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ABSTRACT Background Aims Methods and Results Conclusions Toxoplasma gondii is a very common zoonotic parasite in humans and animals worldwide. Human seroprevalence is high in some regions of Canada's North and is thought to be associated with the consumption of traditionally prepared country foods, such as caribou, walrus, ringed seal and beluga. While numerous studies have reported on the prevalence of T. gondii in these animals, in the general absence of felid definitive hosts in the North there has been considerable debate regarding the source of infection, particularly in marine mammals. It has been proposed that fish could be involved in this transmission.The objectives of the present study were to perform a targeted survey to determine the prevalence of T. gondii DNA in various tissues of anadromous Arctic charr sampled in Nunavik, Québec, and to investigate the possible role of this commonly consumed fish in the transmission of infection to humans and marine mammals in Canada's North.A total of 126 individual Arctic charr were sampled from several sites in Nunavik, and various tissues were tested for the presence of T. gondii DNA using PCR. Overall, 12 out of 126 (9.5%) Arctic charr tested in the present study were PCR‐positive, as confirmed by DNA sequencing. Brain tissue was most commonly found to be positive, followed by heart tissue, while none of the dorsal muscle samples tested were positive.Although the presence of T. gondii DNA in brain and heart tissues of Arctic charr is very intriguing, infection in these fish, and their possible role in the transmission of this parasite to humans and marine mammals, will need to be confirmed using mouse bioassays. Arctic charr are likely exposed to T. gondii through the ingestion of oocysts transported by surface water and ocean currents from more southerly regions where the definitive felid hosts are more abundant. If infection in Arctic charr can be confirmed, it is possible that these fish could play an important role in the transmission of toxoplasmosis to Inuit, either directly through the consumption of raw fish or indirectly through the infection of fish‐eating marine mammals harvested as country foods. [ABSTRACT FROM AUTHOR]

Background: Seasonal movements of animals often result in the transfer of large amounts of energy and nutrients across ecosystem boundaries, which may have large consequences on local food webs through various pathways. While this is known for both terrestrial- and aquatic organisms, quantitative estimates on its effects on food web structure and identification of key pathways are scarce, due to the difficulty in obtaining replication on ecosystem level with negative control, i.e. comparable systems without migration. Methods: In this study, we estimate the impact of Arctic charr (Salvelinus alpinus) migration on riverine ecosystem structure, by comparing multiple streams with strictly resident populations above natural migration barriers with streams below those barriers harboring partially migratory populations. We compared density estimates and size structure between above and below populations. Diet differences were examined through the analysis of stomach contents, changes in trophic position were examined by using stable isotopes. To infer growth rate of resident individuals, back-growth calculation was performed using otoliths. Results: We find higher densities of small juveniles in partially migratory populations, where juvenile Arctic charr show initially lower growth, likely due to higher intraspecific competition. After reaching a size, where they can start feeding on eggs and smaller juveniles, which are both more frequent in partially migratory populations, growth surpasses that of resident populations. Cannibalism induced by high juvenile densities occurred almost exclusively in populations with migration and represents an altered energy pathway to the food web. The presence of large cannibalistic charr feeding on smaller ones that have a similar trophic level as charr from strictly resident populations (based on stomach content) coupled with steeper δ15N-size regression slopes illustrate the general increase of food chain length in systems with migration. Conclusions: Our results thus suggest that the consumption of migration-derived resources may result in longer food chains through middle-up rather than bottom-up effects. Furthermore, by occupying the apex of the food chain and feeding on juvenile conspecifics, resident individuals experience reduced competition with their young counterparts, which potentially balances their fitness with migratory individuals. [ABSTRACT FROM AUTHOR]

We explore optimal harvest conditions for Nunatsiavut's Arctic charr, a data-deficient yet economically and culturally important fishery for Labrador Inuit. In the past, arbitrarily set quotas in the absence of data on science and climate shifts have led to sustainability concerns. The fishery, adhering to conservation principles, continues at low intensity today, so as to support local employment and maintain sociocultural values, despite its low economic viability. Using the only available data for Nain's commercial fishery, we estimate intrinsic growth, catchability, and carrying capacity, which we then use in a bioeconomic model to estimate maximum economic yield. Results indicate that foregone commercial harvests are 75%–93% below optimal, before accounting for subsistence harvest. Improved understanding of the conditions under which subsistence and commercial fishing coexist alongside more investments in data collection to address scientific uncertainty can help provide clearer management guidance to meet harvest needs of both sectors and allow for better policies and governance of the fishery. [ABSTRACT FROM AUTHOR]

Trophic polymorphism and temporal reproductive isolation are the drivers of sympatric differentiation in many fish taxa. We present a new case of ecologically based diversification of Arctic charr in a Transbaikalian mountain lake inhabited by reproductively isolated dwarf and normal forms. These forms differ in size, diets and morphology and breed, respectively, in April–May and in September–October representing a rare example of sympatric spring- and autumn-spawning charr pair. Microsatellite analysis reveals clear-cut genetic differences and low-level hybridization between them. Dwarf form charr are planktivorous and manifest uniform slow growth. Normal form charr, though genetically homogeneous, are highly heterogeneous in size-at-age. They are subdivided into omnivorous small-size and piscivorous large-size groups, which can be considered as incipient forms at an early divergence stage. As evidenced by back-calculated growth data, their size-at-age heterogeneity results from highly variable individual growth patterns, which include different combinations of slow and fast growth periods presumably associated with spawning and non-spawning years. Growth acceleration in late ontogeny may result in the transformation of some normal charr from the smaller into the larger group during their lifetime. [ABSTRACT FROM AUTHOR]

Temperature variation is affecting fish biodiversity worldwide, causing changes in geographic distribution, phenotypic structure, and even species extinction. Incubation is a critical stage for stenothermic species, which are vulnerable to large temperature fluctuations, and its effects on the phenotype at later developmental stages are understudied, despite the fact that the phenotype being essential for organism ecology and evolution. In this study, we tested the effects of heat shocks during the embryonic period on the phenotype of Arctic charr (Salvelinus alpinus). We repeatedly quantified multiple phenotypic traits, including morphology, development, and behavior, over a period of 4 months, from hatching to juvenile stage in individuals that had experienced heat shocks (+ 5°C on 24 h, seven times) during their embryonic stage and those that had not. We found that heat shocks led to smaller body size at hatching and a lower sociability. Interestingly, these effects weakened throughout the development of individuals and even reversed in the case of body size. We also found an accelerated growth rate and a higher body condition in the presence of heat shocks. Our study provides evidence that heat shocks experienced during incubation can have long‐lasting effects on an individual's phenotype. This highlights the importance of the incubation phase for the development of ectothermic organisms and suggests that temperature fluctuations may have significant ecological and evolutionary implications for Arctic charr. Given the predicted increase in extreme events and the unpredictability of temperature fluctuations, it is critical to further investigate their effects on development by examining fluctuations that vary in frequency and intensity. [ABSTRACT FROM AUTHOR]

Lakes in the High Arctic are characterized by their low water temperature, long-term ice cover, low levels of nutrients, and low biodiversity. These conditions mean that minor climatic changes may be of great importance to Arctic freshwater organisms, including fish, by influencing vital life history parameters such as individual growth rates. In this study, Arctic charr sampled from two Svalbard lakes (78–79° N) over the period 1960–2008 provided back-calculated length-at-age information extending over six decades, covering both warm and cold spells. The estimated annual growth in young-of-the-year (YOY) Arctic charr correlated positively with an increasing air temperature in summer. This increase is likely due to the higher water temperature during the ice-free period, and also to some extent, due to the winter air temperature; this is probably due to thinner ice being formed in mild winters and the subsequent earlier ice break-up. However, years with higher snow accumulation correlated with slower growth rates, which may be due to delayed ice break-up and thus a shorter summer growing season. More than 30% of the growth in YOY charr could be explained specifically by air temperature and snow accumulation in the two Arctic charr populations. This indicated that juvenile Svalbard Arctic charr may experience increased growth rates in a future warmer climate, although future increases in precipitation may contradict the positive effects of higher temperatures to some extent. In the longer term, a warmer climate may lead to the complete loss of many glaciers in western Svalbard; therefore, rivers may dry out, thus hindering migration between salt water and fresh water for migratory fish. In the worst-case scenario, the highly valuable and attractive anadromous Arctic charr populations could eventually disappear from the Svalbard lake systems. [ABSTRACT FROM AUTHOR]

Iteroparity occurs when organisms reproduce more than once, and is seen as a bet-hedging reproductive strategy. Despite a wealth of research on iteroparous Atlantic salmon, steelhead, brown trout, and Arctic charr, the determinants of reproductive investment, the intra- and interspecific differences in the degree of iteroparity, the drivers of repeat spawning, and the contribution of repeat spawners to populations and sustainability remain unclear. In particular, the knowledge base is stronger for Atlantic salmon and brown trout, but relatively weak for Arctic charr and steelhead. While juveniles, maiden spawners and repeat spawners are facing similar challenges, many threats specific to the kelt stage are emerging (e.g., downstream migration passed barriers after spawning). Recent work has quantified the benefits of iteroparity for population resilience, and the potential for iteroparity to increase when anthropogenic stressors are mitigated. This is the first literature review paper synthetizing the growing knowledge base that exists on various aspects of the ecology and biology of repeat spawners in freshwater and at sea, the threats they face, the proximate and ultimate mechanisms underlying iteroparity in salmonids, the importance of iteroparity for population-level processes, as well as highlighting pressing areas of research. Collectively, this work offers a valuable resource to fisheries scientists and managers by shedding light on an important life-history stage that warrants more attention to mitigate these threats and restore healthy wild salmonid populations. [ABSTRACT FROM AUTHOR]

Background: Substantial variation in male fertility is regularly observed in farmed Arctic charr. However, detailed investigations of its fluctuation during a reproductive season and across years are lacking. Furthermore, information about the effect of underlying genetic factors influencing sperm quality is scarce. The current study focused on seasonal and age-related factors that may affect sperm quality characteristics in males reared in natural and delayed photoperiods. Animals were sampled three times for two consecutive years, and sperm quality parameters were recorded using a computer-assisted sperm analysis (CASA) system. Thereafter, high-throughput sequencing technologies were applied, aiming to identify genomic regions related to the variation of sperm quality throughout the reproductive season. Results: An across-season variation in the recorded sperm quality parameters was evident. Overall, 29% and 42% of males from the natural and delayed spawning groups had a highly variable total progressive motility. Males at four years of age showed significantly higher sperm motility and velocities during the early October and November recordings compared to the following year when the same animals were five years of age. On the other hand, the opposite was observed regarding sperm concentration during the last sampling. A genome-wide FST scan detected SNP differentiation among males with high and low variability in total progressive motility (PM) on eight chromosomes (FST > 0.17), Genome wide windows with the highest FST contained SNPs in proximity (within 250 kb up- and downstream distance) to 16 genes with sperm quality biological functions in mammalian species. Conclusion: Our findings provide a detailed view of seasonal, age-related, and genetic effects on sperm quality and can be used to guide decisions on broodstock selection and hatchery management. [ABSTRACT FROM AUTHOR]

Arctic charr (Salvelinus alpinus [L.] complex) has been widely used as a model system for studies in evolutionary ecology because of its diversity in feeding ecology, habitat use, life history forms, and associated morphologies observed in matured individuals. However, we still know relatively little about traits exhibited early in life of the species, although the trait diversity of matured individuals may largely be shaped during development. Egg size is a key determinant of various traits exhibited early in life. Therefore, describing egg size variation within- and between-individuals as well as the link between egg size and adult traits will be a useful step in understanding the early life trait diversity of Arctic charr. Here, using Greenlandic Arctic charr, which includes alternative life history forms (i.e. anadromous and resident) and spawning habitat use (i.e. lake and river spawner), we described egg size variation (i.e. clutch-mean egg diameter and within-clutch variation) and explored the link between egg size variation and female body length, life history form, and spawning habitats. As in many other fishes, clutch-mean egg diameter increased with female body length. No significant effect of other female traits on clutch mean-egg diameter was detected, suggesting that female body size variation could be a direct cause of early life history trait variation. On the other hand, we found that the degree of within-clutch variation of the anadromous life history form was higher than that of the resident life history form. The pattern could be interpreted in an adaptive context. For instance, given that the anadromous life history form tends to be semelparous, anadromous females could decrease the likelihood of complete reproductive failure by producing variable-sized offspring within a clutch since at least some offspring are expected to be matched to the prevailing environment. [ABSTRACT FROM AUTHOR]

Arctic charr (Salvelinus alpinus) is a niche‐market high‐value species for Nordic aquaculture. Similar to other salmonids, both anadromous and landlocked populations are encountered. Whole‐genome re‐sequencing (22X coverage) was performed on two farmed populations of anadromous (Sigerfjord; n = 24) and landlocked (Arctic Superior; n = 24) origin from Norway and Sweden respectively. More than 5 million SNPs were used to study their genetic diversity and to scan for selection signatures. The two populations were clearly distinguished through principal component analysis, with the mean fixation index being ~0.12. Furthermore, the levels of genomic inbreeding estimated from runs of homozygosity were 6.23% and 8.66% for the Norwegian and the Swedish population respectively. Biological processes that could be linked to selection pressure associated primarily with the anadromous background and/or secondarily with domestication were suggested. Overall, our study provided insights regarding the genetic composition of two main strains of farmed Arctic charr from Scandinavia. At the same time, ample genomic resources were produced in the magnitude of millions of SNPs that could assist the transition of Nordic Arctic charr farming in the genomics era. [ABSTRACT FROM AUTHOR]

Host density, host body size and ambient temperature have all been positively associated with increases in parasite infection. However, the relative importance of these factors in shaping long‐term parasite population dynamics in wild host populations is unknown due to the absence of long‐term studies. Here, we examine long‐term drivers of gill lice (Copepoda) infections in Arctic charr (Salmonidae) over 32 years. We predicted that host density and body size and water temperature would all positively affect parasite population size and population growth rate. Our results show that fish size was the main driver of gill lice infections in Arctic charr. In addition, Arctic charr became infected at smaller sizes and with more parasites in years of higher brown trout population size. Negative intraguild interactions between brown trout and Arctic charr appear to drive smaller Arctic charr to seek refuge in deeper areas of the lake, thus increasing infection risk. There was no effect of host density on the force of infection, and the relationship between Arctic charr density and parasite mean abundance was negative, possibly due to an encounter‐dilution effect. The population densities of host and parasite fluctuated independently of one another. Water temperature had negligible effects on the temporal dynamics of the gill lice population. Understanding long‐term drivers of parasite population dynamics is key for research and management. In fish farms, artificially high densities of hosts lead to vast increases in the transmission of parasitic copepods. However, in wild fish populations fluctuating at natural densities, the surface area available for copepodid attachment might be more important than the density of available hosts. [ABSTRACT FROM AUTHOR]

It is considered that allopatric speciation proceeds slower than sympatric speciation and rarely results in rapid differentiation of populations. In particular, high intraspecific divergence in fishes from recently glaciated freshwater systems is typically observed within flocks of sympatric forms, not between geographically isolated populations. We present an alternative case of fast and profound eco-morphological and genetic divergence between two allopatric Transbaikalian populations of Arctic charr. In one, charr are predominantly piscivorous with sparse short gill rakers; in the other, predominantly planktivorous with dense long gill rakers. Gill raker number differs with no overlap and there is considerable differentiation in other meristic and morphometric characters. Both populations manifest exceptionally low variability at microsatellite loci coupled with substantial interpopulational differences in allele composition obviously resulting from genetic drift. Still, they form a monophyletic clade in microsatellite phylogenetic tree of Transbaikalian charr and share the same mtDNA control region haplotype, which evidences their common origin. According to genetic dating, the divergence of the populations occurred about 14 thousand years ago. Our study shows that high differentiation between local charr populations can emerge in allopatry over a short time if speciation is driven by trophic specialization and is facilitated by small population sizes. [ABSTRACT FROM AUTHOR]

The formation of reproductive isolation barriers is fundamental to sympatric speciation. In teleost fishes, an important mechanism for the reduction of gene flow between emerging species and intraspecific forms is the divergence in reproductive strategies, in particular in spawning time. Large time difference between spawning periods of sympatric forms typically provides strong pre-zygotic isolation and rapid genetic and morphological divergence between them. However, our results indicate that it may not always be the case. We investigated genetic divergence between recently discovered autumn-spawning and spring-spawning subpopulations of the small planktivorous Arctic charr form in one of the Transbaikalian lakes using 14 microsatellite loci and found that it was very low (Fst = 0.0028) as compared with their differentiation from a sympatric large piscivorous form (Fst = 0.284–0.301). Charr of these subpopulations manifested subtle differences in morphology and life history and had similar diets. We consider that low genetic, phenotypic and ecological differentiation between autumn and spring spawners of the small form is the result of their incomplete reproductive isolation due to the transformation between them (change of spawning time) in successive generations. [ABSTRACT FROM AUTHOR]

One of the greatest challenges for researchers today is understanding climate-change impacts on fish populations, particularly in vulnerable and understudied ecosystems such as the Canadian Arctic. Among other impacts, northern fishes will undergo thermal stress as atmospheric and sea surface temperatures are projected to rise globally. Models that consider how both environmental factors such as temperature and potential species interactions will impact population extirpation and species’ range contraction can help project the future distribution of a species in the face of a warming climate. Here, we investigate the climate-change impacts of rising temperatures and the potential northward distributional shift of brook charr (Salvelinus fontinalis) on Arctic charr (Salvelinus alpinus), Canada’s northernmost freshwater fish species. Specifically, we used a logistic regression model to establish baseline relationships between the current distribution of Arctic charr and the variables, degree-days (a key climate variable), geographical location, and brook charr occurrence. We developed the model applying the expected changes in degree-days to 2050 (25–50% increase from the average of 1976–2005) and 2080 (50–100% increase) while incorporating the historical distribution of Arctic charr to estimate the change in Arctic charr distribution over that time. We found that growing degree-days, longitude, latitude, and brook charr occurrences correctly classified 93% of Arctic charr historical occurrences in Canada. We estimate that in a high-carbon scenario, where degree-days are expected to increase by 50 to 100%, Arctic charr range is projected to decrease by 18% in Canada by 2051–2080 and decrease even further by 3% with the presence of brook charr. The Canadian high Arctic may provide refuge for Arctic charr, likely maintaining temperatures optimal for species persistence. Regardless, management that considers the climate stresses on Arctic charr populations will be important to preserve this highly valued resource that is pivotal for food security and traditional ways of life for northerners. [ABSTRACT FROM AUTHOR]

Arctic charr has emerged as a valuable candidate for diversifying commercial salmonid products for human consumption. The selective process is ongoing and the species has not been fully domesticated yet. Considering these factors, the impact of fish meal replacement on Arctic charr may differ from that observed in other farmed salmonids. The aim of this multidiciplinary study was to determine whether enhancements to SBM (enzyme pre-treatment and prebiotic addition) facilitate beneficial changes in the growth performance, gut microbiome, and behavior of Arctic charr. The results show that juvenile Arctic charr can tolerate relatively high inclusion levels (25 %) of soybean when supplemented with a prebiotic. However, enzyme pre-treatment of SBM had no beneficial effect on this species. The gut microbiota, mainly consisting of one dominant taxon, Mycoplasma sp., did not appear to be influenced by feed-related bacterial remnants or by the type of feed applied. Behavioral differences and similarities were observed in fish fed different diets. High consistency in the exploration trait was noted, with no impact of diet treatment on its mean value. A response to light stress on swimming activity occurred, regardless of diet treatment. Fish fed the untreated soybean diet exhibited greater boldness, while those fed the enzyme pre-treated diet showed high consistency in boldness. A negative correlation between boldness and growth performance was identified; however, no relationship was found between exploration and growth performance, nor was there a boldness-exploration syndrome in fish fed any of the diet treatments. These differences could not be attributed to variations in the gut microbiome, but other mechanisms that remain to be elucidated might be involved. Further research is needed on the impact of dietary proteins on the behavior and welfare of Arctic charr to optimize existing and new protein sources. • Impact of enhancements to soybean meal is assessed on Arctic charr. • Traits such as growth, gut microbiome and behavior are examined. • High inclusion levels (25 %) of soybean, when supplemented with a prebiotic, could be successfully used. • Microbiota does not appear to be influenced by the diets. • Behavior consistency and mean value vary according to diets. [ABSTRACT FROM AUTHOR]

Simple Summary: Fish is an important source of nutritious fatty acids, which are necessary for the prevention of cardiovascular and neurological diseases. Many fish species are a major component of the human diet, especially for indigenous peoples from Siberia, Russia, but information about their fatty acid profiles is scarce. We studied the fatty acid content of four salmonid fish (Arctic cisco, least cisco, muksun, and Arctic charr) inhabiting water bodies of the Gydan Peninsula, Kara Sea basin. We found a high content of essential polyunsaturated fatty acids in local salmonid fishes. Arctic charr was the fish species with the highest concentration of fatty acids in the flesh. The results of our multivariate analysis may be useful for anglers, stakeholders, and local consumers. We assayed fatty acids in the flesh of Arctic cisco Coregonus autumnalis (adult and juvenile), least cisco Coregonus sardinella, muksun Coregonus muksun, and Arctic charr Salvelinus alpinus inhabiting water bodies of the Gydan Peninsula, Siberia, Russia. The highest concentrations of total and polyunsaturated fatty acids (PUFAs) were found in Arctic charr (27.8 and 9.5 mg g−1) and adult Arctic cisco (20.2 and 7.6 mg g−1), while the lowest concentrations occurred in juvenile Arctic cisco (7.5 and 3.6 mg g−1). Multivariate analyses divided all studied fish into five distinct groups with the highest similarity between least cisco and muksun and the highest dissimilarity between juvenile Arctic cisco and Arctic charr. Coregonid fish from the study area had a higher content of docosahexaenoic and eicosapentaenoic acids than their conspecifics from subarctic and temperate habitats. The flesh of the studied fish is a source of a healthy diet for humans. Taking into account that all the studied fish are components of the traditional diet of indigenous peoples in northwestern Siberia, our data may be useful not only for local consumers and anglers but also for stakeholders focused on food policy and food security in the area. [ABSTRACT FROM AUTHOR]

The ecology of salmonids is tightly linked to their spawning habitats, but the link between spawning site selection and phenology is poorly understood. To address this, we studied the Arctic charr (Salvelinus alpinus) from the postglacial lake Thingvallavatn (Iceland) through a multidisciplinary approach involving aerial surveys, behavioural observations, temperature monitoring and embryo rearing experiments. Aerial footage revealed that most nests (i.e. redds) were established in shallow parts of the spawning area, and we reported through direct observations trends for stronger male–male competition and for more frequent courtship behaviours in shallow than in deep redds. While water depth did not correlate with temperature at the time of spawning, the temperatures recorded at the shallow redds were consistently lower in the two months following the video recordings, likely because of the proximity of glacial outlets. Laboratory experiments demonstrated that the temperature regimes in shallow waters can delay hatching with about a month, likely impacting the phenology of the offspring. The viability of the Arctic charr in Thingvallavatn may thus depend on physical features like groundwater springs and upwelling water flows acting as "temperature shelters". [ABSTRACT FROM AUTHOR]

Arctic charr Salvelinus alpinus (L.) complex has two or more sympatric forms in many lakes representing a subject for discussions on the mechanisms of their origin and taxonomic status. To determine the number of sympatric forms in three large lakes of the Norilo-Pyasinskaya water system (Taimyr) and their reproductive and phylogenetic relationships, 17 microsatellite loci, sequences of the mtDNA control region, and several morphological characteristics were analyzed. Our data indicate that eight reproductively isolated forms inhabit lakes Lama and Kapchuk, and at least three forms are distributed in Lake Sobach'e. The origin of the forms is associated with the secondary contact and hybridization of the European and Siberian phylogenetic lineages. The same names of the forms from different lakes of Taimyr and Chukotka, for example, Boganida charr and Dryagin's charr, may reflect their certain morphological similarity, but rarely close relationships. Our data indirectly indicate that introgressive hybridization and biogeographical changes of the lakes within the region in the last glacial and post-glacial periods played a significant role in the formation of a high Arctic charr biodiversity. The problem associated with systematics, taxonomy, and conservation of the forms in Taimyr lakes is complex and should be solved gradually. [ABSTRACT FROM AUTHOR]

Trait expression of natural populations often jointly depends on prevailing abiotic environmental conditions and predation risk. Copepods, for example, can vary their expression of compounds that confer protection against ultraviolet radiation (UVR), such as astaxanthin and mycosporine‐like amino acids (MAAs), in relation to predation risk. Despite ample evidence that copepods accumulate less astaxanthin in the presence of predators, little is known about how the community composition of planktivorous fish can affect the overall expression of photoprotective compounds. Here, we investigate how the (co‐)occurrence of Arctic charr (Salvelinus alpinus) and threespine stickleback (Gasterosteus aculeatus) affects the photoprotective phenotype of the copepod Leptodiaptomus minutus in lake ecosystems in southern Greenland. We found that average astaxanthin and MAA contents were lowest in lakes with stickleback, but we found no evidence that these photoprotective compounds were affected by the presence of charr. Furthermore, variance in astaxanthin among individual copepods was greatest in the presence of stickleback and the astaxanthin content of copepods was negatively correlated with increasing stickleback density. Overall, we show that the presence and density of stickleback jointly affect the content of photoprotective compounds by copepods, illustrating how the community composition of predators in an ecosystem can determine the expression of prey traits that are also influenced by abiotic stressors. [ABSTRACT FROM AUTHOR]

Females in mutually ornamented species are often less conspicuously ornamented than their male conspecifics. It has been hypothesized that offspring quality may decrease if females invest more resources into ornaments at the expense of resources in eggs. An experiment was carried out to test whether natural variation in carotenoid in the eggs from a wild population of Arctic charr (Salvelinus alpinus) was associated with survival and growth of their offspring until hatching. Wild Arctic charr were caught at a spawning ground during the spawning period. Eggs from two different females, one female with yellowish carotenoid‐rich eggs and one with paler eggs, were fertilized by sperm from the same male. This was repeated until gametes were collected from 42 females and 21 males, giving a total of 21 groups. After fertilization, the zygotes from each of the two females were reared in four replicated groups. These 168 groups were reared separately until hatching when the surviving larvae were counted and their body length measured. For the two response variables survival and body length at hatching, no effect was demonstrated of any of the predictors (i) amount of carotenoid in the unfertilized eggs, (ii) the mothers' body condition, or (iii) ornament intensity of their red carotenoid‐based abdominal ornament. Thus, this study gives no support for the hypothesis that females investing less carotenoid into their eggs suffer from decreased offspring quality until hatching. This lack of association between female ornament intensity and their fitness is not as expected if female ornaments evolved due to direct sexual selection from males on the more ornamented females ("direct selection hypothesis"). [ABSTRACT FROM AUTHOR]

Routine implementation of genomic information for guiding selection decisions is not yet common in the majority of aquaculture species. Reduced representation sequencing approaches offer a cost‐effective solution for obtaining genome‐wide information in species with a limited availability of genomic resources. In the current study, we implemented double‐digest restriction site‐associated DNA sequencing (ddRAD‐seq) on an Arctic charr strain with the longest known history of selection (approximately 40 years) aiming to improve selection decisions. In total, 1730 animals reared at four different farms in Sweden and spanning from year classes 2013–2017 were genotyped using ddRAD‐seq. Approximately 5000 single nucleotide polymorphisms (SNPs) were identified, genetic diversity‐related metrics were estimated, and genome‐wide association studies (GWAS) for body length at different time points and age of sexual maturation were conducted. Low genetic differentiation amongst animals from the different farms was observed based on both the results from pairwise Fst values and principal component analysis (PCA). The existence of associations was investigated between the mean genome‐wide heterozygosity of each full‐sib family (year class 2017) and the corresponding inbreeding coefficient or survival to the eyed stage. A moderate correlation (−0.33) was estimated between the mean observed heterozygosity of each full‐sib family and the corresponding inbreeding coefficient, while no linear association was obtained with the survival to the eyed stage. GWAS did not detect loci with major effect for any of the studied traits. However, genomic regions explaining more than 1% of the additive genetic variance for either studied traits were suggested across 14 different chromosomes. Overall, key insights valuable for future selection decisions of Arctic charr have been obtained, suggesting ddRAD as an attractive genotyping platform for obtaining genome‐wide information in a cost‐effective manner. [ABSTRACT FROM AUTHOR]

From video recordings of spawning events, we quantified protective and cannibalistic behavior of Arctic charr occurring immediately after spawning. The number of fish cannibalizing on stray eggs was examined regarding (a) whether more than one male shed milt during the spawning event, that is, whether sperm competition occurred, (b) whether the sperm competition included few or many males, that is, the intensity of sperm competition, and (c) the density of fish at the spawning site. Response behavior toward egg cannibalism was also examined among females and dominant males in order to determine any parental investment toward protecting the eggs after spawning. Cannibalistic behavior was seen in almost 50% of the spawnings, and the multiple spawning events showed the highest numbers of fish cannibalizing on eggs. Both the number of males releasing milt and the number of fish approaching the spawning site were positively correlated with egg cannibalism. Sperm competition was, however, not a prerequisite for egg cannibalism. Although we also observed partial filial cannibalism, protective behavior of eggs was seen both among dominant males and females, suggesting that charr actually conduct parental care. [ABSTRACT FROM AUTHOR]

The Arctic charr breeding programme has been a main driving force for developing the aquaculture industry in Sweden. Selection has been performed for almost 40 years using animals from a closed breeding nucleus. The aim of the current study was to evaluate the potential of further improving growth‐related traits taking into account the existence of genotype‐by‐environment interaction. Furthermore, we investigated the magnitude of the genetic component associated with survival to the eyed stage and potential associations with inbreeding coefficients. A preliminary heritability estimate of 0.23 (SE 0.20) was obtained for survival to the eyed stage using records spanning from 2000 to 2017 (n = 230). Moreover, moderate‐to‐high heritability estimates (0.27–0.49) were obtained for growth‐related traits (body weight and length), using animals from the latest generation of selection (year class 2017). Those animals (n = 2,776), originating from 55 full‐sib families, were split into two groups and reared in separate land‐based facilities of commercial fish farms in Sweden. The growth‐related traits were recorded twice in both sites when animals were of >1 and >2 years of age. Existence of sexual growth dimorphism was indicated with the males having on average 6%–8% higher total length and 22%–34% higher body weight. Furthermore, high genetic correlations regarding growth traits were obtained amongst animals reared at the two different sites (0.82–0.95). In addition, we assessed the accuracy of best linear unbiased prediction (BLUP)‐derived estimated breeding values (EBVs) when phenotypes from each rearing site were subsequently masked and used as a validation set. A mean prediction accuracy of 0.60 (length) and 0.64 (weight) were derived for both rearing sites. Overall, our results suggest that further growth improvements should be possible in the subsequent generations of selection. Finally, even though indications for the existence of an underlying genetic component(s) involved in survival to the eyed stage were obtained additional data will be required for elucidating its magnitude. [ABSTRACT FROM AUTHOR]

Currently, no information is available on the effect of progressively decreasing temperatures on the sensory quality of Arctic charr. The objective of this study was to investigate if and how different and progressively changing rearing temperatures affect the sensory quality of cooked and raw fillets of Arctic charr. The effects of rearing temperature on the sensory quality of Arctic charr (weight range 622–888 g) were investigated. Rearing temperature was changed during the experimental period as the fish were reared at constant or decreased temperature during October to April and subsequently reared at two constant temperatures from April to August establishing six different rearing temperature combinations. Significant differences were seen in all four main sensory attributes groups, that is odour, appearance, flavour and texture. Freshness characteristics such as sweet odour and flavour, and metallic odour and flavour increased with decreasing rearing temperature, whereas musty odour and flavour decreased. Rearing temperature had a clear effect on the colour of the fillets. Lower rearing temperature increased colour intensity substantially. Softness, juiciness and tenderness increased with decreased rearing temperature. A trend was seen towards more effect from final rearing temperature than initial temperature on the sensory attributes studied. Spoilage characteristics, that is, sour and rancid odour and flavour, and off‐odour and flavour were either very weak or not noticeable in all sample groups. [ABSTRACT FROM AUTHOR]

Many life-history events in aquatic invertebrates are triggered by seasonal changes in water temperature, but other ecological factors may be important as well. To rule out the confounding effects of changing water temperature, we studied the seasonal dynamics of an aquatic invertebrate community and their effect on a top fish predator in a thermally stable freshwater spring in South Iceland. We sampled benthic invertebrates five times over a year and conducted a mark-recapture study on the top predator in the system, small benthic Arctic charr, Salvelinus alpinus (L.). We assessed variation in diet composition and feeding preferences by calculating the electivity and individual specialisation of each fish at each sampling time. There was a clear separation of winter and summer communities for the benthic invertebrates. The variation in prey availability was also reflected in the fish diet, with higher feeding selectivity in summer than in winter for the highly abundant Chironomidae larvae. In contrast, individual specialisation as a measure of intrapopulation niche variation was higher in winter when prey availability was lower. We furthermore found that groundwater amphipods might play an important role in the winter diet of spring-dwelling Arctic charr. In conclusion, seasonal variation in the invertebrate community is an important factor to consider and has the potential to alter the phenotype (e.g. growth rates) and behaviour (e.g. feeding preferences) of higher trophic levels. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genomes were sequenced in two individuals of charr Salvelinus alpinus erythrinus from Arctic Canada. The genome sequences were 16,652 bp in length; the genome organization and GC content (45.6%) are consistent with those of charr mitochondrial genomes published previously. The difference between the two genomes studied is low, 0.02%. Our results indicate the phylogenetic closeness of S. alpinus erythrinus and Salvelinus sp. 4 from Lake Nachikinskoe, Kamchatka and their origin from a common ancestor. [ABSTRACT FROM AUTHOR]

As the global climate warms, the fate of lacustrine fish is of huge concern, especially given their sensitivity as ectotherms to changes in water temperature. The Arctic charr (Salvelinus alpinus L.) is a salmonid with a Holarctic distribution, with peripheral populations persisting at temperate latitudes, where it is found only in sufficiently cold, deep lakes. Thus, warmer temperatures in these habitats particularly during early life stages could have catastrophic consequences on population dynamics. Here, we combined lake temperature observations, a 1-D hydrodynamic model, and a multi-decadal climate reanalysis to show coherence in warming winter water temperatures in four European charr lakes near the southernmost limit of the species' distribution. Current maximum and mean winter temperatures are on average ~ 1 °C warmer compared to early the 1980s, and temperatures of 8.5 °C, adverse for high charr egg survival, have frequently been exceeded in recent winters. Simulations of winter lake temperatures toward century-end showed that these warming trends will continue, with further increases of 3–4 °C projected. An additional 324 total accumulated degree-days during winter is projected on average across lakes, which could impair egg quality and viability. We suggest that the perpetuating winter warming trends shown here will imperil the future status of these lakes as charr refugia and generally do not augur well for the fate of coldwater-adapted lake fish in a warming climate. [ABSTRACT FROM AUTHOR]

Ecotoxicological research detailing trace metal contamination and seasonal variation in the tissues of northern fishes such as Arctic charr (Salvelinus alpinus) has been poorly represented in the literature beyond examination of mercury. In an effort to address this, anadromous Arctic charr were collected from the Deception River watershed in the late summer and post-winter season, before quantifying seasonal and organotropic variations in dorsal muscle and liver concentrations of arsenic, cadmium, chromium, copper, nickel, lead, and zinc. Potential linkages with biological variables (fork length, age, and somatic condition) and indicators of feeding behavior (δ13C and δ15N) were also assessed. Trace metal organotropism favouring elevation in liver tissue concentrations was exhibited by cadmium, copper, nickel and zinc, while arsenic, chromium and lead exhibited no significant organotropic variation. Seasonal differences in concentrations were metal and tissue dependent, but generally increased in tissues collected from post-winter sampled Arctic charr. Significant correlations with biological and trophic descriptors were also determined to be element and tissue dependent. These parameters, in addition to season, were incorporated into multi-predictor variable models, where variations in trace metal concentration data were often best explained when season, somatic condition, and trophic descriptors were included. These variables were also of greatest relative importance across all considered trace metals and tissue types. These findings suggest that seasonally linked processes have the greatest influence on trace metal concentrations in anadromous Arctic charr. Future metal-related research on Arctic charr and other northern fish species should further consider these variables when evaluating elemental accumulation. [ABSTRACT FROM AUTHOR]

Possible effects of short‐term starvation on flesh quality in Arctic charr were studied in spring (March) and summer (August). Groups of juvenile Arctic charr (mean weight March 536 g ± 24; August 461 g ± 15 SEM) were starved for 1, 2 and 4 weeks (March) and 1, 2 and 3 (August). After each starvation period, the fish were slaughtered, and flesh samples collected in order to investigate quality and textural properties in the different experimental groups. Starvation had a positive effect on flesh quality giving firmer texture and lower gaping scores. Starved fish had lower cathepsin activity at slaughter, and a similar difference was seen one‐week post mortem. The results showed that the effect of starvation period was seasonally dependent. Starvation had a larger effect in summer, where a three‐week starvation resulted in firmer texture, whereas this was not seen during spring. [ABSTRACT FROM AUTHOR]

Farming of Arctic charr mainly takes place in land‐based farms applying intensive rearing methods with relatively high production costs. Depending on local conditions at each site, it is possible to regulate important environmental factors to improve productivity and well‐being of the fish. Knowledge about how these different environmental factors affect various farming traits is important to reduce production costs. This review shows how rearing temperature, photoperiod, salinity and feeding rate can affect farming traits such as growth rate, maturation and feed conversion efficiency of Arctic charr. High growth rate during juvenile phase when the fish are reared at higher temperatures can result in higher incidence of maturation during the on‐growing period. Overall, more moderate rearing temperature regimes seem to result in better long‐term growth rates. Photoperiod manipulation and feed ration can be used as tools to improve growth and reduce maturation. It is possible to rear Arctic charr successfully up to market size in salinities up to c. 27–28 ppt. However, extended rearing resulted in higher ratio of sexually mature fish at 29 than at 25 possibly linked to higher rearing temperatures in brackish water. Future studies should focus on better preserving the potential high growth rate of Arctic charr during juvenile phase into the on‐growing period and establish protocols to improve the seawater tolerance of Arctic charr. [ABSTRACT FROM AUTHOR]

Arctic charr (Salvelinus alpinus) is a species of high economic value for the aquaculture industry, and of high ecological value due to its Holarctic distribution in both marine and freshwater environments. Novel genome sequencing approaches enable the study of population and quantitative genetic parameters even on species with limited or no prior genomic resources. Low coverage genotyping by sequencing (GBS) was applied in a selected strain of Arctic charr in Sweden originating from a landlocked freshwater population. For the needs of the current study, animals from year classes 2013 (171 animals, parental population) and 2017 (759 animals; 13 full sib families) were used as a template for identifying genome wide single nucleotide polymorphisms (SNPs). GBS libraries were constructed using the PstI and MspI restriction enzymes. Approximately 14.5K SNPs passed quality control and were used for estimating a genomic relationship matrix. Thereafter a wide range of analyses were conducted in order to gain insights regarding genetic diversity and investigate the efficiency of the genomic information for parentage assignment and breeding value estimation. Heterozygosity estimates for both year classes suggested a slight excess of heterozygotes. Furthermore, FST estimates among the families of year class 2017 ranged between 0.009 - 0.066. Principal components analysis (PCA) and discriminant analysis of principal components (DAPC) were applied aiming to identify the existence of genetic clusters among the studied population. Results obtained were in accordance with pedigree records allowing the identification of individual families. Additionally, DNA parentage verification was performed, with results in accordance with the pedigree records with the exception of a putative dam where full sib genotypes suggested a potential recording error. Breeding value estimation for juvenile growth through the usage of the estimated genomic relationship matrix clearly outperformed the pedigree equivalent in terms of prediction accuracy (0.51 opposed to 0.31). Overall, low coverage GBS has proven to be a cost-effective genotyping platform that is expected to boost the selection efficiency of the Arctic charr breeding program. [ABSTRACT FROM AUTHOR]

Ecosystems at high latitudes are exposed to some of the highest rates of climate warming on earth, and freshwater ecosystems in those regions are already experiencing extended ice‐free seasons and warmer waters. The dominant fish species in these ecosystems are cold‐water salmonids, which play a central ecological role in lake ecosystems, where they are often exposed to size‐selective fisheries that truncate their size and age distributions, making them potentially vulnerable to exploitation and environmental perturbations.Here, we address the combined effects of climate‐induced water temperature increase (using regionally downscaled climate models based on the RCP‐4.5 and RCP‐8.5 climate scenarios together with an air‐to‐water temperature model) and gillnet harvesting, over the period from 1950 to 2100, on the somatic growth, demography and vulnerability of Arctic charr Salvelinus alpinus (L.), using an eco‐genetic individual‐based model. The model captures successive annual life‐history events, including the key processes of size‐dependent mortality, age‐ and size‐dependent maturation described by a probabilistic reaction norm, temperature‐dependent growth, size‐dependent reproduction and density‐dependent recruitment.Our model predicts that higher water temperatures will increase the somatic growth of Arctic charr, leading to larger body size at age and increased stock biomass: for RCP‐8.5, we predict an 80% increase in stock biomass in the year 2100 relative to the year 2000 in the absence of fishing. Interestingly, this potential increase in biomass in future climate scenarios will be partially masked by harvesting: for a fishing mortality of 0.3 year−1, we predict a mere 40% increase in stock biomass in 2100 relative to 2000. Despite the predicted increase in stock biomass, yield will increase substantially only when fishing mortality is low. In addition, climate warming will accentuate the age‐truncation effect of harvesting, which will target younger individuals, including immatures, thus elevating the vulnerability of the population to environmental perturbations.Synthesis and applications. Our model‐based analyses highlight the combined effects of climate change and size‐selective fishing, emphasizing the emerging vulnerability of fish populations to multiple stressors. We recommend carefully climate‐adapted management strategies permitting only a narrow range of gillnet mesh sizes for inland fisheries at high latitudes. [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]

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]

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]

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]

Abstract Governance of fisheries in Canada's North is shared between communities, Inuit land claim management boards and the Canadian Department of Fisheries and Oceans under co-management systems outlined in the Nunavut Land Claim Agreement and the Inuvialuit Final Agreement. The management, conservation and optimization of Arctic Charr resources remain complicated by data paucity; by biological complexity of Arctic Charr stocks; climate change impacts; and by the lack of adapted stock assessment tools and co-management frameworks linking Inuit traditional knowledge with scientific expertise. The current state of Arctic Charr fisheries in Nunavut and the Northwest Territories is reviewed and alternatives presented for the evaluation of Arctic Charr stocks using intra-specific life history diversity as a basis for risk and quantitative assessments. The approach fits well with the shared governance model in that the biological characteristics at the root of the analysis, such as size at spawning and maximum length (life history metrics), can be observed through Inuit knowledge and/or through scientific sampling carried out by community members. Assessment is developed as a two stage process using productivity-susceptibility analysis and life history invariant models to determine the maximum sustainable production. The resulting analytical model can but updated through further ecological observations from the community and field sampling. The approach provides for active engagement by the fishers in the process of stock assessment. These science alternatives can be used by managers within the co-management framework to maximize sustainability of Arctic Charr fisheries. [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]

With respect to salmonid aquaculture, one of the most important bacterial pathogens due to high mortality and antibiotic usage is the causative agent of typical furunculosis, Aeromonas salmonicida spp. salmonicida (Asal). In Atlantic salmon, Salmo salar , the host response during infections with Asal is well-documented, with furunculosis outbreaks resulting in significant mortality in commercial settings. However, less is known about the host-pathogen interactions in the emerging aquaculture species, Arctic charr Salvelinus alpinus. Furthermore, there is no data on the efficacy or response of this species after vaccination with commonly administered vaccines against furunculosis. To this end, we examined the immunological response of S. alpinus during infection with Asal , with or without administration of vaccines (Forte Micro®, Forte Micro® + Renogen®, Elanco Animal Health). Artic charr (vaccinated or unvaccinated) were i.p.-injected with a virulent strain of Asal (106 CFUs/mL) and tissues were collected pre-infection/post-vaccination, 8, and 29 days post-infection. Unvaccinated Arctic charr were susceptible to Asal with 72% mortalities observed after 31 days. However, there was 72–82% protection in fish vaccinated with either the single or dual-vaccine, respectively. Protection in vaccinated fish was concordant with significantly higher serum IgM concentrations, and following RNA sequencing and transcriptome assembly, differential expression analysis revealed several patterns and pathways associated with the improved survival of vaccinated fish. Most striking was the dramatically higher basal expression of complement/coagulation factors, acute phase-proteins, and iron hemostasis proteins in pre-challenged, vaccinated fish. Remarkably, following Asal infection, this response was abrogated and instead the transcriptome was characterized by a lack of immune-stimulation compared to that of unvaccinated fish. Furthermore, where pathways of actin assembly and FcγR-mediated phagocytosis were significantly differentially regulated in unvaccinated fish, vaccinated fish showed either the opposite regulation (ForteMicro®), or no impact at all (ForteMicro®Renogen®). The present data indicates that vaccine-induced protection against Asal relies on the pre-activation and immediate control of humoral immune parameters that is coincident with reduced activation of apoptotic (e.g., NF-κB) and actin-associated pathways. [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]

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]

Abstract: The effects of two plant ingredients (solvent‐extracted soybean meal [SBM] and high‐protein sunflower meal [HPSFM]) and three inclusion levels (0 percent, practical diet containing 25 percent fish meal; 12.5 percent; and 25 percent) of these ingredients were investigated on the growth, feed utilization, gut histology and gene expression in the distal intestine of Arctic charr Salvelinus alpinus (average initial weight, 330.1 ± 8.9 g per fish). Feeding experimental diets for 12 weeks resulted in no difference between HPSFM diets in body weight gain (BWG), thermal‐unit growth coefficient (TGC), feed efficiency (FE), feed intake (FI) or pro‐inflammatory mRNA expression (PIE) with increasing dietary inclusion and between SBM FE, FI and PIE. Differences in quadratic contrasts were observed for nitrogen deposition rate (NDR) and nitrogen retention efficiency (NRE) (p < .05), whereby HPSFM diets elicited the strongest positive response. SBM resulted in linear reduction in BWG, TGC and distal intestine simple fold length and width measurements (p < .05) with stepwise increases in dietary inclusion, whereas dietary HPSFM had no effect. Histological observations of individual villi indicated several symptoms of non‐infectious subacute gastrointestinal enteritis in tanks fed SBM, many of which were not present in tanks fed HPSFM. The dietary HPSFM seems to be more adequate to replace fishmeal in Arctic charr diet than SBM, when fed at a level of up to 25 percent at the grow‐out stage. [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]

The complete mitochondrial genomes were sequenced in three individuals of Arctic charr Salvelinus alpinus alpinus. The genome sequences were 16,655 and 16,657 bp in length, and the gene arrangement, composition, and size are very similar to the charr genomes published previously. The difference between the three genomes studied is low, 0.09%. The level of sequence divergence between S. alpinus alpinus and S. alpinus oquassa inferred from the complete mitochondrial genomes is relatively low (0.36%), indicating recent divergence of the taxa and/or potential historical hybridization between different lineages upon secondary contact. [ABSTRACT FROM AUTHOR]

Traditional sources of protein in fish feed for salmonids, such as fishmeal, face sustainability problems. Therefore, ingredients not attractive for human consumption are increasingly being considered for the development of future feeds. However, it is uncertain how this alternative range of ingredients will affect fish growth, quality and consumer opinion. In this experimental study, we tested a new fish feed on Arctic charr, containing a protein mixture from the Baltic Sea and yeast, all ingredients unattractive for human consumption. This feed comprised of sprat ( Sprattus sprattus ) and herring ( Clupea harengus ), blue mussels ( Mytilus edulis ) and baker's yeast ( Saccharomyces cerevisiae ), in a ratio of three parts to the whole. Fish fed with this feed grew 11.5% less than the control group. The digestibility and microscopy analysis of the faeces suggested a lower digestibility of the test feed, presumably caused by the fish's inability to utilize the nutrients from the yeast cells. Consumers' perceptions of the final product were evaluated through a sensory evaluation, indicating no differences in scores of fillet quality between the two treatments. Potential implications of these results are discussed in context of feed composition, quality and other factors including species biology and season, which are relevant topics in the discussions on feed sustainability. Statement of relevance Evaluating a feed mix unattractive for human consumption. [ABSTRACT FROM AUTHOR]

Two lab-based trials quantified the effect of a range of continuous light (LL) treatments overwinter on the somatic growth and incidence of sexual maturation in the fall age 2 of individually identified under-yearling Arctic charr (Labrador strain) at constant 10 °C. Controls were maintained under simulated natural photoperiod (LDN; Latitude 45°N). In trial 1 ( n = 120/trt, mean 54 g initial body weight), LL starting the 1st day of either October, November, December, January or February (all returned to LDN on April l) resulted in a step-wise reduction in maturity of 43, 55, 59, 67 73% compared with 77% in the control (sexes pooled). In trial 2 ( n = 90/trt, mean 24 g initial body weight), LL starting either August 13 or October 1 and ending April 1 reduced maturity to < 10%, compared to 33% (LL Dec1-Apr1) and 50% in the LDN controls. LL starting October 1 and ending either February 1, April 1 or June 1 were equally effective, resulting in < 15% maturity. The importance of returning from LL to LDN in spring to reduce maturity was demonstrated by the LL constant (Oct–Oct) treatment which resulted in relatively high maturity, 31%. The reduction of maturity rate was independent of both somatic growth and condition factor during winter in all treatment groups. Among fish that matured, the timing of completion of sexual maturation was affected by both the LL start and end date. [ABSTRACT FROM AUTHOR]

Arctic charr ( Salvelinus alpinus) are the northernmost distributed freshwater fish and can grow at water temperatures as low as 0.2 °C. Other teleost species have impaired immune function at temperatures that Arctic charr thrive in, and thus, charr may maintain immune function at these temperatures. In this study, a fibroblastic cell line, named ACBA, derived from the bulbus arteriosus ( BA) of Arctic charr was developed for use in immune studies at various temperatures. ACBA has undergone more than forty passages at 18 °C over 3 years, while showing no signs of senescence-associated β-galactosidase activity and producing nitric oxide. Remarkably, ACBA cells survived and maintained some mitotic activity even at 1 °C for over 3 months. At these low temperatures, ACBA also continued to produce MH class I proteins. After challenge with poly I:C, only antiviral Mx proteins were induced while MH proteins remained constant. When exposed to live viruses, ACBA was shown to permit viral infection and replication of IPNV, VHSV IVa and CSV at 14 °C. Yet at the preferred temperature of 4 °C, only VHSV IVa was shown to replicate within ACBA. This study provides evidence that Arctic charr cells can maintain immune function while also resisting infection with intracellular pathogens at low temperatures. [ABSTRACT FROM AUTHOR]

Identifying the processes by which new phenotypes and species emerge has been a long-standing effort in evolutionary biology. Young adaptive radiations provide a model to study patterns of morphological and ecological diversification in environmental context. Here, we use the recent radiation (ca. 12k years old) of the freshwater fish Arctic charr ( Salvelinus alpinus) to identify abiotic and biotic environmental factors associated with adaptive morphological variation. Arctic charr are exceptionally diverse, and in postglacial lakes there is strong evidence of repeated parallel evolution of similar morphologies associated with foraging. We measured head depth (a trait reflecting general eco-morphology and foraging ecology) of 1,091 individuals across 30 lake populations to test whether fish morphological variation was associated with lake bathymetry and/or ecological parameters. Across populations, we found a significant relationship between the variation in head depth of the charr and abiotic environmental characteristics: positively with ecosystem size (i.e., lake volume, surface area, depth) and negatively with the amount of littoral zone. In addition, extremely robust-headed phenotypes tended to be associated with larger and deeper lakes. We identified no influence of co-existing biotic community on Arctic charr trophic morphology. This study evidences the role of the extrinsic environment as a facilitator of rapid eco-morphological diversification. [ABSTRACT FROM AUTHOR]

Sympatric speciation is thought to be strongly linked to resource specialization with alternative resource use acting as a fundamental agent driving divergence. However, sympatric speciation through niche expansion is dependent on foraging specialization being consistent over space and time., Standard metabolic rate is the minimal maintenance metabolic rate of an ectotherm in a post-absorptive and inactive state and can constitute a significant portion of an animal's energy budget; thus, standard metabolic rate and growth rate are two measures frequently used as an indication of the physiological performance of individuals. Physiological adaptations to a specific diet may increase the efficiency with which it is utilized, but may have an increased cost associated with switching diets, which may result in a reduced standard metabolic rate and growth rate., In this study, we use the diet specialization often seen in polymorphic Arctic charr ( Salvelinus alpinus) populations to study the effects of different prey on standard metabolic rate and growth rate as well as the effects that early prey specialization may have on the ability to process other prey types efficiently., We found a significant effect of prey type on standard metabolic rate and growth rate. Furthermore, we found evidence of diet specialization with all fish maintaining a standard metabolic rate and growth rate lower than expected when fed on a diet different to which they were raised, possibly due to a maladaptation in digestion of alternative prey items., Our results show that early diet specialization may be reinforced by the elevated costs of prey switching, thus promoting the process of resource specialization during the incipient stages of sympatric divergence. [ABSTRACT FROM AUTHOR]