Seasonal Changes in Osmotic and Ionic Regulation in Arctic Charr, Salvelinus Alpinus, From a High- and a Sub-arctic Anadromous Population

Seasonal changes in hypoosmoregulatory capacity were studied in hatchery-reared offspring of a high-Arctic strain of anadromous Arctic charr, Salvelinus alpinus, from Svalbard (79°N) and a sub-Arctic strain from Hammerfest, north Norway (70°N). The fish were held in freshwater under simulated, natural light conditions (Tromsø, 69°N) and natural water temperatures, and hypoosmoregulatory capacity was determined by seawater challenge tests between February and November. An improved hypoosmoregulatory capacity was seen in both strains at the time when their wild conspecifics migrate to the sea. The time when maximum hypoosmoregulatory capacity was achieved differed significantly between the two strains, suggesting that there may be genetic differences between the two populations in how environmental cues (e.g. temperature, photoperiod) entrain the development of seawater tolerance. The development and loss of hypoosmoregulatory capacity seemed to be more rapid and abrupt in the Svalbard charr than in the Hammerfest charr. This is hypothesised to be an adaptation to the stochastic and unpredictable variations in the time when the fish are allowed to migrate in the high-Arctic, and the need to prevent migration in years when the ice break occurs very late.     

Growth hormone and cortisol treatment stimulate seawater tolerance in both anadromous and landlocked Arctic charr

In a comparative experiment the effect of cortisol and growth hormone (GH) on the hypo-osmoregulatory ability of a landlocked and an anadromous strain of Arctic charr (Salvelinus alpinus) was investigated. Cortisol and GH were implanted either alone or in combination, and the fish were exposed to a 24 h seawater challenge test (SWT) on days 14 and 28 after implantation. Hypo-osmoregulatory ability, measured as plasma osmolality and chloride concentration after the SWTs, was better in the anadromous than in the landlocked strain, irrespective of treatment. However, cortisol provided a strong stimulation of hypo-osmoregualtory ability in both strains, and this stimulation seemed to be potentiated by GH in an additive manner. Improved hypo-osmoregulatory ability in GH + cortisol treated anadromous Arctic charr was accompanied by increased gill Na⁺, K⁺-ATPase activity and Na⁺–K⁺–2Cl⁻ cotransporter protein abundance, but no changes in gill Na⁺,K⁺-ATPase α1a and α1b mRNA levels. For landlocked charr the improved hypo-osmoregulatory ability in GH +cortisol treated fish was accompanied only with an increase in gill Na⁺–K⁺–2Cl⁻ cotransporter protein abundance. Hormone treatment caused an improvement of hypo-osmoregulatory ability that was of approximately the same magnitude in the landlocked as in the anadromous Arctic charr. This suggests that the lack of spontaneous development of hypo-osmoregulatory ability often seen in landlocked populations of Arctic charr may depend, at least partly, on a lack of the hormonal activation seen in anadromous populations.     

Seawater tolerance in captive high-Arctic Svalbard charr (Salvelinus alpinus): effect of photoperiod and body size

Anadromous Arctic charr (Salvelinus alpinus) returning after spending summer at sea were captured in a fish trap in the Dieset River on Spitsbergen (79°10'N), Svalbard. Fish selected for breeding were transported to Trondheim in mainland Norway. Eggs obtained from the charr were fertilized and incubated in total darkness. First-fed alevins and resulting parr were kept under continuous light until an age of 0+ and 1+ years, respectively. Some 1+ charr were kept as controls under a continuous short-day photoperiod (6L:18D) from autumn until the end of the experiment the following July. Charr aged 0+ and 1+ years old were exposed to a short-day photoperiod from October until January and a simulated natural photoperiod for 80°N from January until the end of the experiments. Challenge tests demonstrated a size-dependent seawater tolerance for charr with a body length less than 18 cm. Fish smaller than 12 cm did not survive the 96-h test period. The larger charr kept under simulated natural photoperiod developed increased hypoosmoregulatory capacity. Charr kept under short-day treatment showed a slight, short-lived increase in seawater tolerance. A 7-days seawater challenge test at the end of the experiment (July) demonstrated that the anticipatory seawater preparation in charr is influenced by photoperiod. We conclude that offspring from anadromous high-Arctic charr must achieve a threshold body size (>25 cm) before they can respond to photoperiod signals which trigger the development of the hypoosmoregulatory capacity typical for smoltifying salmonids.     

Seawater tolerance in first-time migrants of anadromous Arctic charr (Salvelinus alpinus)

Anadromous juvenile Arctic charr (Salvelinus alpinus) were caught in the Sila River (66°21'N, 13°10'E, Nordland County, Norway) by use of a fish trap during their migration towards the sea in May/June. The absence of tags (not captured before) and examination of otoliths from sacrificed fish revealed that none of the experimental charr had previously encountered seawater. During 4 days of exposure to seawater, only minor changes in blood plasma osmolality, and blood plasma concentrations of Na⁺, Cl^- and Mg²⁺ were detected. An increase in Na⁺-K⁺-ATPase activity was measured during the exposure period. These results verified that first-time migrants exhibit hypoosmoregulatory capacity similar to that of smoltified Atlantic salmon (Salmo salar). Accordingly, the Arctic charr first-time migratory behaviour, including late descent and a possible stay within an estuary, cannot be taken as evidence of a poorly developed seawater tolerance.     

Elevated spring temperature stimulates growth, but not smolt development, in anadromous Arctic charr

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

Hypoosmoregulation in an anadromous teleost: influence of sex and maturation

Salinity tolerance and hypoosmoregulatory ability of anadromous brook trout (Salvelinus fontinalis) were investigated in relation to sex and state of maturation. Seawater survival of mature males was significantly poorer than that of females or immature males. Lowered salinity tolerance of adult males became acute during the autumn photoperiod (normal spawning period) when the gonadosomatic index was high. Plasma [Cl-], [Mg2+], osmolarity and hematocrit were significantly higher in mature males after transfer to seawater, relative to mature females. It is postulated that reduced adult male hypoosmoregulatory ability explains skewed sex ratios in anadromous brook trout populations and may limit the extent of brook trout anadromy.     

Same barcode,different biology: differential patterns of infectivity,specificity and pathogenicity in two almost identical parasite strains

Two Norwegian isolates of the monogenean Gyrodactylus salaris Malmberg, 1957 with identical cytochrome c oxidase subunit I barcodes from different hosts, show highly divergent biological and behavioural characteristics. The Lierelva parasite strain, typically infecting Atlantic salmon, Salmo salar L., grew exponentially on Atlantic salmon, but the Pålsbufjorden parasite strain, commonly infecting Arctic charr, Salvelinus alpinus L., grew slowly on both hosts and was non-pathogenic to Atlantic salmon. Both parasite strains reproduced successfully on Arctic charr, but the Atlantic salmon-infecting Lierelva strain grew faster on both hosts. Experiments with isolated worms revealed differences in reproductive rates which may account for the observed population differences. Atlantic salmon parasites consistently gave birth at an earlier age than the Arctic charr parasites, with the differential increasing from 1 day for the first birth up to 2–4 days for the third birth. Arctic charr-infecting parasites were more active on Atlantic salmon than salmon parasites on Arctic charr, a behavioural strategy leading to enhanced G. salaris mortality. Sequencing of 10 kb of nuclear genomic markers revealed only four single nucleotide polymorphisms, confirming that isolates of G. salaris with differences in fitness traits influencing establishment, fecundity and behaviour may be remarkably similar at a molecular level. The framework for reporting and control of G. salaris requires re-appraisal in light of the discovery of variants with such divergent biology.     

Differences in susceptibility of anadromous and resident stocks of Arctic charr to infections of Gyrodactylus salaris, under experimental conditions

The ability of Gyrodactylus salaris , an important pathogen of the Atlantic salmon Salmo salar , in Norway, to infect anadromous and resident stocks of the Arctic charr, Salvelinus alpinus , has been examined in the laboratory. Resident charr (Korssjoen stock) exposed to heavily infected salmon, were considered innately resistant as they lost their infections within 21 days when individually isolated. Isolated anadromous harr (Hammerfest stock) remained infected for up to 150 days, although most infections disappeared within 30–50 days. In many cases the parasite population grew initially, but growth was limited after 20–30 days and infections subsequently disappeared. At the same time, shoals of 50 anadromous charr, swimming in the tanks containing the individually isolated fish in floating cages, remained infected for up to 280 days. Charr isolated from these shoals after 115 days and subsequently monitored individually lost their infections within 30 days, although the parasite persisted within the shoals for a further 75–135 days. This suggests that G. salaris , persisted on shoaling charr despite an immune response which led to the elimination of parasites from isolated hosts. The Hammerfest stock of anadromous charr supports G. salaris , in the laboratory, and the extended period of survival on this host suggests that charr may be important in the epidemiology of G. salaris , in northern Norway.     

Myofibrillar proteins in skeletal muscles of parr,smolt and adult atlantic salmon (Salmo salarl.). Comparison with another salmonid,the arctic charr Salvelinus alpinus (l.)

The heavy and light subunits of myosin from white and red muscles of Atlantic salmon parr, smolt and adult individuals were analyzed by SDS-PAGE and two-dimensional electrophoresis. Tropomyosin was identified by comigration with rat tropomyosins in two-dimensional gels in the presence and absence of urea. These myofibrillar proteins were compared to those of Arctic charr.

• 1.1. The myosin heavy chain from Atlantic salmon red muscles was associated with two types of light chain, 1S and 2S, that comigrated with the light chains 1S and 2S of Arctic charr.
• 2.2. As in the Arctic charr, four myosin light chain spots were detected in white muscles: two fast myosin light chains type 1, one of which comigrated with its analogous in the Arctic charr; one fast myosin light chain type 2, differing slightly in isoelectric point from that of Arctic charr; and one fast myosin light chain type 3 with higher electrophoretic mobility than that of Arctic charr.
• 3.3. Three tropomyosin spots were detected. White muscles contained only one type of β-tropomyosin and red muscles two types of α-tropomyosin. These three tropomyosin spots comigrated with those of Arctic charr.
• 4.4. Two myosin heavy chain bands were observed in red muscles of salmon parrs but only one in the rest of the red muscles analyzed.
• 5.5. Only one myosin heavy chain band was detected in white muscles by SDS-glycerol-polyacrylamide gel electrophoresis. Alfa-chymotryptic peptide mapping of these white myosin heavy chain bands revealed differences attributed to the presence of a new type of myosin heavy chain first detected several months after smoltification.

     

Annual rhythms of swimming behaviour and seawater adaptation in young baltic salmon,Salmo salar,associated with smolting

Synopsis Sexually immature and sexually mature precocious male Baltic salmon,Salmo salar, parr from Umeälven (Ume river) were tested for rheotactic behaviour and adaptation to seawater before, during, and after the time period for smolt migration. Size of fish at the beginning of the experiment in January was on average 13.5 cm. Rheotactic behaviour was tested in annular stream tanks with photocells to measure upstream and downstream movements. Samples of fish were given a Seawater challenge test at monthly intervals in order to determine their ability to adapt to 20%. saltwater. During spring, both immature and sexually precocious parr became silvery and showed progressive development of downstream-directed movements. In early June the fish exhibited good hypoosmoregulatory ability in 20%. saltwater and swimming was predominantly downstream. During late June and early July there was a marked reversal in swimming behaviour, accompanied by a dramatic change in saltwater adaptation. The fish moved mainly upstream and showed decreasing ability to meet the seawater challenge test. This was accompanied by a loss of silvery coloration. The annual cycle of swimming behaviour and seawater adaptation is discussed in relation to the appearance of a smolt-window, i.e., a critical interval for smolt migration.     

SSU rRNA gene sequence reveals two genotypes of Spironucleus barkhanus (Diplomonadida) from farmed and wild Arctic charr Salvelinus alpinus

Spironucleus barkhanus isolated from the blood of Arctic charr Salvelinus alpinus from a marine fish farm were genetically compared with S. barkhanus isolated from the gall bladder of wild Arctic charr. The wild Arctic charr were caught in the lake used as the water source for the hatchery from which the farmed fish originated. Sequencing of the small subunit ribosomal RNA gene (SSU rDNA) from these 2 populations showed that the isolates obtained from farmed and wild Arctic charr were only 92.7 % similar. Based on the sequence differences between these isolates, it is concluded that the parasites isolated from the farmed fish have not been transmitted from wild Arctic charr in the hatchery's fresh water source. It is therefore most likely that the farmed fish were infected by S. barkhanus after they were transferred to seawater. S. barkhanus isolated from diseased farmed Arctic charr were 99.7% similar to the isolates obtained from diseased farmed Chinook (Canada) and Atlantic salmon (Norway). The high degree of sequence similarity between S. barkhanus from farmed Arctic charr, Chinook and Atlantic salmon indicates that systemic spironucleosis may be caused by specific strains/variants of this parasite. The genetic differences between the isolates of farmed and wild fish are of such magnitude that their conspecificity should be questioned.     

Swimming performance of various freshwater Newfoundland salmonids relative to habitat selection and fishway design

Swimming ability of wild brook trout Salvelinus fontinalis , brown trout Salmo trutta , anadromous Atlantic salmon Salmo salar , and landlocked Atlantic salmon was examined using fixed and increasing velocity tests. Although brook trout and salmon parr were collected from the same site, brook trout were found generally in slow-moving pools whereas salmon were more common in faster riffle areas. Salmon parr could hold station indefinitely in currents in which brook trout could only maintain themselves briefly. Therefore, selection of fast-water areas by salmon parr may impose a velocity barrier to sympatric juvenile brook trout, reducing competition between the species. Performance comparisons also indicate that anadromous Atlantic salmon possess slightly greater sustained ability than landlocked salmon, possibly due to altered selective pressure associated with their different life histories. Finally, fishways and culverts in Newfoundland can now be designed using models generated from performance data collected from native salmonid species.     

Age at maturity in landlocked and anadromous Atlantic salmon parr from two Québec rivers

Synopsis Age at maturity in male Atlantic salmon parr from landlocked populations in the Watshishou and Musquaro Rivers is significantly greater than in anadromous populations from the same rivers. We conclude that high post-smolt mortality in anadromous stocks is conducive to male parr maturity at an early age. We also suggest that the lower proportion of maturing male parr in landlocked stocks may be related to competition among males for mates and the smaller ultimate size of spawning adult landlocked salmon.     

Leucocytes of anadromous and landlocked strains of Atlantic salmon (Salmo salar L.) in the smolting period

Using flow cytometry and leucocyte specific monoclonal antibodies, neutrophils and B-cells were studied in blood and head kidney from wild strains of Atlantic salmon. The strains were Vosso and Blege, being an anadromous and landlocked strain, respectively. Smoltification was induced using a simulated natural photoperiod and sampling was performed monthly for 6 months and ended for the Blege strain at the time of seawater transfer while samples were collected from the Vosso strain after 4 weeks in seawater. Throughout the observation period, the mean proportions of neutrophils in both head kidney leucocytes (HKL) and peripheral blood leucocytes (PBL), were highest for the Vosso strain. The opposite was observed for B-cells where the Blege strain had higher or similar mean proportions compared to the Vosso strain. There were some differences between HKL and PBL. The mean proportion of neutrophils was always higher in HKL than in PBL and the mean proportion of B-cells was higher in PBL than in HKL. The fluctuations during the observation period, in the proportions of B-cells and neutrophils of the analysed cell population, showed mainly the same pattern in both strains. Differences between the strains were observed at various times in the mean of total number of leucocytes per gram head kidney and per millilitre of blood. The fluctuations throughout the experimental period in total numbers of leucocytes in head kidney and blood followed mainly the same pattern in both strains. The results of the leucocyte analyses suggest that there are differences between the anadromous and landlocked strains with respect to what cell type is present in highest proportion in the leucocyte samples from head kidney and blood. The striking similarity between the strains is the profiles of proportions of B-cells and neutrophils in HKL and PBL during the smoltification period.     

Polyunsaturated fatty acid profiles of whole body phospholipids and triacylglycerols in anadromous and landlocked Atlantic salmon (Salmo salar L.) fry

We compared the fatty acid compositions and gains of whole body triacylglycerols (TAG) and phospholipids (PL) in anadromous and landlocked Atlantic salmon (Salmo salar) fry, of the same age, fed the same commercial marine oil-rich diet over a 42-day feeding trial. The landlocked strain exhibited significantly (P<0.05) higher growth rate and feed efficiency, due principally to a higher fat retention, particularly of monounsaturated and saturated fatty acids (SFA). n-3 and n-6 long-chain polyunsaturated fatty acid (PUFA) gains and retentions were significantly higher (P<0.05) in the landlocked fry. Great similarities were found in the fatty acid profiles of whole body TAG of both strains. However, marked genotypic differences were observed in the PUFA profiles of whole body PL fractions. The total PUFA, n-3 PUFA and docosahexaenoic acid (DHA) level in PL was significantly higher (P<0.05) while the SFA level, and the PUFA C18/C20 and eicosapentaenoic acid/arachidonic acid ratios were significantly lower (P<0.05) in the anadromous fry than in landlocked fry. Our results indicate that the level of DHA in salmon PL is under strong genetic control and that the capacity for incorporation, and possibly for the conversion of dietary n-3 and n-6 PUFA, is higher in the landlocked strain.     

Migration, growth and survival of wild and hatchery-reared anadromous Arctic charr (Salvelinus alpinus) in Finnmark, Northern Norway

Two groups of anadromous Arctic charr ( Salvelinus alpinus ) (size 200–350 mm) reared in heated water (6–12° C) under simulated natural photoperiod were individually tagged and released in spring 1988. The fish were released at two sites, in the estuary of the River Halselva and in the fjord, 2 km from the river mouth. Growth, timing of migration and survival of these hatchery-reared fish was compared to that of wild anadromous charr of the same size over a 4-year period. The hatchery-reared charr had poorer growth than the wild fish during their first year in sea water. They also resided longer in the sea and had a slightly lower survival than wild fish. During the second year, hatchery-reared charr displayed good growth, and after the third sea-season the fish were ready for slaughter at a size of approximately 800g. The results suggest that the successful development of Arctic charr ranching will be dependent upon production and release strategies that lead to improved migratory and feeding behaviour of the fish during their first season at sea.     

Habitat use and fish activity of landlocked Atlantic salmon and brook charr in a newly developed habitat compensation facility

Degradation and destruction of valuable spawning and rearing habitat due to anthropogenic changes (e.g., flow modification and channelisation) is known to have dramatic impacts on fish populations. To compensate for habitat losses due to hydropower development, an artificial fluvial habitat channel (‘Compensation Creek’) was constructed in south-central Newfoundland, Canada. The creek was designed to include appropriate habitat features for the two dominant salmonid fish species, landlocked Atlantic salmon (Salmo salar L.) and brook charr (Salvenius fontinalis Mitchell). The study examines the habitat use of landlocked Atlantic salmon and brook charr in the Compensation Creek using electromyogram (EMG) radio telemetry. Ten landlocked Atlantic salmon and eight brook charr were captured and tagged with EMG transmitters. In laboratory swimming experiments, the EMG values were calibrated against swimming speed. Fish were then released in the Compensation Creek and tracked on a daily basis. The results show that (1) during residence in the creek, both species used preferentially the habitat features designed to match their rearing habitat preferences, and (2) swimming speed did not vary among habitat types for either species.     

Seasonal dynamics and persistence of Gyrodactylus salaris in two riverine anadromous Arctic charr populations

The seasonal occurrence of the monogenean ectoparasite Gyrodactylus salaris Malmberg infecting Arctic charr, Salvelinus alpinus (L.) in the two rivers Skibotnelva and Signaldalselva in northern Norway was studied in the period from autumn 2003 to autumn 2005. Skibotnelva has been infected with the parasite since 1979, and treated with rotenone twice. Most likely resident Arctic charr avoided the rotenone treatment in small tributary streams, and thus was the source of the repeated re-infection of this river. G. salaris was first recorded in Signaldalselva in the year 2000 and it is still untreated. Unlike Atlantic salmon, which is highly susceptible to G. salaris, Arctic charr can display a wide range of host-responses to G. salaris infections. Arctic charr were sampled by electro fishing with a total sample of 681 Arctic charr. The results from this study demonstrate an evident seasonal dynamic in G. salaris infection in charr in both rivers. Parasite intensities fluctuated with the rise and fall in temperature through the year, with an autumn high and spring low. There was a significantly lower prevalence and mean intensity of G. salaris in Skibotnelva than in Signaldalselva. There were also a lower prevalence and intensity of G. salaris in the older than in the youngest charr. The different history of infection and treatment in the two rivers might be the underlying cause of these observed dissimilarities. The current study indicates that Arctic charr is a good natural host for G. salaris.     

Adaptations to Stochastic Environmental Variations: The Effects of Seasonal Temperatures on the Migratory Window of Svalbard Arctic Charr

The circumpolar Arctic charr, Salvelinus alpinus, is ideal for studying how environmental factors affect life history in fishes. Charr populations demonstrate a tremendous ecological plasticity and adaptations to harsh environments. Arctic charr is the only freshwater fish on Svalbard, including anadromous, resident, and landlocked stocks. Freshwater lake systems on Svalbard are characterized by very low water temperatures, long-term or even permanent ice cover, and low levels of nutrients. Food is thus limited and may lead to growth stagnation and early maturity in Arctic charr. The individual growth pattern may alternatively follow a sigmoid-shaped curve, caused by a shift to either cannibalistic or anadromous (migration to sea) behaviour. In lake systems that include migratory charr, the population may consist of a mixture of parr, postsmolt, and adult migratory individuals, as well as small-sized resident, large-sized resident (cannibals), and large formerly resident individuals transformed to anadromy. Our study in the Lake Dieset watercourse (79°N), Svalbard, demonstrates that the annual water flow in the outlet river is strongly correlated to air temperatures and provides a passage to the sea, allowing the charr access to the nutrient-rich seawater environment, during at most two months each year. During one of the years studied, the youngest and small-sized part of the sea-going stock was prevented from ascending the river and probably suffered mortality during winter. The migratory window of the Arctic charr in Lake Dieset is therefore highly variable among years and thus unpredictable. We hypothesize that in worst case scenarios (cold years, low water discharge), climatic variations may occasionally prevent charr from migrating upstream in Svalbard lake systems in late autumn, resulting in high mortality in the population.     

Sex chromosome polymorphisms in Arctic charr and their evolutionary origins

Current data on the Y-specific sex-determining region of salmonid fishes from genera Salvelinus, Salmo, and Oncorhynchus indicate variable polymorphisms in the homologous chromosomal locations of the sex-specific determining region. In the majority of the Atlantic lineage Arctic charr, including populations from the Fraser River, in Labrador Canada, as well as Swedish and Norwegian strains, the sex-determining locus maps to linkage group AC-4. Previously, sex-linked polymorphisms (i.e., variation in the associated sex-linked markers on AC-4) have been described in Arctic charr. Here, we report further evidence for intraspecific sex linkage group polymorphisms in Arctic charr (i.e., the detection of the SEX locus on either the AC-1 or AC-21 linkage group) and a possible conservation of a sex linkage arrangement in Icelandic Arctic charr and Atlantic salmon, involving sex-linked markers on the AC-1/21 homeologs and the European AS-1/6 homeologous linkage groups in Atlantic salmon. The evolutionary origins for the multiple sex-determining regions within the salmonid family are discussed. We also relate the variable sex-determining regions in salmonids to their ancestral proto-teleost karyotypic origins and compare these findings with what has been observed in other teleost species in general.