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Our understanding of the environmental behavior, bioaccumulation and concentrations of chlorinated paraffins (CPs) and Dechloranes (Dec) in the Arctic environment is still limited, particularly in freshwater ecosystems. In this descriptive study, short chain (SCCPs) and medium chain (MCCPs) CPs, Dechlorane Plus (DP) and analogues, and polychlorinated biphenyls (PCBs) were measured in sediments, benthic organisms, three-spined stickleback (Gasterosteus aculeatus), Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) in two Sub-Arctic lakes in Northern Norway. Takvannet (TA) is a remote lake, with no known local sources for organic contaminants, while Storvannet (ST) is situated in a populated area. SCCPs and MCCPs were detected in all sediment samples from ST with concentration of 42.26--115.29 ng/g dw and 66.18--136.69 ng/g dw for SCCPs and MCCPs, respectively. Only SCCPs were detected in TA sediments (0.4--5.28 ng/g dw). In biota samples, sticklebacks and benthic organisms showed the highest concentrations of CPs, while concentrations were low or below detection limits in both char and trout. The congener group patterns observed in both lakes showed SCCP profiles dominated by higher chlorinated congener groups while the MCCPs showed consistency in their profiles, with C14 being the most prevalent carbon chain length. Anti- and syn-DP isomers were detected in all sediment, benthic and stickleback samples with higher concentrations in ST than in TA. However, they were only present in a few char and trout samples from ST. Dec 601 and 604 were below detection limits in all samples in both lakes. Dec 603 was detected only in ST sediments, sticklebacks and 2 trout samples, while Dec 602 was the only DP analogue found in all samples from both lakes. While there were clear differences in sediment concentrations of DP and Dec 602 between ST and TA, differences between lakes decreased with increasing δ15N. This pattern was similar to the PCB behavior, suggesting the lake characteristics in ST are playing an important role in the lack of biomagnification of pollutants in this lake. Our results suggest that ST receives pollutants from local sources in addition to atmospheric transport. [ABSTRACT FROM AUTHOR]

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

This ethnographic study explores and compares the relationships that locals in Rossfjord, North Norway, have to the oystercatcher and the sea-going Arctic char respectively. Both these animals are highly valued locally, while the valuations at first look very different. The oystercatcher is protected by building bin-cases for its nesting, while the Arctic char is killed and eaten. Discussing these valuations against the value theory of David Graeber, I argue that they both connect to an underlying perception of the freedom and autonomy of wild animals, where what is not fully understood enhances an experience of wonder and appreciation of what I call the wild. [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]

Gyrodactylus spp. (Monogenea) were found on 16.9% (233 out of 1376) Arctic char, Salvelinus alpinus (L.), sampled from September 2010 to October 2011 in the Fustvatnet lake, Northern Norway. Two species were identified: G. salaris Malmberg, 1957, and G. salmonis Yin & Sproston, 1948. Gyrodactylus salaris was only found on Arctic char larger than 28 cm and only in samples obtained in the autumn (September and October). Gyrodactylus salmonis was found on Arctic char of all sizes (11–47 cm) and throughout the year, with a small peak in abundance in the late autumn (November). Gyrodactylus salaris was found to prefer the tail and dorsal fin. Based on the results, we recommend that surveys of Arctic char for the presence of G. salaris are based on the examination of the fins of large fish sampled during the spawning season (autumn). [ABSTRACT FROM AUTHOR]

Analysing the geographical distribution of evolutionary linages can reveal the potential locations of past refugia and colonisation routes and thus can improve understanding of current patterns of genetic variation and adaptive potential. We analysed 94 full mitogenome sequences to assess phylogeographic relationships amongst ten Arctic char (Salvelinus alpinus) populations, from western Greenland, eastern Greenland, Iceland and Norway. In addition, we excised D‐loop sequences, which were combined with previously published data in order to provide a circumpolar phylogeographical overview. In western Greenland, a secondary contact zone between Arctic and Atlantic evolutionary lineages was identified, spanning >1000 km, which geographically parallels a similar contact zone in Labrador, Canada. In eastern Greenland, Iceland and Norway, the Atlantic lineage was exclusively observed, whereas the northernmost western Greenland populations belonged to the Arctic lineage. The Arctic and Atlantic lineages were estimated to have diverged ca. 400,000 years BP, corresponding to the onset of the Saale glaciation, whereas the time of the most recent common ancestor (TMRCA) of the Arctic lineage was ca. 15,000 years BP. The Atlantic lineage comprised two subclades, with an estimated TMRCA of 60,000 BP, suggesting a complex history involving cryptic refugia or multiple recolonisations. Codon‐based tests revealed no evidence for positive selection within the 13 coding genes, indicating that there are no mitochondrial genetic adaptations within or between lineages. Higher genetic diversity observed within the contact zone likely correlates with higher standing genetic variation that could contribute to adaptive responses and morphological diversification, which Arctic char is renowned. [ABSTRACT FROM AUTHOR]

Warming temperatures resulting from climate change may alter the distribution and abundance of many freshwater fish species, especially those in northern latitudes. Owing to interspecific differences in temperature adaptations and tolerances, warming may lead to changes in the fish community as a result of shifts in the abundance of co‐existing species.We investigated how increased temperatures have potentially affected the abundance and catch composition of anadromous salmonids in northern Europe. We used national angling catch statistics over a period of several decades (1993–2018) as a proxy of relative annual abundance of adult Atlantic salmon (Salmo salar), brown trout (Salmo trutta), and Arctic charr (Salvelinus alpinus) in water courses in Iceland and in northern Norway. These are the only locations in the world where the three species coexist naturally as anadromous forms, and where they are distributed across latitudinal gradients characterised by varying temperatures.Interpolated data on average annual air temperatures proximate to the study rivers increased 1–1.7°C in northern Norway and 1.0–1.5°C in Iceland during the 26‐year study period.While the overall total number of fish caught has remained relatively stable during the period of study, gradual climate warming has been accompanied by a marked change in the catch composition of the three species in both countries. Increased temperatures were related to a decreased proportion of Arctic charr and an increased proportion of brown trout, while no temperature effect was found for Atlantic salmon. Controlling for the difference between fluvial and lacustrine systems, brown trout has begun to replace Arctic charr in all regions, whereas the relative catch of Atlantic salmon has been stable.Interpretation of angling data can facilitate understanding of longer‐term trends in catch data and provide insights into possible underlying changes in fish species and alert managers to shifts in abundance that might be mitigated by management actions. However, care must be taken to avoid the confounding effects that changes in fisheries management measures, angler preferences, and effort might have on the metrics of relative change used to make inferences about long‐term trends. [ABSTRACT FROM AUTHOR]

Proliferative kidney disease (PKD), caused by the myxozoan endoparasite Tetracapsuloides bryosalmonae, is of serious ecological and economical concern to wild and farmed salmonids. Wild salmonid populations have declined due to PKD, primarily in rivers, in Europe and North America. Deep lakes are also important habitats for salmonids, and this work aimed to investigate parasite presence in five deep Norwegian lakes. Kidney samples from three salmonid species from deep lakes were collected and tested using real‐time PCR to detect PKD parasite presence. We present the first detection of T. bryosalmonae in European whitefish in Norway for the first time, as well as the first published documentation of the parasite in kidneys of Arctic charr, brown trout and whitefish in four lakes. The observed prevalence of the parasite was higher in populations of brown trout than of Arctic charr and whitefish. The parasite was detected in farmed, but not in wild, charr in one lake. This suggests a possible link with a depth of fish habitat and fewer T. bryosalmonae‐infected and PKD‐affected fish. Towards a warmer climate, cold hypolimnion in deep lakes may act as a refuge for wild salmonids, while cold deep water may be used to control PKD in farmed salmonids. [ABSTRACT FROM AUTHOR]

Acoustic telemetry was utilized to track 49 brown trout (Salmo trutta) and 37 Arctic charr (Salvelinus alpinus) first‐time migrants of wild origin [post‐smolts; mean LF (fork length): 169 and 172 mm] in a large fjord in northern Norway. The S. trutta were registered at sea for more than twice the time of the S. alpinus (medians of 54 and 22 days, respectively). Both species were mostly detected near river mouths (>80% of detections) and almost exclusively spent their time (>95%) within the interior 18 km of the fjord. They were surface oriented, with most detections at <1 m depth and S. trutta deeper on average (median mean depths of 0.7 and 0.5 m, respectively). This study concludes that post‐smolts of both species stay closer to the surface and to river mouths than larger veteran migrants. This study emphasizes the importance of river mouths and upper water layers for the survival of both species during their first marine migration. [ABSTRACT FROM AUTHOR]

The introduced monogenean Gyrodactylus salaris (Malmberg, 1957) is categorized as one of the most severe threats against Atlantic salmon (Salmo salar Linnaeus, 1758) in Norway and has almost eradicated salmon populations in the Skibotn and Signaldalen Rivers in northern Norway. The parasite was unintentionally introduced to the Skibotn River in 1976 via release of infested Atlantic salmon smolt from Sweden. The parasite is restricted to freshwater, and survives at most a few days without its host. Therefore, eradication of all hosts in the infected river systems has been the preferred strategy to eliminate the parasite. After two failed eradication attempts in 1988 and 1995, the parasite spread further to neighbouring rivers. This, along with several other failed rotenone treatments in Norway in the 1990s, resulted in severe criticism of the national eradication strategy for G. salaris. Still, the eradication program continued, and the failed eradication attempts were analysed for possible improvements. Arctic char (Salvelinus alpinus, Linnaeus, 1758) has proved to be a potential long-term host for the parasite and infested char were documented to have survived in small, groundwater-fed tributaries and ponds during the first two eradication attempts in the Skibotn River. Low limits on allowed rotenone concentrations set by the pollution control authorities might also have contributed to the failures. A third attempt at eradicating the parasite from River Skibotnelva was made in 2015 and 2016, using new knowledge about the parasite and its hosts, renewed strategies to map and deal with dilution from groundwater intrusion and an official acceptance of increased concentrations of rotenone. Treatments for two consecutive years was the main strategy improvement from previous eradication attempts. Water samples showed sufficient levels of rotenone concentrations at all sample points during the treatment periods. Significant efforts in collecting all possible surviving fish from the first-year treatment and screening them for G. salaris revealed no surviving parasites at the time of the second-year treatment. The national G. salaris eradication campaign includes a surveillance programme for eradication confirmation. The results so far are positive for the Skibotn Region, but the earliest an eradication confirmation can be issued earliest is 2021. [ABSTRACT FROM AUTHOR]

Adaptive radiation is the diversification of species to different ecological niches and has repeatedly occurred in different salmonid fish of postglacial lakes. In Lake Tinnsjøen, one of the largest and deepest lakes in Norway, the salmonid fish, Arctic charr (Salvelinus alpinus (L.)), has likely radiated within 9,700 years after deglaciation into ecologically and genetically segregated Piscivore, Planktivore, Dwarf, and Abyssal morphs in the pelagial, littoral, shallow‐moderate profundal, and deep‐profundal habitats. We compared trait variation in the size of the head, the eye and olfactory organs, as well as the volumes of five brain regions of these four Arctic charr morphs. We hypothesised that specific habitat characteristics have promoted divergent body, head, and brain sizes related to utilized depth differing in environmental constraints (e.g., light, oxygen, pressure, temperature, and food quality). The most important ecomorphological variables differentiating morphs were eye area, habitat, and number of lamellae. The Abyssal morph living in the deepest areas of the lake had the smallest brain region volumes, head, and eye size. Comparing the olfactory bulb with the optic tectum in size, it was larger in the Abyssal morph than in the Piscivore morph. The Piscivore and Planktivore morphs that use more illuminated habitats have the largest optic tectum volume, followed by the Dwarf. The observed differences in body size and sensory capacities in terms of vision and olfaction in shallow and deepwater morphs likely relates to foraging and mating habitats in Lake Tinnsjøen. Further seasonal and experimental studies of brain volume in polymorphic species are needed to test the role of plasticity and adaptive evolution behind the observed differences. [ABSTRACT FROM AUTHOR]

Changes in abiotic and biotic factors between seasons in subarctic lake systems are often profound, potentially affecting the community structure and population dynamics of parasites over the annual cycle. However, few winter studies exist and interactions between fish hosts and their parasites are typically confined to snapshot studies restricted to the summer season whereas host‐parasite dynamics during the ice‐covered period rarely have been explored. The present study addresses seasonal patterns in the infections of intestinal parasites and their association with the diet of sympatric living Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) in Lake Takvatn, a subarctic lake in northern Norway. In total, 354 Arctic charr and 203 brown trout were sampled from the littoral habitat between June 2017 and May 2018. Six trophically transmitted intestinal parasite taxa were identified and quantified, and their seasonal variations were contrasted with dietary information from both stomachs and intestines of the fish. The winter period proved to be an important transmission window for parasites, with increased prevalence and intensity of amphipod‐transmitted parasites in Arctic charr and parasites transmitted through fish prey in brown trout. In Arctic charr, seasonal patterns in parasite infections resulted mainly from temporal changes in diet toward amphipods, whereas host body size and the utilization of fish prey were the main drivers in brown trout. The overall dynamics in the community structure of parasites chiefly mirrored the seasonal dietary shifts of their fish hosts. [ABSTRACT FROM AUTHOR]

Heat waves are threatening fish around the world, leading sometimes to mass mortality events. One crucial function of fish failing in high temperatures is oxygen delivery capacity, i.e. cardiovascular function. For anadromous salmonids, increased temperature could be especially detrimental during upstream migration since they need efficiently working oxygen delivery system in order to cross the river rapids to reach upstream areas. The migration also occurs during summer and early autumn exposing salmonids to peak water temperatures, and in shallow rivers there is little availability for thermal refuges as compared to thermally stratified coastal and lake habitats. In order to shed light on the mechanisms underpinning the capacity of migrating fish to face high environmental temperatures, we applied a physiological and molecular approach measuring cardiovascular capacities of migrating and resident Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) in Northern Norway. The maximum cardiovascular capacity of migrating fish was significantly lower compared to the resident conspecifics. The onset of cardiac impairment started only 2°C higher than river temperature, meaning that even a small increase in water temperature may already compromise cardiac function. The migrating fish were also under significant cellular stress, expressing increased level of cardiac heat shock proteins. We consider these findings highly valuable when addressing climate change effect on migrating fish and encourage taking action in riverine habitat conservation policies. The significant differences in upper thermal tolerance of resident and migrating fish could also lead changes in population dynamics, which should be taken into account in future conservation plans. [ABSTRACT FROM AUTHOR]

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

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

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

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

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

Reproductive traits differ between intralacustrine Arctic charr morphs. Here, we examine three sympatric lacustrine Arctic charr morphs with respect to fecundity, egg size and spawning time/site to assess reproductive investments and trade-offs, and possible fitness consequences. The littoral omnivore morph ( LO-morph) utilizes the upper water for feeding and reproduction and spawn early in October. The large profundal piscivore morph ( PP-morph) and the small profundal benthivore morph ( PB-morph) utilize the profundal habitat for feeding and reproduction and spawn in December and November, respectively. Females from all morphs were sampled for fecundity and egg-size analysis. There were large differences between the morphs. The PB-morph had the lowest fecundity (mean = 45, SD = 13) and smallest egg size (mean = 3.2 mm, SD = 0.32 mm). In contrast, the PP-morph had the highest fecundity (mean = 859.5, SD = 462) and the largest egg size (mean = 4.5 mm, SD = 0.46 mm), whereas the LO-morph had intermediate fecundity (mean = 580, SD = 225) and egg size (mean = 4.3, SD = 0.24 mm). Fecundity increased with increasing body size within each morph. This was not the case for egg size, which was independent of body sizes within morph. Different adaptations to feeding and habitat utilization have apparently led to a difference in the trade-off between fecundity and egg size among the three different morphs. [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]

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]

• 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]

Background: Parvicapsula pseudobranchicola (Myxozoa) causes widespread infections in farmed Atlantic salmon in northern Norway. Heavily infected salmon become runts, probably due to vision impairment or blindness. The salmon are likely infected by waterborne actinospores, released by an alternating annelid host, but the life cycle of P. pseudobranchicola is unknown. Seatrout and Arctic charr have been considered possible hosts for the parasite, but firm evidence has been lacking. Findings: We show for the first time the presence of mature spores of P. pseudobranchicola in seatrout. The seatrout were infected with high intensities of P. pseudobranchicola in the pseudobranchs in early April. The presence of mature spores in early spring suggests that the fish had been infected late the previous year, a pattern of infection similar to that observed for farmed salmon stocked in autumn. Although heavily infected, the fish did not display any symptoms consistent with parvicapsulosis. The results suggest that the life cycle of P. pseudobranchicola is more adapted to seatrout, rather than to Atlantic salmon. Conclusions: The presence of mature spores of P. pseudobranchicola in seatrout confirms that seatrout is a natural host for this myxosporean and this is also the first record of these spores in the pseudobranch of a wild salmonid. Furthermore, wild trout from non-farming areas may become heavily infected with P. pseudobranchicola, developing pseudobranch pathology resembling that of farmed Atlantic salmon suffering from parvicapsulosis. [ABSTRACT FROM AUTHOR]

Cyclic volatile methyl siloxanes (cVMS) concentrations were analyzed in the pelagic food web of two Norwegian lakes (Mjøsa, Randsfjorden), and in brown trout (Salmo trutta) and Arctic char (Sahelinus alpirtus) collected in a reference lake (Femunden), in 2012. Lakes receiving discharge from wastewater treatment plants (Mjosa and Randsfjorden) had cVMS concentrations in trout that were up to 2 orders of magnitude higher than those in Femunden, where most samples were close to the limit ot quantification (LOQ). Food web bio magnification of cVMS in Mjosa and Randsfjorden was quantified by estimation of trophic magnification factors (TMFs). TMF for legacy persistent organic pollutants (POPs) were analyzed for comparison. Both decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6) biomagnified with TMFs of 2.9 (2.1-4.0) and 2.3 (1.8-3.0), respectively. Octamethylcyclotetrasiloxane (D4) was below the LOQ, in the majority of samples and had substantially lower biomagnification than for D5 and D6. The cVMS TMFs did not differ between the lakes, whereas the legacy POP TMFs were higher in Mjosa than in Randsfjorden. Whitefish had lower cVMS bioaccumulation compared to legacy POPs, and affected the TMF significance for cVMS, but not for POPs. TMFs of D5 and legacy contaminants in Lake Mjosa were consistent with those previously measured in Mjosa. [ABSTRACT FROM AUTHOR]

This is the first comprehensive study on the occurrence and distribution of piscine reovirus ( PRV) in Atlantic salmon, Salmo salar L., caught in Norwegian rivers. PRV is a newly discovered reovirus associated with heart and skeletal muscle inflammation ( HSMI), a serious and commercially important disease affecting farmed Atlantic salmon in Norway. A cross-sectional survey based on real-time RT- PCR screening of head kidney samples from wild, cultivated and escaped farmed Atlantic salmon caught from 2007 to 2009 in Norwegian rivers has been conducted. In addition, anadromous trout (sea-trout), Salmo trutta L., caught from 2007 to 2010, and anadromous Arctic char, Salvelinus alpinus (L.), caught from 2007 to 2009, were tested. PRV was detected in Atlantic salmon from all counties included in the study and in 31 of 36 examined rivers. PRV was also detected in sea-trout but not in anadromous Arctic char. In this study, the mean proportion of PRV positives was 13.4% in wild Atlantic salmon, 24.0% in salmon released for stock enhancement purposes and 55.2% in escaped farmed salmon. Histopathological examination of hearts from 21 PRV-positive wild and one cultivated salmon (Ct values ranging from 17.0 to 39.8) revealed no HSMI-related lesions. Thus, it seems that PRV is widespread in Atlantic salmon returning to Norwegian rivers, and that the virus can be present in high titres without causing lesions traditionally associated with HSMI. [ABSTRACT FROM AUTHOR]

The influence of different climate variables on the first four years of otolith growth in Salangen Arctic charr, Salvelinus alpinus, was studied over the period 1939-2005. Salangen is a coastal, low altitude, subarctic lake system located in northern Norway. Climate data, including water temperature, air temperature, ice-cover and precipitation, were available for most of the 67 year period. Water temperatures in May and June had a significant effect on otolith growth during the second growth year, while no relationship between otolith growth and climate variables was found for the first, third and fourth years of otolith growth. Otolith increment size during the third and fourth growth year was autocorrelated with growth during the previous year. Spring snow fall and timing of ice break-up had an indirect effect on growth, as these variables were highly correlated with spring water temperatures. High variation in otolith growth within years and among individuals suggests that individual and age-specific variations in spatial habitat use may confound the direct effects of changing air temperatures and time of ice break-up. [ABSTRACT FROM AUTHOR]

The article discusses the studies on the role of Arctic charr as a host to Gyrodactylus salaris and its ability to host the parasite. It says that Skibotnelva river located in Norway was treated with the plant poison rotenone to eradicate the parasite. It mentions the fish species which are regarded as resistant to G. salaris including Gasterosteus aculeatus, flounder, and Platichthys Flesus.

A study over a 22-year period of first-time migrants (smolts) of three sympatric salmonids (Atlantic salmon (), brown trout (), and Arctic char ()) in a watercourse in northern Norway demonstrated that although there was considerable overlap in smolt migration timing among the species, Atlantic salmon migrated first, followed by Arctic char, and finally brown trout. The migration period of Arctic char had a smaller range and less annual variation than those of the two other species, possibly partly related to their more lake-dwelling habitat preference. For all species, water flow was important in explaining day-to-day variations in smolt runs. Water flow was most important for brown trout, change in flow for Atlantic salmon, whereas photoperiod was most important for Arctic char. These results suggest that both age and size of smolts and the timing of the smolt migration have been shaped by the different habitat preferences of these species both in fresh water and sea through local selection. [ABSTRACT FROM AUTHOR]

The article presents a study on the outbreaks of spironucleosis in farmed Atlantic salmon, Salmo salar, in northern Norway. It says that the outbreaks were from smolts that came from the same farm after it was found that an outbreak of systemic spirnucleosis in farmed Arctic char showed that the parasite from the gall bladder of wild Arctic char was genetically different from those causing systemic disease in farmed fish through electron microscopy. It explains that through molecular methods, Spironucleus salmonicida, a diplomonad flagellate that causes systemic infections in farmed salmonids, are also present in wild salmonids who serve as reservoir hosts of the diplomonad flagellate.

The myxozoan genus Parvicapsula contains 14 species infecting fish, some of which are known to cause severe disease in farmed and wild salmonids. Parvicapsula pseudobranchicola infections were first reported from seawater-reared Atlantic salmon, Salmo salar, in Norway in 2002 and have since then been an increasing problem. The present study describes a Taqman real-time PCR assay for specific detection of P. pseudobranchicola. The Taqman assay targets the 18S rRNA gene of P. pseudobranchicola and is able to detect as few as ten copies of the target sequence. Using the described assay, P. pseudobranchicola was detected in both farmed and wild salmonids, indicating that wild Atlantic salmon, sea trout, Salmo trutta, and Arctic char, Salvelinus alpinus, may be natural hosts of the parasite. Parvicapsula pseudobranchicola was found in samples from wild salmonids in the far south and the far north of Norway, displaying a wide geographic range of the parasite. Farmed salmonids showed P. pseudobranchicola infection levels many folds higher than that observed for wild sea trout, indicating that farmed Atlantic salmon are subjected to an elevated infection pressure compared with wild salmonids. [ABSTRACT FROM AUTHOR]

Mean ambient water temperatures experienced by individual young-of-the-year (YOY) Arctic charr, Salvelinus alpinus (L.), from a Svalbard lake were estimated using measurements of oxygen stable isotopes (δO) derived from fish otoliths. Otolith-derived water temperatures differed significantly from temperatures recorded at the outlet river of the Dieset watercourse but were consistent with temperatures previously recorded in shallow littoral areas of other Svalbard lakes where YOY charr are commonly found. This indicates that fixed-point monitoring does not necessarily represent the temperatures and thermal habitats used by individual fish. Otolith-derived water temperatures were also positively related to fish length-at-capture and otolith size, although much of the variation remained unexplained. Differences among individuals could be related to variability in food availability and food intake as well as variation in the initial fish size at hatching. Implications for subsequent investigations into how YOY charr respond and adapt to future climate change are discussed. [ABSTRACT FROM AUTHOR]

The trophic niche and parasite infection of Arctic charr ( Salvelinus alpinus) were explored in two lakes with sympatric burbot ( Lota lota) and two lakes without burbot in subarctic Norway. The CPUE of burbot and charr were similar in one lake, but burbot had a low population density in the other. Burbot were benthivorous in both lakes. Other co-occurring species like brown trout ( Salmo trutta), Atlantic salmon parr ( Salmo salar), grayling ( Thymallus thymallus) and minnow ( Phoxinus phoxinus) were also benthivores. At high densities, benthivorous burbot forced the whole Arctic charr population to utilise mainly the limnetic trophic niche. In contrast, at low burbot density or without burbot present, Arctic charr were primarily benthivorous in the littoral zone. Thus, a clear interactive segregation in diet was observed between Arctic charr and burbot at high burbot densities. There was also a high predation pressure from burbot on young Arctic charr along the benthic zones. The extensive use of zooplankton as prey caused a high parasite infection pressure of copepod transmitted Diphyllobothrium spp. larvae, with the potential for high negative impact on the Arctic charr population. As the benthivore trophic niche was occupied by burbot, the ecological opportunities for polymorphism with benthivorous ecotypes or morphs of Arctic charr were probably prevented. Therefore, the sympatry with burbot seems to have large ecological and evolutionary consequences for this Arctic charr population compared with neighbouring lakes where burbot is absent. [ABSTRACT FROM AUTHOR]

Stable coexistence of Arctic charr and whitefish does occur in a number of native lake fish communities in Scandinavia. Even so, whitefish introductions into Arctic charr lakes have resulted in serious decline and possibly local extinction of Arctic charr. In this article, we analyze the habitat use and diet of the two species in five Norwegian lakes differing in basin shape and environmental conditions. In two of the lakes, both species are native, and appear to live in a relatively stable coexistence. Here, whitefish mainly occupy the littoral and upper pelagic zone, while Arctic charr live in the deeper habitats. Diets are generally quite different in terms of the zooplankton species eaten. In the three other lakes, either whitefish or both species have been introduced. In the shallowest lake, habitat segregation is similar to that seen in the pristine lakes, although Arctic charr appears to be on the brink of extinction. In the remaining two lakes, however, Arctic charr dominates, and occurs in higher numbers than whitefish in all the habitats. Our observations indicate that coexistence of the two species in oligotrophic and relatively pristine lakes requires an extensive profundal zone to serve as a refugium for Arctic charr. If the littoral zone is rendered inaccessible or unprofitable for whitefish due to dominance of a third competitor or predator, or as a result of lake regulation, then Arctic charr may be the dominant species. [ABSTRACT FROM AUTHOR]

This study revealed that progeny of sympatric Salangen Arctic char, omitted from any kind of imprinting to home water, returned with high precision to the home river and parental locality upon releases in their native marine environments. Fish did not select river randomly, and the homing precision was the same for progeny whether fertilized in home stream or in foreign water. The progeny studied originate from the lake Øvervatnet and the Salangen River population and were hatched and reared at a hatchery at Voss in southern Norway. Experimental material comprised freshwater resident and smolt released from parr directly. The freshwater resident is partly anadromous exhibiting about 74% smolt when released directly into the sea. Char at all stages (resident, transformed resident, and smolt released from parr directly) returned in significant numbers to the home river system and the site of the specific parental population. [ABSTRACT FROM AUTHOR]

Artificially reared Arctic charr Salvelinus alpinus fry (post yolk-sac stage) from Skibotnelva in northern Norway were exposed to infection with the monogenean ectoparasite Gyrodactylus salaris to determine if the parasite caused mortality in fry. About 95% of the fry became infected within the first week post-exposure, and at the end of the experiment (77 days) all fry carried the parasite. Mortality rate was significantly higher in the groups of infected fry than in the uninfected control groups, and when the experiment was terminated c. 30% of the infected and 8% of the uninfected fish had died. Gyrodactylus salaris had a pronounced negative effect upon fry survival and caused an additive host mortality. Moreover, the concurrent temporal changes in parasite intensities and aggregation indicated that the parasite-induced host mortality was density dependent. [ABSTRACT FROM AUTHOR]

The article presents information on a study which determined the morphological variability of the Arctic charr representing anadromous, landlocked and stationary fluviatile populations occurring in the region of the Hornsund fjord in SW Spitsbergen, Norway in relation to their trophic preferences. It estimates the food preferences of the examined fish based on the contents of their alimentary tracts. It reveals the ersults of single-factor ANOVA testing differences in fork length of the Arctic charr from the region.

The article presents information on a study which examined the summer dynamics of density and biomass of the Arctic charr, Salvelinus alpinus, in a polar stream in Spitsbergen, Norway. It determines the basic population parameters of the freshwater fish species and their changes in the summer period. It describes the changes in the fish size structure of the Salvelinus alpinus population from the Ariebekken stream in the successive electrofishings in summer 2004. It also reveals the results of one-way ANOVA and t-test testing the difference in fish length in different seazones in 2004 and 2005.

This study surveys the distribution of Gyrodactylus salaris on resident Arctic charr, Salvelinus alpinus, in lakes connected to three south-Norwegian watercourses: Numedalsvassdraget, Skiensvassdraget and Hallingdalsvassdraget. Gyrodactylus salaris infected charr was only recorded in Numedalsvassdraget. The parasites had the same mitochondrial haplotype as those previously reported on charr in Lake Pålsbufjorden, which is part of Numedalsvassdraget. Since the G. salaris-charr association is persistent in Pålsbufjorden and has a wide distribution above the stretches of the watercourse inhabited by anadromous salmonids, this is considered a stable, although perhaps relatively young, host-parasite system. More detailed analyses of these interactions revealed seasonal variations in the parasite population dynamics between late summer and late autumn, with heavier infections occurring in males and older fish in October. This is explained by the combined action of seasonal differences in temperature and physiology and ecology of host cohorts. It is assumed that the occurrence of G. salaris on charr in Pålsbufjorden resulted from a host switch to charr from rainbow trout, Onchorynchus mykiss. Host switches may cause significant expansions of the geographical range of pathogenic variants of G. salaris. Therefore, observations of frequently occurring G. salaris on charr have implications for the diagnosis, management and control of salmonid gyrodactylosis. [ABSTRACT FROM AUTHOR]

Eleven Arctic charr ( Salvelinus alpinus) (370–512 mm) and eight sea trout ( Salmo trutta) (370–585 mm in length) were tagged externally or internally with depth- and temperature-measuring data-storage tags (DST) before they were released into the sea in the Alta Fjord in north Norway in June 2002. All sea trout were recaptured after they spent 1–40 days at sea, while all Arctic charr were recaptured after 0.5–33 days at sea. On average, trout preferred water about 0.6 m deeper and 1.3°C warmer than Arctic charr. Arctic charr spent >50% of their time between 0 and 1 m depth, while trout spent >50% of their time between 1 and 2 m depth. Both species spent >90% of their time in water no deeper than 3 m from the water surface. However, sea trout dove more frequently and to greater depths (max. 28 m) than Arctic charr (max. 16 m), and these deep dives were most frequently performed at the end of the sea migration. Arctic charr demonstrated a diel diving pattern, staying on average about 0.5 m deeper between 08:00 hours and about 15:00 hours than during the rest of the 24 h, even though there was continuous daylight during the experiments. When comparing data obtained from the DSTs with temperature measurements within the fjord system, the two species were observed to select different feeding areas during their sea migration, the sea trout choosing the inner and warmer parts of the fjord, in contrast to the Arctic charr that preferred the outer, colder parts of the fjord. The observed differences in migration behaviour between the two species are discussed in relation to species preferences for prey and habitat selection, and their optimal temperatures for growth. [ABSTRACT FROM AUTHOR]

The marine feeding pattern of anadromous brown trout (sea trout) Salmo trutta and Arctic charr Salvelinus alpinus was studied during June to August in 1992–1993 and 2000–2004 in a fjord in northern Norway. In general sea trout fed proportionally more on fishes than on crustaceans and insects (81, 1 and 18% by mass, respectively) by comparison with Arctic charr (52, 25 and 22% by mass, respectively). Herring Clupea harengus dominated the total fish diet of both species, but the Arctic charr also fed significantly on gadoids and sandlance Ammodytes spp. While sea trout became virtually all piscivorous at fork lengths ( LF) ≥250 mm, the Arctic charr was ≥400 mm LF before shifting totally to a fish diet. Despite annual variation in diet and forage ratios, there was a clear shift in diet from 1992–1993 to 2000–2004. Sandlance and different crustaceans constituted most of the diet during the initial period with a shift towards gadoids and especially herring during the latter period. This shift seemed to be associated with a high abundance of herring larvae during the latter sampling period, indicating a preferential selection on herring when present, particularly by sea trout. Furthermore, an index indicated dietary overlap in years with intensive feeding on herring of both species, and usually differences in the trophic ecology during years feeding mostly on other prey species. In combination, it was hypothesized that the two species reflect the type of marine prey present within a fjord system over time, and therefore provide an index of variation in the production and biological diversity of their potential prey within fjords. [ABSTRACT FROM AUTHOR]

1. Experimental growth data for Arctic charr (Salvelinus alpinusL.), all fed on excess rations, from 11 European watercourses between 54 and 70°N were analysed and fitted to a new general growth model for fish. The model was validated by comparing its predictions with the growth rate of charr in the wild.2. Growth performance varied among populations, mainly because of variation in the maximum growth potential, whereas the thermal response curves were similar. The estimated lower and upper temperatures for growth varied between−1.7 to 5.3 and 20.8–23.2 °C, respectively, while maximum growth occurred between 14.4 and 17.2 °C.3. There was no geographical or climatic trend in growth performance among populations and therefore no indication of thermal adaptation. The growth potential of charr from different populations correlated positively with fish body length at maturity and maximum weight in the wild. Charr from populations including large piscivorous fish had higher growth rates under standardised conditions than those from populations feeding on zoobenthos or zooplankton. Therefore, the adaptive variation in growth potential was related to life-history characteristics and diet, rather than to thermal conditions. [ABSTRACT FROM AUTHOR]

Significant genetic differences( FST = 0·032) were found between littoral and profundal morphs of Arctic charrSalvelinus alpinusfrom Fjellfrøsvatn, northern Norway, using microsatellite DNA analysis. The morphs had strong reproductive isolation in time and space; the segregation of a separate profundal morph is rare in postglacial lakes. [ABSTRACT FROM AUTHOR]

We caught smolts of Arctic charr, Salvelinus alpinus (L.), Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in a trap situated at the mouth of the river Halselva (70° N 23° E), northern Norway during a 5-year period. Salmon and charr were the first to leave freshwater at the end of May, while most trout left freshwater about 14 days later. Whereas the midnight sun shines continuously during the downstream migration period, the light intensity has a diel intensity pattern. The majority of the descending migrants were recorded during the night. The number of descending fish was relatively low at water temperatures below 3°C. The increase in water level was largely caused by snowmelt and thus correlated with lower water temperatures. The number of migrants of all three species increased with increasing water level and decreased with increasing water temperature, with the exception of trout, which increased with water temperature. Notably, the increase in number of migrants was also correlated with the increase in water level the following day, indicating that fish movements represent an early response to a later spate. There was no significant relationship between the number of migrants and the daily change in water level or temperature. The three species were highly synchronised in their daily number of migrants. The strongest synchronisation was found between Arctic charr and Atlantic salmon, followed by Arctic charr and brown trout. [ABSTRACT FROM AUTHOR]

We studied the spatial and temporal variation in relative abundance (CPUE), habitat use, and diet of Arctic charr (Salvelinus alpinus (L.)) and brown trout (Salmo trutta L.) in Lake Atnsjøen in southern Norway over a period of 14 years (1985–1998). Fish were sampled with gill nets in epibenthic and pelagic habitats in August each year. Stratified sampling in the epibenthic habitat was carried out with gill net series at three depth zones (0–10, 10–30 and 30–70 m) at one station (1985–1993), and at seven depth zones between 0–3 m and 50–70 m at 10 different stations with multi-mesh gill nets (1994–1998). Lake Atnsjøen is a relatively deep (maximum 80 m), unregulated, subalpine, oligotrophic lake which is not affected to any extent by local or long-range pollution. In shallow epibenthic areas, brown trout is the most abundant species, while Arctic charr dominate deeper epibenthic areas. Epibenthic catches of brown trout at 0–10 m depth were inversely correlated with the catches of Arctic charr. The catches of epibenthic brown trout and Arctic charr did not correlate with mean water temperature in the sampling period. In the pelagic zone, brown trout were mainly caught close to the surface (0–6 m), while Arctic charr were caught between the surface and 12 m depth. Pelagic fish of both species were significantly larger than individuals caught in the epibenthic habitat. The mean size of epibenthic brown trout increased with depth. The opposite trend was evident for Arctic charr, although some larger fish also occupy deeper areas. The size of brown trout in epibenthic areas correlated inversely with CPUE, while no such relationship existed for Arctic charr. The most important food items for Arctic charr in both habitats in August were various species of zooplankton; Daphnia longispina, Bosmina longispina, Bythotrephes longimanus and Polyphemus pediculus. Brown trout mainly foraged near the surface on insects in both habitats, but B. longimanus and P. pediculus were preyed upon to some extent by pelagic specimens. The number of piscivorous individuals was low in both species (1.9–4.5%). [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]

Imatinib mesilate (Glivec®, Novartis Pharmaceuticals) is a novel therapy for the treatment of chronic myeloid leukaemia (CML). We evaluated the cost-effectiveness of imatinib (600?mg daily) when used for the treatment of patients in advanced stages of CML (accelerated phase and blast crisis) against conventional therapies of combination chemotherapy (DAT) and palliative care in hospital or at home. A Markov model simulated the transitions of hypothetical patient cohorts and outcomes were modelled for 5 years from the start of treatment. Costs were estimated from the perspective of the UK National Health Service. Over 5 years, a patient in accelerated phase will, on average, accrue an additional 2.09 QALYs with imatinib compared to conventional therapies, while patients in blast crisis will accrue an additional 0.58 quality-adjusted life-years (QALYs) with imatinib compared to conventional therapies. The costs per additional QALY gained from treatment with imatinib compared with conventional therapies were £29?344 (accelerated phase) and £42?239 (blast crisis). The results were particularly sensitive to the price of imatinib, improvements in quality of life, and the duration of haematological responses. We conclude that treatment of CML with imatinib confers considerably greater survival and quality of life than conventional treatments but at a cost.British Journal of Cancer (2003) 89, 634-640. doi:10.1038/sj.bjc.6601151 www.bjcancer.com [ABSTRACT FROM AUTHOR]

The Arctic charr Salvelinus alpinus populations of the subarctic lakes Takvatn and Fjellfrøsvatn, north Norway, concentrated in the littoral zones (0-15 m) of the lakes during the entire winter (December to May) despite very low temperatures (0.2 and 0.7°C). High prey availability, low predation and competition and comparatively better light under snow and ice in shallow compared with deep water are probable reasons. At ice break in June, all Arctic charr moved to the profundal zone for a brief period, probably in response to the sudden light increase and a profundal resource peak of chironomid pupae. In the summer, the Arctic charr are found in the pelagic, profundal and littoral zones of the lakes. These populations therefore perform regular habitat shifts between the littoral zone in the winter, the profundal zone at ice break and the whole lake in the summer and autumn. The fish fed continuously during winter despite the cold water and the poor light. Amphipods and chironomid larvae dominated the diet. Catch per unit effort, numbers of stomachs with food and food intake rates varied with the subarctic light cycle but were lowest after the winter solstice. The winter assimilation of energy was about equal to the standard metabolism in Takvatn but was higher in Fjellfrøsvatn. The assimilation increased in both lakes under the spring ice in May. The habitat choice, diet and energy assimilation indicate that the Arctic charr is well adapted to the extreme winter conditions of subarctic lakes. [ABSTRACT FROM AUTHOR]

Arctic charr (Salvelinus alpinus L.) were fed diets based on a commercial recipe supplemented with either linseed, soybean or marine oil prior to cohabitant challenge with Aeromonas salmonicida ssp. salmonicida. Mortality varied significantly between the three dietary groups. Highest mortality (48%) was observed in fish fed the marine oil and the lowest mortality (20%) was in the group fed soybean oil. Transmission electron microscopy (TEM) examination of the digestive tract of uninfected fish demonstrated substantial numbers of bacterial cells between microvilli. However, only a few bacteria were recovered that were associated with the microvilli of infected fish. Immunocytochemical staining/labelling investigations using TEM and an immunogold method were performed on mid-gut segments of fish fed the marine oil diet and showed augmentation of goblet cells and the presence of A. salmonicida ssp. salmonicida in the gastrointestinal tract of diseased fish after challenge with the pathogen. It is suggested that the gastrointestinal tract could be an infection route of A. salmonicida ssp. salmonicida. The greater prevalence of goblet cells supports the suggestion that sloughing off mucus is a protective response against bacterial infections. These results make an important contribution to our understanding of how nutrition can affect the disease resistance of fish. [ABSTRACT FROM AUTHOR]

- Production of cannibalistic Arctic char ( Salvelinus alpinus (L.)) and their prey conspecifics were estimated in an allopatric population, situated in an alpine ultraoligotrophic lake in central Norway. Estimates of population abundance were obtained by mark recapture and successive removal experiments. Assuming stable age distribution, we estimated mean yearly biomass (±95% CL) of char in sampled size groups vulnerable to predation (60 to 150 mm) to 7.93 (5.11-14.30) kg · ha−1. Similarly, mean yearly biomass (±95% CL) of cannibalistic char (> 250 mm) was estimated to 0.62 (0.50-1.06) kg · ha−1. Annual production (±95% CL) of char in length groups 60 to 150 mm was estimated to be 4.31 (2.74-8.03) kg · ha−1 · year−1, and production (±95% CL) of cannibalistic char to 0.19 (0.15-0.33) kg · ha−1 · year−1. Depending on the food conversion factor (set to vary from 0.1 to 0.4), the cannibalistic char removed from 10% to 40% of the production of char in sampled size-classes vulnerable to predation yearly. The overall ecological efficiency in energy transfer between the prey and predator population was 4.4%. [ABSTRACT FROM AUTHOR]

Density estimation of pelagic fish was performed by means of single beam echosounding in 17 lakes within a period of 34 years, from 1985 to 2018. Surveys were performed repeatedly (two to fourteen times) in five lakes. The density estimates ranged from 34 to 4720 fish/ha and were significantly correlated with total phosphorus concentration. The high density in relatively phosphorus rich lakes (TP > 10 µg/L) was comprised of small fish (<20 cm) and was partly due to the higher number of pelagic fish species. The number of pelagic species varied from one, Arctic charr, in the most elevated and oligotrophic lakes, and whitefish dominated in less elevated oligotrophic lakes. In lowland lakes characterized as mesotrophic or tending to mesotrophy, smelt, vendace, and two to three cyprinids comprised the pelagic fish stock. These fish species predate zooplankton effectively, and species composition and body size of planktonic cladocerans was affected by fish density. Large species of Daphnia were lacking in lakes with high fish density, and body size of present species, D. galeata, D. cristata, and Bosmina spp. were negatively correlated with pelagic fish density. [ABSTRACT FROM AUTHOR]