The critical thermal limits for juvenile Arctic charr Salvelinus alpinus

The chief objective was to determine the critical thermal limits for alevins, fry and parr of Arctic charr, Salvelinus alpinus , (L.) from four races living in Windermere (northwest England). The experimental fish were reared in a hatchery but were the progeny of wild parents. As comparisons between tethal temperatures at four acclimation temperatures (5, 10, 15, 20° C) revealed few significant racial differences, the data were pooled to estimate the lethal values for survival over 7 days (incipient lethal temperature) and over only 10 min (ultimate lethal temperature) for each life stage. Upper lethal values increased with acclimation temperatures for alevins but this effect was negligible for fry and parr, Alevins were generally less tolerant than fry and parr at lower, but not higher, acclimation temperatures; e.g. after acclimation at 5° C, mean upper ultimate values were 23·3, 25·1 and 25·7° C and mean upper incipient values were 18·7, 21·5 and 21·5° C for alevins, fry and parr respectively; after acclimation at 20° C, mean upper ultimate and incipient values were 26·2, 26·1 and 26·6° C and 20·8, 20·8 and 21·6° C for alevins, fry and parr respectively. The area of the temperature tolerance polygon (expressed as ° C²) for juvenile Arctic charr is amongst the lowest recorded for salmonids; being 409, 439 and 461° C² for alevins, fry and parr respectively. These low values are due to lower upper tolerance limits, not high lower tolerance limits; the latter being close to 0° C (<1°C for parr and fry, <0·3° C for alevins) at all acclimation temperatures. Arctic charr are therefore amongst the least resistant of salmonids to high temperatures but probably the most resistant to low temperatures.     

The influence of previous feeding regime on the compensatory growth response of maturing and immature Arctic charr, Salvelinus alpinus

Alternating periods of food deprivation with those of unlimited provision of food depressed the growth of Arctic charr, Salvelinus alpinus , below that of controls. Fish that were deprived of food and then fed on alternate weeks (1:1) were larger than those that were exposed to periods of 1 5- or 3-week deprivation and feeding (1·5:1·5 or 3:3). On receiving excess food supplies following 24 weeks on the restricted feeding regimes the previously-restricted fish grew more rapidly than the controls. The greatest compensatory growth was displayed after the 3:3 regime, followed by the 1·5: 1·5 and then the 1:1 feeding regime. At the termination of the experiment there were no significant differences in body weight between fish fed according to the different regimes during the period that food restriction was imposed. Growth patterns of the immature males and females were similar, but mature males were significantly lighter than the immature fish by the end of the experiment. Both immature and maturing fish displayed a compensatory growth response on return to adequate feeding. Beginning food restriction in May did not influence the proportions of male fish ( c . 60%) which were mature in the autumn.     

Effects of thermal regime on energy and nitrogen budgets of an early juvenile Arctic charr, Salvelinus alpinus, from Lake Inari

The feed intake, growth, oxygen consumption and ammonia excretion of juvenile Arctic charr were measured over period of four weeks at different temperatures which were either constant (11.0, 14.4, 17.7 °C) or fluctuated daily (14.3 ± 1 °C). Maximum feed intake was estimated to occur at 14.3 °C, while oxygen consumption and nitrogen excretion were highest at the highest temperature, and growth rate was estimated to be highest at 13.9 °C. Feed conversion efficiency was estimated to be highest at 13.2 °C, where over 62.7% of ingested energy was allocated to growth. Metabolic rate accounted for 16–30% of ingested energy and nitrogen excretion was under 3% of ingested energy. The nitrogen budget was under similar thermal influences to the energy budget. Thermal fluctuation increased metabolic rate, but not feed intake, leading to a reduction in feed conversion efficiency under fluctuating temperature conditions.     

Seasonal patterns of growth, lipid deposition and lipid depletion in anadromous Arctic charr

Seasonal patterns of growth, lipid deposition and lipid depletion were studied in anadromous Arctic charr from a north Norwegian population. Samples were collected in late May when fish were migrating between fresh water and the sea, and in mid-July when the fish re-entered fresh water. A sample of maturing fish captured in mid-July was held in captivity until late September to assess lipid mobilization linked to the final stages of maturation. The fish increased substantially in weight during their 40–50-day summer residence in sea water (immatures from c . 300 to 600 g; maturing fish from c . 500 to 800 g), and body lipid stores were increased approximately fivefold. The carcass (head, skeleton and skin) was the major lipid depot, accounting for c . 50% of the total lipid content when the fish re-entered fresh water from the sea. The muscle of the ascending charr contained 35–40% of the body lipids, whereas the gut and liver each held 4–5%. Body lipid decreased 30–40% during the period between the re-entry of the fish to fresh water and spawning; although lipids were depleted from all depots the carcass and muscle were quantitatively the most important. By the time of spawning, the gonads of the females held almost 25% of the body lipid, whereas in the males the gonads accounted for <3% of the total lipids. Females lost c . 80% of their body lipid during spawning and overwintering, and, consequently, the lipid depots were severely depleted by the early spring. By contrast, lipid depletion in the males amounted to 50–55% of total lipid in the same period. These data suggest that the combination of spawning and overwintering in fresh water imposes a greater load on the females than on the males. It may be that the severity of the depletion prevents females from spawning in successive years.     

Phenotype-specific feeding behaviour of two arctic charr Salvelinus alpinus morphs

The feeding performance of two morphs of a trophically polymorphic fish, the arctic charr Salvelinus alpinus, feeding on zooplankton, was studied in the laboratory. Limnetic morphs, with a fusiform body, terminal mouth, short pectoral fins, and relatively long and dense gill rakers, fed at significantly higher rates on Daphnia and Cyclops than did benthic morphs. The benthic morphs were characterized by a chunky body form, subterminal mouth, long pectoral fins, and relatively short and spaced-out gill rakers. The limnetic morphs attacked the prey at significantly higher rates and were more successful in capture. Benthic morphs were more reluctant to start feeding on zooplankton and reaction time was longer than in limnetic morphs. In the absence as well as presence of zooplankton food, the position of the two morphs in the aquaria differed markedly. The results agree with dietary differences found in field-collected fish. The limnetic morphs consume zooplankton, whereas benthic morphs specialize on Lymnaea gastropods. The results suggest that benthic morphs are phenotypically inferior at using the pelagic food niche. This implies that the current role of competitive or predatory interactions in segregating the morphs may be minor.     

Tolerance of parr of Arctic charr, Salvelinus alpinus, to reduced dissolved oxygen concentrations

One year old pan Item Windermere (north west England) tolerated lower incipient lethal levels of oxygen [18 20 mg 1 ¹: 15 17% air saturation value (ASV)] at lower (5, 10°C) than at higher (15, 20°C) an elimation temperatures (2·2 2·4 mg 1 ¹ 22 25% ASV). Values were not significantly different for two races of charr in the lake and are amongst the lowest recorded for salmenid species.     

Smolting characters in anadromous and resident Arctic charr, Salvelinus alpinus (L.)

Morphological differences, haematocrit value and chloride cells were examined in downstream migrating Arctic charr, Salvelinus alpinus (L.) from the Hals River, North Norway, and resident charr from Lake Storvann. Fish were classified as visual parr, silvery parr or smolt based on the degree of silvering and the Occurrence of lateral parr marks. On average, 47% of downstream migrating Arctic charr were classified as visual molts, but only 14% of the resident charr. Charr longer than 20 cm fork length were mainly classified as visual molts. Morphometrical analyses of body size and shape revealed that most of the variations could be explained in terms of variations in fork length. Length adjusted ratios of post-anal distances were significantly higher in migrating charr than in resident charr. The number of developed chloride cells, the cell nucleus diameter in the basin of secondary gill lamellae and blood haematocrit values were significantly higher among downstream migrating charr than in resident charr. However, morphological differences between anadromous and resident Arctic charr were not necessarily synchronized with the development of chloride cells.     

Molecular genetic examination of the polymorphic Arctic charr Salvelinus alpinus of Thingvallavatn, Iceland

Thingvallavatn, Iceland contains two sympatric morphotypes (benthic and limnetic) of Arctic charr Salvelinus alpinus. Each morphotype is composed of two morphs and these differ markedly in ecology, behaviour and life history. We used molecular genetic approaches to test whether (i) genetic heterogeneity exists among morphs and (ii) if morphs arose in allopatry and came into secondary contact or arose sympatrically within the lake through genetic segregation and/or phenotypic plasticity. Direct sequencing of 275 bp of the mitochondrial DNA (mtDNA) control region, mtDNA restriction fragment length polymorphisms and single locus minisatellite analyses detected insufficient variation to test our hypotheses. Analysis of multilocus minisatellite band sharing detected no significant differences between morphs within the same morphotype. However, significant differences among morphs belonging to different morphotypes suggest some genetic heterogeneity in Thingvallavatn charr. Limnetic charr from Thingvallavatn were more similar to sympatric benthic charr than to allopatric limnetics from two other Icelandic lakes. This suggests that the Thingvallavatn morphs arose sympatrically within the lake rather than in allopatry followed by secondary contact.     

Parasites of freshwater resident and anadromous Arctic charr (Salvelinus alpinus) in Greenland

Twenty-one metazoan parasite species were found in Arctic charr at three coastal sites in west Greenland, including Neascus sp. and the nematode Pseudoterranova decipiens , new records for Arctic charr. Twelve species are new records for Arctic charr in Greenland. The quantitative composition of the parasite communities varied, but the freshwater species ( Diphyllobothrium ditremwn, Eubothriutn salvelini, Proteocephalus longicollis, Crepidostotnutn farianis ) were usually numerically dominant, even in anadromous fish. The absence from Greenland of Mysidacea, Amphipoda, Ephemeroptera and Odonata excludes parasites requiring such organisms as intermediate hosts, including the cestode Cyathocephalus truncatus , nematodes of the genus Cystidicola , and freshwater acanthocephalans.     

Sibling recognition in juvenile Arctic charr, Salvelinus alpinus (L.)

Juvenile Arctic charr, Salvelinus alpinus (L.), from two full sibling groups were studied concerning the possible existence of chemical cues with information about kinship. Each full sibling group was divided into two groups with the same number of specimens and placed in two separate aquaria. The division coincided with the start of exogenous feeding. Preference tests were performed about 7 and 10–13 months after the division. Due to the increasing size of experimental fish, two different sizes of apparatus were used. The first series of experiments was performed in a small Y-maze fluviarium and the second series in the large standard fluviarium. The momentary positions of one fish at a time in the test area were recorded by time-lapse photography with a 16-mm film camera and filtered flashlight (no transmittance <670 nm). The fish were given a choice between two water qualities; thus the following comparisons were made: (i) unconditioned water ν. water scented by siblings from the same aquarium; (ii) unconditioned water ν. unfamiliar non-siblings; (iii) siblings from the same aquarium ν. unfamiliar non-siblings; (iv) siblings from a separate aquarium ν. unfamiliar non-siblings; (v) siblings from the same aquarium ν. siblings from a separate aquarium. The test fishes preferred water scented by siblings over non-siblings, even though the siblings were taken from a separate aquarium. Nevertheless, they were attracted to water scented by unfamiliar non-siblings in preference to unconditioned water. No preference was shown between chemical cues from siblings taken from the same and a separate aquarium.     

Cannibalism and protective behavior of eggs in Arctic charr (Salvelinus alpinus)

From video recordings of spawning events, we quantified protective and cannibalistic behavior of Arctic charr occurring immediately after spawning. The number of fish cannibalizing on stray eggs was examined regarding (a) whether more than one male shed milt during the spawning event, that is, whether sperm competition occurred, (b) whether the sperm competition included few or many males, that is, the intensity of sperm competition, and (c) the density of fish at the spawning site. Response behavior toward egg cannibalism was also examined among females and dominant males in order to determine any parental investment toward protecting the eggs after spawning. Cannibalistic behavior was seen in almost 50% of the spawnings, and the multiple spawning events showed the highest numbers of fish cannibalizing on eggs. Both the number of males releasing milt and the number of fish approaching the spawning site were positively correlated with egg cannibalism. Sperm competition was, however, not a prerequisite for egg cannibalism. Although we also observed partial filial cannibalism, protective behavior of eggs was seen both among dominant males and females, suggesting that charr actually conduct parental care.     

Digestive capacities,inbreeding and growth capacities in juvenile Arctic charr Salvelinus alpinus

Genetic variation in growth performance was estimated in 26 families from two commercial strains of Arctic charr Salvelinus alpinus. Physiological determinants of growth and metabolic capacities were also assessed through enzymatic assays. A relatedness coefficient was attributed to each family using parental genotypes at seven microsatellite loci. After 15 months of growth, faster growing families had significantly lower relatedness coefficients than slower growing families, suggesting their value as indicators of growth potential. Individual fish that exhibited higher trypsin activity also displayed higher growth rate, suggesting that superior protein digestion capacities can be highly advantageous at early stages. Capacities to use amino acids as expressed by glutamate dehydrogenase (GDH) activities were lower in the liver of fast‐growing fish (13–20%), whereas white muscle of fast‐growing fish showed higher activities than that of slow‐growing fish for amino acid metabolism and aerobic capacity [22–32% increase for citrate synthase (CS), aspartate aminotransferase (AAT) and GDH]. The generally higher glycolytic capacities (PK and LDH) in white muscle of fast‐growing fish indicated higher burst swimming capacities and hence better access to food.     

Spring climate and summer otolith growth in juvenile Arctic charr, Salvelinus alpinus

The influence of different climate variables on the first four years of otolith growth in Salangen Arctic charr, Salvelinus alpinus, was studied over the period 1939?C2005. Salangen is a coastal, low altitude, subarctic lake system located in northern Norway. Climate data, including water temperature, air temperature, ice-cover and precipitation, were available for most of the 67?year period. Water temperatures in May and June had a significant effect on otolith growth during the second growth year, while no relationship between otolith growth and climate variables was found for the first, third and fourth years of otolith growth. Otolith increment size during the third and fourth growth year was autocorrelated with growth during the previous year. Spring snow fall and timing of ice break-up had an indirect effect on growth, as these variables were highly correlated with spring water temperatures. High variation in otolith growth within years and among individuals suggests that individual and age-specific variations in spatial habitat use may confound the direct effects of changing air temperatures and time of ice break-up.     

PCB impairs smoltification and seawater performance in anadromous Arctic charr (Salvelinus alpinus)

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

Racial differences in eggs and juveniles of Windermere charr, Salvelinus alpinus

At least four races of charr occur in Windermere, the largest natural lake in England: north basin and south basin autumn spawners, north basin and south basin spring spawners. This study examines racial differences between eggs and juveniles, and relates juvenile size and survival to egg size. There were no major differences between races for egg incubation times and the percentage of eggs hatching successfully, the latter being high (mean values 76–96%) with a negligible proportion of abnormal alevins (<0.8%). Although there were no significant differences in the lengths of the female parents, both eggs and alevins were significantly larger for the autumn spawners than the spring spawners. Size differences in alevins, especially live weight, were positively related to egg size but not female parent size. Mean percentage survival for juveniles attaining the independent feeding stage was higher for the progeny of autumn spawners (32%) than spring spawners (3%). Racial differences in the egg and alevin stages therefore appear to have a significant effect on subsequent survival, and could be ultimately responsible for the relatively small proportion of spring spawners (only 4–6%) in the Windermere population of charr.     

Social rank and brain levels of monoamines and monoamine metabolites in Arctic charr,Salvelinus alpinus (L.)

Summary Dominance hierarchy was determined in 5 groups of juvenile Arctic charr (Salvelinus alpinus), each group consisting of 4 fish. Telencephalon and brain stem (remaining parts of the brain) were analyzed with regard to their content of monoamines and monoamine metabolites. No significant differences were observed in the concentrations of norepinephrine (NE), dopamine (DA), or serotonin (5-hydroxytryptamine, 5-HT) between fish with different social rank. However, the concentration of 5-hydroxyindoleacetic acid (5-HIAA), the principle metabolite of 5-HT, was significantly higher in subordinate fish, and a significant inverse linear correlation was found between 5-HIAA concentration and social rank (as measured by dominance index) in the brain stem. In the telencephalon the dominant fish had a significantly higher level of homovanillic acid (HVA), a major DA metabolite. These findings indicate a greater serotonergic activity, possibly associated with increased stress, as well as a lower dopaminergic activity, possibly associated with reduced aggression, in subordinate charr. The differences between dominant and subordinate fish could either be caused by social interactions or reflect innate individual differences in monoamine utilization, predisposing individuals for dominant or subordinate positions in the dominance hierarchy.Abbreviations DA dopamine - DI dominance index - NE norepinephrine - 5-HT serotonin (5-hydroxytryptamine) - 5-HIAA 5-hydroxyindoleacetic acid - 5-HTOH 5-hydroxytryptophol - HVA homovanillic acid     

Experimental evidence for paternal effects on offspring growth rate in Arctic charr (Salvelinus alpinus)

Sexual selection theory predicts that females should choose males that signal viability and quality. However, few studies have found fitness benefits among females mating with highly ornamented males. Here, we use Arctic charr (Salvelinus alpinus), a teleost fish with no parental care, to investigate whether females could gain fitness benefits by mating with highly ornamented and large-sized males. Carotenoid-based coloration signalled by males during spawning is believed to be an indicator of good genes for this species. Paternal effects on offspring size (body length and dry body mass) were examined experimentally by crossing eggs and sperm in vitro from 12 females and 24 males in a split-brood design and raising larvae to 30 days past hatching. We clearly demonstrated that there was a relationship between offspring size and paternal coloration. However, a negative interaction between paternal length and coloration was evident for offspring length, indicating that positive effects of paternal coloration were only present for smaller males. Thus, the red spawning coloration of the male Arctic charr seems to be an indicator of good genes, but the effect of paternal coloration on offspring length, an indicator of 'offspring quality', is size dependent.     

Epigenetic regulation of trophic morphology through feeding behaviour in Arctic charr, Salvelinus alpinus

Several models of speciation suggest that in species that are phenotypically plastic, selection can act on phenotypic variation that is environmentally induced in the earliest stages of divergence. One trait that could be subject to this process is foraging behaviour, where discrete foraging strategies are common. One species which is highly plastic in the expression of phenotype, the Arctic charr, Salvelinus alpinus (L.), is characterized by discrete variation in the anatomy of the head and mouthparts. These traits have been shown to have a functional significance, but the expression of which is thought to be at least partly phenotypically plastic. Here we test the hypothesis that foraging behaviour may regulate the anatomy of the head and mouthparts in Arctic charr. In a dyad experiment, size‐matched pairs of fish from a mixed family group were fed a diet of either Mysis (a hard‐bodied shrimp) or Chironomid larvae. Nine morphometric measures of head dimensions that describe wild trophic morphs were measured at the start of the experiment and 24 weeks later. Principal component scores of size‐corrected morphometric measures showed highly significant differences between fish exposed to the two diets. Univariate ANOVA analysis of the head morphometric variables showed that fish fed on Chironomids developed longer, wider jaws, longer heads and a larger eye for a given body length than did those fish fed upon Mysis. We conclude that foraging anatomy in Arctic charr is phenotypically plastic and that variation in foraging behaviour that results in feeding specialization in the wild could induce variation in head anatomy. This in turn could reinforce foraging specialization. Very rapid epigenetic divergence into distinct feeding morphs (as demonstrated here) would allow selection to act at more than one mode and thus could promote rapid evolutionary divergence, initially prior to genetic segregation, in species which are highly plastic. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78 , 43–49.     

The growth of a Welsh strain of Arctic charr Salvelinus alpinus (L.) and investigations into its aquaculture potential

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

Holarctic phylogeography of Arctic charr (Salvelinus alpinus L.) inferred from mitochondrial DNA sequences

This study evaluated mitochondrial DNA (mtDNA) sequence variation in a 552-bp fragment of the control region of Arctic charr (Salvelinus alpinus) by analyzing 159 individuals from 83 populations throughout the entire range of the complex. A total of 89 (16.1%) nucleotide positions were polymorphic, and these defined 63 haplotypes. Phylogenetic analyses supported the monophyly of the complex and assigned the observed haplotypes to five geographic regions that may be associated with different glacial refugia. Most notably, a formerly defined major evolutionary lineage (S. a. erythrinus) ranging from North America across the Arctic archipelago to the Eurasian continent has now been partitioned into the Arctic group and the newly identified Siberian group. The Beringian group, formed entirely by specimens assigned to S. malma (Dolly Varden), encompassed the area formerly assigned to S. a. taranetzi. The latter, due to a unique haplotype, became the basal member of the Arctic group. Overall, the S. alpinus complex reflects divergent evolutionary groups coupled with shallow intergroup differentiation, also indicated by an analysis of molecular variance that attributed 73.7% (P < 0.001) of the total genetic variance among groups. Time estimates, based on sequence divergence, suggest a separation of the major phylogeographic groups during early to mid-Pleistocene. In contrast, colonization of most of today's range started relatively recently, most likely late Pleistocene during the last retreat of ice sheets some 10,000-20,000 years ago. This time scale obviously is too shallow for detecting significant variation on a smaller scale using mtDNA markers. However, other studies using nuclear microsatellite DNA variation strongly suggested ongoing evolution within groups by revealing strong population-genetic substructuring and restricted gene flow among populations. Thus, Arctic charr could serve as a model organism to investigate the linkage between historical and contemporary components of phylogeographic structuring in fish, and, with a global perspective of the distribution of genetic variation as a framework, meaningful comparisons of charr studies at a smaller geographic scale will now be possible.