Search

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]

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]

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]

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]

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]

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]

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]

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]

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]

In relation to stock enhancement programmes, wild salmon broodfish have been routinely screened for the presence of Renibacterium salmoninarum antigens (Rs-Ag) for decades. A sudden increase in the prevalence of Rs-Ag experienced caused extensive problems to this industry as eggs from positive fish are discarded. The prevalence and level of Rs-Ag were examined in resident and anadromous salmonids in the River Ellidaár system and the progress of Rs-Ag in a cohort of salmon followed. Both prevalence and Rs-Ag levels were high in resident salmonids and emigrating salmon smolts in the river system. When the smolts re-entered their home river as adults the following summer, they were almost free of Rs-Ag, but the longer they stayed in the river, the more Rs-Ag they acquired; the majority being positive at spawning. This study demonstrates a high level of Rs-Ag in salmonids in the River Ellidaár system which significantly reduces in the salmon during its seawater phase. Accordingly, it seems ideal to sample salmon broodfish as soon as possible after ascending the river and subsequently transfer to Rs-free environment for storage until stripping, which could result in lower Rs-prevalence and minimize the problems that stock enhancement programmes have faced due to Rs-positive wild broodfish. [ABSTRACT FROM AUTHOR]

This study examined the abiotic and biotic characteristics of ecosystems that allow expression of a life history called ferox trout, the colloquial name given to brown trout Salmo trutta adopting a piscivorous life history strategy, an apex predator in post-glacial lakes in northern Europe. One hundred and ninety-two lakes in Scotland show evidence of currently, or historically, supporting ferox S. trutta; their presence was predicted in logistic models by larger and deeper lakes with a large catchment that also support populations of Arctic charr Salvelinus alpinus. [ABSTRACT FROM AUTHOR]

Individual measurements of annual, or within-season growth were determined from tag-recaptured Arctic charr and examined in relation to summer sea surface temperatures and within-season capture timing in the Ungava and Labrador regions of Eastern Canada. Differences between two years of growth (2010-2011) were significant for Ungava Bay Arctic charr, with growth being higher in the warmer year. Growth of Labrador Arctic charr did not vary significantly among years (1982-1985). Regional comparisons demonstrated that Ungava Arctic charr had significantly higher annual growth rates and experienced warmer temperatures than Labrador Arctic charr. The higher annual growth of Ungava Bay Arctic charr was attributed to the high sea surface temperatures experienced in 2010-2011 and the localised differences in nearshore productivity as compared to Labrador. Within-season growth rates of Labrador Arctic charr peaked in June, declined towards August and were negatively correlated with the length of time spent at sea and mean experienced sea surface temperatures. A quadratic model relating growth rate to temperature best explained the pattern of within-season growth. Collectively, results suggest that increases in water temperature may have profound consequences for Arctic charr growth in the Canadian sub- Arctic, depending on the responses of local marine productivity to those same temperature increases. [ABSTRACT FROM AUTHOR]

Spawning is a key but often fragile event in the life cycles of fish populations. Nevertheless, it has been relatively little studied for lithophilic lacustrine species requiring hard spawning substrates, such as gravels or stones, largely devoid of fine sediments. Twelve demonstrated or putative spawning grounds of Arctic charr ( Salvelinus alpinus) in shallow and deep areas of the north and south basins of the eutrophicated lake of Windermere, UK, were described by hydroacoustic, physical and visual surveys. In addition, their current conditions were compared with their original qualitative descriptions made over 50 years ago. Spawning ground characteristics were found to be more complex than originally described, with considerable overlaps in depth ranges and only limited areas of appropriate hard substrates. Moreover, extensive gill netting surveys in recent years have found spawning Arctic charr at only seven of the original 12 demonstrated or putative spawning grounds, although several new spawning areas have also been found. The distribution of unsuitable fine sediments is widespread in the lake, particularly in the more eutrophicated south basin where suitable spawning habitat within the putative spawning areas is limited. Windermere faces a number of environmental problems including climate change and species introductions. However, the temporal and spatial patterns of the lake's eutrophication suggest that associated increases in fine sediments have been a major driver of the observed deterioration of Arctic charr spawning grounds and so may have also contributed to a marked decline recently observed in the local abundance of this species. [ABSTRACT FROM AUTHOR]

Landscape genetics holds promise for the forecasting of spatial patterns of genetic diversity based on key environmental features. Yet, the degree to which inferences based on single species can be extended to whole communities is not fully understood. We used a pristine and spatially structured community of three landlocked salmonids ( Salvelinus fontinalis, Salmo salar, and Salvelinus alpinus) from Gros Morne National Park (Newfoundland, Canada) to test several predictions on the interacting effects of landscape and life history variation on genetic diversity, neutral divergence, and gene flow ( m, migration rate). Landscape factors consistently influenced multispecies genetic patterns: (i) waterfalls created strong dichotomies in genetic diversity and divergence between populations above and below them in all three salmonids; (ii) contemporary m decreased with waterway distance in all three species, while neutral genetic divergence ( θ) increased with waterway distance, albeit in only two taxa; (iii) river flow generally produced downstream-biased m between populations when waterfalls separated these, but not otherwise. In contrast, we expected differential life history to result in a hierarchy of neutral divergence ( S. salar > S. fontinalis > S. alpinus) based on disparities in dispersal abilities and population size from previous mark-recapture studies. Such hierarchy additionally matched varying degrees of spatial genetic structure among species revealed through individual-based analyses. We conclude that, whereas key landscape attributes hold power to predict multispecies genetic patterns in equivalent communities, they are likely to interact with species-specific life history attributes such as dispersal, demography, and ecology, which will in turn affect holistic conservation strategies. [ABSTRACT FROM AUTHOR]

Two modal size groups of sexually mature Arctic charr ( Salvelinus alpinus) differing in shape and found at different depths in Lake Aigneau in the Canadian sub-Arctic are described and tested for genetic and ecological differentiation. Forms consisted of a small littoral resident, mean size 21.7 cm, and a large profundal resident, mean size 53.9 cm. Mitochondrial DNA analysis indicated that seven of eight haplotypes were diagnostic for either the littoral or profundal fish, with 66.6% of the variation being found within form groupings. Pairwise tests of microsatellite data indicated significant differences in nine of 12 loci and a significant difference between the forms across all tested loci. Molecular variation was partitioned to 84.1% within and 15.9% between forms and suggestive of either restricted interbreeding over time or different allopatric origins. Stable isotope signatures were also significantly different, with the profundal fish having higher δ13C and δ15N values than the littoral fish. Overlap and separation, respectively, in the range of form δ13C and δ15N signatures indicated that carbon was obtained from similar sources, but that forms fed at different trophic levels. Littoral fish relied on aquatic insects, predominantly chironomids. Profundal fish were largely piscivorous, including cannibalism. Predominantly empty stomachs and low per cent nitrogen muscle-tissue composition among profundal fish further indicated that the feeding activity was limited to the winter when ice-cover increases the density of available prey at depth. Results provide evidence of significant differences between the modal groups, with origins in both genetics and ecology. [ABSTRACT FROM AUTHOR]

The morphology of three lake-resident Arctic charr, Salvelinus alpinus, populations was studied at two life-history stages in a common-garden experiment. The fish of the same year class were reared under standard hatchery conditions, and 27 morphometric variables (a truss network) were measured from the sampled individuals. Most of the total variation was explained by the overall body robustness, dimensions of the head and caudal peduncle length. After controlling for a body size, significant heterogeneity in body shape was found among populations at both ages. Independent of age, the populations were morphologically highly distinct, although some integration of characters could be found as the fish reached sexual maturity. Sexual divergence accounted for a large part of the within-population shape variation, the mature males having more robust bodies, larger head dimensions and longer pectoral fins compared with the mature females/immature fish. Although the cultured fish may not be totally representative of their wild counterparts, it is reasonable to expect that the observed morphological differences have a genetic basis, presumably reflecting adaptation to local environmental conditions experienced by the charr in their original habitat. [ABSTRACT FROM AUTHOR]

The growth in captivity of a wild Welsh strain (Llyn Cowlyd) of Arctic charr Salvelinus alpinus was compared to that of a commercial Scottish strain over the course of a 12 month experiment. At the conclusion of the study, the Welsh strain had a lower mass and condition factor than the commercial fish, but a similar length. Aspects of the growth and population structure of the Welsh strain imply that it could be a subject for aquaculture development, but such practises will be dependant on further work on selection and broodstock development. [ABSTRACT FROM AUTHOR]

Although photoperiod is considered as a major environmental cue for timing of seasonal events in fish, little is known about the photic information perceived by fish in different aquatic environments. The strongly seasonal Arctic charr, Salvelinus alpinus, reside in lakes covered by thick ice and snow throughout the dark winter in the north. In the present study, we have measured diel changes in their plasma melatonin concentrations from September to June in Lake Storvatnet (70°N), northern Norway. In addition, we have measured the in vitro melatonin production of Arctic charr pineal glands held at experimental light conditions. From September to April a diel profile in plasma melatonin was seen in the charr in Lake Storvatn, with highest concentrations at night. This profile reflected the prevailing above-surface photoperiod, even in February when there were minimal changes in sub-surface irradiance between day and night. In June, plasma melatonin was low throughout the 24-hr cycle, despite there being a marked sub-surface difference in irradiance between night and day. At this time the irradiance in night probably remained above the threshold for suppression of melatonin production. The in vitro experiments revealed no endogenous rhythm in the pineal melatonin secretion, supporting the conclusion that the diel profile seen in the Arctic charr in their natural habitat was driven by ambient photoperiod. In conclusion, the Arctic charr appear to keep track of time even under the extreme conditions of high latitudes during winter, when lakes have thick ice and snow cover. [ABSTRACT FROM AUTHOR]

We investigated how Arctic charr young respond behaviourally to olfactory cues from skin-damaged conspecifics, charr-fed pikeperch, and the combination of food-deprived pikeperch and skin-damaged conspecific cues in a two-channel Y-maze fluviarium test arena. Significant antipredator responses were found to skin-damaged conspecifics in three behavioural traits, to charr-fed pikeperch in two traits and to the combination of pikeperch and skin-damaged conspecific cues in all six behaviours investigated. The combination of predator and conspecific cues significantly increased spatial avoidance and cautiousness to approach the source of scent compared with odours from charr-fed predators. The results suggest that damage-released alarm cues exist in charr, and they strengthen the antipredator responses in conspecifics. As the charr used different behaviours and levels of response in the presence of different cues, they seem to have sophisticated skills to distinguish between different odour combinations and be able to adjust their behaviour according to the current predation risk level. [ABSTRACT FROM AUTHOR]

The association of genetic markers linked to the sex-determining locus (SEX) was investigated in five Arctic charr Salvelinus alpinus full sib families, all originating from the Fraser River strain, Labrador, Canada. Two distinct sex-linkage classes were identified: type I (two families), with previously reported markers on linkage group 4 (AC-4) linked with SEX; and type II (three families), with two unlinked segments of the AC-4 linkage group, but with markers in only one cluster associated with SEX. Large differences in recombination rates, pseudolinkage assembly or various chromosomal rearrangements may explain these findings. [ABSTRACT FROM AUTHOR]

Summer habitat use by sympatric Arctic charr Salvelinus alpinus, young Atlantic salmon Salmo salar and brown trout Salmo trutta was studied by two methods, direct underwater observation and electrofishing, across a range of habitats in two sub-arctic rivers. More Arctic charr and fewer Atlantic salmon parr were observed by electrofishing in comparison to direct underwater observation, perhaps suggesting a more cryptic behaviour by Arctic charr. The three species segregated in habitat use. Arctic charr, as found by direct underwater observation, most frequently used slow (mean ±s.d. water velocity 7·2 ± 16·6 cm s−1) or often stillwater and deep habitats (mean ±s.d. depth 170·1 ± 72·1 cm). The most frequently used mesohabitat type was a pool. Young Atlantic salmon favoured the faster flowing areas (mean ±s.d. water velocity 44·0 ± 16·8 cm s−1 and depth 57·1 ± 19·0 cm), while brown trout occupied intermediate habitats (mean ±s.d. water velocity 33·1 ± 18·6 cm s−1 and depth 50·2 ± 18·0 cm). Niche overlap was considerable. The Arctic charr observed were on average larger (total length) than Atlantic salmon and brown trout (mean ±s.d. 21·9 ± 8·0, 10·2 ± 3·1 and 13·4 ± 4·5 cm). Similar habitat segregation between Atlantic salmon and brown trout was found by electrofishing, but more fishes were observed in shallower habitats. Electrofishing suggested that Arctic charr occupied habitats similar to brown trout. These results, however, are biased because electrofishing was inefficient in the slow-deep habitat favoured by Arctic charr. Habitat use changed between day and night in a similar way for all three species. At night, fishes held positions closer to the bottom than in the day and were more often observed in shallower stream areas mostly with lower water velocities and finer substrata. The observed habitat segregation is probably the result of interference competition, but the influence of innate selective differences needs more study. [ABSTRACT FROM AUTHOR]

Whole-genome duplication in the ancient ray-finned fish and subsequent tetraploidization in the ancestor to the salmonids have complicated genomic and candidate gene studies in these organisms as many genes with multiple copies are present throughout their genomes. In an attempt to identify genes with a potential influence on growth and development, we investigated the genomic positions of insulin-like growth factors 1 and 2 ( IGF1, IGF2), myogenic factors 5 and 6 ( MYF5, MYF6) and growth hormone-releasing factor/pituitary adenylate cyclase-activating polypeptide ( GRF/ PACAP) in three salmonid species: rainbow trout ( Oncorhynchus mykiss), Atlantic salmon ( Salmo salar) and Arctic charr ( Salvelinus alpinus). Our results suggest a tight association between the IGF1, MYF5 and MYF6 genes in all three species. We further localized the duplicated copies of IGF1 to the homeologous linkage groups RT-7/15 in rainbow trout and AC-3/24 in Arctic charr, and the two copies of MYF6 to homeologous linkage groups AS-22/24 in Atlantic salmon. Localization of GRF/ PACAP to RT-7, AS-31 and AC-27 and IGF2 to RT-27, AS-2 and AC-4 in rainbow trout, Atlantic salmon and Arctic charr respectively is consistent with previously reported homologies among these chromosomal segments identified using other genetic markers. However, localization of the second copy of GRF/ PACAP to RT-19 and AC-14 and the duplicated copy of IGF2 to AC-19 suggest a possible new homology/homeology between these chromosomes. These results might also be an indication of a more ancient polyploidization event that occurred deep in the ray-finned fish lineage. [ABSTRACT FROM AUTHOR]

To evaluate whether paternal effects occur on offspring traits, eggs from Arctic charr Salvelinus alpinus were fertilized with similar amount of sperm from size-matched dominant and subordinate males, in a nested design. Eggs fertilized by subordinate fathers resulted in more offspring produced than eggs fertilized by the same amount of sperm from dominant fathers. Yet, paternal status showed no significant effect on measurements of larvae total length, yolk area and yolk red intensity. [ABSTRACT FROM AUTHOR]

The Arctic charr Salvelinus alpinus (L.), or Torgoch (‘red belly’) in Welsh, is found in seven lakes in North Wales comprising three native populations (Bodlyn, Cwellyn and Padarn) and four translocated populations (Cowlyd, Diwaunedd, Dulyn and Ffynnon Llugwy). The Welsh charr populations have not been studied much, but the available data are summarised in this short review. Analysis of stomach contents of the native charr populations shows that they are planktivores feeding mainly on cladocerans and copepods. Adult fish attain a size of 14–24 cm (fork length) and fecundity is low (100–800 eggs per female). The available growth data reveal that Welsh charr grow at a similar rate and attain a size similar to most other planktivorous charr populations that have been studied in the UK. Genetic studies using allozymes indicate that the three native populations are distinct from each other. [ABSTRACT FROM AUTHOR]

In this study, we synthesised the views of 34 participants in a workshop to consider the status and future conservation and management of the Arctic charr ( Salvelinus alpinus L.). These are expressed as a series of resolutions deriving from a conference on Arctic charr conservation held in Perth, Scotland in June 2004. Agreed resolutions from the conference were as follows. (i) The unique diversity of Arctic charr should be recognised for the contribution it makes to biodiversity of northern aquatic communities. (ii) The recognition by the public, nongovernmental organisations and national governments of the importance of Arctic charr in northern ecosystems is an important step to the management and protection that should be pursued. (iii) The taxonomic status of highly variable charr populations requires to be reviewed. (iv) There should be a separate system, complementary to the taxonomic one, which systematically catalogues the biological diversity of S. alpinus. (v) The Arctic charr provides a unique natural resource to study the process of evolution and this requires the highest level of protection from anthropogenic effects. (vi) The status of conservation policy for Arctic charr needs to be urgently reviewed to take account of its unique position in the fauna. [ABSTRACT FROM AUTHOR]

Hydroacoustic surveys are an important tool for assessing the abundance of Arctic charr ( Salvelinus alpinus (L.)) in lakes, the requirement for which is increasing because of new environmental legislation. Consequently, survey demand is now such that assessments must be undertaken with the minimum of effort compatible with scientific validity. One major complication is seasonal variability in abundance, with which surveyors have attempted to deal by defining somewhat arbitrary seasonal sampling windows. The definition of more objective windows was pursued by analysing variations in the seasonal abundance of Arctic charr in Windermere, UK, recorded using day and night hydroacoustic surveys at monthly intervals from 1991 to 2001. Two alternative sampling windows for night surveys free of significant internal seasonal effects were revealed, i.e., December to September and September to December. It was also found that day surveys gave a useful, although lower, estimate of abundance as compared with night surveys. [ABSTRACT FROM AUTHOR]

From both a modern and a historical perspective there is little doubt that the Arctic charr, Salvelinus alpinus, in Britain and Ireland (as well as elsewhere) is a ‘difficult’ species. Historically 15 separate species have been recognised from populations in Britain and Ireland and there have been recent attempts to reassert these specific names. Here we review the evidence for the status of these ‘species’. We conclude that the evidence for these 15 being afforded full species status is poor. However, both historical and contemporary data show that Salvelinus alpinus (Linnaeus 1758) in Britain and Ireland exhibits levels of variability in form that is much greater than in other species. We argue that a comprehensive genotypic and phenotypic survey of charr populations in Britain and Ireland is required to determine the full extent of variability and the status of populations with a view of providing suitable protection. [ABSTRACT FROM AUTHOR]

The effects of formalin and ethanol preservation on the δ13C and δ15N isotope signatures of Arctic charr Salvelinus alpinus muscle tissue were examined. The lipid content of the tissue samples studied ranged from 3·6 to 6·1% and was not correlated with the magnitude of observed isotopic shifts in preserved samples. Ethanol and formalin significantly depleted and enriched, respectively, the δ13C isotope signatures of preserved tissues when compared to control samples. Ethanol did not significantly enrich δ15N signatures in comparison to controls, whereas formalin did. A meta-analysis of multiple species effects further demonstrated significant preservation effects in fish tissue. Statistical analysis of data obtained by correcting preserved tissue isotope signatures with literature, bootstrapped or meta-analysis derived correction factors demonstrated significant differences between corrected and control sample isotope signatures or failure to produce a unity slope when the data sets were regressed against one another. Species-specific, bootstrapped linear correction models resulted in no such errors. Results suggest that species-specific correction methods should be used for fishes because of the known wide variation in fish tissue lipid content and composition. Accordingly, the use of pilot studies will be required to develop correction factors that properly adjust for preservation effects when interpreting temporal patterns in historic analyses of food webs. [ABSTRACT FROM AUTHOR]

Arctic charr, Salvelinus alpinus (L.), is one of the several northern fishes that show resource polymorphisms in postglacial lakes. Two reproductively isolated morphs of Arctic charr coexist in distinct ecological niches in the subarctic lake Fjellfrøsvatn, North Norway. Offspring of the two morphs (termed littoral charr and profundal charr) were reared separately but under identical conditions. Their feeding behaviour was compared experimentally using different kinds of live prey. The fishes had no experience with natural prey before the experiments. The littoral morph were more effective in eating live plankton ( Daphnia) and littoral benthos ( Gammarus), and had a higher attack rate against pleuston (surface prey, Gerris) compared with the profundal morph. The two morphs behaved in accordance with expectations from their in situ niche utilisation towards the three prey types. This indicates a case of incipient ecological speciation where divergence in resource utilisation in contrasting niches has evolved adaptations in feeding behaviour by natural selection. [ABSTRACT FROM AUTHOR]

A hatchery experiment was organised to find out if the high loss rate of coded wire tags, noticed in connection with an Arctic charr Salvelinus alpinus (L.) restocking programme, was size-dependent and also to test head moulds for future taggings. Six moulds made by Northwest Marine Technology Inc. and five moulds made at the Finnish Game and Fisheries Research Institute were used. A total of 100 charr were tagged with standard-length coded wire tags using each mould. One-summer old charr at tagging were held for 534 days and two-summer old charr for 320 days. The tag loss rate varied between 0% and 54% and was negatively related to the size of the charr at tagging. The high loss rate was connected with the poor alignment of some moulds, such that a large proportion of the tags were located in the nasal cavity instead of the nasal cartilage. Testing of the moulds and careful grading of the fish for tagging is emphasised, especially if Arctic charr smaller than 20 g in weight are to be tagged. [ABSTRACT FROM AUTHOR]

The relationship between parasite infection and breeding ornamentation in an Arctic charr Salvelinus alpinus population was examined. Interrelationships between the intensities of parasites with different dietary transmission routes suggested that hosts were segregated by habitat and diet preferences. That is, intensities of parasites transmitted through intermediate hosts that share habitat were, in both sexes, positively interrelated. Negative interrelationships in the intensities of parasites transmitted through different hosts were found only in females. The intensity of breeding colouration was positively correlated with intensities of amphipod-transmitted parasites in both sexes. Intensities of parasites transmitted through copepods showed no relationship to morphological or ornamental characters. Seen in the context of morphology and ornaments of previously described sympatric populations of Arctic charr, these relationships suggested that individual variation in niche background may provide a source for the initial variation in morphology and secondary sexual traits leading to sympatric speciation through sexual selection. [ABSTRACT FROM AUTHOR]

Food ingestion to assess dominance status, indicated that dominant Arctic charrSalvelinus alpinusdisplayed significantly higher white muscle pyruvate kinase(PK) and lactate dehydrogenase(LDH) activities compared to subordinate fish[PK = 429·57 ± 76·37v. 331·00 ± 61·73 U g−1 tissue( P = 0·022) and LDH = 929·33 ± 61·03v. 775·25 ± 110·96 U g−1 tissue;( P = 0·0007)]. [ABSTRACT FROM AUTHOR]

To examine the immunological impacts of polychlorinated biphenyls (PCBs) in an environmentally relevant way, we orally contaminated Arctic charr (Salvelinus alpinus) with Aroclor 1254. After contamination, fish were either fed (0 and 100 mg Aroclor 1254 kg-1 fish wt) or fasted (0, 1, 10, and 100 mg kg-1) to mimic cycles of feeding--fasting experienced by Arctic animals. After four months, PCB concentrations in muscle were the same in fasted and fed fish; however, PCBs in kidneys of fed fish were 33 to 50% of those in fasted fish. Arctic charr were exposed to Aeromonas salmonicida, the bacteria responsible for furunculosis, by cohabitation with infected conspecifics. Fasted fish had a significant trend toward lower survival with higher dose of PCBs--from 68% in controls to 48% in treatment involving 100 mg kg-1. Independent of PCB contamination, fed fish had the lowest survival; we attribute this to stress associated with establishing and maintaining feeding hierarchies. A significant decrease in the activity of lysozyme was observed in skin mucus, as was hemagglutination ability of a putative rhamnose lectin in fasted, but not in fed, PCB-treated fish. These results demonstrate the immunosuppressive effects of PCBs on Arctic charr, and they illustrate the importance of considering environmentally relevant nutritional status in ecotoxicological studies. [ABSTRACT FROM AUTHOR]

Differences in gonadal development and time of spawning were found in two coexisting morphotypes of Arctic charr Salvelinus alpinus in Kalandsvatnet, Norway. Spawning depth and some main life-history variables also differed. These observations suggest that the two morphotypes do not interbreed freely. [ABSTRACT FROM AUTHOR]

The effects of induced water level fluctuations and introduction of the mysid Mysis relicta Lovén on population structure of brown trout, Salmo trutta L., and Arctic charr, Salvelinus alpinus (L.), were studied during 1953–1995 in Limingen hydroelectric reservoir, Norway. The main response was a marked reduction in catch-per-unit-effort (CPUE) for trout and charr, probably caused by reduced recruitment following increased variation in water level. For both species, mean length decreased until 1967 and increased thereafter, whereas mean mass-at-length increased for the whole period. Both length and mass-at-length were negatively correlated with CPUE. The increases in mean length and mass-at-length were probably because of reduced competition following the reduced recruitment. Mysis relicta has become an important food item for charr but not for brown trout, but the increases in mean length and mass-at-length of charr started prior to the appearance of M. relicta in the charr diet. [ABSTRACT FROM AUTHOR]

No difference in attraction was observed in sibling Artic charr Salvelinus alpinus between water scented by dominant or subordinate major histocompability complex (MHC) identical fish observed in a two-choice fluviarium. In a second experiment, MHC identical sibling donors were given different types of food pellets before the preference test. The test fish showed a significant attraction to the sibling given the same kind of food as the test fish itself during the first 6 h of the fluviarium tests. The results suggest that diet has an influence on the odours released and can, in addition to MHC related odours, be used for information relating to group member identity. [ABSTRACT FROM AUTHOR]

Habitat use, growth and food composition of native and stocked Arctic charr, Salvelinus alpinus (L.), were studied in the subarctic Lake Muddusjärvi, northern Finland, to investigate reasons for poor stocking success. Samples were collected with pelagic and epibenthic gill nets. Stocked and native charr occurred in similar epibethic habitats, whereas pelagic habitat was avoided. Native charr grew fast after shifting to piscivory. Growth rate of stocked charr was slow because only a small proportion of stocked fish became piscivorous during the first year after stocking. During the first lake year, stocked charr divided into slow-growing planktivores and fast-growing piscivores. Piscivorous stocked and native charr consumed only whitefish, Coregonus lavaretus (L.), as their prey. Small-sized (<10 cm) whitefish were preferred when shifting to piscivory. [ABSTRACT FROM AUTHOR]

Like the spermatozoa of most other fish species spawning in fresh water, Arctic charr Salvelinus alpinus sperm were short-lived (mean 42 s) after activation and their swimming speed declined rapidly during this period, e.g. from a mean speed of 106 μm s−1 at 10 s after activation in fresh water to 21 μm s−1 only 20 s later. Ovarian fluid significantly influenced sperm longevity (duration of forward mobility), per cent motility, swimming speed and the linearity of sperm movement. All of these variables generally increased as the concentration of ovarian fluid increased from 0 to 50%, even though ovarian fluid is more than three times as viscous as fresh water. It is concluded that ovarian fluid enhances sperm movement in this species and thus has the potential to influence both fertilization success and the outcome of sperm competition. Copyright 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved. [Copyright &y& Elsevier]

Aggressive interactions were initially higher in groups comprised of equally sized large and intermediate Arctic charr Salvelinus alpinus than in groups of small sized individuals and in groups with a normal size distribution. Size composition had no effect on growth. Copyright 2002 The Fisheries Society of the British Isles. Published by Elsevier Science. All rights reserved. [Copyright &y& Elsevier]

Planktivorous and benthivorous morphs of wild Arctic charr Salvelinus alpinus from Loch Rannoch, Perthshire, Scotland, reared in the laboratory from artificially fertilized eggs under identical conditions, were morphologically distinct (based on a series of head measurements) from an early age. For some morphometric characters, these differences became more marked with increasing body size, reflecting differences in the allometric growth patterns of the two forms. These data show that the observed phenotypic differences between these two trophic variants were, to some extent at least, inherited. Thus it is concluded that the mechanisms regulating expression of phenotype in the sympatric morphs of Loch Rannoch are significantly different from the environmentally determined body size polymorphisms reported from Norway but are closer to the more completely divergent forms from Thingvalavatn, Iceland. [Copyright &y& Elsevier]

The growth of Arctic charr Salvelinus alpinus in five high altitude lakes differed between lakes during the first 2 years but was similar thereafter. The average temperature during the summer had a direct effect on growth and an indirect effect on the productivity level of the lakes, particularly on the abundance of planktonic crustaceans. The results highlight the importance of planktonic crustacea in the growth of Arctic charr. [Copyright &y& Elsevier]

Stable isotopes of carbon and nitrogen were used to examine differences in the feeding ecology of sympatric morphotypes of Arctic charr Salvelinus alpinus from Lake Hazen, Ellesmere Island, in the Canadian High Arctic. Large and small morphotypes possessed significantly different carbon and nitrogen signatures with large-form Arctic charr being more depleted in 13C and more enriched in 15N than the small-form. Isotope and stomach content analyses yielded consistent results and indicated short- and long-term reliance on fish as a food for large Arctic charr. Large-form individuals predate on juveniles but do not predate on small-form individuals ≥250 mm. The observed cannibalism by large-form individuals, therefore, does not act to maintain the bimodal length-frequency distribution in Lake Hazen. Bimodality is argued to arise for ecological reasons connected with differing habitat use by the morphotypes and the associated differences in resource consumption opportunities. [Copyright &y& Elsevier]

In the present study we investigated the effect of stress and cortisol on cytochrome P450 (CYP) expression in Arctic charr exposed to benzo[a]pyrene (BaP). Expression of hepatic CYP1A and CYP3A was monitored 8 d after a single oral dose of BaP (10 mg/kg fish) and compared to that in unexposed fish. During this period the fish were subjected to one of the following stress regimes: no stress, no stress and cortisol implantation, 10 min of daily handling and confinement stress, and confinement stress during the last 6 h before sampling. In BaP-exposed fish daily stress resulted in significantly lower (53%) CYP1A protein levels as compared to those in unstressed fish. For CYP1A catalytic activity (measured as 7-ethoxyresorufin-O-deethylase [EROD] activity), the suppressive response to stress was less pronounced. These results contrast to previous findings of a potentiation by corticosteroids on xenobiotic-dependent CYP1A induction in vitro in cultured fish hepatic cells. No effects of high cortisol levels or BaP were found on the steroid-metabolizing CYP3A enzyme levels. The lack of any alterations in the CYP3A protein level indicates that CYP3A expression is not inducible by cortisol in the Arctic charr under the conditions used here. The conclusion was made that short-term stress associated with sampling (i.e.,6 h ofconfinement stress before sampling) of wild charr does not compromise the EROD activity as a reliable biomarker. [ABSTRACT FROM AUTHOR]