log[THg] versus δ13C have remained constant over time in the Rat River, but not in the Firth River, while relationships between log[THg] versus δ15N have remained constant in the Firth River, but not in the Rat River. Changes in the significance and the slope of the relationships relating δ13C and δ15N to log[THg] suggests underlying bioaccumulative processes are temporally variant and will be sensitive to climate-driven changes in the aquatic environments within which fish live and feed. [ABSTRACT FROM AUTHOR]

Abstract The reproductive performance of farmed Arctic charr exhibits substantial individual variation. The causes behind this variation have not yet been properly explained, despite the species relatively long history in aquaculture. The aim of the present study was to provide better understanding of the issue by evaluating parent and gamete traits in relation to fertility and offspring viability under routine hatchery conditions. Are losses mainly due to failed fertilisation or mortality? Are maternal or paternal factor more predominant? The study covered sex hormone status of the broodstock, egg traits (egg size and wateriness of egg batches), milt traits (volume, density, and sperm motility characteristics), and symmetry of early cell division. We found that the majority of offspring loss occurred as embryo mortality, although a significant additional loss could be assigned fertilisation failure. Fertilisation and mortality rates were not inter-correlated. Neither of the evaluated egg traits, egg size and wateriness of newly stripped egg batches, proved to be useful indicators of egg quality. With regard to sperm traits, milt density as well as several computer assisted sperm analysis (CASA) parameters, i.e. swimming speed (VAP, VSL, and VCL) and beat cross frequency (BCF), were correlated with reproductive performance and could potentially be used as quality indicators for Arctic charr. Together, male 17,20β-P levels and BCF explained 69.5% of the between male variation in proportion of successfully eyed eggs. The results support previous indications that post-ovulatory aging of oocytes is contributing to the impairment of reproductive performance in farmed Arctic charr. In addition, a significant paternal factor to this impairment has been exposed. However, the cause and mechanism involved are still far from clear. Highlights • Broodstock and gamete traits were evaluated together with fertility and embryo viability under routine hatchery conditions. • Embryo mortality, rather than failed fertilisation, was the main cause for egg loss in the studied Arctic charr broodstock. • Besides post-ovulatory aging of oocytes, paternal fertility issues, which needs to be investigated further, were revealed. [ABSTRACT FROM AUTHOR]

We have generated a high-density, high-throughput genotyping array for characterizing genome-wide variation in Arctic charr (Salvelinus alpinus). Novel single nucleotide polymorphisms (SNPs) were identified in charr from the Fraser, Nauyuk and Tree River aquaculture strains, which originated from northern Canada and fish from Iceland using high coverage sequencing, reduced representation sequencing and RNA-seq datasets. The array was designed to capture genome-wide variation from a diverse suite of Arctic charr populations. Cross validation of SNPs from various sources and comparison with previously published Arctic charr SNP data provided a set of candidate SNPs that generalize across populations. Further candidate SNPs were identified based on minor allele frequency, association with RNA transcripts, even spacing across intergenic regions and association with the sex determining (sdY) gene. The performance of the 86,503 SNP array was assessed by genotyping Fraser, Nauyuk and Tree River strain individuals, as well as wild Icelandic Arctic charr. Overall, 63,060 of the SNPs were polymorphic within at least one group and 36.8% were unique to one of the four groups, suggesting that the array design allows for characterization of both within and across population genetic diversity. The concordance between sdY markers and known phenotypic sex indicated that the array can accurately determine the sex of individuals based on genotype alone. The Salp87k genotyping array provides researchers and breeders the opportunity to analyze genetic variation in Arctic charr at a more detailed level than previously possible. [ABSTRACT FROM AUTHOR]

Temperature and individual egg size have been long studied in the development of fishes because of their direct effects on individual fitness. Here we studied the combined effects of three important factors for fish development, i.e. egg size, social environment and water temperature. Arctic charr (Salvelinus alpinus), a coldwater fish known to be phenotypically plastic, was used to investigate how these factors may affect growth and foraging behaviour of juvenile fish in a benign environment. We accounted for the social environment during early development by comparing fish raised in groups and in isolation. We examined the effect of egg size and a 2 °C difference on foraging behaviour, activity and growth a few weeks after first feeding. Growth trajectories of fish originating from large and small eggs were similar within each temperature: larger fish coming large eggs were at all time larger than smaller fish. There was no indication that small fish raised at a higher temperature grew faster than larger fish raised at a lower temperature. A 2 °C difference in temperature affected the behaviour of fish differently according to body size and/or social context. The foraging probability difference between fish raised in groups and fish briefly isolated was higher at 4.5 °C than at 6.5 °C for both size fish. Finally, there was no repeatability in foraging behaviour and mobility for isolated individuals. These results highlight the importance of small changes in temperature when evaluating growth and behaviour of fishes, and reveal the importance of considering the interaction of temperature with other factors, e.g. individual size and social environment, especially at early stages of development in fishes. We discuss these findings in the context of rapid changes in temperature and how temperature and its interaction with other factors may affect the phenotypes, ecology and evolution of coldwater fishes. [ABSTRACT FROM AUTHOR]

Non‐anadromous forms of Arctic char (Salvelinus alpinus), those that are restricted to lakes and rivers, typically have higher mercury (Hg) concentrations than anadromous forms, which migrate to and from the sea. Using tissue burden data from the literature and our own analyses, we performed a screening‐level risk assessment of methylmercury (MeHg) for non‐anadromous Arctic char. Our assessment included 1569 fish distributed across 83 sites. Site‐specific mean total Hg concentrations in non‐anadromous Arctic char muscle varied considerably from 0.01 to 1.13 µg/g wet weight, with 21% (17 of 83 sites) meeting or exceeding a threshold‐effect level in fish of 0.33 µg/g wet weight, and 13% (11 of 83 sites) meeting or exceeding a threshold‐effect level in fish of 0.5 µg/g wet weight. Of the sites in exceedance of the 0.33‐µg/g threshold, 7 were located in Greenland and 10 in Canada (Labrador, Nunavut, and Yukon). All but one of these sites were located in interfrost or permafrost biomes. Maximum total Hg concentrations exceeded 0.33 µg/g wet weight at 53% of sites (40 of the 75 sites with available maximum Hg values), and exceeded 0.5 µg/g wet weight at 27% (20 of 75 sites). Collectively, these results indicate that certain populations of non‐anadromous Arctic char located mainly in interfrost and permafrost regions may be at risk for MeHg toxicity. This approach provides a simple statistical assessment of MeHg risk to non‐anadromous Arctic char, and does not indicate actual effects. We highlight the need for studies that evaluate the potential toxic effects of MeHg in non‐anadromous Arctic char, as well as those that aid in the development of a MeHg toxic‐effect threshold specific to this species of fish. Environ Toxicol Chem 2019;38:489–502. © 2018 SETAC [ABSTRACT FROM AUTHOR]

In 2017, a PCR‐based survey for Piscine orthoreovirus‐3 (PRV‐3) was conducted in wild anadromous and non‐anadromous salmonids in Norway. In seatrout (anadromous Salmo trutta L.), the virus was present in 16.6% of the fish and in 15 of 21 investigated rivers. Four of 221 (1.8%) Atlantic salmon (Salmo salar L.) from three of 15 rivers were also PCR‐positive, with Ct‐values indicating low amounts of viral RNA. All anadromous Arctic char (Salvelinus alpinus L.) were PCR‐negative. Neither non‐anadromous trout (brown trout) nor landlocked salmon were PRV‐3 positive. Altogether, these findings suggest that in Norway PRV‐3 is more prevalent in the marine environment. In contrast, PRV‐3 is present in areas with intensive inland farming in continental Europe. PRV‐3 genome sequences from Norwegian seatrout grouped together with sequences from rainbow trout (Oncorhynchus mykiss Walbaum) in Norway and Coho salmon (Oncorhynchus kisutch Walbaum) in Chile. At present, the origin of the virus remains unknown. Nevertheless, the study highlights the value of safeguarding native fish by upholding natural and artificial barriers that hinder introduction and spread, on a local or national scale, of alien fish species and their pathogens. Accordingly, further investigations of freshwater reservoirs and interactions with farmed salmonids are warranted. [ABSTRACT FROM AUTHOR]

A comparative analysis of the mitochondrial DNA variability in Salvelinus taranetzi (and closely related taxa) from Asia and Salvelinus alpinus erythrinus from the Northwest Territories (NWT), North America, representing the Arctic phylogenetic group of charrs of the genus Salvelinus, has been carried out. The estimated divergence of the combined nucleotide sequences of the mtDNA CoI and Cytb genes and CR region within the discussed phylogroup varies in the range of 0.001–0.003 and does not exceed the intraspecific variability of S. taranetzi. A genealogical analysis confirms the phylogenetic proximity of S. a. erythrinus from NWT and S. taranetzi from Asia. By assuming a common origin of S. taranetzi and S. a. erythrinus, we have shown a significant differentiation between the geographical populations as a result of probable fragmentation of their common ancestor's range. According to the hierarchical analysis of molecular variance (AMOVA), the intergroup component accounts for the major part (83% of variance) of the mtDNA variability (490 bp, CR) with a low genetic diversity within the groups (10%). The region of Anadyr–Kolyma Basin, which determines the heterogeneity of the phylogroups, stands out on a broad geographical scale. [ABSTRACT FROM AUTHOR]

Samples from 11 populations of the Arctic char of the North-European part of Russia belonging to the anadromous and resident forms and two samples from Lake Sobach'e (Taimyr) were studied. The nucleotide sequence of the mitochondrial COI gene was determined in 60 individuals. In the majority of populations, the same COI haplotype was found. In some populations of the resident chars, haplotypes differing from the widespread haplotype in a single nucleotide substitution were found. The obtained genetic data give no reason to distinguish the resident form of the Arctic char from lakes of Karelia and the Kola Peninsula as an independent species, Salvelinus lepechini. The adaptation of the Arctic char to the unstable environmental conditions is ensured primarily by its phenotypic plasticity. [ABSTRACT FROM AUTHOR]

Abstract Yearling Salvelinus alpinus (ca. 30 g body weight) at constant 10 °C were subjected to one of four food deprivation regimes: Fall (7 weeks no food: Oct. 10 to Nov. 30), Winter (8 weeks: Dec. 1 to Jan. 31), Fall + Winter (15 weeks, Oct. 10 to Jan. 31) or fed to satiation daily (control). Each feeding regime was sub-divided between three photoperiod treatments (n = 70 fish/trt.) each lasting 15 weeks (Oct. 10 to Feb. 1): either 24 h light (LL), 18 h light:6 h dark (LD 18:6) or simulated natural daylength (LDN). On Feb. 1, all fish were returned to daily feeding and LDN for a further 8 months. The incidence of maturation in October age 2 was reduced seven-fold to <6%, (sexes pooled) by both LL and LD 18:6 overwinter compared to 43% in the control (LDN and daily feeding), independent of the feeding regime. Fall + Winter food deprivation under LDN reduced female maturity six-fold to 11%, but male maturity was unaffected (♂:27%). Food deprivation under LDN in fall had no significant effect on maturation (♀:52%; ♂:42%) but in winter was more effective, significantly reducing maturity in both sexes (♀:32%; ♂:15%). The changes in mean body weight and condition factor between incipient maturing and immature charr within treatments through fall and winter were similar. From March onwards, however, mean condition factor decreased significantly following the decrease in photoperiod from LL or LD 18:6 to LDN associated with a low incidence of maturation age 2. Neither food deprivation nor LL raised welfare concerns based on survival, behavior and growth, and the reduction in the maturity was a health benefit. Highlights • Absolute daylength was not important in suppressing maturation. • Food deprivation for 15 weeks reduced the maturity rate among females only. • Animal welfare transgressions from food deprivation and 24 h light were not evident. [ABSTRACT FROM AUTHOR]

Arctic freshwater ecosystems have been profoundly affected by climate change. Given that the Arctic charr (Salvelinus alpinus) is often the only fish species inhabiting these ecosystems, it represents a valuable model for studying the impacts of climate change on species life‐history diversity and adaptability. Using a genotyping‐by‐sequencing approach, we identified 5,976 neutral single nucleotide polymorphisms and found evidence for reduced gene flow between allopatric morphs from two high Arctic lakes, Linne'vatn (Anadromous, Normal, and Dwarf) and Ellasjøen (Littoral and Pelagic). Within each lake, the degree of genetic differentiation ranged from low (Pelagic vs. Littoral) to moderate (Anadromous and Normal vs. Dwarf). We identified 17 highly diagnostic, putatively adaptive SNPs that differentiated the allopatric morphs. Although we found no evidence for adaptive differences between morphs within Ellasjøen, we found evidence for moderate (Anadromous vs. Normal) to high genetic differentiation (Anadromous and Normal vs. Dwarf) among morphs within Linne'vatn based on two adaptive loci. As these freshwater ecosystems become more productive, the frequency of sympatric morphs in Ellasjøen will likely shift based on foraging opportunities, whereas the propensity to migrate may decrease in Linne'vatn, increasing the frequency of the Normal morph. The Dwarf charr was the most genetically distinct group. Identifying the biological basis for small body size should elucidate the potential for increased growth and subsequent interbreeding with sympatric morphs. Overall, neutral and adaptive genomic differentiation between allopatric and some sympatric morphs suggests that the response of Arctic charr to climate change will be variable across freshwater ecosystems. The Arctic charr Salvelinus alpinus (Linnaeus, 1758) has a broad, circumpolar distribution and is the most northerly distributed freshwater fish species (primarily above 60°N; Klemetsen, 2010; Wilson et al., 2004). Using a genotyping‐by‐sequencing approach (Elshire et al., 2011), we investigate how Arctic charr morphs may respond to climate change by identifying neutral and putatively adaptive loci to determine the degree of reproductive isolation among morphs that can be attributed to genetic drift or local adaptation. [ABSTRACT FROM AUTHOR]

Aim: The Pleistocene glaciation event prompted the allopatric divergence of multiple glacial lineages of Arctic char (Salvelinus alpinus), some of which have come into secondary contact upon their recolonization of the Holarctic. While three glacial lineages (Arctic, Atlantic, and Acadian) are known to have recolonized the western Atlantic, the degree of overlap of these three lineages is largely unknown. We sought to determine the distribution of these three glacial lineages in Labrador and Newfoundland at a fine spatial scale to assess their potential for introgression and their relative contribution to local fisheries. Location: Labrador and Newfoundland, Canada. Methods: We sequenced a portion of the D‐loop region in over 1,000 Arctic char (S. alpinus) samples from 67 locations across Labrador and Newfoundland. Results: Within Labrador, the Arctic and Atlantic lineages were widespread. Two locations (one landlocked and one with access to the sea) also contained individuals of the Acadian lineage, constituting the first record of this lineage in Labrador. Atlantic and Acadian lineage individuals were found in both eastern and western Newfoundland. Multiple sampling locations in Labrador and Newfoundland contained fish of two or more different glacial lineages, implying their introgression. Glacial lineage did not appear to dictate contemporary genetic divergence between the pale and dark morph of char present in Gander Lake, Newfoundland. Both were predominately of the Atlantic lineage, suggesting the potential for their divergence in sympatry. Main conclusions: Our study reveals Labrador and Newfoundland to be a unique junction of three glacial lineages which have likely hybridized extensively in this region. Using the D‐loop mitochondrial region, we investigated the extent and potential introgression of three glacial lineages (Arctic, Atlantic, and Acadian) of Arctic char in Labrador and Newfoundland at a fine spatial scale. Our results demonstrate the widespread secondary contact and introgression of these lineages despite thousands of years of allopatric divergence. Glacial lineage was not consistently different between two morphs found in Gander Lake, indicating the potential for the sympatric divergence of this morph pair from an ancestral population founded by multiple glacial lineages. [ABSTRACT FROM AUTHOR]

Abstract The problem of early sexual maturation among farmed Arctic charr and other salmonids can be effectively reduced by 24 h light overwinter, provided it is bright enough to over-ride interference from the natural daylength cycle. To determine the threshold light intensity to suppress the nocturnal elevation of plasma melatonin, three groups of individually tagged fish (n = 26–28/group ca. 1040 g) were reared on 12 h light: 12 h dark (LD 12:12) and subjected to nighttime light intensities of either 50–65, 0.1–0.3 or 0 (control) lux for five months (November to April). Daytime light intensity was 720–750 lx. Diel plasma melatonin profiles in both November and April were similar; mean daytime levels ranged from 20 to 100 pg/ml, and nighttime levels were inversely proportional to light intensity. In the control group at 0 lx, plasma melatonin increased about four-fold after lights-off, ranging between 320 and 430 pg/ml. Nighttime light intensity of 0.1–0.3 lx halved plasma melatonin levels to 140–220 pg/ml, and 50–65 lx further reduced the levels to one quarter of the control group, 68–108 pg/ml. Among the lit groups, daytime plasma melatonin levels were about 20–30 pg/ml, significantly lower than the nocturnal levels suggesting the diel hormonal rhythm was not completely abolished. Fish grew steadily from about 1100 g to 1600 g between November and April, independent of light intensity (P =.67). Overall, the study demonstrated the sensitivity of pineal melatonin hormone to different light intensities in Arctic charr. Highlights • Arctic charr were sensitive to nighttime illumination as low as 0.1–0.3 lx. • Light intensity above 50 lx was effective to suppress the nocturnal plasma melatonin. • Somatic growth was independent of nighttime lighting. [ABSTRACT FROM AUTHOR]

Gene expression during development shapes the phenotypes of individuals. Although embryonic gene expression can have lasting effects on developmental trajectories, few studies consider the role of maternal effects, such as egg size, on gene expression. Using qPCR, we characterize relative expression of 14 growth and/or skeletal promoting genes across embryonic development in Arctic charr (Salvelinus alpinus). We test to what extent their relative expression is correlated with egg size and size at early life‐stages within the study population. We predict smaller individuals to have higher expression of growth and skeletal promoting genes, due to less maternal resources (i.e., yolk) and prioritization of energy toward ossification. We found expression levels to vary across developmental stages and only three genes (Mmp9, Star, and Sgk1) correlated with individual size at a given developmental stage. Contrary to our hypothesis, expression of Mmp9 and Star showed a non‐linear relationship with size (at post fertilization and hatching, respectively), whilst Sgk1 was higher in larger embryos at hatching. Interestingly, these genes are also associated with craniofacial divergence of Arctic charr morphs. Our results indicate that early life‐stage variation in gene expression, concomitant to maternal effects, can influence developmental plasticity and potentially the evolution of resource polymorphism in fishes. [ABSTRACT FROM AUTHOR]

This study finds that non‐native species and warming temperatures have significant negative effects on Arctic char Salvelinus alpinus abundance in Irish lakes. Eutrophication was not important at the range of total phosphorus tested (0.005–0.023 mg l−1). Model results predict that S. alpinus occur across the temperature range sampled (8.2–19.7°C) when non‐natives are absent, but S. alpinus catch is predicted to be close to zero irrespective of temperature when non‐native catch is high. This result indicates that to persist, S. alpinus may require a habitat where non‐natives are at low abundance or absent. Salvelinus alpinus segregated from other species along the thermal axis, inhabiting significantly colder water and actively avoided non‐native species, which appeared to limit their distribution. The thermal niche realized by S. alpinus in non‐native dominated lakes was thus compressed relative to native dominated lakes and S. alpinus population density was significantly lower. These findings were consistent even when the only non‐native present was Perca fluviatilis. Temperature appeared to limit the distribution of non‐native species, such that the presence of deep thermal refugia is currently facilitating S. alpinus co‐existence with non‐natives in associated lakes. Diet analysis identified P. fluviatilis as potential predators and competitors. This study provides strong evidence that non‐native species are a key driver of low S. alpinus abundance in Irish lakes. Temperature increases associated with climate change are identified as a secondary concern, as they could erode S. alpinus' thermal niche and lead to their extirpation. The lower thermal buffering capacity of shallow lakes identifies these as higher risk systems. Salvelinus alpinus conservation in Ireland should focus on preventing future illegal non‐native species introductions because unlike other stressors (e.g., eutrophication etc.), species introductions are rarely reversible. [ABSTRACT FROM AUTHOR]

We review three long‐term research programs performed over the last four decades on the ecology and management of oligotrophic lake systems with different fish communities at 69° N in Norway. Through whole‐lake perturbation experiments, intensive culling of stunted fish removed 35 tons (1984–1991) of Arctic charr Salvelinus alpinus in Takvatn (15 km2) and 153 tons (1981–1983, 2002–2004) of European whitefish Coregonus lavaretus in Stuorajavri (25 km2). In Takvatn, the overcrowded charr population decreased to 20% of the initial abundance, whereas brown trout Salmo trutta abundance increased. Somatic growth improved strongly in both species. In charr, ontogenetic habitat shifts broke down, the diet changed to more benthos, and plankton‐borne parasites decreased. High abundance of juvenile, littoral charr provided new prey for trout, creating an alternative, predator‐regulated stable state. Similar density reductions, positive effects on growth and reduced parasite loads occurred in whitefish in Stuorajavri. Despite the heavy culling, however, a new stable state did not occur and the fish community returned to the pre‐culling situation. In the Pasvik watercourse, vendace Coregonus albula invaded around 1990 after an upstream introduction. The population of this non‐native, highly specialized planktivore increased rapidly, resulting in steep density declines in zooplankton and the native planktivorous whitefish morph, and large changes in energy flow and structure and dynamics of the lacustrine food web. These programs show that long‐term research is essential for understanding the ecology of manmade disturbances and providing a scientific basis for management efforts. [ABSTRACT FROM AUTHOR]

Abstract Refeeding, following a period of food deprivation will often lead to compensatory growth. Although many studies have focused on molecular mechanisms behind this accelerated growth response in fish, little is known on the roles of protein and metabolism. We also assessed, for the first time, the potential roles of miRNAs in regulating compensatory growth. Artcic charr, Salvelinus alpinus , a northern freshwater species, was deprived of food for 101 days and then fed to satiety for 126 days. The refeeding period resulted in compensatory growth, with a partial compensation of body mass. The feed deprivation period lead to a decrease in hepatosomatic index (HSI) and intestinal somatic index (ISI). HSI and ISI were then gradually replenished during early refeeding, following a lag phase prior to the compensatory growth response. mRNA transcripts regulating protein degradation via the autophagy pathway (Cathepsin D and Cathepsin L) in muscle were upregulated during feed restriction and downregulated after refeeding, which could allow for greater protein accretion in muscle, facilitating compensatory growth. Transcript levels from the ubiquitin proteasome pathway (Mafbx and Murf1) and the calpain system (Calpain 7 and Calpastatin) suggested that these pathways were not involved in regulating compensatory growth. Furthermore, we've shown that miRNAs (miR-29a and miR-223) could be involved in fish glycogen homeostasis during the early stages of refeeding. These findings provide a deeper understanding of the molecular mechanisms regulating growth in fish. [ABSTRACT FROM AUTHOR]

Anadromous Arctic char (Salvelinus alpinus) migrate back to fresh water in late summer to spawn and (or) overwinter. Upon freshwater entry, feeding is reduced or absent, and movement activity is restricted. While the physiological responses to low temperatures (e.g., growth, metabolism) are understood, specifics of the use of thermal habitat for overwintering remains poorly characterized. This study used acoustic and archival telemetry data from two lakes in southern Labrador, Canada, to study thermal habitat use during the ice-covered period. Results showed that lake-dwelling anadromous Arctic char predominantly occupied a narrow range of temperatures (0.5–2 °C) and used cooler temperatures available within the middle and upper water column. Use of the selected temperatures is likely a strategy that lowers metabolic costs and minimizes energy expenditure, preserving stored lipids for overwinter survival and the energetic costs of preparation for seaward migration. As Arctic char are visual feeders, use of the upper water column is also thought to aid foraging efficiency by increasing the likelihood of prey capture. [ABSTRACT FROM AUTHOR]

Abstract: This experiment investigated a blood smear method as an alternative to flow cytometry for ploidy determination in Arctic charr, Salvelinus alpinus. Fertilized eggs were either treated with hydrostatic pressure (putative triploids) or untreated (diploid controls), and the embryos, alevins, and juveniles were then reared under identical conditions. Blood samples were collected from alevins (2 g average body weight) for blood smear analysis, and from juveniles (120 g average weight) for both blood smear analysis and flow cytometry. Student's t tests revealed significant (p < 0.0001) differences in mean erythrocyte length between the two groups, with pressure‐treated fish having higher values than the control group as alevins (20.43 ± 0.53 μm and 15.90 ± 0.45 μm respectively) and juveniles (22.83 ± 0.66 μm and 17.68 ± 0.45 μm respectively). Ploidy assignment obtained with blood smear analysis perfectly matched results obtained with flow cytometry. The blood smear method is therefore a valid, simple, and less expensive alternative to flow cytometry for the assessment of ploidy level in Arctic charr. [ABSTRACT FROM AUTHOR]

The Swedish breeding program for Arctic charr ( Salvelinus alpinus L.) has been running for 30 years and includes seven selected generations. In this study, we evaluated the differences in growth between the first generation of selected Arctic charr and the present generation. We demonstrate that not only has growth been improved through selective breeding but also that a change in the seasonal growth capacity has occurred. Selection has induced a high winter growth capacity, but the largest weight gain between generations was seen during summer. As a result of selective breeding, the production time to reach a slaughter weight of 600–700 g has been reduced by 10 months since the start of the breeding program in 1985, and improvements in the final weight have been of the magnitude of 11% per generation. To be able to keep up with the faster growth and altered seasonality of this strain, feeding management needs to be adapted. In this study, a model based on the theoretical energy need of the Arctic charr is presented, which makes it possible to make such adaptions in feeding management. [ABSTRACT FROM AUTHOR]