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The trophic niches of Arctic charr and brown trout differ when the species occur in sympatry. Their trophically transmitted parasites are expected to reflect these differences. Here, we investigate how the infections of Diphyllobothrium dendriticum and D. ditremum differ between charr and trout. These tapeworms use copepods as their first intermediate hosts and fish can become infected as second intermediate hosts by consuming either infected copepods or infected fish. We examined 767 charr and 368 trout for Diphyllobothrium plerocercoids in a subarctic lake. The prevalence of D. ditremum was higher in charr (61.5%) than in trout, (39.5%), but the prevalence of D. dendriticum was higher in trout (31.2%) than in charr (19.3%). Diphyllobothrium spp. intensities were elevated in trout compared to charr, particularly for D. dendriticum. Large fish with massive parasite burdens were responsible for the high Diphyllobothrium spp. loads in trout. We hypothesize that fish prey may be the most important source for the Diphyllobothrium spp. infections in trout, whereas charr predominantly acquire Diphyllobothrium spp. by feeding on copepods. Our findings support previous suggestions that the ability to establish in a second piscine host is greater for D. dendriticum than for D. ditremum. [ABSTRACT FROM AUTHOR]

The Arctic char ( Salvelinus alpinus) species 'complex' has fascinated biologists for decades particularly with respect to how many species there are and their geographic distributions. I review recent research on the species complex, focussing on biodiversity within northwestern North America, which indicates (i) what was once considered a single taxon consists of three taxa: S. alpinus (Arctic char), S. malma (Dolly Varden), and S. confluentus (bull trout), (ii) morphological and genetic data indicate that S. alpinus and S. malma, and S. malma and S. confluentus exist as distinct biological species in sympatry, (iii) sympatric forms of S. alpinus exist in Alaska as in other areas of the Holarctic, (iv) Dolly Varden comprises two well-differentiated subspecies, S. m. malma and S. m. lordi, in the eastern Pacific and the northwestern Canadian Arctic that meet at a contact zone on the southern edge of the Alaska Peninsula, and (v) Dolly Varden and bull trout consist of several population assemblages that have legal status as distinct conservation units under US and Canadian law. This research has significantly revised what constitutes the S. alpinus species 'complex', provided insights into the ecology and genetics of co-existence, and promoted conservation assessment that better represents biodiversity within Salvelinus. A geographically and genetically comprehensive analysis of relationships among putative taxa of Pan-Pacific Salvelinus is still required to better quantify the number of taxa and their origins. [ABSTRACT FROM AUTHOR]

Arctic charr ( Salvelinus alpinus) is generally considered an inferior piscivore compared to brown trout ( Salmo trutta). However, we demonstrate that a recently described profundal spawning piscivore PP-morph of Arctic charr in a subarctic lake has evolved typical piscivore traits (i.e. large jaws, robust skulls), similar to the co-occurring brown trout but different from the sympatric littoral spawning omnivore LO-morph of Arctic charr. A few large-sized LO-morph, most large-sized PP-morph and trout constitute the piscivore guild, but they differed in prey fish selection. Of the fish-eating deep-water PP-morph, 52% had consumed charr, with a peak during the polar night period (68-80% in November-January). In contrast, the LO-morph and trout were mainly (~90%) inter-specific piscivores eating stickleback. Consequently, the PP-morph was the main charr predator and started to feed on fish at a smaller size and took larger prey relative to their body length than the trout. Stable isotope (δC, δN) ratios reflect the dietary specialisations in the upper-water (LO-morph, trout) and the deep-water (PP-morph) environments, besides the piscivorous behaviour of the PP-morph and trout. The existence of a shallow-water piscivore (trout) may explain the origin of this PP-morph, taking benefit of underutilised resources of small-sized Arctic charr in the deep-water habitat. [ABSTRACT FROM AUTHOR]

Phenotypic variation in populations of fishes that inhabit postglacial lakes is often associated with trophic specialisations. A common sympatric foraging divergence seen in Arctic charr is into either plankton or littoral-zoobenthos feeding specialisms. In this study, we report a sympatric polymorphic Arctic charr population which is not centred on this divergence but instead manifests as a plankton (pelagic)-profundal zoobenthos foraging specialisms. The head shape of profundal fish was round and robust, the body thick set and pectoral fins long and wide. In contrast, the head of pelagic fish was pointed and slender, the body fusiform in shape and with short, narrow pectoral fins. There was no difference between profundal and pelagic fish in gill raker number. Body lipid content was significantly higher in pelagic fish as were the number or Diphyllobothrium cysts. The carbon isotope ratio was more heavily depleted in profundal fish. There was no dietary overlap in the prey items recovered from stomach contents of profundal and pelagic fish. We suggest the proximate driver behind the sympatric divergence was the successful exploitation of the profundal zone. The consequences of this have led to the development of adaptations in morphology and behaviour to support and maintain this divergence. [ABSTRACT FROM AUTHOR]

The influence of interspecific interactions and habitat characteristics on the ecological niche of species' populations is a controversial issue in ecology. We explored the niche use of Arctic charr ( Salvelinus alpinus L.) in seven relatively large and deep lakes in southern Norway. We aimed to investigate how the presence of potentially competitive fish species, such as whitefish ( Coregonus lavaretus L.), perch ( Perca fluviatilis L.) and brown trout ( Salmo trutta L.), and the lake morphometry affects the littoral reliance and niche breadth of Arctic charr. Stable isotope (δC and δN) analyses showed that Arctic charr relied less on littoral food resources than brown trout and perch but had largely overlapping niche with whitefish. Arctic charr showed narrower niche use (i.e. less individual variation in δC and δN) than the other fish species in all seven lakes, particularly in communities where both littoral and pelagic competitors were present. Our results demonstrate that Arctic charr rely much less on littoral resources (<50%) in large and deep lakes in southern Scandinavia than in small, shallower subarctic lakes, and that interspecific interactions with both littoral and pelagic resource competitors can lead to niche compression of this generalist salmonid fish. [ABSTRACT FROM AUTHOR]

A population of small-sized Arctic charr living their entire life cycle in deep water was recently found in Lake Skogsfjordvatn, Northern Norway. Their phenotype and life history closely resembles the profundal charr morph in another subarctic Norwegian lake, Fjellfrøsvatn. Fjellfrøsvatn has one littoral omnivorous and one small profundal benthivorous (PB) charr morph coexisting with brown trout, whereas Skogsfjordvatn has migratory salmon, trout, charr and eel populations in addition to threespined sticklebacks, resident trout and three resident charr morphs of which one is a large piscivorous profundal morph. We predicted that the small profundal charr morph in Skogsfjordvatn would have a similar trophic niche to the PB-morph in Fjellfrøsvatn and tested this by using stomach content and stable isotope (δC and δN) analyses. Profundal benthic invertebrates, mainly chironomid larvae, Pisidium sp. mussels and small crustaceans, dominated the diets, and the δC and δN values indicated almost identical long-term trophic niches of the PB-morphs in both lakes. The prediction was therefore supported. This seems to indicate that the small profundal Arctic charr morphs in these lakes have evolved in parallel, in nearly identical and stable habitat and dietary niches in spite of likely different ecological interactions within the contrasting fish communities. [ABSTRACT FROM AUTHOR]

We contrast the genetic consequences of allopatric and sympatric divergence from the littoral spawning Arctic charr morph from Lake Fjellfrøsvatn. The littoral spawning Arctic charr has sympatrically diverged into a natural profundal adapted morph and via a recent (1930) translocation of about 40 adult Arctic charr established a new allopatric population in a nearby lake (Takvatn). The sympatric morph-pair in Fjellfrøsvatn was more genetically differentiated ( F = 0.121), the derived profundal morph had higher genetic variation (H = 0.740 ± 0.220; N = 4.87), and had a higher proportion of linkage disequilibrium among loci, than the Takvatn charr derived in allopatry ( F = 0.066; H = 0.584 ± 0.193; N = 0.29). The genetic differentiation in allopatry supports a scenario of rapid population expansion, despite genetic founder effects, whereas the genetic differentiation found in the sympatric morph-pair suggests that this divergence is older and supports a scenario of divergence under ongoing gene flow. We suggest that the differences between the two types of divergence may originate from temporal effects and differences in life histories between the two derived populations along with specific factors related to the initial stages of the divergence. [ABSTRACT FROM AUTHOR]

Seasonal dietary shifts by Arctic charr ( Salvelinus alpinus (L.)) are common in subarctic lakes, but less is known about how the shift to pelagic zooplankton feeding during the growing season affects stable isotope ratios and mercury concentrations. We sampled Arctic charr, zooplankton and benthic macroinvertebrates from oligotrophic Lake Galggojavri, northern Norway, in June, August and September. Stomach content, age, total length, weight, condition and sex were recorded for all individuals, and liver and muscle tissues were sampled for stable isotope (δC, δN) and total mercury analyses. We predicted that a dietary shift to zooplankton would lead to depleted C and increased mercury levels in charr. Arctic charr consumed benthic prey in June, but shifted to zooplankton feeding in August-September. Stable isotope mixing models revealed increased pelagic reliance towards September. Mercury content in liver increased from June to September, whereas muscle showed opposite trend. In stepwise multiple regression analyses, mercury content in muscle was explained by fish length, month and δC ( R = 0.46), whereas in liver month, δC and δN were the main explaining factors ( R = 0.69). Seasonal dietary shifts appeared to have an effect on total mercury content in charr, and thus sampling month should be considered when designing future monitoring programmes. [ABSTRACT FROM AUTHOR]

Temperature changes affect salmonids across a hierarchy of spatial and temporal scales, so that shifts in thermal river regimes may influence interspecific interactions in sympatric species. In Northern Norway, anadromous populations of Arctic charr ( Salvelinus alpinus) and Atlantic salmon ( Salmo salar) coexist, but in recent years landings of Arctic charr have decreased, while those of Atlantic salmon have been stable or even increased. Here we studied relative abundance, habitat use and growth rate of sympatric stream-living juveniles of both species in Veidnes River, where they are the only fish species present. In 1998/2000, juvenile Arctic charr dominated, especially in the upper and colder part of the river. In 2010, however, Atlantic salmon juveniles were now prominent in all habitat types, whereas nearly all Arctic charr were captured in slow-flowing water near the river bank. Summer air temperature has increased in the region during the last decade. Positive correlations between summer temperatures and back-calculated growth rates were documented in both species, but the growth response was significantly higher in Atlantic salmon. Accordingly, we suggest that juvenile Atlantic salmon may benefit from a warmer climate in northernmost Norway, at the expense of the more cold-water-adapted Arctic charr. [ABSTRACT FROM AUTHOR]

The occurrence of trophically transmitted intestinal parasites in Arctic charr was analyzed from data material collected over two decades from Lake Takvatn, northern Norway. The main objectives were to investigate (i) between-year variation in parasite infracommunity composition, (ii) between-host variation in infracommunity composition, and (iii) possible interspecific interaction between parasites. The trematode Crepidostomum spp. and the cestode Eubothrium salvelini were most prevalent and had the highest mean intensities whereas the cestodes Proteocephalus sp. and Cyathocephalus truncatus were uncommon taxa. No clear indication of interspecific parasite interactions was evident. By far the most frequent infracommunity composition was E. salvelini co-existing with only Crepidostomum spp. Despite some indications of individual dietary specialization in Arctic charr, this strong species co-occurrence suggests that the majority of fish had been preying on the very different intermediate hosts of both parasites. Overall, even though some sporadic between-year variation was present, no long-term or cyclical variation in infracommunity composition and mean intensity was revealed, suggesting that the host-parasite system is in a steady state. Minor between-year variation was likely the result of changes in habitat and dietary utilization by Arctic charr, possibly linked to documented changes in the fish community structure of the lake. [ABSTRACT FROM AUTHOR]

The article discusses the international symposium focusing on Arctic charr (Salvelinus alpinus). Topics include mercury concentration in Arctic charr which is cause by the anthropogenic contamination of the Arctic environment, evolutionary models explaining the patterns of divergence among Salvelinus populations in the wild, and habitat destruction because of human activities and industrial development resulting to environmental pollution.

Three genetically discrete morphs of Arctic charr in Loch Rannoch, Scotland originated from a recent divergence within the lake (in situ) (piscivore and benthivore morphs) and from secondary contact of two older lineages (ex situ; a planktivore-piscivore/benthivore divergence). To test if the expression of traits with strong functional roles was linked to the age of the divergence, fin and gill anatomy, and dentition were quantified and compared across morphs. Five additional working hypotheses suggesting a rank order of trait expression amongst morphs were also tested. The planktivorous morph had more rays in the dorsal and pectoral fins, longer gill rakers (but not more) as well as a smaller gill cavity than the other two morphs. The piscivorous morph had more palatine teeth and longer teeth on the mandible, pre-maxillary and glossohyal bones, and a larger buccal cavity. These differences indicate a differential response to selection in these functional anatomical features most likely related to morph foraging specialisms. Notably, between-morph divergences in the expression of these traits were not simply linked to the length of divergence between morphs and have arisen equally quickly in the recent (in situ ) divergence as they have in older, ex situ divergences. [ABSTRACT FROM AUTHOR]

Arctic charr, Salvelinus alpinus (L.), occur as anadromous, resident, and landlocked populations within their circumpolar distribution. While resident Arctic charr reside in freshwater their entire life, anadromous Arctic charr migrate to sea in the summer due to the increased resource availability, but return to freshwater to overwinter and/or spawn. The migratory behaviour in Arctic charr is generally restricted to the northern range of their distribution area. The objective of this study was to estimate the amount of straying and contemporary gene flow among anadromous Arctic charr from eight river systems in northern Norway to illuminate the role of straying for the contemporary genetic stability of the populations. The results revealed that Arctic charr frequently stray among watercourses, especially among those in close geographical proximity, although strays were found nearly 500 km from their river of origin. While straying was revealed among six river systems, the results also revealed limited or no contemporary gene flow among the nine populations identified in the eight sampled river systems. The study also shows that Arctic charr may be a potential host for spreading diseases and parasites among watercourses. [ABSTRACT FROM AUTHOR]

We assessed the food resource partitioning of three fish species (Arctic charr, Atlantic salmon and alpine bullhead) living in sympatry in a subarctic river. Fish were sampled monthly during the ice-free season (May-October), and dietary overlap among the species was calculated according to Schoener's index. In October, the diet overlap among all three species was high (>70%). In contrast, large to modest food resource partitioning occurred among Arctic charr and the other two species from May to September (27-59% overlap), whereas there was a distinct diet overlap between Atlantic salmon and alpine bullhead in May, August and September (>64%), but not in July (53%). Surface prey (terrestrial and emerged aquatic insects), probably caught at the surface, were important for Arctic charr in August and September (24.9 and 46.6%, respectively), whereas the other fish species mainly fed on Apatania stigmatella, Mystrophora intermedia and Ephemerella aurivilli. Alpine bullhead seemed to feed close to the bottom, Atlantic salmon used both the bottom and water of various depths, whereas Arctic charr showed the greatest capacity to forage at the water surface. This vertical segregation may be important for fish assemblages in subarctic rivers, allowing food resource partitioning and coexistence of sympatric species. [ABSTRACT FROM AUTHOR]

Arctic charr ( Salvelinus alpinus) were fed for 99 days on experimental diets with 40% of fish meal replaced, on a crude protein basis, with intact yeast ( Saccharomyces cerevisiae) ( ISC), extracted yeast ( ESC), Rhizopus oryzae fungus ( RHO) or de-shelled blue mussels ( Mytilus edulis) ( MYE). The fish were evaluated for growth performance, nutrient digestibility and fish intestinal function. Growth performance, retention of crude protein and sum of amino acids were not affected in fish fed diets ISC or MYE compared with those fed the reference ( REF) diet. However, fish fed diet ISC displayed decreased digestibility of crude protein and indispensable amino acids and decreased intestinal barrier function compared with fish fed the REF diet. Fish fed diet ESC exhibited decreased growth performance and protein retention, but had comparable digestibility to fish fed the REF diet. Fish fed diets MYE and RHO showed similar performance in terms of growth, nutrient digestibility and intestinal barrier function. Overall, the results indicated that blue mussel and intact S. cerevisiae yeast are promising protein sources for Arctic charr. [ABSTRACT FROM AUTHOR]

Teleost fishes are prominent vertebrate models of evolution, illustrated among old-world radiations by the Cichlidae of East African Great Lakes and new-world radiations by the circumpolar Arctic charr Salvelinus alpinus. Herein, we describe variation in lake charr S. namaycush morphology, life history, physiology and ecology, as another example of radiation. The lake charr is restricted to northern North America, where it originated from glacial refugia and diversified in large lakes. Shallow and deepwater morphs arose in multiple lakes, with a large-bodied shallow-water 'lean' morph in shallow inshore depths, a small-bodied mid-water ' humper' morph on offshore shoals or banks, a robust, large-bodied moderate to deep-water ' redfin'; morph and a large-bodied deep-water ' siscowet' morph at depths > 100 m. Eye position, gape size, and gillraker length and spacing adapted for feeding on different-sized prey, with piscivorous morphs (leans, siscowets and presumably redfins) reaching larger asymptotic size than invertivorous morphs (humpers). Lean morphs are light in colour, whereas deepwater morphs are drab and dark, although the pattern is reversed in dark tannic lakes. Morphs shift from benthic to pelagic feeding at a length of 400-490 mm. Phenotypic differences in locomotion, buoyancy and lipid metabolism evolved into different mechanisms for buoyancy regulation, with lean morphs relying on hydrodynamic lift and siscowet morphs relying on hydrostatic lift. We suggest that the Salvelinus genus, rather than the species S. alpinus, is a diverse genus that should be the subject of comparative studies of processes causing divergence and adaptation among member species that may lead to a more complete evolutionary conceptual model. [ABSTRACT FROM AUTHOR]

An evaluation of different thermal regimes during incubation of Arctic charr Salvelinus alpinus L. egg was conducted with regard to embryo survival and development. The study consisted of two major parts: In experiment A, a range of commonly used thermal regimes, constant and variable ranging from 2.7°C to 7°C, were tested for differences in embryo survival and developmental status of newly hatched alevins. Experiment B assessed the timing of a shift from autumn (6°C) to winter temperature (2.5°C) and its effect on embryo survival and the occurrence of spinal deformities in newly hatched alevins. In general, incubations that were initiated at temperatures below 3°C resulted in significantly higher mortality rates and spinal deformity frequencies than other treatments. Hence, Arctic charr eggs require an initial warmer period for unimpaired embryonic development. A general negative correlation was found between the duration of this warmer period (6°C) and both mortality rates and frequency of spinal deformities. The total absence of the 6°C period had the most detrimental effect, with deformity frequencies at least four times higher than all treatments with an initial warmer period. The upper incubation temperature threshold was not reached in the study. The highest temperature tested (7°C) did not result in excess mortality or increased deformity frequency. Higher incubation temperature resulted in less developed alevins at hatching, i.e. alevins were smaller with more yolk remaining. However, measurements on alevins from incubations at variable temperatures revealed different temperature effects on growth and yolk consumption during different parts of embryonic development. [ABSTRACT FROM AUTHOR]

To address the problem of high maturity at 2 years of age among Salvelinus alpinus (Labrador strain), PIT-tagged yearlings (ca. 110 g) were reared for 18 weeks overwinter (Nov. 16 to Apr. 1) under six treatments (90 fish per treatment) that combined three factors: photoperiod (natural day length, LDN or 24 h light, LL), temperature (10 or 5 °C), and food (fed daily or no food). On April 1 all fish were returned to LDN, 10 °C and fed daily for a further six months. In November, the maturity rate was very high among fish reared the previous winter under LDN and fed daily at both 10 °C (♀ 94%, ♂ 43%) and 5 °C (♀ 87%, ♂ 45%). Replacing LDN with LL overwinter, at 10 °C halved the maturity rate (♀ 49%, ♂ 19%), and at 5 °C eliminated maturity among females, and male maturity was 6%. Food deprivation for 18 weeks posed no health problems, and combined with LL also was highly effective at preventing maturation, both at 10 °C (♀ 0%, ♂ 2%) and 5 °C (♀ 0%, ♂ 7%). Compensatory growth following the suppression of growth overwinter indicates this approach to reducing maturity can be a commercially viable means to produce 1 kg immature product around 2 years old. A new two-step gating mechanism is proposed to explain the photoperiod prevention of maturation, one independent of somatic growth, the other dependent. Statement of relevance This study shows that the combination of LL, reduced temperature and food deprivation can significantly reduce the incidence of maturation and improve the productivity among diploid Arctic charr. This combination approach can potentially be applied to other farmed salmonids and non-salmonids to improve the efficacy of controlling sexual maturation. [ABSTRACT FROM AUTHOR]

The salmonid fish Arctic charr Salvelinus alpinus shows pronounced individual variation in skin colouration and density of carotenoid-based spots. It has earlier been shown that spot density is a heritable trait, and may be used as an indicator of stress coping style in Arctic charr. Individuals with few spots tend to be more aggressive and less responsive to stress (proactive) than those with many spots (reactive). Here, we evaluate the potential of grading individuals into proactive and reactive individuals by the density of light-coloured spots. This non-invasive method would be useful for selective breeding and to reduce within-treatment variation in biological research. Our aim was to investigate stability of spot density over time and to compare methods to estimate spottiness on Arctic charr, using photographs as well as live fish. The consistency of spot density was significant over a period of 8 months, but with stronger correlations between September and December than between May and September. Also, repeatability of spot number was higher between the two last months than when including May. The spots were more stable on the left than the right side, thus, it is more reliable to estimate spottiness on the left side. There was a significant relationship between the ratio of spotted area (rsa) from automated image analysis and number of spots from visual counts. Both methods fitted well into a visual grading into three categories (few, medium and many spots). In another test, a large number of live fish were visually categorized according to spot density. The previous validation process, in combination with a significant family effect showed that large numbers of fish can be effectively graded. [ABSTRACT FROM AUTHOR]

Despite the high number of studies concerning seasonality of immune response in fish, information for some fish species is still scarce. Here, we assess seasonal changes in leukocyte counts and several immune parameters in three groups of farmed salmonids, i.e. brook trout (Salvelinus fontinalis) , brook trout x Arctic charr hybrids (Salvelinus fontinalis x Salvelinus alpinus alpinus) and rainbow trout (Oncorhynchus mykiss) reared under the same conditions and fed with the same feed. Fish were sampled in five periods of the year (late April, early July, late August, early November and early February) and leukocyte counts, respiratory burst of blood phagocytes, lysozyme concentration in skin mucus and total complement activity were measured. Generalized linear models using fish body length as a continuous predictor and sampling period and fish species as categorical predictors, were significant for each of the parameters analysed. The highest seasonal variations in measured parameters were found in rainbow trout and lowest in hybrids. Our results confirm that measures of innate and adaptive immunity are strongly affected by season in all three groups of salmonids. The results will contribute to the improved assessment of immunocompetence in farmed fishes, essential for future sustainable development in aquaculture. [ABSTRACT FROM AUTHOR]

Earlier studies have shown that the carotenoid pigmentation in Arctic char ( Salvelinus alpinus (L., 1758)) is connected to stress responsiveness. These studies also suggested that the pigmentation is dynamic and can change quickly. Therefore, we wanted to investigate the effect of a short-term stressor on the number of carotenoid spots before and after certain time intervals after the stressor. Individuals were exposed to a net-restraint stressor for 1 min and then assigned a recovery time of either 0, 1, 2, 8, or 24 h. Photographs were taken before the stressor and after the recovery time to count carotenoid spots and to look at the relative changes over time. Behaviour during the stressor and cortisol levels after the assigned recovery time were evaluated. We found that the change in spottiness, measured as the ratio of spots after and before the stressor, changed with recovery time on the right side but not on the left side. Furthermore, left-side spots were correlated with struggling activity. Thus, carotenoid pigmentation seems to be lateralized, with more static spots on the left side connected to stress responsiveness, whereas spots on the right side seem to be more dynamic. [ABSTRACT FROM AUTHOR]

Metabolomics involves systematic study of low-molecular-mass metabolites in cells, tissues, or biofluids and is nowadays widely applied to characterize the physiological status of aquatic organisms under a set of conditions, such as disease and toxin exposure. Liver, an important metabolic center in the fish body, is often used for metabolomics analysis. Compared with the whole fish liver, the proportion of liver sample needed for metabolomics analysis is relatively small. The homogeneity of metabolites in liver is thus an important issue, especially for comparative studies and biomarker discovery. This study examined the homogeneity of the metabolic profile in liver of Arctic char ( Salvelinus alpinus (L., 1758)) using a NMR-based metabolomics approach. For the analysis, whole liver samples were cut into four parts along the direction of gall bladder and at right angles to this, and metabolites in each part of the liver were extracted and analyzed by multivariate and univariate data analyses. Although the multivariate model was not significant due to variation within the data, the metabolic differences in polar portion of liver extract between the parts were seen, indicating non-homogeneity of Arctic char liver. Therefore, when sampling fish liver for further metabolomics studies, this heterogeneity should be taken into consideration. [ABSTRACT FROM AUTHOR]

We used an array of fixed acoustic receivers ( N = 42) to track the summer marine movements of 121 anadromous Arctic char ( Salvelinus alpinus) equipped with acoustic transmitters at three locations in the Cambridge Bay region, where commercial and subsistence fisheries target the species. The timing of transitions between salt and fresh water was influenced by the putative river of origin of tagged individuals, but not by their size or sex. Females, however, were more likely to remain proximate to rivers where they were tagged throughout the summer. A majority of fish migrated west from their rivers of origin, primarily moving between estuarine environments. Individuals occupied estuaries for several days between bouts of marine movement, and these periods of residency coincided with spring tides in some estuaries. We also recorded increased numbers of detections on receivers located less than 1.5 km from the coast, indicating a preference for nearshore habitats. Finally, we report evidence of extensive stock mixing throughout the summer, including at known fishing locations and periods, a finding with implications for fisheries management. [ABSTRACT FROM AUTHOR]

Where anadromous fishes occur in the Canadian Arctic, they provide the mainstay of local subsistence fisheries of varying intensities. Many of these fisheries harvest a mixture of stocks at discrete locations and it is often not known which stocks, specifically, are being harvested and to what extent. In the Darnley Bay area of the Northwest Territories, Arctic char, Salvelinus alpinus, in particular have long provided an important subsistence resource to residents of Paulatuk, and char from two systems (the Hornaday and Brock Rivers) are thought to contribute to the coastal fishery for this species. Genetic mixed-stock analysis (GMA) is routinely applied for resolving stock contributions to such fisheries, yet studies incorporating GMA to understand specifically which stocks are being harvested in the Canadian Arctic, and to what extent, are relatively scarce. In this study, we assayed microsatellite DNA variation among 987 Arctic char from two important coastal subsistence fisheries and several inland sampling locations in the Darnley Bay area to (1) assess the degree of genetic structuring between the Hornaday and Brock Rivers and (2) resolve the proportional contributions of these stocks to coastal mixed-stock fisheries in the region using GMA. Overall, genetic differentiation was relatively high and significant (? = 0.117; 95% C.I. = 0.097-0.142) among baseline sampling locations. Overall patterns of genetic stock structure also support previous hypotheses that additional life history types (e.g., landlocked or freshwater-resident char, or both) exist in the Hornaday system, as indicated by elevated levels of genetic differentiation between some of our sampling locations. The GMA suggested that, while both river systems contribute to the coastal fishery, catches were dominated by Arctic char from the Hornaday River, which highlights the importance of this system. All told, our results may be relevant to the management of the subsistence fishery in Darnley Bay and for furthering the collective understanding of char biodiversity and life history variation in the Canadian Arctic. [ABSTRACT FROM AUTHOR]

Arctic charr Salvelinus alpinus did not appear to invest in acoustic communication during courtship and agonistic interactions in captivity. Salvelinus alpinus did, however, produce four different types of sounds which were found to be associated with three different types of air exchange behaviours which probably have a swimbladder regulation function. Since air passage sounds appear to be common among Salmonidae, it is suggested that the potential of passive acoustics techniques for behavioural and ecological monitoring should be further investigated in future field and laboratory investigations. [ABSTRACT FROM AUTHOR]

The trophic ecology (diet and head morphology) and migration patterns of two closely related salmonid fishes, Arctic char ( Salvelinus alpinus (L., 1758)) and Dolly Varden ( Salvelinus malma (Walbaum, 1792)), were examined in tributaries of Lake Aleknagik, southwestern Alaska, to test for differentiation between species. Schoener's index of proportional overlap and multivariate analyses of diets suggested that these species had significantly different trophic niches. Arctic char and the largest individuals of both species had the most diverse diets, and sockeye salmon ( Oncorhynchus nerka (Walbaum, 1792)) eggs dominated the diet of both species, especially Arctic char. Arctic char had larger jaws and wider heads than Dolly Varden of similar body length, which may contribute to interspecific diet difference. The species also differed in migration patterns; otolith microchemistry indicated that juvenile Arctic char were produced by nonanadromous mothers, whereas the mothers of the Dolly Varden had been to sea in the season prior to spawning. The species also segregate in spawning habitat (Arctic char in the lakes and Dolly Varden in streams), as well as in juvenile rearing habitat. Our study provides the first evidence of divergent feeding and migratory ecology between sympatric juvenile Arctic char and Dolly Varden, differences that may constrain hybridization and introgression between them. [ABSTRACT FROM AUTHOR]

The flooding dose technique of Garlick et al. ( 1980 ) has become the main method for measuring tissue and whole-animal rates of protein synthesis in ectotherms. However, single tissue samples are used to determine rates of protein synthesis and no studies have examined the pattern of flooding in large tissues such as the white muscle in fishes, which can comprise up to 55% of the wet body mass of a fish and which is poorly perfused. The present study has examined, for the first time, the patterns of flooding and measured rates of protein synthesis in five different regions of the white muscle in the Arctic charr Salvelinus alpinus ranging in size from 25 g to 1.6 kg following a flooding dose injection of L-[ 3 H]-phenylalanine. The results indicate that the degree of flooding ( i.e. free pool specific radioactivity relative to that of the injection solution) and elevation in free phenylalanine concentrations can vary between regions but the calculated fractional rates of protein synthesis were similar in four of the five regions studied. The variability in rates of protein synthesis increased with body size with greater variability observed between regions for fish > 1 kg in body mass. For consistency between studies, it is recommended that samples are taken from the epaxial muscle in the region below the dorsal fin when measuring fractional rates of white muscle synthesis in fishes. [ABSTRACT FROM AUTHOR]

The bacterium Aeromonas salmonicida ssp. achromogenes (Asa) causes atypical furunculosis in salmonids that may lead to extensive financial losses in intensive fish farming. The commercially available vaccine commonly used against the ssp. achromogenes in the production of Arctic charr in Iceland has been developed for Atlantic salmon (Salmon salar) against the subspecies salmonicida which causes typical furunculosis, but it has insufficient efficacy in Arctic charr. In response to this, a novel vaccine against Asa in Arctic charr was developed in cooperation with Spanish vaccine company; HIPRA, and the antibody response of Arctic charr against Asa investigated using enzyme-linked immunosorbent assay. Fish used for testing were vaccinated using the novel, monovalent autogenous experimental vaccine and a commercially available vaccine Alpha Ject® 3000 developed for Atlantic salmon that was used as a comparison. The study was conducted in commercial production units where the fish were continually exposed to natural outbreaks of atypical furunculosis. Blood samples were collected from the fish prior to vaccination and thereafter at approximately ten-week intervals in each production unit throughout the production period until the fish reached harvesting size. Fish growth and mortality was recorded throughout the study. The results indicated that both vaccines induced antibody response in fish against Asa antigens and that antibody titers obtained during the first weeks following vaccination were maintained throughout the production period. However, significantly higher antibody titers were observed in fish vaccinated with the experimental novel vaccine and fish mortality was significantly lower in production units containing fish vaccinated with the novel vaccine in comparison to the Alpha Ject 3000® vaccine. These results suggest that the novel vaccine may be a promising candidate for protective immunity against atypical furunculosis caused by Asa in Arctic charr. • The specific antibody responses in Arctic charr against Aeromonas salmonicida ssp. achromogenes were analyzed using ELISA. • A novel experimental vaccine developed for Arctic charr and a commercial vaccine developed for Atlantic salmon were compared. • The novel experimental vaccine induced a higher specific antibody response and with more extended duration. • Significantly reduced fish mortality was observed in the group vaccinated using the experimental vaccine. [ABSTRACT FROM AUTHOR]

• A novel evolutionary model (JBGP) was developed. • The JBGP classifies the presence of Arctic charr in the Teno River catchment. • The JBGP is superior to the jittered decision tree model. • Macroinvertebrates, mires and slope are the dominant indicators. Arctic charr is one of the fish species most sensitive to climate change but studies on their freshwater habitat preferences are limited, especially in the fluvial environment. Machine learning methods offer automatic and objective models for ecohydrological processes based on observed data. However, i) the number of ecological records is often much smaller than hydrological observations, and ii) ecological measurements over the long-term are costly. Consequently, ecohydrological datasets are scarce and imbalanced. To address these problems, we propose jittered binary genetic programming (JBGP) to detect the most dominant ecohydrological parameters affecting the occurrence of Arctic charr across tributaries within the large subarctic Teno River catchment, in northernmost Finland and Norway. We quantitatively assessed the accuracy of the proposed model and compared its performance with that of classic genetic programming (GP), decision tree (DT) and state-of-the-art jittered-DT methods. The JBGP achieves the highest total classification accuracy of 90% and a Heidke skill score of 78%, showing its superiority over its counterparts. Our results showed that the dominant factors contributing to the presence of Arctic charr in Teno River tributaries include i) a higher density of macroinvertebrates, ii) a lower percentage of mires in the catchment and iii) a milder stream channel slope. [ABSTRACT FROM AUTHOR]

Intraspecific competition plays a significant role in shaping how animals use and share habitats in space and time. However, the way individuals may modify their diel activity in response to increased competition has received limited attention. We used juvenile (age 1+) Arctic charr Salvelinus alpinus to test the prediction that individuals at high population density are more active and distribute their foraging activity over a greater portion of the 24-h cycle than individuals at low population density. Individually tagged fish were stocked in seminatural stream enclosures at low (2 fish/m2) and high (6 fish/m2) density. During each of two 2-week experimental rounds, activity of all fish within each enclosure was recorded every 3 h over seven 24-h cycles. At high density, fish were more active and distributed their activity over a greater portion of the 24-h cycle, with increased activity particularly at crepuscular times. Fluctuations in ecological conditions (e.g., water temperature and light intensity) also affected activity. Fish at high density grew as fast as fish at low density. This study demonstrates that individuals exhibit a degree of behavioral flexibility in their response to changes in ecological conditions and suggests that intraspecific competition can cause animals to modify temporal aspects of their activity to gain access to resources and maintain growth. [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]

Protein metabolism, including the interrelated processes of synthesis and degradation, mediates the growth of an animal. In ectothermic animals, protein metabolism is responsive to changes in both biotic and abiotic conditions. This study aimed to characterise responses of protein metabolism to food deprivation that occur in the coldwater salmonid, Arctic charr, Salvelinus alpinus. We compared two groups of Arctic charr: one fed continuously and the other deprived of food for 36 days. We measured the fractional rate of protein synthesis (KS) in individuals from the fed and fasted groups using a flooding dose technique modified for the use of deuterium-labelled phenylalanine. The enzyme activities of the three major protein degradation pathways (ubiquitin proteasome, lysosomal cathepsins and the calpain systems) were measured in the same fish. This study is the first to measure both KS and the enzymatic activity of protein degradation in the same fish, allowing us to examine the apparent contribution of different protein degradation pathways to protein turnover in various tissues (red and white muscle, liver, heart and gills). KS was lower in the white muscle and in liver of the fasted fish compared to the fed fish. There were no observable effects of food deprivation on the protease activities in any of the tissues with the exception of liver, where the ubiquitin proteasome pathway seemed to be activated during fasting conditions. Lysosomal proteolysis appears to be the primary degradation pathway for muscle protein, while the ubiquitin proteasome pathway seems to predominate in the liver. We speculate that Arctic charr regulate protein metabolism during food deprivation to conserve proteins. [ABSTRACT FROM AUTHOR]

Apparent digestibility coefficients ( ADCs) for four protein-rich alternative feed ingredients, intact baker's yeast ( Saccharomyces cerevisiae), extracted baker's yeast ( S. cerevisiae), zygomycetes ( Rhizopus oryzae) and blue mussel ( Mytilus edulis), were determined for Arctic charr ( Salvelinus alpinus) and Eurasian perch ( Perca fluviatilis). Diets contained 30% of test ingredients, and ADCs were compared to a reference diet containing fish meal. For Arctic charr, ADCs for dry matter ( DM, 71-99%), sum of amino acids ( SAA, 84-99%) and gross energy (70-99%) were significantly lower for intact S. cerevisiae than for extracted S. cerevisiae, R. oryzae and M. edulis. The ADCs for the indispensable amino acids ( IAA) in Arctic charr varied between 84% and 99%. Significant differences were found in ADCs for IAA between the test ingredients for Arctic charr, with higher values for extracted S. cerevisiae and M. edulis. The ADCs in Eurasian perch varied between 83% and 95% for DM, 89% and 98% for CP, 92% and 100% for SAA, 81% and 96% for gross energy. No significant differences were found for ADCs between the test ingredients in Eurasian perch, indicating a species effect on digestibility. Furthermore, the absence of intact cell walls had a positive effect on digestibility of S. cerevisiae for Arctic charr. [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]

In Arctic and alpine lakes, Arctic char [ Salvelinus alpinus (L.)] often form two distinct morphs: invertebrate feeders ('dwarfs') and piscivores ('giant or cannibals'). Here, we test for early life history growth variation in dimorphic Arctic char as a proximate explanation for the observed life history variation between the two forms. Char were sampled in 11 alpine and Arctic Norwegian lakes. Dwarfs (defined as sexually mature char less than 15 cm long; N = 304) had a mean total length of 105 mm, whereas the typical cannibal (body length above 20 cm; N = 153) was 388 mm long. A positive correlation between egg size and otolith hatching ring were ascertained in a separate hatching experiment with brown trout ( Salmo trutta) and it is assumed that this relationship also is valid for Arctic char, and otolith size was used as a proxy for length. Otolith hatching ring from Arctic char cannibals was larger (mean ± SD; 187 ± 24 μm) than those from dwarfs (mean ± SD; 164 ± 23 μm). There were only minor size differences between dwarfs and cannibals during the next three years, after which dwarfs usually matured. Two mutually nonexclusive, proximate explanations for the differentiation into separate morphs (dwarfs and cannibals) are therefore maternal effects and/or genetic based differentiation. The high catchability of large piscivorous char and low production in alpine and Arctic lake ecosystems may make these stocks particularly vulnerable to overexploitation. [ABSTRACT FROM AUTHOR]

In the last 20 years, research has been directed towards possible differences in the mating behaviour of species belonging to the Salmonidae family that may reproductively isolate wild populations from escaped hatchery or farmed fish. Despite these studies, a detailed description of the overall behavioural repertoire of Salmonidae species from wild and farmed environments is still lacking. Furthermore, although Arctic charr has been described as the most variable between all vertebrate species, possible behavioural plasticity outside of the breeding season has not been widely investigated, and a complete ethogram for Arctic charr not in breeding condition is currently unavailable. This study presents the first complete ethogram of captive Arctic charr behaviour outside of the breeding season. The completeness of this ethogram was validated based on the Behavioural Accumulation Curves methodology, a reliable and easy to use tool for assessing the best compromise between sampling effort and ethogram completeness. Additionally, a new way of presenting an ethogram has been proposed and validated using a dichotomous key to describe behaviour types. This proved to be a more effective operational tool for identifying Arctic charr behaviour than the ethogram. The dichotomous key of behaviour led to a significantly less ambiguous identification of behavioural units, thus reducing observer, recording errors and enhancing accuracy. This study therefore represents an effective step forward to a more in-depth and rigorous comparison of Arctic charr behavioural adaptation between and within artificial and natural settings. [ABSTRACT FROM AUTHOR]

This paper presents description and interpretation of the Pembroke site, the earliest known Thule Inuit occupation in the southeastern Victoria Island region, Nunavut. The site has 11 extant dwellings, including five heavy tent rings, five light semi-subterranean dwellings, and a qalgiq (large communal structure). The site's economy revolved mainly around the acquisition of caribou, Arctic char, and lake trout, with minimal consumption of sea mammals. Radiocarbon dates, reinforced by artifact analyses, indicate an occupation around AD 1400. Based on several lines of evidence, including the extremely small artifact samples, the site is interpreted as having been occupied relatively briefly. It represents the first colonization of the region by Thule people, approximately 200 years after the initial Thule migration from Alaska into the eastern Arctic. Thus, it documents a second migration wave: an expansion of Thule peoples from their initially occupied territories to other, in some ways less optimal, regions. [ABSTRACT FROM AUTHOR]

The Swedish breeding programme for Arctic charr aims to improve traits that are important for farming. Selection has been ongoing since the 1980s, and the aim of this study was to re-estimate the genetic parameters in the selected population. In addition, the genetics of skin pigmentation was studied, as previous work indicated a relationship between pigmentation and the ability to cope with stress. One hundred twenty-five full sib families of Arctic charr were hatched and reared separately until they were individually tagged (n = 12,266). In connection with the tagging, three replicates were formed, which were subsequently reared at different sites. The genetic relationships were known from a seven-generation pedigree. Body weight and length were at one site measured at six occasions until 27 months old, and these measurements were used to estimate the DGC (daily growth coefficient) and condition factor. At a second site fish were measured at 21 and 27 months age and at a third site at 27 months age. Skin pigmentation was measured using image analysis. The final weight at 27 months of age varied widely between rearing sites, ranging from 529 g to 1443 g. Weight heritability differed among the sites, at 0.45, 0.11, and 0.07. At one of the sites, where growth was followed closely, weight heritability varied among growth periods, ranging from 0.01 to 0.25, and similar results were obtained for the DGC. In contrast, condition factor heritability did not show such pronounced variations within and among sites. The magnitude of the differences in heritability of weight and growth among different sites that was observed here was not observed previously with this charr population. In particular, the low heritability among the fastest growing fish is unprecedented. Skin pigmentation showed a high heritability of 0.76, indicating a strong additive genetic component. At most ages, pigmentation showed a weak positive genetic correlation with growth. The genotype environment interaction (GEI) was estimated using genetic correlations among sites. For the final weight, genetic correlations were high, indicating weak GEI, although the presence of GEI was suggested from the DGC data. Statement of relevance The ms will impact charr breeding for commercial farming. [ABSTRACT FROM AUTHOR]

Substantial seasonal changes in resource use associated with enhanced water-column use were revealed in stream-living YOY Arctic charr Salvelinus alpinus during the ice-free season. In July, YOY individuals showed a diet dominated by aquatic invertebrates (mainly Chironomidae larvae), but despite the small size of the fish, the abundance of terrestrial insects in their diet increased markedly from July to September (from 1·9 to 62·8%). Similarly, the frequency of surface drifting foragers, i.e. individuals feeding on allochthonous resources, increased from July to September (from 20·6 to 80%); allochthonous resources thus constituting an important energy subsidy for YOY S. alpinus during the late sub-Arctic summer. [ABSTRACT FROM AUTHOR]

A 20-week feeding trial was conducted to measure growth, nutrient utilization and faecal/gut bacterial counts in triplicate groups of red hybrid tilapia, Oreochromis sp., when fed diets supplemented with 0.5% organic acids blend ( OAB), 1.0% OAB, 0.5% oxytetracycline ( OTC) or a control diet (no additives). At the end of the feeding trial, tilapia were challenged with Streptococcus agalactiae for 22 days. Fish fed the OTC diet had significantly higher ( P < 0.05) growth than the control treatment, while growth between fish fed the OTC or OAB diets was not significantly different ( P > 0.05). Phosphorus, dry matter and ash digestibility were significantly higher in the 1.0% OAB diet than the control diet. Fish fed the OAB diets had significantly lower colony-forming units of adherent gut bacteria compared to the control or OTC treatments while those fed the 1.0% OAB diet had the lowest total faecal bacterial counts. Tilapia fed the 0.5% OTC or OAB diet had significantly higher resistance to S. agalactiae than those fed the control diet. This study indicates that dietary organic acids can potentially replace OTC as a growth promoter and antimicrobial in tilapia feeds. [ABSTRACT FROM AUTHOR]

Several fish species, including three-spined stickleback, Gasterosteus aculeatus, have shown a more northerly distribution in the Norwegian Sea into the eastern part of the Arctic Ocean during the last decades. Three-spined stickleback has however never been recorded in freshwaters on Svalbard, whereas Arctic charr, Salvelinus alpinus, has been the only reproducing fish with anadromous, resident, and landlocked populations. On this background, we sampled fish by gillnetting, electrofishing, and trapping in two watercourses on the island of Spitsbergen, Svalbard, during the summers 2001 and 2006. During these surveys, three-spined sticklebacks were captured in both localities. To our knowledge, this represents the first records of the species in Svalbard freshwaters. The presence of a few adult sticklebacks does not provide evidence that breeding populations are established. However, increased temperatures associated with climate change in recent years in both Arctic marine and freshwater environments may have facilitated the appearance of the species in these localities and thus may be a first indication of the potential establishment of this species in Svalbard freshwaters. [ABSTRACT FROM AUTHOR]

Aims We investigated post-glacial recolonization of the North American Arctic by Arctic char ( Salvelinus alpinus) and examined potential hybridization between different glacial lineages upon secondary contact. Location North American Arctic and adjacent areas. Methods We collected mt DNA sequence data from 1355 individuals from 110 sampling locations and data from nine microsatellite loci from 931 individuals from 37 locations. We assessed the phylogenetic relationships and geographical distribution of mt DNA haplotypes and conducted historical demographic analyses. We used a Bayesian clustering analysis method to detect potential hybridization between glacial lineages. Results Two highly divergent mt DNA lineages were identified in the Arctic region with distinct but overlapping geographic distributions: one in Beringia and the other over the entire Arctic Archipelago and coastal mainland east of Alaska. The microsatellite data also implied the existence of these two lineages. Evidence of hybridization was detected between the Arctic lineage and an Atlantic lineage in eastern North America. Main conclusions Our data suggested survival and recolonization from two northern glacial refugia: one in Beringia and another in a smaller refugium, perhaps in the Arctic Archipelago itself or a separate refugium within Beringia. Patterns of hybridization detected supported the presence of a secondary contact zone between glacial lineages in the eastern Canadian Arctic. [ABSTRACT FROM AUTHOR]

Variation in presumably neutral genetic markers can inform us about evolvability, historical effective population sizes and phylogeographic history of contemporary populations. We studied genetic variability in 15 microsatellite loci in six native landlocked Arctic charr (Salvelinus alpinus) populations in northern Fennoscandia, where this species is considered near threatened. We discovered that all populations were genetically highly (mean FST ≈ 0.26) differentiated and isolated from each other. Evidence was found for historical, but not for recent population size bottlenecks. Estimates of contemporary effective population size (Ne) ranged from seven to 228 and were significantly correlated with those of historical Ne but not with lake size. A census size (NC) was estimated to be approximately 300 individuals in a pond (0.14 ha), which exhibited the smallest Ne (i.e. Ne/NC = 0.02). Genetic variability in this pond and a connected lake is severely reduced, and both genetic and empirical estimates of migration rates indicate a lack of gene flow between them. Hence, albeit currently thriving, some northern Fennoscandian populations appear to be vulnerable to further loss of genetic variability and are likely to have limited capacity to adapt if selection pressures change. [ABSTRACT FROM AUTHOR]

The evaluation of new diet composition is commonly achieved by performing time-consuming growth trials, which may negatively impact the welfare of a large number of fish if the feed is not accepted. Instead, the fish's behavioural responses to a new diet composition can be used as a first step in the evaluation of new diet composition. The taste acceptance of a new diet by Arctic charr ( Salvelinus alpinus ) was evaluated over 16 days based on the self-selection of a test diet and a control diet. The test diet contained ingredients from the nutrient-enriched Baltic Sea, and it is hoped that this diet can contribute nutrients to the nutrient-poor waters in northern Sweden in which Arctic charr are farmed. The main ingredients in the test feed were blue mussel meat ( Mytilus edulis ), meat from sprat ( Sprattus sprattus ) and herring ( Clupea harengus ), baker's yeast ( Saccharomyces cerevisiae ), fish oil and regionally produced rapeseed oil. Individual fish ( n = 15) were allowed to choose between abundances of both the test diet and a fishmeal based control diet that mimicked a standard feed for Arctic charr. After only a few days, the fish demonstrated a significant preference for the Baltic Sea test feed. These results may depend on betaine, which was found at concentrations that were four times higher in the test feed than in the control feed. Betaine is a known attractant for many fish species and is abundant in marine animals, such as mussels. Thus, the test diet can be evaluated further without additional taste stimulants before the new feed formula can be used commercially to ensure fish welfare, the product quality and the economic feasibility of the new formula. [ABSTRACT FROM AUTHOR]

The metalloendopeptidase AsaP1 is one of the major extracellular virulence factors of A. salmonicida subsp. achromogenes, expressed as a 37- kDa pre-pro-peptide and processed to a 19- kDa active peptide. The aim of this study was to construct mutant strains secreting an AsaP1-toxoid instead of AsaP1-wt, to study virulence of these strains and to test the potency of the AsaP1-toxoid bacterin and the recombinant AsaP1-toxoids to induce protective immunity in Arctic char. Two A. salmonicida mutants were constructed that secrete either AsaP1E294A or AsaP1Y309F. The secreted AsaP1Y309F-toxoid had weak caseinolytic activity and was processed to the 19- kDa peptide, whereas the AsaP1E294A-toxoid was found as a 37- kDa pre-pro-peptide suggesting that AsaP1 is auto-catalytically processed. The LD50 of the AsaP1Y309F-toxoid mutant in Arctic char was significantly higher than that of the corresponding wt strain, and LD50 of the AsaP1E294A-toxoid mutant was comparable with that of an AsaP1-deficient strain. Bacterin based on AsaP1Y309F-toxoid mutant provided significant protection, comparable with that induced by a commercial polyvalent furunculosis vaccine. Detoxification of AsaP1 is very hard, expensive and time consuming. Therefore, an AsaP1-toxoid-secreting mutant is more suitable than the respective wt strain for production of fish bacterins aimed to protect against atypical furunculosis. [ABSTRACT FROM AUTHOR]

Resource polymorphism may play an important role in the process of speciation. The Arctic char ( Salvelinus alpinus) exhibits great phenotypic and genetic diversity across its range, making it an ideal species for studies of resource polymorphism and divergence. Here, we investigated genetic variation at 11 microsatellite loci among 287 Arctic char from five isolated yet proximate postglacial lakes in south-western Alaska that were previously examined for resource polymorphism. Significant differences in pairwise FST were detected among all lakes (range from 0.05 to 0.28, all P < 0.02). In one lake (Lower Tazimina Lake), we found evidence for two genetic groups of char and for significant differences in the distribution of microsatellite variability among at least two of the three previously described body size morphotypes ('large'-, 'medium'-, and 'small'-bodied char; maximum FST = 0.09; differences in admixture proportions). We also found a significant association between genetic admixture proportions and gill raker counts among body size morphs ( r = −0.73, P < 0.001). Our data represent the first record of genetically distinct sympatric morphs of Arctic char in Alaska and provide further evidence that differences in morphology associated with feeding (gill rakers) and growth trajectories reflect niche diversification and promote genetic divergence in Holarctic populations of Arctic char. [ABSTRACT FROM AUTHOR]

This study tests the basic hypothesis that the removal of charr, Salvelinus alpinus ( L.), would cause an increase in both the growth and density of a sympatric trout population, Salmo trutta L. The charr population was characterised by slow-growing individuals, with a high proportion of mature fish, that is typical for so-called overpopulated populations. A total of 31,000 charr was removed from the lake in the period 1990-1992, and the density of younger trout (1+, 2+), but not older trout (3+, 4+), increased. The growth of older trout (3+, 4+) increased, but the evidence for similar growth increases of younger trout (1+, 2+) was limited. From 1989 to 1990, the proportion of trout increased from 30 to only 40% of the total catch, but from 1991 to 1994, it was significantly higher (60-80%) than that of charr. Total trout biomass increased to a maximum in 1992 and then decreased so that the biomass of 1994 was nearly similar to that of 1989, that is before the start of the charr removal. Back-calculated lengths of trout from otoliths showed that 2+ and 3+ trout caught in the pelagic were growing consistently faster over previous years than those caught in the littoral, while this was not the case for the 4+ fish. Therefore, the hypothesis was partially supported; the growth rate of trout increased (age groups 1+ to 4+), while the density of juvenile trout (1+, 2+), but not the older trout (3+, 4+), increased after the removal of charr. [ABSTRACT FROM AUTHOR]

The highly seasonal anadromous Arctic charr (Salvelinus alpinus) was used to investigate the possible involvement of altered gene expression of brain neuropeptides in seasonal appetite regulation. Pro-opiomelanocortin (POMCA1, POMCA2), Cocaine and amphetamine regulated transcript (CART), Agouti related Peptide (AgRP), Neuropeptide Y (NPY) and Melanocortin Receptor 4 (MC4-R) genes were examined. The function of centrally expressed Leptin (Lep) in fish remains unclear, so Lep (LepA1, LepA2) and Leptin Receptor (LepR) genes were included in the investigation. In a ten months study gene expression was analysed in hypothalamus, mesencephalon and telencephalon of immature charr held under natural photoperiod (69°38’N) and ambient temperature and given excess feed. From April to the beginning of June the charr did not feed and lost weight, during July and August they were feeding and had a marked increase in weight and condition factor, and from November until the end of the study the charr lost appetite and decreased in weight and condition factor. Brain compartments were sampled from non-feeding charr (May), feeding charr (July), and non-feeding charr (January). Reverse transcription real-time quantitative PCR revealed temporal patterns of gene expression that differed across brain compartments. The non-feeding charr (May, January) had a lower expression of the anorexigenic LepA1, MC4-R and LepR in hypothalamus and a higher expression of the orexigenic NPY and AgRP in mesencephalon, than the feeding charr (July). In the telencephalon, LepR was more highly expressed in January and May than in July. These results do not indicate that changes in central gene expression of the neuropeptides investigated here directly induce seasonal changes in feeding in Arctic charr. [ABSTRACT FROM AUTHOR]

Pigmentation often signals status and in general melanin-based pigmentation is indicative of aggression and stress resilience in vertebrates. This is evident in the salmonids Atlantic salmon ( Salmo salar ) and rainbow trout ( Oncorhynchus mykiss ) where more melanin spotted individuals are more stress resilient. However, in the salmonid Arctic charr ( Salvelinus alpinus ) it seems as if it is carotenoid-based pigmentation that signals aggression and stress resilience. In our study, social stress effects on carotenoid-based spots, and behavioural and physiological stress responses were investigated. Socially stressed individuals have more spots, and behavioural stress responses were associated with spots. Some of the results concerning physiological stress responses, such as plasma cortisol levels and monoaminergic activity, are associated with spottiness. Further, the earlier proposed lateralization of spots, with left side connected to stress responsiveness and right side to aggression, is to some extent validated although not conclusively. In conclusion, this study provides further evidence that more stressed charr have more carotenoid spots, and for the first time monoaminergic activity is shown to be connected with carotenoid pigmentation. [ABSTRACT FROM AUTHOR]