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.     

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.     

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.     

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,...     

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.     

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     

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.     

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.     

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.     

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.     

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.     

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.     

Overwintering mortality of migratory Arctic charr, Salvelinus alpinus, (L.) reared in salt water

The mortality of Arctic charr, Salvelinus alpinus , previously grown-on in salt water during the summer months, was studied during the winter 1980–81. Mortality did not appear to be related to a' critical size' but rather to rates of growth shown by the fish during the summer months. Mortality was high amongst the slow-growing fish.
The results are discussed in relation to published data on the osmoregulatory capabilities of Salvelinus spp.     

Behaviour,physiology and carotenoid pigmentation in Arctic charr Salvelinus alpinus

The behaviour during an exploration task and the response to a confinement stress of Arctic charr Salvelinus alpinus were evaluated. Behaviour of individuals during 90 min of exploration was classified into high and low activity. High‐activity individuals had higher plasma cortisol levels following stress compared to low‐activity individuals. This indicates that high‐ and low‐activity individuals correspond to reactive and proactive stress‐coping styles. Further, a pigmentation analysis showed that high‐activity individuals had a higher number of carotenoid spots cm^?2 than low‐activity individuals. Thus, carotenoid pigmentation, as melanin pigmentation in other salmonids, could be linked to stress‐coping style in S. alpinus.     

An investigation of factors controlling food intake in Arctic charr, Salvelinus alpinus L.

Digestibility values were determined for diets of varying protein content fed to Arctic charr. The use of these values, in conjunction with food intake data made possible the study of the effects of various parameters on the control of food consumption. Dietary energy content may be more important than protein content in regulating consumption. The regulation of food intake may be partially mediated through factors influencing gastric emptying coupled with mechanisms monitoring dietary metabolizable energy.     

Reproductive strategies of Arctic charr Salvelinus alpinus (L.) forms in Kiryalta lakes,Transbaikalia, Russia

Lake Abaya and Lake Chamo are the two largest Ethiopian Rift Valley lakes; they are located close to each other, but have a strikingly different water transparency. We explain key differences in the structure and the functioning of the food web with variation in limnological variables and major pelagic food web compartments within and across both lakes. Data from a detailed comparative investigation of physical and chemical variables and zooplankton community characteristics during the wet and dry season from two consecutive years revealed major differences in key limnological variables between Lake Abaya and Lake Chamo. The most pronounced differences were related to water transparency and the amount of suspended solids in the water column. Lake Abaya is much more turbid, has lower phyto- and zooplankton biomass, and has considerably lower primary production than Lake Chamo. Based on our results, we infer that the profound differences in food web structure between both lakes probably result from differences in sediment load. Finally, our results indicate that conservation programs should focus on reducing sediment inflow from the catchments into the lakes.

     

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.