Arctic Charr Salvelinus Alpinus Research Articles

Determinants of parasite distribution in Arctic charr populations: catchment structure versus dispersal potential.

Parasite distribution patterns in lotic catchments are driven by the combined influences of unidirectional water flow and the mobility of the most mobile host. However, the importance of such drivers in catchments dominated by lentic habitats are poorly understood. We examined parasite populations of Arctic charr Salvelinus alpinus from a series of linear-connected lakes in northern Norway to assess the generality of lotic-derived catchment-scale parasite assemblage patterns. Our results demonstrated that the abundance of most parasite taxa increased from the upper to lower catchment. Allogenic taxa (piscivorous birds as final host) were present throughout the entire catchment, whereas their autogenic counterparts (charr as final hosts) demonstrated restricted distributions, thus supporting the theory that the mobility of the most mobile host determines taxa-specific parasite distribution patterns. Overall, catchment-wide parasite abundance and distribution patterns in this lentic-dominated system were in accordance with those reported for lotic systems. Additionally, our study highlighted that upper catchment regions may be inadequate reservoirs to facilitate recolonization of parasite communities in the event of downstream environmental perturbations.

Effects of soybean meal and high-protein sunflower meal on growth performance, feed utilization, gut health and gene expression in Arctic charr (Salvelinus alpinus ) at the grow-out stage

The effects of two plant ingredients (solvent-extracted soybean meal [SBM] and high-protein sunflower meal [HPSFM]) and three inclusion levels (0 percent, practical diet containing 25 percent fish meal; 12.5 percent; and 25 percent) of these ingredients were investigated on the growth, feed utilization, gut histology and gene expression in the distal intestine of Arctic charr Salvelinus alpinus (average initial weight, 330.1 ± 8.9 g per fish). Feeding experimental diets for 12 weeks resulted in no difference between HPSFM diets in body weight gain (BWG), thermal-unit growth coefficient (TGC), feed efficiency (FE), feed intake (FI) or pro-inflammatory mRNA expression (PIE) with increasing dietary inclusion and between SBM FE, FI and PIE. Differences in quadratic contrasts were observed for nitrogen deposition rate (NDR) and nitrogen retention efficiency (NRE) (p < .05), whereby HPSFM diets elicited the strongest positive response. SBM resulted in linear reduction in BWG, TGC and distal intestine simple fold length and width measurements (p < .05) with stepwise increases in dietary inclusion, whereas dietary HPSFM had no effect. Histological observations of individual villi indicated several symptoms of non-infectious subacute gastrointestinal enteritis in tanks fed SBM, many of which were not present in tanks fed HPSFM. The dietary HPSFM seems to be more adequate to replace fishmeal in Arctic charr diet than SBM, when fed at a level of up to 25 percent at the grow-out stage.

Diel activity and foraging mode of juvenile Arctic charr in fluctuating water flow

AbstractStreams fluctuate in water flow because of natural (e.g., rain) and human‐induced events (e.g., hydropeaking). Magnitude, frequency, and predictability of these events can have drastic consequences for fish populations. We studied how rapid modifications of water flow affect diel activity and foraging mode of juvenile Arctic charr Salvelinus alpinus in stream enclosures exposed to either stable (intermediate) or fluctuating (low vs. high) water flow. Under stable conditions, Arctic charr showed limited activity (9.4%). In fluctuating water flow, charr increased activity during low flow periods, especially during the first hours after the flow decreased, but ceased activity almost completely at high flow. Charr were mostly nocturnal, and more nocturnal at low than intermediate water flow. Fish were more mobile and swam faster during prey search and attacked prey at longer distances at low water flow. Activity and foraging mode differed between the first and second day after reduced water flow, suggesting that Arctic charr require time to adjust their foraging behaviour. This study demonstrates the importance of behavioural flexibility for population ecology in fluctuating environments such as regulated rivers.

Small-scale fisheries in Canada's Arctic: Combining science and fishers knowledge towards sustainable management

In remote and data-limited situations such as encountered in Arctic regions, traditional ecological knowledge (TEK) is an important and valuable information source. TEK from local fishers (fishers knowledge, FK) is highly relevant to fisheries management. The integration of FK in fisheries assessments remains complicated by the lack of tools to combine scientific and FK observations. This study implements a productivity-susceptibility analysis (PSA) for assessing the risk from fishing to fish stocks and incorporate FK in the assessment process. The PSA method consists of scoring productivity attributes of fish populations and susceptibility attributes affecting fisheries exposure and intensity. The method can be adapted to incorporate FK on two levels: (1) in the validation of biological data (indirect inclusion); and (2) in the definition and scoring of independent FK attributes (direct inclusion). Risk scores measured along the productivity-susceptibility gradient serve to identify areas and populations most vulnerable to fishing activities and formulate science advice for prioritisation and management. We apply the method to small-scale fisheries for Arctic char Salvelinus alpinus in Cumberland Sound, Baffin Island, Nunavut. These fisheries are key to food security and economic growth in Canada's Arctic territories, yet management remains complicated by data paucity; by the widespread distribution and biological complexity of Arctic char stocks; and by growing uncertainties related to climate change impacts on Arctic fish and ecosystems. This paper demonstrates the usefulness of the method for combining science and FK information to improve management advice for Arctic char stocks, and applicability to other small-scale, data-limited fisheries.

Egg Size Versus Number of Offspring Trade-Off: Female Age Rather Than Size Matters in a Domesticated Arctic Charr Population

Understanding how organisms adjust reproductive allocation trade-offs between offspring size versus number (OSN trade-off) is a central question in evolutionary biology. In organisms with indeterminate growth, changes in OSN according to maternal size or age have been reported in numerous taxa. The relative contribution of age and size remains largely unclear, as they are often highly correlated. In this study, we investigated how females adjust the offspring size versus number trade-off and analyzed the relative contribution of female age and size in a domesticated population of Arctic charr Salvelinus alpinus (Linnaeus, 1758) that exhibit large variation in size within five age classes. Our results show that the reproductive output (i.e. as measured by the clutch mass), was strongly correlated to female mass and age suggesting that the proportion of resources allocated to reproduction do not vary along lifetime. Egg mass and fecundity (egg number) increased with female mass overall. However, within an age class, larger females had higher fecundity but egg mass was poorly related to female mass. At the population level, a positive relationship was observed between fecundity and egg mass but within each class age the relation was negative revealing a OSN trade-off. Overall, our results show that, in our model Arctic charr population, allocation trade-off to reproduction and the way females allocate to egg mass and fecundity is largely determined by their age rather than mass.

Maternal effects in vulnerability to eye-parasites and correlations between behavior and parasitism in juvenile Arctic charr.

Hatchery‐reared fish show high mortalities after release to the wild environment. Explanations for this include potentially predetermined genetics, behavioral, and physiological acclimation to fish farm environments, and increased vulnerability to predation and parasitism in the wild. We studied vulnerability to Diplostomum spp. parasites (load of eye flukes in the lenses), immune defense (relative spleen size) and antipredator behaviors (approaches toward predator odor, freezing, and swimming activity) in hatchery‐reared juvenile Arctic charr (Salvelinus alpinus) using a nested mating design. Fish were exposed to eye‐fluke larvae via the incoming water at the hatchery. Fish size was positively associated with parasite load, but we did not find any relationship between relative spleen size and parasitism. The offspring of different females showed significant variation in their parasite load within sires, implying a dam effect in the vulnerability to parasites. However, the family background did not have any effect on spleen size. In the mean sire level over dams, the fish from the bolder (actively swimming) families in the predator trials suffered higher loads of eye flukes than those from more cautiously behaving families. Thus, the results indicate potentially maternally inherited differences in vulnerability to eye‐fluke parasites, and that the vulnerability to parasites and behavioral activity are positively associated with each other at the sire level. This could lead to artificial and unintentional selection for increased vulnerability to both parasitism and predation if these traits are favored in fish farm environments.

Energy Density and Dry Matter Content in Fish: New Observations and an Evaluation of Some Empirical Models

AbstractEnergy density (ED) is an indicator of fish nutritional status, physiological status, and fitness. Estimates of ED of predators and prey are also needed for bioenergetics modeling, but direct measurements of ED are difficult to obtain. Hence, investigators often borrow published values from the same species or related species. Alternatively, models have been developed that predict ED from dry matter content (DM). The scarcity of published ED values makes data borrowing and the generality of predictive modeling difficult to evaluate. We report new ED measurements derived from bomb calorimetry for six freshwater fish species (Arctic Char Salvelinus alpinus, Brown Trout Salmo trutta, kokanee Oncorhynchus nerka, Lake Trout Salvelinus namaycush, Rainbow Trout O. mykiss, and White Sucker Catostomus commersonii) and compared them to previously published data. We used our data to validate existing ED:DM models and to fit new ones. We also quantified bias that could result from borrowing inappropriate ED values for bioenergetics modeling. We collected a range of fish sizes from two reservoirs of differing productivity and measured whole‐body ED (wet‐mass basis) and DM. Our data substantially increase the range of ED data for Arctic Char, kokanee, and White Suckers. Two multispecies ED:DM models predicted the ED of our samples accurately (mean root mean square error [RMSE] &lt; 500 J/g), even at the extremes for the range of prediction where data used for model development were limited. Taxon‐specific models performed less well (mean RMSE = 775 J/g), and some appeared highly biased (RMSE 956−1,900 J/g). Bioenergetics model simulations showed that Lake Trout prey consumption could be overestimated by as much as 22% when using borrowed EDs for Lake Trout and their prey, but prey consumption estimates fell within ±2% of observed when ED was predicted from DM. When direct measures of ED are unattainable, measurement of DM and prediction of ED from one of the published multispecies models offer a practical and accurate method for bioenergetics modeling and other studies requiring information on fish energy content.

Use of Electricity to Sedate Lake Trout for Intracoelomic Implantation of Electronic Transmitters

AbstractUse of telemetry data to inform fisheries conservation and management is becoming increasingly common; as such, fish typically must be sedated before surgical implantation of transmitters into the coelom. Given that no widely available, immediate‐release chemical sedative currently exists in North America, we investigated the feasibility of using electricity to sedate Lake Trout Salvelinus namaycush long enough for an experienced surgeon to implant an electronic transmitter (i.e., 180 s). Specifically, our study objectives were to determine (1) whether some combination of electrical waveform characteristics (i.e., duty cycle, frequency, voltage, and pulse type) could sedate Lake Trout for at least 180 s; and (2) whether Lake Trout that were sequentially exposed to continuous DC and pulsed DC had greater rates of spinal injury and short‐term mortality than control fish. A Portable Electrosedation System unit was used to sedate hatchery and wild Lake Trout. Dual‐frequency pulsed‐DC and two‐stage approaches successfully sedated Lake Trout and had similar induction and recovery times. Lake Trout sedated using the two‐stage approach did not have survival rates or spinal abnormalities that were significantly different from those of control fish. We concluded that electricity was a viable alternative to chemical sedatives for sedating Lake Trout before surgical implantation of an electronic transmitter, but we suggest that Lake Trout and other closely related species (e.g., Arctic Char Salvelinus alpinus) may require morphotype‐specific electrical waveforms due to their morphological diversity.Received January 28, 2017; accepted April 24, 2017 Published online June 20, 2017

Climate and productivity shape fish and invertebrate community structure in subarctic lakes

Summary Climate change and land‐use intensification are increasing productivity in subarctic lakes. Simultaneously, fish and invertebrate species adapted to temperate conditions are expanding their range northwards into subarctic habitats. Community level studies are required to predict long‐term effects of these dual stressors on subarctic freshwater ecosystems. We conducted a space‐for‐time study examining the fish, benthic invertebrate and pelagic zooplankton communities in littoral, profundal and pelagic habitats in 19 subarctic lakes situated on a temperature, land‐use and productivity gradient in northern Europe. Fish density (ranging between 0.5 and 150.5 fish per net series h−1) and biomass (range between 92 and 5,147 g per net series h−1) increased significantly with increasing lake temperature and productivity. This was associated with significantly decreasing body size (26 to 12 cm total length; 174 to 19 g body mass) and a shift in fish community structure from salmonid (Arctic charr Salvelinus alpinus, whitefish Coregonus lavaretus), to percid (ruffe Gymnocephalus cernua, perch Perca fluviatilis) and ultimately cyprinid (roach Rutilus rutilus, bleak Alburnus alburnus) dominance. Changes in fish community composition were most apparent in littoral and pelagic zones. Benthic macroinvertebrate density peaked in mesotrophic lakes, zooplankton density was highest at either end of the gradient, indicating habitat specific differences in predation pressure and top‐down control. Body size of zooplankton and benthic macroinvertebrates was negatively related to temperature and productivity. These results suggest that climate change and intensification of land‐use practices are gradually turning subarctic lakes into warmer, less transparent and more productive systems harbouring abundant, small‐sized and warmer adapted communities.

Experimental challenges with Renibacterium salmoninarum in Arctic charr Salvelinus alpinus.

Arctic charr Salvelinus alpinus L. is an important species in Icelandic aquaculture and the most common wild salmonid in Iceland. A study on the course of infection with the bacterium Renibacterium salmoninarum was conducted using 3 different challenge methods in brackish and fresh water. Bacterial isolation, ELISA and PCR tests were used for detection of the bacterium in multiple organ samples. In an experiment, run for 34 wk in brackish water, infection was established by intraperitoneal injection with 5 × 106 colony forming units (CFU) fish-1. There were external and internal symptoms of bacterial kidney disease (BKD) and mortalities between 6 and 13 wk after injection. A cohabitation trial was run simultaneously and infection was well established after 4 wk, as demonstrated by the detection methods applied. Symptoms of BKD were not seen and all but 1 cohabitant survived. In a separate experiment, infection was established by pumping a fixed amount of water from a tank with fingerlings infected by intraperitoneal injection into tanks with naïve fish, in fresh or brackish water, for 6 wk. Fish in the inflow tanks were reared for an additional 3 wk. There were neither macroscopic symptoms nor mortalities. ELISA and PCR tests showed that infection started to take hold after 3 wk. The challenge trials demonstrated that Arctic charr is susceptible to R. salmoninarum. Cohabitation and inflow of water from tanks with infected fish provide useful models for further studies on R. salmoninarum infection acquired in a natural way in Arctic charr.

Reproduction of Lake Trout Morphotypes at Isle Royale in Northern Lake Superior

AbstractThe reproductive biology of male and female lean, siscowet, redfin, and humper Lake Trout Salvelinus namaycush was assessed by measuring the gonadosomatic index (GSI) and by histological analysis of the gonads over 2 years from spring to fall at sites surrounding Isle Royale National Park, Lake Superior. Whole livers, otoliths, and ovaries were also collected to measure hepatosomatic index (HSI), age, and fecundity. In general, GSIs increased from spring to summer in male and female siscowets, leans, redfins, and humpers, and this was accompanied by a large increase in the number of vitellogenic (&gt;2.0 mm) follicles in females. Postspawned ovaries and regressing testes were predominant in all morphotypes by October but were also observed in September, indicating that some spawning occurred at least by September. Further, preovulatory siscowet females (GSIs &gt; 10) and siscowet males with fully mature and even regressing testes were observed in the spring and summer, indicating that spawning occurs at least in the spring and fall in siscowets at Isle Royale. For all morphotypes, average male HSIs were significantly lower than female HSIs. Absolute fecundity was positively related to size and age for all morphotypes. Humpers had the lowest absolute fecundity. Leans, redfins, and siscowets had similar fecundity relationships. The results conclusively demonstrate that deepwater siscowet Lake Trout reproduce at least during the spring and fall at Isle Royale and that leans, humpers, and redfins reproduce during the fall. In lakes that exhibit sympatric populations of deepwater and shallow‐water ecotypes of Arctic Char Salvelinus alpinus, the deepwater form also spawns in both spring and fall. Our data and those on Arctic Char suggest that there is an adaptive strategy for maintaining alternative spawning times in the deepwater ecotypes in these populations.Received June 20, 2016; accepted November 2, 2016 Published online January 31, 2017

Behaviour of Arctic charr Salvelinus alpinus during an induced mating season in captivity: how male relative size influences male behavioural investment and female preference over time.

The behaviour of sexually mature Arctic charr Salvelinus alpinus specimens (fifth farm generation) was observed in captivity for four consecutive days. Only agonistic interactions between males of different size were facilitated on the first 2 days, while both agonistic and courtship interactions were possible from the third day up to the end of the experiment. The reliability of behavioural analysis was assessed in order to reduce the possibility of observer errors within the generated datasets. The behavioural investment of big males, small males and females was analysed using general linear models (two-way repeated measures ANOVAs with time and male size as factors). A peak in the agonistic interactions between males occurred during the first day of interactions, where the agonistic investment of big males was significantly higher than that of small males. This resulted in an increased investment in submissive behaviour by the small males, who consistently performed submissive behaviours from the second day of interactions up to the end of the trial. Big males were found to invest significantly more than small males in courtship behaviours for the duration of the trial. Even though females performed inter-sexual behaviours towards both big and small males for the entire observation period, female interaction rate towards big males was higher than towards small males. This study suggests that both male investment in mating behaviour and female preference might be related to male characteristics such as body length and that S. alpinus behavioural patterns and mate choice cues might be strongly context-related and characterized by high levels of behavioural plasticity (i.e. presence-absence of certain behavioural units or potential reversal of a mate choice cue) within the same species. Finally, in light of this, some conservation measures are discussed. In particular, effective management plans should take into account the high level of behavioural plasticity likely to be occurring in this species.

Genetic Stock Structure of Anadromous Arctic Char in Canada's Central Arctic: Potential Implications for the Management of Canada's Largest Arctic Char Commercial Fishery

AbstractThe Arctic Char Salvelinus alpinus is widely considered the most important subsistence fish species in the Canadian Arctic. Throughout the species’ range, commercial fisheries for Arctic Char also exist, the management of which primarily follows river‐specific harvest strategies. Such an approach, however, may not be appropriate if the management unit or stock does not accurately reflect a demographically independent population or if mixtures of populations are being harvested. We assayed microsatellite DNA variation among 744 Arctic Char from the Cambridge Bay region, Nunavut, where the largest commercial fishery for the species exists, in order to identify the most appropriate spatial scale at which these stocks should be managed. Our sampling design specifically mirrored that of the commercial fishery in order to describe patterns of genetic structure and genetic variation within and among the harvested component. We also included Arctic Char from more geographically distant sampling locations to provide a spatial context for genetic stock structuring in the region. Overall, we found moderate but significant structure across the entire study area. In contrast, commercially harvested stocks were weakly differentiated, especially among the stocks that are considered part of the Wellington Bay complex. We propose several hypotheses for this weak differentiation, including (1) our sampling design that mirrored the commercial harvest, (2) high rates of potential gene flow, and (3) large effective population sizes. Our results may have important implications for commercial and subsistence fisheries management, including the notion that there are several potential units of conservation below the species level.Received September 29, 2015; accepted August 17, 2016 Published online November 28, 2016

Divergent functional traits in three sympatric Arctic charr Salvelinus alpinus morphs are not coupled with the age of the lineage divergence

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

Distinguishing Arctic charr with different stress coping styles by visual screening of spottiness – reliability and consistency over time

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.

Low Annual Fidelity and Early Upstream Migration of Anadromous Arctic Char in a Variable Environment

AbstractThe life histories of anadromous Arctic Char Salvelinus alpinus are complex and vary greatly between populations and environments. Here, we detail key aspects of the physical environment and life history of a population of Arctic Char from Nulahugyuk Creek, Nunavut, Canada, to characterize migration traits in a highly variable environment. Over the course of this migration, creek discharge declined precipitously, forcing Arctic Char to migrate through shallow water with large diel temperature fluctuations (&gt;10°C) and high temperature extremes (&gt;21°C). The downstream migration of adults (&gt;55 cm) began in mid‐June and continued into early July, while the downstream migration of smolts (&lt;30 cm) began in late June and continued until late July. The upstream adult migration began in late June and ended in late July, far earlier than most upstream migrations in the region. There was no appreciable upstream migration of juveniles, and Arctic Char 30 to 55 cm in length were absent from the up‐ and downstream migrations. The average age at first migration was 4 years, and the youngest adult Arctic Char migrating upstream were 8 and 9 years old. The missing size‐ and age‐classes, and the fact that most upstream migrants were near reproductive maturity, indicate that Arctic Char in this system typically leave at a length of 19 cm and an age of 4 years and do not return for 4 to 5 years, when they are ready to reproduce. Anadromous Nulahugyuk Creek Arctic Char appear to employ strategies that limit their exposure to restrictive migratory conditions and facilitate their existence in an otherwise uninhabitable system. Understanding such population‐specific migratory strategies is critical to the management of Arctic Char fisheries, which are comprised of populations with highly diverse life histories, and to our understanding of how these life histories may contribute to the adaptability and persistence of the species as climate change progresses.Received November 24, 2015; accepted March 23, 2016 Published online July 28, 2016

Taste attractiveness of free amino acids and their physicochemical and biological properties (as exemplified by fishes)

Using fishes as an example (32 species, II families) the relationship between taste attractiveness of free amino acids (L-isomers) and their physicochemical and biological properties was analyzed. It is shown that the essential amino acids, which are of the highest nutritional requirement for an organism, have lower taste attractiveness in fishes than nonessential ones. Only in 6 species of 32 investigated ones (sun- bleak Leucaspius delineatus, European minnow Phoxinus phoxinus, dace Leuciscus leuciscus, chub Leu- ciscus cephalus, blue gourami Trichopodus trichopterus, pearl gourami Trichopodus leerii) the relation- ship between taste preference and molecular weight of amino acids was confirmed statistically, in all cases being negative. Only in 2 species a statically significant correlation between taste properties of amino acids and the dissociation constant (K₁) was found (positive in stone loach Barbatula barbatula and negative in lake charr Salvelinus namaycush). A positive correlation between taste preference and the value of isoelectric point (pI) of amino acids was found in one species (roach Rutilus rutilus) and negative correlation - in 2 species (brown trout Salmo trutta, Arctic char Salvelinus alpinus erythrinus). A significant correlation between taste attractiveness and solubility of amino acids in water.was found in 2 species (chum salmon Oncorhynchus keta and navaga Eleginus nawaga), negative in both cases. Acidic and polar uncharged amino acids more often possess flavor that stimulates food consumption than basic and non-polar ones, L-isomers of amino acids than D-isomers, amino acids with an amino group in cc-position than in β-position. Amino acids are more attractive than their salts. Aromatic amino acids possess attrac- tive taste much less than sulfur-containing or acyclic ones. Thus, in the majority of fish species the relationship between taste attractiveness of free amino acids and many of their physical, chemical and biolo- gical properties is absent or low, indicating their indirect nature and difficulty of revealing these relation- ships.

Does the Arctic charr Salvelinus alpinus produce sounds in a captive setting?

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.

Density-dependent diel activity in stream-dwelling Arctic charr Salvelinus alpinus.

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.

The developmental transcriptome of contrasting Arctic charr ( Salvelinus alpinus) morphs

Species and populations with parallel evolution of specific traits can help illuminate how predictable adaptations and divergence are at the molecular and developmental level. Following the last glacial period, dwarfism and specialized bottom feeding morphology evolved rapidly in several landlocked Arctic charr Salvelinus alpinus populations in Iceland. To study the genetic divergence between small benthic morphs and limnetic morphs, we conducted RNA-sequencing charr embryos at four stages in early development. We studied two stocks with contrasting morphologies: the small benthic (SB) charr from Lake Thingvallavatn and Holar aquaculture (AC) charr.The data reveal significant differences in expression of several biological pathways during charr development. There was also an expression difference between SB- and AC-charr in genes involved in energy metabolism and blood coagulation genes. We confirmed differing expression of five genes in whole embryos with qPCR, including lysozyme and natterin-like which was previously identified as a fish-toxin of a lectin family that may be a putative immunopeptide. We also verified differential expression of 7 genes in the developing head that associated consistently with benthic v.s.limnetic morphology (studied in 4 morphs). Comparison of single nucleotide polymorphism (SNP) frequencies reveals extensive genetic differentiation between the SB and AC-charr (~1300 with more than 50% frequency difference). Curiously, three derived alleles in the otherwise conserved 12s and 16s mitochondrial ribosomal RNA genes are found in benthic charr.The data implicate multiple genes and molecular pathways in divergence of small benthic charr and/or the response of aquaculture charr to domestication. Functional, genetic and population genetic studies on more freshwater and anadromous populations are needed to confirm the specific loci and mutations relating to specific ecological traits in Arctic charr.