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

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

The effects of dietary lipid oxidation on fish are diverse and contradictory. In this study, herring oil was oxidized to five different levels (peroxide values (POV): 20.44, 182.97, 56.12, 33.27 and 0.00 meq kg − 1 ) and used to formulate five experimental diets. Juvenile Arctic charr ( Salvelinus alpinus , mean body mass ± SD: 2.41 ± 0.11 g) were reared on the five diets for 67 days. In another experiment, juvenile Nile tilapia ( Oreochromis niloticus ) (1.71 ± 0.40 g) were reared on three diets formulated with oxidized oils having POV of 19.55, 447.27 and 32.72 respectively, for 90 days. Growth responses were monitored in quadruplicate groups of 60 individuals of Arctic charr and 100 for Nile tilapia, respectively. The activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were only studied in Arctic charr. At the end of the study, the Arctic charr group reared on a diet with oils in the primary oxidation state had significantly lower body mass and specific growth rate, but higher hepatosomatic index compared to the rest of the groups. The activities of CAT and GPx increased with dietary lipid oxidation while that of SOD remained fairly stable. In Nile tilapia, both final body mass and condition factor were significantly lower in the group fed fresh oil than in the groups fed oxidized oils. Fillet lipid content decreased with lipid oxidation while ash and protein did not differ amongst tilapia groups. The results suggest that Arctic charr are more susceptible to lipid oxidation than are Nile tilapia. These differences may be the result of species differences in tolerance to oxidized lipids, variable lipid intake or access to vitamin E/tocopherol in feed. Statement of Relevance Important for Arctic charr and Nile tilapia feed development. [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]

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]

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

We investigated whether Fraser strain Arctic charr Salvelinus alpinus L. reared in fresh water ( FW) differed in survival and growth from full siblings transferred to brackish water ( BW) and whether family performance was consistent throughout 1 year of commercial growth. Fish were grown communally ( n = 3600) in either FW or BW from May 2008 to May 2009. Mean family survival in BW was moderately correlated with mean family survival in FW ( r = 0.342; P = 0.032). Fish which survived until the conclusion of the experiment were significantly heavier in body weight at the baseline assessment than their full-sibs which died. Family by treatment interactions were detected for body weight, condition factor and specific growth across all measurement dates (May 2008, October 2008 and May 2009) and growth intervals. Despite the varied response of families to treatment, mean family body weight in FW was correlated phenotypically with BW body weight in October 2008 ( r = 0.633, P < 0.0001) and marginally correlated in May 2009 ( r = 0.289, P = 0.061). These data suggest that body weight in FW and body weight in BW should be analysed as separate, but correlated traits in Arctic charr breeding programs. [ABSTRACT FROM AUTHOR]

Abstract: The short and long term effects of short photoperiods on growth and maturity were investigated in 240 individually tagged juvenile Arctic charr (Salvelinus alpinus). The Arctic charr were reared at constant temperature (12°C) and on four different light regimes; one group on continuous light (LD24:0) as control and three groups experienced a period of short day (LD8:16) on a three subsequent 6week periods i.e. 24th September–6thNovember (LD8:16Sep–Nov), 6th November–19th December (LD8:16Nov–Dec), 19th December-29th January (LD8:16Dec–Jan). Before and after the short photoperiod treatment the groups were reared at continuous light. The growth of the fish was monitored over a period of 11months. At the termination of the experiment in September 2009, the body mass of the three groups receiving a short day period (LD8:16 Sep–Nov, LD8:16 Nov–Dec and LD8:16 Dec–Jan) was significantly higher (13.9%, 12.9% and 10.7% respectively) than that of the group reared at continuous light (LD24:0). The three groups receiving the short photoperiod did not differ in weight at the end of the trial so the time of the year at which the short photoperiod was applied did not seem to be of importance regarding the growth enhancement. The maturation rate did not appear to be affected by the photoperiod treatments. The improved growth was mainly a result of a higher feed intake and improved feed conversion efficiency for the period following transfer of the charr from a short photoperiod to the continuous light. Application of such a winter photoperiod during the juvenile phase can, therefore, be used as a tool to increase the biomass and growth rate in Arctic charr farming. [Copyright &y& Elsevier]

Abstract: Groups of Arctic charr (Salvelinus alpinus) were reared in duplicate tanks supplied with freshwater, and subjected to two different ration levels, 100% (full ration) and 50% (half ration) in two six week periods during autumn (Sept.–Nov.) and winter (Dec.–Feb.). In between the restricted ration periods and from February onwards, all fish were fed full ration. After the first and second 42day restricted feed periods, the 50% had lower mean weight than the 100% group in both sexes, but this size difference diminished as the trial progressed, and full final size compensation was seen for both males and females in the 50% group. Specific growth rates for both sexes were higher in the 100% group during the two reduced feeding periods, whereas growth was higher in the 50% group in the subsequent periods after feed restriction. No differences in growth were seen from May onwards. Feed conversion efficiency was higher in the 50% group during, and after, feed restriction, and daily feeding rate (F%) was higher in the 50% group in the periods subsequent to feeding restriction. In the following summer and autumn signs of lower maturation were seen for females in the feed restricted group. No differences were found in fillet water- and fat content in the experimental groups. The present findings indicate that intermittent feeding during autumn and winter could be a cost-effective strategy for Arctic charr farmers. [Copyright &y& Elsevier]

The effect of rearing temperature on the growth and maturation of Arctic charr ( Salvelinus alpinus) was investigated. Arctic charr juveniles were reared for 6 months (phase I, October-April, size range 20-500 g) at constant temperatures of 9, 12 and 15 °C and according to two temperature-step groups ( T) i.e. fish transferred from 15 to 12 °C or from 12 to 9 °C. All the previous treatments were then reared either at 7 °C or at 12 °C for an additional 4 months (phase II, size range 300-1000 g) and then slaughtered in August 2008. The overall growth rate was the highest at a constant temperature of 15 °C for the first 6 months of the trial, with the fish in this group being 44% and 78% heavier than the fish reared at a constant temperature of 12 or 9 °C respectively. Arctic charr showed a negative response in terms of the growth rate when transferred from higher to lower temperatures, especially for groups previously reared at 15 °C. There was a trend for higher gonadosomatic index values at the end of the experiment for groups of fish that were exposed to higher rearing temperatures during the juvenile phase i.e. 4.18% (±0.79) and 7.29% (±0.89), for the temperature groups of 12 and 15 °C, respectively, compared with 2.49% (±0.74) for the 9 °C group. Our results suggest that for the production of fish >1000 g, moderate or low temperatures (here 9 °C) should be applied during the juvenile phase in order to reduce the negative effects arising from maturation. Farmers with access to heat sources should accordingly choose more moderate rearing temperatures during the juvenile stage, especially if the fish is to be moved down in the temperature regime during the on-growing period. [ABSTRACT FROM AUTHOR]

Biological data from 66 populations of Arctic charr, Salvelinus alpinus, from eastern North America were analysed to test the applicability of the countergradient hypothesis as an explanation of differences in seasonally adjusted growth rates. Samples were obtained along a 37° latitudinal gradient and partitioned among anadromous, normal lacustrine, and dwarf lacustrine Arctic charr morphotypes. Models relating length-at-age or age-specific growth rates to latitude were estimated for each morphotype. Length-at-age declined with latitude for anadromous and lacustrine charr. Age-specific growth rates also varied with latitude, particularly for normal lacustrine charr. Results of analyses provide support for the countergradient hypothesis in growth performance of normal lacustrine morphotypes, where northern populations compensate for the shorter growth season with a greater rate of growth than southern populations. Anadromous charr exhibited equivocal evidence of countergradient variation, while results for dwarf lacustrine Arctic charr populations were inconclusive owing to the limited range of ages, and latitudes for which data were available. [ABSTRACT FROM AUTHOR]

Results and experiences from a selective breeding programme aiming at improving the performance of an Arctic charr strain in aquaculture are presented. The programme, which has been running since 1985, uses traditional quantitative genetic methods based on relatedness and trait measurements. Traits considered included growth, age at sexual maturity, flesh colour, fat content and other features. Estimates in the early phase of the programme showed promising heritabilities for most traits, e.g. growth heritabilities of 0.34–0.52, and suggested that improvement by selection was feasible. Several traits such as a high rate of early maturation and poor flesh colour that were considered problematic by the Arctic charr farming industry at the programme’s start no longer hamper farming. Considerable improvement of growth by selection, estimated at 8% per generation, has contributed to shortening the production cycle in commercial farming. Results from studies of genotype–environment interactions are presented and discussed. Poor survival of fertilised eggs is a major problem in Swedish Arctic charr farming as indicated by presented survival rates. Efforts have consistently been made to avoid inbreeding in the selected strain, and at the present seventh generation the accumulated increase in inbreeding is estimated from pedigree data to be only approximately 5%. [ABSTRACT FROM AUTHOR]

Abstract: Anadromous (sea-migrating) Arctic charr (Salvelinus alpinus) display pronounced seasonal variations in food intake and growth and is an interesting model for studying mechanisms of appetite regulation. In this study cDNAs encoding for ghrelin (GHRL) and leptin (LEP) in Arctic charr were cloned, after which stomach GHRL and liver LEP mRNA expressions were examined by qPCR during a seasonal feeding cycle of semi-wild anadromous Arctic charr. The fish were captured as they returned from summer feeding in seawater and transferred to an indoor tank where they were fed in excess until October the year after. Growth rate was low in late winter, increased in late spring and reached a peak during summer, and then declined during autumn, when the fish became sexually mature. The changes in growth rate were associated with corresponding changes in the proportion of fish that had been eating at each sampling date, and whole body lipid status. Stomach GHRL mRNA expression was high in late winter, decreased to a nadir in mid-summer and increased again to a high level in early autumn. Liver LEP mRNA remained low during winter, spring and early summer, after which there was a gradual, 7-fold increase until October. The seasonal changes in ghrelin and leptin support a role of these hormones in the long-term regulation of energy homeostasis in the anadromous Arctic charr. It cannot be excluded, however, that the increase in liver leptin expression during autumn is related to sexual maturation. [Copyright &y& Elsevier]

Abstract: This study evaluated the survival and growth of juvenile Arctic charr in comparison to their diploid siblings. Eight triploid full-sib families were produced by hydrostatic pressure treatment of eggs (5 min at 65.5×103 kPa) beginning 210 °C-min post-fertilization. Diploid siblings came from the same eight families, but without pressure treatment. Mean survival from eyed-egg to first size-grading (at 1980 °C-days post-hatch) was 70% for triploids and 84% for diploids. In two growth studies using 4 m3 tanks containing 100 juveniles per ploidy level of each family, triploidization resulted in higher levels of phenotypic variance for growth traits. Specifically, triploids consistently had smaller mean body weight and fork length than their diploid siblings. Juveniles were first measured at 850 °C-dph and again every four weeks over a 24 week period. The proportion of the overall variance in weight was due to ploidy level in the first tank experiment whereas this variance was due to the effect of family in the second tank experiment. Mean specific growth rates of triploids and diploids were 2.01 and 2.09% for weight and 0.64 and 0.66% for length, respectively, which was not significant. The condition factor of triploids was less than that of diploids at every sampling date, except for the initial assessment. After transfer to a commercial site following completion of the tank trials, the same families were grown until market size (1 kg) and were measured again nine and 11 months after the conclusion of the growth studies. The condition factor of triploids improved at the commercial site and was not different from that of diploids. The difference in weight of triploid and diploid populations was significant at the conclusion of the study. These results indicate that as juveniles, triploids have reduced performance in important aquaculture traits. However, because triploid performance was reduced in a predictable fashion in comparison to sibling diploids, triploids of some full-sib families outperformed diploids of others. Any overall advantage of triploids may not be realized until the diploids begin to mature. [Copyright &y& Elsevier]

Abstract: This study investigates how simulation of condensed winter light conditions effects the growth of wild caught Arctic charr (Salvelinus alpinus L.) held in culture. After capturing from Altevatn, Northern Norway, juvenile Arctic charr were cultivated and subsequently individually divided into two groups. The fish were held under identical conditions from May to October including continuous light. Starting from week 41 after capture (October) one group was subjected to a winter light regime of 6 h light and 18 h dark per day (Winter Light group—WL), while light regimes in the second group remained continuous (Light group). After an eight weeks treatment period the WL-group was reverted to the continuous light regime until the experiment ended in May 2007. Results revealed no pre-treatment differences in growth between the two groups. However, starting from two months after the short day treatment, fishes from the WL group had significant higher growth rates compared to L group fish. At the end of the experiment, e.g. five months after the light treatment, fishes from WL group had increased their average body weight by 353 g as compared to 252 g in the L group. Consequently, results show that simulation of winter light conditions can increase the productivity of land-based Arctic charr (Salvelinus alpinus L.) cultivation by 25 to 30%. Thus, management of wild caught charr farming, great care should be taken as to what light regimes the fish are exposed to. [Copyright &y& Elsevier]

Abstract: Parr–smolt transformation and growth were studied in captive offspring of anadromous Arctic charr (Salvelinus alpinus) from the Hals watercourse in northern Norway (70°N), held either at a natural temperature (<1 °C until May) or at a temperature elevated to 6 °C in late March. In mid-May, 5 weeks after the increase in photoperiod from 8:16 h light:dark to continuous light, gill Na+, K+-ATPase activity started to increase in both temperature groups, concurrent with the final development of full seawater tolerance. Temperature had no effect on the development of gill Na+, K+-ATPase activity, or on hypoosmoregulatory ability. The fish in both treatments resumed growth in mid-May, but from then on growth was faster in the elevated than in the ambient temperature group. In the former group, fish mass doubled in 6 weeks (from 65 to 137 g), and growth ceased at the time when the fish were about to complete their parr–smolt transformation. These findings show that an early vernal temperature increase advances the seasonal growth cycle, but not the parr–smolt transformation, in anadromous Arctic charr. [Copyright &y& Elsevier]

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

The article presents an experimental study which examines the positive effects of exposure to increased water velocity on the growth of newly hatched Arctic charr also known as Salvelinus alpinus L. The experiment used 1224 newly hatched fish with the aid of water velocity treatment which has an effect on growth in terms of length and weight. It was found out the use of a higher water velocity immediately after hatching is associated with a significant increase in growth. The study also suggests that environmental growth advantages achieved early in the life history of cod.

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

The annual variability in growth and life history traits of brown trout (Salmotrutta L.) and Arctic charr (Salvelinus alpinus (L.)) in Lake Atnsjøen, a Norwegian subalpine lake, was studied over a period of 13 years (1985–1997). The extent to which life-history characteristics recorded on one occasion can be regarded as representative for the population was explored. We found inter-cohort variation in growth for both species; estimates of asymptotic length (L∞) in ten cohorts ranged between 225–305 mm (CV = 10.5%) for brown trout and 273–301 mm (CV = 4.1%) for Arctic charr. However, this variation was much lower than inter-population variation for brown trout based on single samples from 169 populations (CV = 24.6%). In Lake Atnsjøen, annual growth increment correlated highly with the number of days warmer than 7 °C (R2=0.60–0.89) for brown trout, and days warmer than 10 °C (R2=0.40–0.58) for Arctic charr. Females of Arctic charr were younger at sexual maturity than males, while no such difference was found in brown trout. Generally speaking, early maturing individuals of both species grew faster, particularly from age-2 and onwards, than immature individuals. Early maturing individuals, however, were smaller at maturity than those maturing one year older. Age and size at maturity were significantly correlated with asymptotic lengths only in Arctic charr females. [ABSTRACT FROM AUTHOR]

The impacts of polychlorinated biphenyl (PCB) exposure on smoltification and subsequent seawater performance were investigated in hatchery-reared, anadromous Arctic charr (Salvelinus alpinus). The fish were subjected to a 2-month summer seawater residence, after which they were orally dosed with 0 (Control, C), 1 (Low Dose, LD) or 100 mg Aroclor 1254 kg−1 body mass (High Dose, HD) in November. They were then held in fresh water, without being fed (to mimic their natural overwintering in freshwater), until they had smolted in June the next year. The smolts were then transferred to seawater and fed to mimic their summer feeding residence in seawater, followed by a period without food in freshwater from August until maturation in October. Compared with C and LD charr, the HD charr had either a transient or a permanent reduction in plasma growth hormone, insulin-like growth factor-1, and thyroxin and triiodothyronine titers during the period of smoltification. These hormonal alterations in the HD charr corresponded with impaired hyposmoregulatory ability in May and June, as well as reduced growth rate and survival after transference to seawater. Consequently, fewer fish in the HD group matured in October compared to the other two treatments. The HD fish had a liver PCB concentration ranging between 14 and 42 mg kg−1 wet mass, whereas there were similar, and very low, liver PCB concentrations in LD and C fish throughout the smolting period. Our findings suggest that PCB might compromise mechanisms important for fitness in a fish species living in an extreme environment. [Copyright &y& Elsevier]

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

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