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Personality is now recognized as an ecologically and evolutionarily significant phenomenon because it can affect fitness directly. However, empirical studies specifically tackling the importance of personality in the processes of adaptive divergence and speciation are scarce. Whether selection favours plasticity or canalization of personality traits in specific contexts and how ecological conditions affect the presence and the structure of personalities remain to be elucidated. We used five populations of Arctic charr, Salvelinus alpinus , chosen along a gradient of genetic and phenotypic divergence: an anadromous population supposedly close to the ancestral population and two pairs of sympatric lake morphs. Fish were raised individually from eggs in a common garden experiment to specifically assess the genetic bases of the boldness trait in these populations. Thirty-two individuals per morph were repeatedly tested at 11 months old in an open field test with a shelter to assess boldness. The repeatability of the boldness trait (i.e. personality), within- and among-individual variation and temporal variation were assessed within each population. Then, the temporal plasticity in boldness and boldness mean score were assessed among populations. The results show differences between populations for the three variables, with the highest repeatability in the most diverged population, an increase in boldness over time and a lower mean value (especially the first time they were exposed to the novel environment) in the anadromous population. This suggests that boldness and temporal plasticity differ between the anadromous population and the more diverged lake populations under a controlled embryonic/juvenile environment. Further research is needed to verify the contribution of temporal plasticity for personality traits in the context of rapid adaptive radiation such as that seen in Arctic charr. • Boldness and related parameters were measured in five populations of Arctic charr. • Temporal variation in boldness was assessed by repeated measures. • Lower boldness and higher temporal plasticity are shown in the ancestral population. • Contribution of temporal plasticity in adaptive radiation remains to be elucidated. [ABSTRACT FROM AUTHOR]

Mucins are highly glycosylated proteins that make up the mucus covering internal and external surfaces of fish. Mucin O -glycans regulate pathogen quorum sensing, growth, virulence and attachment to the host. Knowledge on this mucosal defense system can enable alternative treatments to diseases posing a threat to productivity and welfare in aquaculture. Here, we characterize the rainbow trout (Oncorhynchus mykiss) gill, skin, pyloric ceca and distal intestinal mucin O -glycosylation and compare it to known teleost O -glycomes. We identified 54 O -glycans, consisting of up to nine monosaccharide residues. Skin glycans were most acidic, shortest on average and consisted mainly of NeuAcα2-6GalNAc. Glycans from the gills were less acidic with predominantly core 1 and 2 glycans, whereas glycans from pyloric ceca and distal intestine expressed an increased number of core 5 glycans, distinctly decorated with NeuAcα2-8NeuAc- like epitopes. When compared to Atlantic salmon and Arctic charr, trends on the core distribution, average size and overall acidity remained similar, although the epitopes varied. Rainbow trout mucins from gill and intestine bound A. salmonicida and A. hydrophila more efficiently than skin mucins. This is in line with a model where skin mucins with small glycans limit bacterial adhesion to the fish surface whereas the complex intestinal mucin glycans aid in trapping and removing pathogens from the epithelial surface. • Mucins from rainbow trout skin, gills and intestine are differentially glycosylated. • 54 identified glycans provide a platform for studying host-pathogen interactions. • Skin glycans are short whereas gill and intestinal mucins are large and complex. • The short skin glycans provide few binding sites for Aeromonas spp. • The gill and intestinal mucins carry many binding sites for Aeromonas spp. [ABSTRACT FROM AUTHOR]

Divergent selection is a powerful driver of speciation and has been widely studied in relation to the physical characters of organisms. Behavioural traits also significantly contribute to the evolutionary processes of divergence. However, studying such effects is fraught with difficulties as the development of behavioural traits is likely to be complex and is moulded by ontogenetic processes such as shifts in habitat use. Here we explored how several aspects of juvenile behavioural variation may relate to adaptive divergence in a freshwater fish. We assessed whether and how juveniles of two recently evolved, sympatric morphs of Arctic charr, Salvelinus alpinus , a small benthivorous and a planktivorous charr, show genetically based differences in personality that conform to their respective ecological niches, and whether these differences could contribute to reproductive isolation by generating maladaptive hybrid behaviours. Studying three aspects of behavioural variation (average trait value, consistent individual differences and trait correlations), we assessed the sociality and risk-taking propensity of hybrids and pure-morph offspring reared in common conditions. While no difference in average behavioural responses could be observed, the hybrids tended to show less repeatable behaviours and were not intermediate for behavioural syndromes that appear to differ between the two morphs. These results provide limited evidence of personality trait divergence among polymorphic fish, and suggest subtle, nonadditive effects of hybridization on the development of such traits. • Average personality traits differences between charr morphs were not observed. • Trait correlations appear to differ between morphs. • Consistent individual differences tended to be altered in their hybrids. • Intermediate trait correlations were not observed in the hybrids. [ABSTRACT FROM AUTHOR]

Killer whales (Orcinus orca) historically restricted to certain Arctic regions due to extensive sea ice have recently been documented farther north and for longer durations in the Canadian Arctic. These apex predators accumulate high levels of persistent organic pollutants (POPs). The objective of this study was to evaluate the concentrations and profiles of POPs in killer whales of the Canadian Arctic, thus determining potential risks for Inuit communities if consumed. Biopsies were collected from 33 killer whales across areas of the Canadian Arctic between 2009 and 2021. Significant variability in POP concentrations was observed among whales. The cumulative POP concentrations ranged from 12 to >2270 mg/kg lw, representing ∼200-fold increase from the least to the most contaminated individual. The rank order of concentrations of the top five contaminant classes was ∑DDT, ∑PCB, ∑CHL, ∑Toxaphene, and Dieldrin. Several emerging Arctic contaminants were detected, including chlorpyrifos, endosulfan, pentachloroanisole, and polychlorinated naphthalenes, although at relatively lower concentrations than legacy POPs. Considering the elevated blubber POP levels in killer whales, recommended daily consumption thresholds, established based on human tolerable daily intake (TDI) values, were notably restricted for ∑PCB (<0.14 g), ∑DDT (<6.9 g), ∑CHL (<13 g), dieldrin (<8 g) and heptachlor epoxide (<5 g). Killer whales in the Canadian Arctic exhibited higher POP concentrations than other commonly hunted species such as polar bears, ringed seals, and Arctic char. We acknowledge that a more holistic risk assessment of diet is required to assess the cumulative impacts of contaminant mixtures as well as nutritional quality of tissues commonly consumed by northern communities. [Display omitted] • Climate change is increasing Inuit interactions with killer whales in the Canadian Arctic. • Some Nunavut communities within the Qikiqtaaluk region have expressed interest in hunting killer whales. • 200-fold difference in sum POPs from least to most contaminated killer whale blubber. • Killer whale contaminant levels far higher than traditional country foods. • Safe human consumption of killer whale blubber is limited to <0.1–10 g per day. [ABSTRACT FROM AUTHOR]

Despite vast research attention, the knowledge about central mechanisms of appetite regulation in teleost remains inconclusive. A common strategy in studies on appetite regulating mechanisms is to measure the response to feed restriction or – deprivation, but responses vary between fish species and between experiments, and are also likely dependent on the degree of energy perturbation. The anadromous Arctic charr is an interesting model for studying appetite regulation as its feeding cycle comprises months of winter anorexia, and hyperphagia during summer. Here we studied how the gene expression of putative hypothalamic appetite regulators were affected by two days, one week and one month feed deprivation during summer, and subsequent re-feeding and exposure to feed flavour. Short-term feed deprivation caused only a minor reduction in condition factor and had no effect on hypothalamic gene expression. Long-term feed-deprivation caused a marked reduction in weight and condition factor which contrasted the increase in weight and condition factor seen in ad libitum fed controls. A marked energy perturbation by feed deprivation was also indicated by a lower hypothalamic expression of the genes encoding insulin-like growth factor 1 (IGF1) and IGF1 binding protein 5 in the feed deprived charr compared to fed controls. Surprisingly, long-term feed deprivation and energy perturbation did not induce changes in hypothalamic appetite regulators. Unexpectedly, re-feeding and exposure to feed flavour caused an increase in the expression of the genes encoding the orexigenic agouti-related peptide and the anorexigenic melanocortin receptor 4 and cocaine- and amphetamine-regulated transcript. Our study gives strong evidence for a role of these in appetite regulation in Arctic charr, but their mechanisms of action remain unknown. We suggest that changes in gene expression are more likely to be registered during transition phases, e.g. from fasting to feeding and upon stimulatory inputs such as feed flavour. [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]

The increasing exploratory efforts in the Greenland mineral industry, and in particular, the proposed rare earth element (REE) mining projects, requires an urgent need to generate data on baseline REE concentrations and their potential environmental impacts. Herein, we have investigated REE concentrations in anadromous Arctic char (Salvelinus alpinus) and shorthorn sculpins (Myoxocephalus scorpius) from uncontaminated sites in Northwest Greenland, along with the relationships between the element concentrations in gills and liver, and gill histology and serum biochemical parameters. Concentrations of arsenic, silver, cadmium, cerium, chromium, copper, dysprosium, mercury, lanthanum, neodymium, lead, selenium, yttrium, and zinc in gills, liver and muscle are presented. No significant statistical correlations were observed between element concentrations in different organs and gill histology or serum biochemical parameters. However, we observed positive relationships between age and histopathology, emphasizing the importance of including age as a co-variable in histological studies of fish. Despite no element-induced effects were observed, this study is considered an important baseline study, which can be used as a reference for the assessment of impacts of potential future REE mine sites in Greenland. • We analyzed elements with focus on REE, histology and serum biochemistry in 2 Arctic fish species. • Arctic chars had higher concentrations of REEs than what was found in shorthorn sculpins. • A positive relationship was found between age and histopathology. • Gill histology and serum biochemical parameters indicate no evidence of toxicological effects from element concentrations. This study provides baseline data for REE concentrations and histopathology and serum biochemistry in Arctic fish species. [ABSTRACT FROM AUTHOR]

Abstract: Aeromonas salmonicida subsp. achromogenes, the causative agent of atypical furunculosis in many fish species, secretes the toxic metalloendopeptidase AsaP1. This study aimed to analyze innate and adaptive immune parameters induced in Arctic charr (Salvelinus alpinus, L.) infected with wild type (wt) A. salmonicida subsp. achromogenes and its isogenic asaP1 deletion mutant (AsaP1-deficient). Head-kidney, liver and spleen were obtained from i.p. infected charr (wt, AsaP1-deficient), during a time schedule of 7 d post infection. Reverse transcription quantitative real-time PCR (RT-qPCR) was applied to study the expression of immune parameters: pro-inflammatory cytokines IL-1β and TNF-α; anti-inflammatory cytokine IL-10; chemokines CXCL-8 (IL-8) and CC-chemokine; the cytokines IFN-γ and IL-4/13A as tracers for Th1 and Th2 immune responses, respectively; and the cell markers CD8α and CD83. In addition, lymphoid organs were histopathologically examined at days 3 and 7 post infection, including B (IgM) and T (CD3ε) cell staining. The detected immune responses were initially driven by innate mechanisms represented by the up-regulation of pro-inflammatory cytokines and chemokines and later on by adaptive Th2 related responses cumulating in B-cell recruitment as shown by regulation of immune parameters in spleen and head-kidney, with significant differences between mutant and wt infected fish. Histological sections revealed IgM-positive cells around ellipsoid arterioles in spleen, while CD3ε positive cells were found in clusters scattered all over the section. However, histopathological differences were only detected between infected and non-infected fish, but not between AsaP1-deficient mutant and wt infected fish. This work represents the first study on innate and adaptive immune responses of Arctic charr induced by a bacterial infection. [Copyright &y& Elsevier]

Abstract: The aim of this study was to investigate whether the seasonal feeding cycle of the anadromous Arctic charr (Salvelinus alpinus) is regulated by a lipostatic mechanism and if leptin (Lep) might act as an endocrine signal of adiposity. Offspring of anadromous Arctic charr with a body mass of 121g were divided into two treatment groups; one was given feed in excess from March to November, and the other was fasted between April and early June and fed in excess thereafter. In the continuously fed group there was an 8-fold increase in body mass, and a doubling of percentage body fat, from March to August, after which there was no further increase. Fish in the other group lost weight and body fat during fasting, but grew rapidly on being fed, and had partially compensated for their deficit in body mass by August. Differences in percentage body fat between treatment groups were eliminated by August, providing evidence for a lipostatic regulation of feeding and energy homeostasis in Arctic charr. Neither liver total LepA gene expression nor plasma Lep concentrations correlated positively with fish adiposity, so there was no evidence that Lep acts as a signal of adiposity in this species. On the other hand, there was a strong increase in liver LepA1 gene expression at the end of the fasting period, concomitant with fat mobilization and increased plasma glucose, indicating that LepA1 may play a role in regulating metabolic processes associated with fasting. [Copyright &y& Elsevier]

Abstract: Plasma levels of 17,20β-dihydroxy-4-pregnen-3-one (17,20βP), and the timing of ovulation were investigated in female Arctic charr (Salvelinus alpinus) reared at 5°C and at 10°C during the pre-spawning period. The effects of switching from 5 to 10°C, and from 10 to 5°C were also investigated. 17,20βP plasma levels were higher at 5°C than at 10°C. A switch from 10 to 5°C stimulated 17,20βP secretion, whereas a switch from 5 to 10°C had the opposite effect. Ovulation occurred spontaneously in the females kept at 5°C, and in those switched from 10 to 5°C. In contrast, ovulation was inhibited in females reared at 10°C, and in those switched from 5 to 10°C. Oocyte maturation at 5°C and at 10°C in the presence of LH or of 17,20βP was also investigated in vitro using donor females reared at 5 or 10°C. Both LH and 17,20βP stimulated oocyte maturation more effectively in oocytes incubated at 5°C than at 10°C. At both incubation temperatures, the rearing temperature of the donor females had a significant impact on their responsiveness to LH stimulation, but had no effect on their responsiveness to 17,20βP stimulation. In addition to the inhibition of LH secretion, which had already been reported, the results reported here show that in Arctic charr raising the temperature above the physiological range reduces both follicular responsiveness to LH stimulation and the sensitivity of oocytes to 17,20βP stimulation. [Copyright &y& Elsevier]

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: The present study was conducted to establish a homologous radioimmunoassay (RIA) for quantifying plasma leptin (Lep) levels in salmonid species, and to study Lep levels in relation to nutritional status. A part of the Lep peptide, a 14 amino acid long sequence, identical between a Salmo and an Oncorhynchus species was synthesised. Polyclonal antibodies were raised in rabbit against this antigen and both were subsequently used in the development of a RIA protocol for assessing plasma Lep levels. The limit of detection of the assay was 0.3nM, and intra- and interassay coefficient of variation (CV) were 8.4% and 13%, respectively. Apart from Atlantic salmon and rainbow trout, the assay exhibits measuring parallelism for a range of fish species, including arctic char, Atlantic cod and turbot, suggesting that the established RIA is useful for quantifying Lep levels in several fish species. The RIA indicates that Lep is found in salmonid plasma at levels of 0.5–5nM, which is comparable with other peptide hormones, and well within the measuring range of the RIA. A study of fed and fasted rainbow trout showed elevated plasma Lep levels during fasting. In addition there was no correlation between Lep levels and condition factor. These data suggest that the relation between circulating Lep levels and energy status differs from that in mammals. While Lep is linked to energy balance, it may not act as an adiposity signal in salmonids, possibly pointing to functional divergence among ectothermic and endothermic vertebrates. [Copyright &y& Elsevier]

Abstract: The timing of ovulation and LH plasma levels were investigated in Arctic charr reared at 5°C and 10°C, exposed to the ambient photoperiod, or short or long-day photoperiod regimes during the prespawning period. The effectiveness of sGnRHa alone, or sGnRHa combined with a dopamine antagonist, in stimulating LH secretion and inducing ovulation was also investigated. With the natural photoperiod, ovulation occurred spontaneously at 5°C, but was inhibited at 10°C. A transition from 10 to 5°C soon resulted in suppression of the inhibition. At 5°C, the effectiveness of sGnRHa was similar to that of sGnRHa combined with pimozide in stimulating LH secretion and inducing ovulation. At 10°C, sGnRHa+pimozide was more effective that sGnRHa alone in stimulating LH secretion and inducing a high rate of ovulation, suggesting that dopamine-induced inhibition of LH secretion could occur naturally in Arctic charr at 10°C. Exposure of Arctic charr to a long day (LD) photoperiod regime in fall and winter did not completely inhibit ovulation, but markedly delayed it and prolonged the ensuing ovulation period. The LD photoperiod also reduced LH plasma levels in females while they were ovulating, but did not modify the responsiveness of the pituitary to GnRHa stimulation compared to a control group exposed to a short-day (SD) photoperiod. There was an interval of several weeks after a transition from LD to SD before LH secretion and ovulation were stimulated. [Copyright &y& Elsevier]

Abstract: This study investigated the influence of nutritional status on the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis in Arctic charr (Salvelinus alpinus). The objectives were to study the regulation of GH secretion in vitro by somatostatin-14 (SRIF) and hIGF-I, and to determine whether pituitary sensitivity to these factors is dependent upon nutritional status. Arctic charr were fed at three different ration levels (0, 0.35, and 0.70% BWd−1), and pituitary glands were harvested at 1, 2, and 5 weeks for in vitro study. Both SRIF and hIGF-I inhibited GH secretion from Arctic charr pituitary tissue in long-term (18h) static hemipituitary culture, as well as after acute exposure in a pituitary fragment perifusion system. This response appeared to be dose-dependent for SRIF in static culture over the range of 0.01–1nM, but not for hIGF-I. The acute inhibitory action of hIGF-I on GH release in the perifusion system suggests an action that is initially independent of any effects on GH gene expression or protein synthesis. Nutritional status did not affect the sensitivity of Arctic charr pituitary tissue to either SRIF or hIGF-I in vitro, indicating that changes in abundance of pituitary SRIF or IGF-I receptors may not explain the alterations in plasma GH levels found during dietary restriction. [Copyright &y& Elsevier]

Estrogens induce both vitellogenin (Vtg) and egg shell (zona pellucida; ZP) protein synthesis in salmonids. However, while Vtg is strictly under estrogenic control, recent reports suggest that additional mechanisms are involved in ZP protein synthesis. During sexual maturation both estrogen and glucocorticoid levels increase in the circulation of female fish. As glucocorticoids have been shown to interfere with Vtg induction in fish we investigated whether cortisol (F) had similar effects on ZP regulation. In the present study we determined both the natural variation in Vtg and ZP during an annual reproductive cycle in female Arctic char (Salvelinus alpinus), and the effect of co-treatment of juvenile Arctic char with 17β-estradiol (E2) and F. During sexual maturation the expression of Vtg and ZP correlated to plasma levels of E2 and F. Determination of Vtg and ZP protein levels following co-treatment with E2 and F showed that F antagonized E2 induction of Vtg. However, F was observed to potentiate the expression of ZP protein in the same fish. These results indicate that in Arctic char Vtg and ZP proteins are not regulated by the same mechanisms and suggest that ZP protein expression does not necessarily imply exposure to estrogenic compounds alone, and may thus not be ideally suited as a biomarker of exposure to estrogenic compounds. [Copyright &y& Elsevier]

Fushi tarazu factor-1 (FTZ-F1) genes belong to the nuclear receptor family 5A (NR5A). The distribution pattern of NR5A genes in teleosts suggests that they control functions separate to, or in addition to, those of other vertebrates. In mammals NR5A1 genes, including steroidogenic factor-1 (SF-1), are primarily involved in steroidogenesis. NR5A2 contain the α-fetoprotein transcription factor (FTF) genes, which protect mammalian embryos against maternal estrogens, and are involved in cholesterol transfer and metabolism. In this study we have analysed the expression of two Arctic char FTZ-F1 forms belonging to the NR5A2 group. The expression starts during early development and the transcripts are present in embryonic liver/pancreas and gonadal regions. The genes are up-regulated during embryogenesis as the embryo develops towards hatch, as shown by increased mRNA and protein levels. In adult Arctic char the FTZ-F1 forms are primarily located to tissues involved in steroidogenesis as well as cholesterol metabolism. Thus, a division of NR5A into SF-1 (NR5A1) and FTF (NR5A2) specific functions does not appear to have occurred in teleosts. [Copyright &y& Elsevier]

Examines the proposition that differences in foraging behavior of benthivorous, planktivorous and piscivorous morphs of arctic charr in Iceland are genetically based. Different habitats; Segregation in diet; Separation due to adaptive trophic specializations; Level of activity; Prey rejection; Feeding rate at high prey density; Innate predation-risk versus energy-gain trade-off.

Investigates the effect of early social experience on sibling recognition in Arctic charr, Salvelinus alpinus L. From the egg stage, fish from two full-sibling families were raised either in isolation, or in groups consisting of siblings. M ethods; Results; Discussion.

Cites a study which investigated the kin recognition and discrimination behavior in the Arctic charr, Salvelinus apinus. Examination of whether kin recognition and discrimination in the juvenile Arctic charr are influenced by the major histocompatibility complex (MHC); What the use of fluviarium tests revealed; Details on the results of the study.

High levels of organochlorines (OCs) have been measured in arctic char (Salvelinus alpinus) from Lake Ellasjøen on Bjørnøya, Norway (74.30°N, 19.0°E). In a nearby lake, Laksvatn, the OC-levels in arctic char were low. A previous study has shown that char from Ellasjøen had significantly higher levels of DNA double strand breaks (DSBs) than char from Lake Laksvatn. Even though there is increasing evidence of the genotoxic effects of OCs, little is known about the effects of OCs on the DNA repair system. The aim of the present study was to determine if the two main DNA DSB repair mechanisms, homologous recombination (HR) and non-homologous end-joining (NHEJ), are affected by the higher OC and DSB level in char from Ellasjøen. This was analysed by comparing the transcript level of 11 genes involved in DNA DSB repair in char liver samples from Ellasjøen (n = 9) with char from Laksvatn (n = 12). Six of the investigated genes were significantly upregulated in char from Ellasjøen. As the expression of DNA DSB repair genes was increased in the contaminant-exposed char, it is likely that the DNA DSB repair capacity is induced in these individuals. This induction was positively correlated with the DNA DSB and negatively correlated with one or several OCs for four of these genes. However, the strongest predictor variable for DNA repair genes was habitat, indicating genetic differences in repair capacity between populations. As char from Ellasjøen still had significantly higher levels of DSBs compared to char from Laksvatn, it is possible that chronic exposure to OCs and continued production of DSB has caused selective pressure within the population for fixation of adaptive alleles. It is also possible that DSB production was exceeding the repair capacity given the prevailing conditions, or that the OC or DSB level was above the threshold value of inhibition of the DNA repair system resulting in the rate of DNA damage exceeding the rate of repair. ga1 • In contaminated char, expression of several DNA DSB repair genes was induced. • Expression of 3 DNA DSB repair genes was positively correlated with DNA DSB level. • Expression of 4 DNA DSB repair genes was negatively correlated with OC levels. [ABSTRACT FROM AUTHOR]