An experimental comparison of cannibalistic response in different Arctic charr (Salvelinus alpinus (L.)) stocks

Abstract– The cannibalistic response of four domesticated Arctic charr stocks were compared experimentally using a radiographic technique. Charr from Arctic Spitsbergen (80°N) consistently exhibited a much higher frequency of cannibalistic response than fish from three charr strains from mainland Norway (70°N). The results indicate that the extent of cannibalistic feeding in Arctic charr is population specific and support the hypothesis that charr from Arctic populations have stronger cannibalistic tendencies than do fish from more temperate regions.     

Long-term variation in the population structure of Arctic charr, Salvelinus alpinus, and brown trout, Salmo trutta

The effects of induced water level fluctuations and introduction of the mysid Mysis relicta Lovén on population structure of brown trout, Salmo trutta L., and Arctic charr, Salvelinus alpinus (L.), were studied during 1953–1995 in Limingen hydroelectric reservoir, Norway. The main response was a marked reduction in catch‐per‐unit‐effort (CPUE) for trout and charr, probably caused by reduced recruitment following increased variation in water level. For both species, mean length decreased until 1967 and increased thereafter, whereas mean mass‐at‐length increased for the whole period. Both length and mass‐at‐length were negatively correlated with CPUE. The increases in mean length and mass‐at‐length were probably because of reduced competition following the reduced recruitment. Mysis relicta has become an important food item for charr but not for brown trout, but the increases in mean length and mass‐at‐length of charr started prior to the appearance of M. relicta in the charr diet.     

An experimental test of the genetic component of the ontogenetic habitat shift in Arctic charr (Salvelinus alpinus)

Abstract— Fry of the Arctic charr, Salvelinus alpinus , were experimentally stocked into a small fish-free lake to test the hypothesis that the size-dependent habitat shift from the epibenthic to the pelagic habitat is genetically determined. The charr originated from a nearby lake inhabiting predatory brown trout Salmo trutta. The cohort of stocked charr was investigated for three years. The Arctic charr started to exploit the pelagic habitat in their first summer at a size of 7–9 cm in contrast to about 15 cm in the donor lake. In the next two summers, the pelagic fraction of the cohort increased. The main fraction lived in epibenthic areas, utilizing the same prey as pelagic charr. Water temperature moderated the habitat use of juveniles such that they avoided warm (>16°C) waters and resided in cool, deep areas. The result was consistent with the hypothesis of a tradeoff between feeding benefit and the predation risk producing spatial segregation of Arctic charr and demonstrated that the fish can facultatively respond to predation risk and adjust the size at which they migrate to the pelagic zone to feed on zooplankton.     

Littoral spawning habitats of three southern Arctic charr (Salvelinus alpinus L.) populations

Abstract Arctic charr populations in southern latitudes are nonmigratory, with all life‐stages limited to freshwater lakes and in‐ or out‐flowing tributaries. Although many of these populations are reported to also spawn in lake littorals, little is known about the physical characteristics of putative spawning grounds. A total of 23 discrete spawning sites within three Irish lakes were located by fyke netting of spawning adults and snorkelling in littoral habitats. Spawning sites were found to be long, narrow strips running parallel to the shore at a maximum depth of 124 cm. Spawning sites were limited to areas of coarse mineral substrate with an adequate (c. 8 cm) depth of clean interstitial spaces. In individual lakes, combined areas of spawning sites made up 0.4–0.7% of available littoral. Egg densities varied considerably between sites (33–900·eggs m^?2) and were significantly correlated with gradient and width of spawning sites. No evidence of redd digging was found. The shallow, localised and restricted nature of spawning grounds makes such populations vulnerable to anthropogenically induced postoviposition changes in surface water level, eutrophication processes such as increased lake sedimentation and elevated nutrient status.     

Effects of variable egg incubation temperatures on the embryonic development in Arctic charr Salvelinus alpinus

An evaluation of different thermal regimes during incubation of Arctic charr Salvelinus alpinus L. egg was conducted with regard to embryo survival and development. The study consisted of two major parts: In experiment A, a range of commonly used thermal regimes, constant and variable ranging from 2.7°C to 7°C, were tested for differences in embryo survival and developmental status of newly hatched alevins. Experiment B assessed the timing of a shift from autumn (6°C) to winter temperature (2.5°C) and its effect on embryo survival and the occurrence of spinal deformities in newly hatched alevins. In general, incubations that were initiated at temperatures below 3°C resulted in significantly higher mortality rates and spinal deformity frequencies than other treatments. Hence, Arctic charr eggs require an initial warmer period for unimpaired embryonic development. A general negative correlation was found between the duration of this warmer period (6°C) and both mortality rates and frequency of spinal deformities. The total absence of the 6°C period had the most detrimental effect, with deformity frequencies at least four times higher than all treatments with an initial warmer period. The upper incubation temperature threshold was not reached in the study. The highest temperature tested (7°C) did not result in excess mortality or increased deformity frequency. Higher incubation temperature resulted in less developed alevins at hatching, i.e. alevins were smaller with more yolk remaining. However, measurements on alevins from incubations at variable temperatures revealed different temperature effects on growth and yolk consumption during different parts of embryonic development.     

Muscle carotenoid concentrations in sexually maturing and immature Arctic charr, Salvelinus alpinus (L.)

Muscle carotenoid concentrations were measured in immature and maturing 2+ Arctic charr, Salvelinus alpinus (L.), sampled from April until ovulation started in November. In immature fish, muscle carotenoid concentration increased steadily and had reached about 10 mg kg^?1 by the end of the experiment. In mature fish of both sexes, pigment concentrations decreased during the autumn and muscle carotenoid concentrations were significantly lower than in the immature fish during the latter stages of the trial. No significant difference in muscle pigmentation was observed between sexes. Carotenoid concentrations were lowest in the cranial region of the fillet, but decreased in all parts of the fillet when the charr became mature. In females, the decrease seemed to be most marked in the caudal region. At the termination of the experiment, fillets accounted for about one-half of the carotenoid content in mature fish of both sexes. High concentrations of pigment were recorded in the skin and fins of mature males. In mature female charr, pigment was almost equally distributed among skin, fins and ovaries     

Optimal protein requirements of young Arctic charr (Salvelinus alpinus) fed practical diets

Young Arctic charr, Salvelinus alpinus (L.), mean weight 2.56 ± 0.02 g, were fed nine isoenergetic (?16.6 MJ digestible energy (DE) kg^?1) practical diets formulated to supply digestible crude protein (DCP) at 40g kg^?1 increments from 230 to 550g kg^?1, for 84 days. Mean weight gain (MWG) and specific growth rate (SGR) were determined every 14 days while carcass composition was determined at the start and end of the experiment. Growth responses attained the highest values in the fish fed the diet with 350 g kg^?1 DCP. Carcass moisture gain, protein gain and apparent net lipid accumulation increased as DCP levels increased to a maximum at 350 g kg^?1 after which there were no differences among treatments. Total carcass lipid and lipid gain decreased as dietary DCP increased up to 470 g kg^?1 with no differences thereafter. Apparent net protein accretion decreased with increasing DCP levels up to 350 g kg^?1 after which there were few differences among treaments. Protein requirements were estimated by fitting MWG and SGR data to broken line regression, quadratic and saturation kinetics models. Results from these analyses suggest that dietary DCP should be provided at between 340 and 392 g kg^?1 (equivalent to ?370 and 420g kg^?1 crude protein) for optimal growth of young Arctic charr reared in similar conditions.     

The effect of dietary inulin on aerobic bacteria associated with hindgut of Arctic charr (Salvelinus alpinus L.)

The primary aim of the present study was to evaluate the population level of adherent (autochthonous) aerobic and facultative anaerobic bacteria in the hindgut of healthy Arctic charr (Salvelinus alpinus L.) fed dextrin or inulin. This was assessed by the dilution plate technique, and visualized using both transmission and scanning electron microscopy. A population level of 4.8 × 10⁵ adherent bacteria per gram wet mass was found in the hindgut of fish fed a casein‐based diet supplemented with 15% dextrin. However, substituting dextrin with 15% inulin reduced the bacterial population level in the hindgut (3.56 × 10⁴). A total of 217 bacterial isolates were identified by key phenotypical and biochemical characteristics. In addition, 22 strains were also identified by partial sequencing of the 16S rRNA gene. The composition of bacteria colonizing the hindgut of Arctic charr fed dextrin was dominated by the genera Staphylococcus, Pseudomonas, Micrococcus, Psychrobacter glacincola and Streptococcus. However, bacteria colonizing the hindgut of fish fed inulin were dominated by Gram‐positive bacteria of the genera Staphylococcus, Streptococcus, Carnobacterium and Bacillus. While Carnobacterium divergens‐like strains were isolated from charr fed dextrin, Carnobacterium maltaromicus‐like strains were isolated from the hindgut of fish fed inulin. Electron microscopical analysis of hindgut regions confirmed traditional culture‐based microbial analysis as fewer bacterial cells were observed between microvilli and associated with the surfaces of enterocytes of fish fed inulin rather than dextrin.     

The influence of predation risk on habitat selection and food intake by Arctic charr, Salvelinus alpinus (L.)

Abstract— Large piscivorous fish are assumed to affect habitat selection and food intake of prey fish. To study the effects of cannibalistic Arctic charr, Salvelinus alpinus (L.), on smaller stunted charr, we sampled the prey fish in littoral and pelagic habitats using gill nets, before and shortly after the release of large charr in a small lake (0.52 km²). In the habitats where the risk of predation was highest, the catch per unit effort de creased from 13.3 to 4.8 fish per 100 m² of gillnet after release of pred ators. The large decrease in numbers of charr < 18 cm corresponded with the predicted vulnerable prey sizes, according to a model based on the size distribution of predators. The occurrence of planktivorous fish and weight-specific food intake decreased in the high risk habitat and remained unaffected in the low risk habitats. Changes in the food intake of prey fish could not be explained in terms of fish length, indicating that prey fish changed diet when the risk of predation was high.     

Divergent, genetically based feeding behaviour of two sympatric Arctic charr, Salvelinus alpinus (L.), morphs

Abstract –  Arctic charr, Salvelinus alpinus (L.), is one of the several northern fishes that show resource polymorphisms in postglacial lakes. Two reproductively isolated morphs of Arctic charr coexist in distinct ecological niches in the subarctic lake Fjellfrøsvatn, North Norway. Offspring of the two morphs (termed littoral charr and profundal charr) were reared separately but under identical conditions. Their feeding behaviour was compared experimentally using different kinds of live prey. The fishes had no experience with natural prey before the experiments. The littoral morph were more effective in eating live plankton ( Daphnia ) and littoral benthos ( Gammarus ), and had a higher attack rate against pleuston (surface prey, Gerris ) compared with the profundal morph. The two morphs behaved in accordance with expectations from their in situ niche utilisation towards the three prey types. This indicates a case of incipient ecological speciation where divergence in resource utilisation in contrasting niches has evolved adaptations in feeding behaviour by natural selection.     

Influence of feeding frequency on growth and size dispersion in Arctic charr Salvelinus alpinus (L.)

Abstract Dominance hierarchy formation in groups of fish is thought to be a major reason for the development of size heterogeneity. The objective of the current experiment was to examine the influence of different feeding frequencies on growth and changes in size distribution in groups of Arctic charr Salvelinus alpinus (L.). The fish were fed equivalent excess rations continuously for 24 h a day, for 2 h twice a day (early morning and evening), for 2 h once a day in the morning or for 2 h once every other day also in the morning. Growth was measured by individual weighing of fish four times during the 130‐day experiment. Coefficient of variation in size within rearing groups was used to assess size dispersion and the possible development of hierarchies within the groups. Feeding frequency did not influence variation in size within groups, and there were no signs of hierarchy formation.     

Effects of stocking of piscivorous brown trout, Salmo trutta L., on stunted Arctic charr, Salvelinus alpinus (L.)

To study the effects on a stunted freshwater population of Arctic charr, Salvelinus alpinus (L.), two groups of large (26–45 cm) individually tagged brown trout, Salmo trutta L., were released and recaptured with gillnets after 1, 7, 11 and 63 weeks. One group of trout was trained on a fish diet before release, and the other, reared on commercial dry pellets, served as a control. Specific growth rates in both groups were negative 1 week after release and approached zero after 63 weeks. Condition factor and internal fat content decreased during the experiment. Although only 11% of the trout stomachs examined contained fish prey, charr represented 79% of the total stomach weight content. Gillnet samples of charr before and 63 weeks after the release of trout indicated a decreasing population size of charr. Individual growth and mean length of charr increased after release of trout, especially for charr at age 4 years. After the release of trout, 35% of the charr were longer than 20 cm as compared with 6% before the release.     

Effects of short‐term starvation periods on flesh quality in Arctic charr (Salvelinus alpinus) in different seasons

Possible effects of short‐term starvation on flesh quality in Arctic charr were studied in spring (March) and summer (August). Groups of juvenile Arctic charr (mean weight March 536 g ± 24; August 461 g ± 15 SEM) were starved for 1, 2 and 4 weeks (March) and 1, 2 and 3 (August). After each starvation period, the fish were slaughtered, and flesh samples collected in order to investigate quality and textural properties in the different experimental groups. Starvation had a positive effect on flesh quality giving firmer texture and lower gaping scores. Starved fish had lower cathepsin activity at slaughter, and a similar difference was seen one‐week post mortem. The results showed that the effect of starvation period was seasonally dependent. Starvation had a larger effect in summer, where a three‐week starvation resulted in firmer texture, whereas this was not seen during spring.     

Effect of rearing temperatures on the growth and maturation of Arctic charr (Salvelinus alpinus) during juvenile and on‐growing periods

The effect of rearing temperature on the growth and maturation of Arctic charr (Salvelinus alpinus) was investigated. Arctic charr juveniles were reared for 6 months (phase I, October–April, size range 20–500 g) at constant temperatures of 9, 12 and 15 °C and according to two temperature‐step groups (T_step) i.e. fish transferred from 15 to 12 °C or from 12 to 9 °C. All the previous treatments were then reared either at 7 °C or at 12 °C for an additional 4 months (phase II, size range 300–1000 g) and then slaughtered in August 2008. The overall growth rate was the highest at a constant temperature of 15 °C for the first 6 months of the trial, with the fish in this group being 44% and 78% heavier than the fish reared at a constant temperature of 12 or 9 °C respectively. Arctic charr showed a negative response in terms of the growth rate when transferred from higher to lower temperatures, especially for groups previously reared at 15 °C. There was a trend for higher gonadosomatic index values at the end of the experiment for groups of fish that were exposed to higher rearing temperatures during the juvenile phase i.e. 4.18% (±0.79) and 7.29% (±0.89), for the temperature groups of 12 and 15 °C, respectively, compared with 2.49% (±0.74) for the 9 °C group. Our results suggest that for the production of fish >1000 g, moderate or low temperatures (here 9 °C) should be applied during the juvenile phase in order to reduce the negative effects arising from maturation. Farmers with access to heat sources should accordingly choose more moderate rearing temperatures during the juvenile stage, especially if the fish is to be moved down in the temperature regime during the on‐growing period.     

Temperature–growth patterns of individually tagged anadromous Arctic charr Salvelinus alpinus in Ungava and Labrador,Canada

Individual measurements of annual, or within‐season growth were determined from tag‐recaptured Arctic charr and examined in relation to summer sea surface temperatures and within‐season capture timing in the Ungava and Labrador regions of Eastern Canada. Differences between two years of growth (2010–2011) were significant for Ungava Bay Arctic charr, with growth being higher in the warmer year. Growth of Labrador Arctic charr did not vary significantly among years (1982–1985). Regional comparisons demonstrated that Ungava Arctic charr had significantly higher annual growth rates and experienced warmer temperatures than Labrador Arctic charr. The higher annual growth of Ungava Bay Arctic charr was attributed to the high sea surface temperatures experienced in 2010–2011 and the localised differences in nearshore productivity as compared to Labrador. Within‐season growth rates of Labrador Arctic charr peaked in June, declined towards August and were negatively correlated with the length of time spent at sea and mean experienced sea surface temperatures. A quadratic model relating growth rate to temperature best explained the pattern of within‐season growth. Collectively, results suggest that increases in water temperature may have profound consequences for Arctic charr growth in the Canadian sub‐Arctic, depending on the responses of local marine productivity to those same temperature increases.     

Genetic divergence among broodstocks of Arctic charr Salvelinus alpinus in eastern Canada derived from the same founding populations

We examined the amount and distribution of molecular variation at microsatellite loci in 21 broodstocks of Arctic charr Salvelinus alpinus derived from the Fraser River, Labrador and the Nauyuk Lake, Nunavut, Canada. Our goal was to assess the amount of genetic diversity and differentiation as broodstocks are subdivided and propagated in different hatcheries and grow‐out facilities. We observed significant heterogeneity across pairs of ancestral and descendant broodstocks in the mean numbers of alleles at microsatellite loci. We detected a significant decrease in the observed heterozygosity between ancestors and descendants but the amount of decrease did not depend on either the degree of removal from the wild (number of sequential transfers) or the strain (Fraser vs. Nauyuk). Based on allele frequency distributions, there was little genetic evidence of bottlenecks during the creation of subsequent broodstock populations after the initial founding events. All broodstock samples were significantly differentiated from each other but those within the same strain were more similar to each other than to broodstocks from different strains. Broodstocks from the Nauyuk Lake broodstocks showed greater differentiation from each other than did Fraser River broodstocks, which could be attributed to differences in the number of founders.     

Amino acid composition of Arctic charr, Salvelinus alpinus (L.) and the prediction of dietary requirements for essential amino acids

Embryo somatic tissues, non‐somatic yolk‐sac materials, and whole, individual fingerlings (age 0+) of Arctic charr, Salvelinus alpinus (L.), as well as a commercial trout diet, were analysed for a wide spectrum of amino acids. Analytical material consisted of prefeeding swim‐up fry that were separated into discrete yolk sac and somatic embryo tissue samples. Amino acid concentrations in fry somatic tissue and whole fingerlings were generally very similar to each other, but were lower than those measured in yolk materials. Higher correlations were observed between the majority of specific amino acid concentrations in the trout diet when compared with fingerling data (r² = 0.91) and fry somatic tissue data (r² = 0.89), than when correlated with fry yolk sac material (r² = 0.76). These results indicate that the essential amino acid profiles of fry somatic tissue and whole fingerlings are closer to that of a commercial feed than they are to the endogenous profiles found in the embryonic yolk sac material itself. The dietary ratios of individual essential amino acids were also compared with the total essential amino acid concentrations (A/E ratios) in whole fingerling tissues, and these ratios could be used to accurately estimate the apparent essential amino acid requirements of Arctic charr. The rationale for using carcass amino acid composition data to estimate the dietary essential amino acid requirements of Arctic charr is discussed.     

Morphological variability among three geographically distinct Arctic charr (Salvelinus alpinus L.) populations reared in a common hatchery environment

Abstract –  The morphology of three lake-resident Arctic charr, Salvelinus alpinus , populations was studied at two life-history stages in a common-garden experiment. The fish of the same year class were reared under standard hatchery conditions, and 27 morphometric variables (a truss network) were measured from the sampled individuals. Most of the total variation was explained by the overall body robustness, dimensions of the head and caudal peduncle length. After controlling for a body size, significant heterogeneity in body shape was found among populations at both ages. Independent of age, the populations were morphologically highly distinct, although some integration of characters could be found as the fish reached sexual maturity. Sexual divergence accounted for a large part of the within-population shape variation, the mature males having more robust bodies, larger head dimensions and longer pectoral fins compared with the mature females/immature fish. Although the cultured fish may not be totally representative of their wild counterparts, it is reasonable to expect that the observed morphological differences have a genetic basis, presumably reflecting adaptation to local environmental conditions experienced by the charr in their original habitat.