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

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

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

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

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

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

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

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]

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

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

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

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

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

Arctic CharSalvelinus alpinusis a highly desirable species for aquaculture due to their fast growth, culture conditions, and reputation as a sustainably produced fish as a result of closed containment culture. A study was conducted to evaluate performance and highly unsaturated fatty acid retention in two Arctic Char stocks—one commercial stock and one from the U.S. Department of Agriculture (USDA)—fed one of three diets containing different lipids (27% total): 11% fish oil and 11% soy–canola (diet 1, reference diet), 5% fish oil and 18% canola oil (diet 2), and 5% fish oil and 17% poultry oil (diet 3). Protein sources did not vary among the diets, and the lipid sources for the reference diet were similar to those included in commercial grower diets. After 250 d, fish from the USDA stock (1,736 ± 28 g [mean ± SE]) had significantly higher average weight, approximately 510 g greater, compared with the commercial stock (1,226 ± 19 g). Average weight gain was not significantly different among the diets but tended to be higher in diet 2 (P= 0.09), and the USDA stock (~1,409 ± 27 g gained) had higher average weight gain compared with the commercial stock (~924 ± 18 g gained). Specific growth rate (SGR) was significantly different among the diets; fish fed diet 2 had the highest growth rate (0.62%/d compared with 0.59%/d and 0.58%/d for the other two diets) and the USDA stock had a significantly higher SGR compared with the commercial stock (0.65 ± 0.01%/d compared with 0.54 ± 0.01%/d). Fillet yield did not vary among diets or stocks. The average fillet yield was 67.4% of the gutted weight and 62.2% of the total weight. Selected fatty acid profiles did vary by stock and all fatty acid profiles showed dietary effects. The USDA stock had superior growth, and diet had the greatest influence on the fatty acid profile of the fillets. Received September 25, 2015; accepted February 13, 2016 Published online June 24, 2016 [ABSTRACT FROM PUBLISHER]

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

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

We sampled landlocked Arctic char ( Salvelinus alpinus ) from four lakes (Small, 9-Mile, North, Amituk) in the Canadian High Arctic that span a gradient of mercury contamination. Metals (Hg, Se, Tl, and Fe) were measured in char tissues to determine their relationships with health indices (relative condition factor and hepatosomatic index), stable nitrogen isotope ratios, and liver histology. A subcellular partitioning procedure was employed to determine how metals were distributed between potentially sensitive and detoxified compartments of Arctic char livers from a low- and high-mercury lake (Small Lake and Amituk Lake, respectively). Differences in health indices and metal concentrations among char populations were likely related to differences in feeding ecology. Concentrations of Hg, Se, and Tl were highest in the livers of Amituk char, whereas concentrations of Fe were highest in Small and 9-Mile char. At the subcellular level we found that although Amituk char had higher concentrations of Tl in whole liver than Small Lake char, they maintained a greater proportion of this metal in detoxified fractions, suggesting an attempt at detoxification. Mercury was found mainly in potentially sensitive fractions of both Small and Amituk Lake char, indicating that Arctic char are not effectively detoxifying this metal. Histological changes in char livers, mainly in the form of melano-macrophage aggregates and hepatic fibrosis, could be linked to the concentrations and subcellular distributions of essential or non-essential metals. [ABSTRACT FROM AUTHOR]

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

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

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

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

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

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]