Allometric trajectories of body and head morphology in three sympatric Arctic charr (Salvelinus alpinus (L.)) morphs

A study of body and head development in three sympatric reproductively isolated Arctic charr (Salvelinus alpinus (L.)) morphs from a subarctic lake (Skogsfjordvatn, northern Norway) revealed allometric trajectories that resulted in morphological differences. The three morphs were ecologically assigned to a littoral omnivore, a profundal benthivore and a profundal piscivore, and this was confirmed by genetic analyses (microsatellites). Principal component analysis was used to identify the variables responsible for most of the morphological variation of the body and head shape. The littoral omnivore and the profundal piscivore morph had convergent allometric trajectories for the most important head shape variables, developing bigger mouths and relatively smaller eyes with increasing head size. The two profundal morphs shared common trajectories for the variables explaining most of the body and head shape variation, namely head size relative to body size, placement of the dorsal and pelvic fins, eye size and mouth size. In contrast, the littoral omnivore and the profundal benthivore morphs were not on common allometric trajectories for any of the examined variables. The findings suggest that different selective pressures could have been working on traits related to their trophic niche such as habitat and diet utilization of the three morphs, with the two profundal morphs experiencing almost identical environmental conditions.     

Stable isotope-based determinations of the average temperatures experienced by young-of-the-year Svalbard Arctic charr (Salvelinus alpinus (L.))

Mean ambient water temperatures experienced by individual young-of-the-year (YOY) Arctic charr, Salvelinus alpinus (L.), from a Svalbard lake were estimated using measurements of oxygen stable isotopes (δ¹⁸O) derived from fish otoliths. Otolith-derived water temperatures differed significantly from temperatures recorded at the outlet river of the Dieset watercourse but were consistent with temperatures previously recorded in shallow littoral areas of other Svalbard lakes where YOY charr are commonly found. This indicates that fixed-point monitoring does not necessarily represent the temperatures and thermal habitats used by individual fish. Otolith-derived water temperatures were also positively related to fish length-at-capture and otolith size, although much of the variation remained unexplained. Differences among individuals could be related to variability in food availability and food intake as well as variation in the initial fish size at hatching. Implications for subsequent investigations into how YOY charr respond and adapt to future climate change are discussed.     

Trophic ecology of piscivorous Arctic charr (Salvelinus alpinus (L.)) in subarctic lakes with contrasting food-web structures

Hydrobiologia - The trophic ecology of piscivorous Arctic charr (Salvelinus alpinus (L.); charr) in the food webs of large subarctic lakes is not well understood. We assessed charr diets,...     

Quantitative protein requirements of Arctic charr, Salvelinus alpinus (L)

Arctic charr, Salvelinus alpinus , require diets with protein energy (PE): total energy (TE) ratios of at least 0.35 in order to maintain good rates of growth. The protein requirement is, therefore, similar to that of rainbow trout, Salmo gairdneri . Protein retention efficiency (PPV) declined as the protein content of the diet was increased, the relationship being described by the equation: It is suggested that charr will maintain good rates of growth if fed on diets used for commercial culture of rainbow trout and special formulations for charr should not be necessary.     

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.     

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.     

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.     

Diet of Arctic charr (Salvelinus alpinus (L.)) and brown trout (Salmo trutta L.) in sympatry in two high altitude alpine lakes

Lake Pisses and Lake Labarre are two oligotrophic high altitude alpine lakes that have sympatric populations of Arctic charr and brown trout. These two lakes have similar morphometric, physical and chemical characteristics. The zooplanktonic and benthic fauna show little diversity. But the density of benthos (Chironomidae) and zooplankton is higher in Lake Pisses. The fish fauna of Lake Pisses is slightly more abundant than that of Lake Labarre, althought in both lakes fish density is low. A study of the diet of the two species revealed differences. In Lake Pisses, where the food supply is better, Arctic charr takes exclusively pelagic and benthic prey, whereas in Lake Labarre it also takes exogenous prey and thus comes into competition with trout. Length and body weight growth rates for Arctic charr are higher in Lake Pisses than in Lake Labarre. For trout, maximum length recorded was in Lake Pisses. The results show that the abundance of Chironomidae favours coexistence of the two species in Lake Pisses and confirm that, in the face of shortage of food, Arctic charr is better adapted than trout. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mitochondrial DNA analysis of Scottish populations of Arctic charr, Salvelinus alpinus (L.)

Mitochondrial DNA analysis of a total of 82 individuals from seven Scottish populations of Arctic charr ( Salvelinus alpinus L.) using restriction fragment length polymorphism and direct nucleotide sequencing of the cytochrome b gene revealed little variation within or between populations. One of 19 restriction enzymes showed a polymorphism that was present in three of the seven populations. Only one nucleotide substitution was detected in a 288 base pair segment of the cytochrome b gene examined in 26 fish. Approximately 4% of the mitochondrial genome was surveyed with these complementary procedures.     

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.     

Seasonal changes in sea-water tolerance of Arctic charr (Salvelinus alpinus)

Summary Groups of Arctic charr,Salvelinus alpinus, which had been acclimated to water with a salinity of 7 g·l^–1 and natural temperature and photoperiod, were exposed to water with different salinities and temperatures in June, September and February. At a salinity of 15 g·l^–1, plasma osmolality, plasma Na⁺, Cl^–, Mg²⁺ concentrations and the activity of gill Na-K-ATPase were stable, irrespective of temperature and season. In June, the charr were able to regulate blood plasma ionic levels within narrow limits when exposed to a salinity of 34 g·l^–1 (sea water) and a temperature of 8°C. The hypo-osmoregulatory capacity was less, but sufficient if the temperature was only 1°C during the seawater exposure. At the start of the experiment, the gill Na-K-ATPase activity was significantly higher in June than corresponding enzyme activities in September and February. Furthermore, an increase in gill Na-K-ATPase activity during the seawater exposure (8°C) was seen in June. Irrespective of ambient temperature and salinity, no fish died during the June experiments. In September and February, exposure to sea water produced marked increases in plasma osmolality and plasma ion concentrations. There were no changes in gill Na-K-ATPase activity. Consequently, the fish became dehydrated and were moribund after a short period of seawater exposure. Highest mortality was recorded when charr were exposed to winter sea conditions (34 g·l^–1 and 1°C) in February. The results indicate that an increase in daylength induce a hypo-osmoregulatory capacity in the Arctic charr during summer. In fall and winter, however, reduced daylength are accompanied by poor hypo-osmoregulatory capacity. This leads to high mortality as a result of increased electrolyte levels and dehydration.     

Ecological parasitology of polymorphic Arctic charr, Salvelinus alpinus (L.), in Thingvallavatn, Iceland

The helminth endoparasite fauna in four Arctic charr morphs, Salvelinus alpinus (L.), small benthivorous (SB), large benthivorous (LB), planktivorous (PL) and piscivorous (PI) charr, from Thingvallavatn, Iceland consisted of: Crepidostomum farionis (Trematoda: Allocreadiidae); Diplosttomum sp. (Trematoda: Diplostomatidae); Eubothrium salvelini; Diphyllobothrium dendriticum; D. ditremum (Cestoda: Pseudophyllidae); Proteocephalus longicollis (Cestoda: Proteocepha-lidae): and Philonema oncorhynchi (Nematoda: Filariidae). The morphs exhibited distinctive patterns in prevalences and parasite burdens (mean intensity and mean relative density of parasites). SB charr had high prevalence and parasite burden of the eye fluke Diplostomum sp. and none to very light infections of the other parasite species. LB charr had relatively high prevalence and parasite burden of the intestinal fluke C. farionis , whereas infections of the remaining parasite species were light to moderate. PL and PI charr had high prevalences and worm burdens of Diphyllobothrium spp. and P. longicollis . PL charr differed from PI charr in higher worm burden off P. longicollis and lighter burden of £. salvelini . Prevalences of P. oncorhynchi were high in PL and PI charr. Association of parasite intensities and age and length offish were investigated. The different infection patterns among the morphs agree well with their partitioning in food and habitat utilization, and confirm that there is a high degree of ecological segregation between the morphs. The results demonstrate the importance of ecological factors influencing transmission efficiency of parasites to the fish host.     

Effects of food quality on maturation rate in Arctic charr, Salvelinus alpinus (L.)

The effects of food quality on maturation rate were followed in progeny from wild Arctic charr, caught in Lake Fattjaure, northern Sweden. The fish were reared at five different food quality levels. In the first summer, the fry were given feed of three qualities: diluted with cellulose in three proportions (0, 15 and 25%). During the second winter the impact of changed food quality level was studied by transferring half the fish from the high (control) to the low food quality level and vice versa.
Maturation rate was lower in males reared at the high and improved food quality levels than in males reared at the medium, low and reduced food quality levels. The maturation rate in females was similar at all levels, though the rate tended to increase at the reduced food quality level.
Fish reared at the high and medium levels had similar growth rates, whereas fish at the low food quality level experienced slower growth. Reduced food quality did not arrest the growth offish, whereas improved food quality enhanced their growth.     

The effect of stocking density on the behaviour of Arctic charr (Salvelinus alpinus L.)

Recent studies have demonstrated that Arctic charr ( Salvelinus alpinus ) exhibit higher growth rates when held at high stocking densities. It has been argued that these increased growth rates are a result of decreased social interactions at the increased densities. The current study was designed to test this hypothesis by examining: (1) the frequency of agonistic interactions, (2) the proportion of time spent swimming and (3) growth rates among groups of young of the year Arctic charr held at different stocking densities. It was found that charr reared at higher densities exhibited significantly higher mean weights and lengths than those at the lower densities. The behavioural observations revealed that charr initiated significantly fewer agonistic interactions and spent a significantly greater amount of time shoaling at high densities than charr held at the medium or low densities. It is argued that these behavioural responses may serve to lower energy expenditures, resulting in the increased growth rates.     

Temperature influence on Arctic charr (Salvelinus alpinus L.) antibody response to a cellular antigen

In order to elucidate the immune responses of Arctic charr in relation to temperature, groups were acclimated to a moderate (9°C) and a cold temperature regime (4°C), as well as subjected to a temperature decrease (from 9 to 4°C) immediately prior to an immunization with sheep red blood cells. The charr kept at 9°C responded with increased primary and secondary antibody titres, as seen by direct haemagglutination, while fish at 4°C, as well as the fish subjected to a temperature reduction, displayed lower and lowest antibody titres, respectively, and only after a second immunization. It is concluded that Arctic charr can respond to a cellular antigen with a humoral immune response typical for other teleosts, but that the immune response is delayed and diminished at low temperatures. This temperature-induced immune suppression is intensified if the fish have not been acclimated to cold water prior to immunization. Accepted: 10 October 1999     

The periodicity of primary increment formation in the otoliths of Arctic charr Salvelinus alpinus (L.)

The role of environmental factors in the regulation of sub-annual increment formation in fish otoliths appears to differ markedly between species. To examine the periodicity of primary increment formation in the otoliths of O + Arctic charr, Salvelinus alpinus (L.), and the effects of temperature, and photoperiod on their formation, fish were held under controlled environmental conditions. Primary growth increments were found in the otoliths of fish held at constant temperature (18° C) and at ambient temperature [fluctuating with a circadian and circannual rhythm (4–18° C)]. Consistent and significant disruptions in increment formation occurred however, in experimental groups subjected to rapid change from ambient photoperiod to a 6L: 6D photo-period for 96 h. Disruptions in increment formation were also observed immediately following transportation of fish between holding facilities and following disease treatment. The number of otolith increments formed in fish held on an ambient photoperiod regime, correlated closely with time elapsed in days since checkmark formation ( r = 0.989, P ≤0.001) in fish sampled sequentially over a period of 10 to 105 days. Thus we demonstrate that under conditions of ambient photoperiod, primary increments are formed daily.     

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.