Effect of temperature on heart rate in diploid and triploid brook charr, Salvelinus fontinalis, embryos and larvae

Increased cell size in triploid fish likely affects rates of respiratory gas exchange. Respiratory deficiencies can be addressed in fish by adjustments in cardiac output, through changes in heart rate and stroke volume. The aim of this study was to determine whether heart rate differs between triploid and control (diploid) brook charr, Salvelinus fontinalis, at embryo-larval stages, when the heart is easily visible and the fish are relatively inactive. Heart rate was measured at 6, 9 and 12 degrees C at three developmental stages: eyed-egg, hatch and yolk absorption. Heart rate was unaffected by ploidy, but increased with temperature and age from a low of 43.4+/-2.2 beats/min (6 degrees C, eyed egg) to a high of 73.3+/-1.5 beats/min (12 degrees C, yolk absorption). The Q(10) for heart rate was unaffected by ploidy and age, but decreased with temperature from 1.99+/-0.28 at 6-9 degrees C to 1.72+/-0.17 at 9-12 degrees C. Triploid brook charr thus do not use adjustments in heart rate as a mechanism to deal with the physiological consequences of altered haematology at embryo-larval stages.     

The ghost of hybrids past: fixation of arctic charr (Salvelinus alpinus) mitochondrial DNA in an introgressed population of lake trout (S. namaycush)

Complete fixation of arctic charr ( Salvelinus alpinus ) mitochondrial DNA (mtDNA) was observed in a southern Québec population of lake trout ( S. namaycush ). This introgressed population otherwise appeared to be normal with regard to lake trout morphology and three species-diagnostic microsatellite loci. Arctic charr do not occur in the area, suggesting that the hybridization event was prehistoric. Of several possible hypotheses, the most plausible explanation for this aberrant population is that hybridization occurred in situ soon after deglaciation, with repeated backcrossing of hybrids with lake trout. Fixation of S. alpinus mtDNA in the population may have occurred either by chance (drift) or selection, although indirect evidence and data from similarly introgressed brook trout ( S. fontinalis ) populations in the region suggest that selection favouring the S. alpinus mitochondrial type and/or associated nuclear genes may have been involved.     

Seasonal changes in the hypo-osmoregulatory ability of brook charr: the role of environmental factors

In winter, brook charr Salvelinus fontinalis demonstrated poor osmoregulatory ability. Saltwater (SW) transfer resulted in sharp increases in plasma osmolality and chloride levels, a decrease in white muscle water content and high mortality. A clear improvement of the hypo-osmoregulatory mechanism e.ciency was observed in spring; by May or June, fish achieved full acclimation within 1 week of SW transfer. In early fall, the time needed to restore osmotic and ionic balance increased once again. A high level of stress was detected only in winter and fall, as indicated by plasma cortisol and glucose concentrations. Great improvement in osmotic and ionic regulation was observed when brook charr were transferred to 80 C SW in February and April while impaired SW adaptability was recorded in individuals transferred to 2·50° C SW in June and August. Temperature itself was more important than a thermal gradient between fresh and salt water. Stress indicators substantiate this temperature-dependent improvement of osmotic and ionic regulation in brook charr. The results support the hypothesis of a minor contribution of cortisol to hypo-osmotic regulation in brook charr, as the cortisol response always seemed to be associated with stress in the experiments.     

The feeding response of diploid and triploid Atlantic salmon and brook trout

Pair and group experiments were conducted to determine whether differences exist in feeding success between juvenile diploid and triploid salmonids in a competitive situation. In the pair experiments, 22 pairs (one diploid and one triploid) of size-matched Quebec-strain brook trout Salvelinus fontinalis (7·2–46·3 g) were fed an unlimited number of pellets three times a day for 5 days. Dominance was assigned to the fish which ate the most pellets within each pair. In the group experiments, groups of three diploid and three triploid size-matched fish were fed a restricted ration three times a day for 5 days. Hierarchical rank within the group was assigned based on the number of pellets consumed by each fish. The group experiment was repeated 10 times with Atlantic salmon Salmo salar (5·1–62·7 g), Quebec-strain brook trout (11·8-110·8 g), and large UNB-strain brook trout (18·2–33·0 g), and 12 times with smaller UNB-strain brook trout (0·6–2·0 g). A statistically significant difference in rank between ploidies was found only for the smaller UNB-strain brook trout in the group experiments, with diploids dominant over triploids. This suggests that there may be a difference in competitive feeding success between diploid and triploid brook trout early in development, but that this difference diminishes as the fish grow.     

Isolation and cross‐familial amplification of 41 microsatellites for the brook charr (Salvelinus fontinalis)

The brook charr (Salvelinus fontinalis; Osteichthyes: Salmonidae) is a phenotypically diverse fish species inhabiting much of North America. But relatively few genetic diagnostic resources are available for this fish species. We isolated 41 microsatellites from S. fontinalis polymorphic in one or more species of salmonid fish. Thirty‐seven were polymorphic in brook charr, 15 in the congener Arctic charr (Salvelinus alpinus) and 14 in the lake charr (Salvelinus namaycush). Polymorphism was also relatively high in Oncorhynchus, where 21 loci were polymorphic in rainbow trout (Oncorhynchus mykiss) and 16 in cutthroat trout (Oncorhynchus clarkii) but only seven and four microsatellite loci were polymorphic in the more distantly related lake whitefish (Coregonus clupeaformis) and Atlantic salmon (Salmo salar), respectively. One duplicated locus (Sfo228Lav) was polymorphic at both duplicates in S. fontinalis.     

Critical thermal maxima of diploid and triploid brook charr, Salvelinus fontinalis

The purpose of this experiment was to determine whether diploid and triploid brook charr, Salvelinus fontinalis, differ in their critical thermal maxima (CTM). Two age classes were tested (underyearlings, having average weight of 25 g, and yearlings, having average weight of 668 g) at two rates of temperature increase (2° C h^-1 and 15° C h^-1). No effect of ploidy on CTM was found. Fish exposed to the faster rate of temperature increase had higher CTM values than those exposed to the slower rate (underyearlings: 29.5 ± 0.1° C versus 29.1 ± 0.1° C in one trial and 29.8 ± 0.1° C versus 28.3 ± 0.1° C in a second trial; yearlings: 29.3 ± 0.1° C versus 27.7 ± 0.1° C in two trials, p < 0.001 in all cases). Underyearlings had higher CTM values than yearlings (29.2 ± 0.1° C versus 28.5 ± 0.1° C, p < 0.05). Female yearlings, which were immature, had higher CTM values than males, which had previously matured as one-year-olds (28.8 ± 0.1° C versus 28.3 ± 0.1° C, p < 0.001).     

Salinity tolerance of freshwater acclimated, small-sized Arctic charr, Salvelinus alpinus from northern Labrador

Arctic charr, Salvelinus alpinus , less than 150 mm in size were frequently captured at sea in northern Labrador in areas where salinities of 30‰ or higher had been recorded. These captures were inconsistent with many earlier reports for other areas that indicated Arctic charr less than 150 mm in size were not found at sea. A series of salinity challenge tests was carried out in the field, using wild Ikarut River charr, and in the laboratory, using cultured Fraser River charr, to understand more about the potential fate of these small fish. The results of challenge tests with small Arctic charr (< 120 mm) indicated that at intermediate salinities (10–20‰), these fish can readily survive. In laboratory tests with salinities at 30‰, survival was size dependent and would suggest that in natural situations, small charr would require periodic access to fresh or brackish water to stay alive. The influence of water temperature on salinity tolerance may be important when fish are exposed to temperatures that are below 0° C.     

Quantitative genetic analysis of the physiological stress response in three strains of brook charr Salvelinus fontinalis and their hybrids

Three strains [domestic (D), Laval (L) and Rupert (R)] of brook charr Salvelinus fontinalis and their reciprocal hybrids were submitted to transport stress to measure stress resistance. Primary (cortisol) and secondary (glucose, osmolality and haematocrit) stress responses were measured for each cross. Significant heritabilities were observed for both levels of stress response, with mean ± S.E. heritability (h(2)) = 0.60 ± 0.20 for plasma cortisol and 0.61 ± 0.20 for plasma glucose. There were strain differences whereby the R strain was the least sensitive to stress at the primary and secondary levels. No heterosis was detected, and only one case of outbreeding depression was present. The outbreeding depression was observed in the D(♀) R(♂) hybrid, which had a 27% increase of plasma glucose compared to parental strains. The D(♀) R(♂) and R(♀) L(♂) hybrids had more pronounced variations (increase or decrease) in plasma osmolality than their respective parental strains, but these variations were difficult to relate definitively with the potential secondary stress response. These results indicate a strong potential for genetic improvement in the stress response to transport with the use of purebred crosses while hybridization has little value in this regard.     

The critical swimming velocity of diploid and triploid brook trout

No significant difference was found in the critical swimming velocity of diploid and triploid brook trout Salvelinus fontinalis , suggesting that the triploid state is not associated with a reduced aerobic capacity.     

Mitochondrial DNA variation of Salvelinus species found in Finland

Mitochondrial DNA (mtDNA) was purified from the Arctic charr, Salvelinus alpinus , the brook charr, Salvelinus fontinalis , and the lake charr, Salvelinus namaycush , and digested with restriction enzymes Ava II, Hinf I, Eco R V, Pst I and Xba I. Two Arctic charr samples were from natural populations and they represented two different morphotypes of Arctic charr. All other studied populations were hatchery maintained. Eight additional restriction enzymes and double digestions were employed to study morphotypes of Arctic charr. We distinguished two morphotypes with restriction enzyme Nci I. Sequence divergence among mtDNA types was 2.9–3.8% between S. alpinus and S. fontinalis , 3.4–4.6% between S. alpinus and S. namaycush , and 4.7–5.3% between S. fontinalis and S. namaycush . lntraspecific variation was lowest in Arctic charr, the average of nucleon diversity for three populations being 0.179, while for brook charr and for lake charr nucleon diversity was 0.334 and 0.550, respectively. According to the number of mtDNA types, it is obvious that introduction to Finland and hatchery propagation have not greatly affected the mtDNA variation of brook charr or lake charr.     

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.     

An atypical brook charr (Salvelinus fontinalis) spawning area

Synopsis Brook charr (Salvelinus fontinalis) spawned successfully on a 0.3 m thick aggregation of waterlogged sticks, woodchips and debris overlying the soft ooze bottom of a small Precambrian Shield lake. Brook charr were apparently attracted to groundwater seeping up through the aggregation and utilized the tangle of various sized sticks as a spawning substrate. Eggs were deposited in late October and alevins emerged from the area in late March, periods that coincide with the conventional spawning of native brook charr on gravel areas in nearby lakes. Our observations support the contention that upwellin, water is more important than bottom type in stimulating brook charr to select a spawning site.     

Detection of interstitial telomeric sequences in the Arctic charr (Salvelinus alpinus) (Teleostei: Salmonidae)

Highly polymorphic Arctic charr ( Salvelinus alpinus Linnaeus, 1758) chromosomes were studied using conventional and molecular methods. The diploid chromosome number in the studied individuals was 2n = 81 or 2n = 82, with a fundamental arm number (NF) = 100. These differences are due to Robertsonian fusions. Interindividual variation in the number and size of DAPI and CMA(3) positively stained chromatin sites was observed in studied specimens. In the case of two individuals, the subtelomeric region of the long arm (q) of the largest acrocentric chromosome (chromosome number 10) was positively stained by CMA(3) fluorochrome. Both primed in situ labelling (PRINS) and fluorescence in situ hybridization (FISH) revealed that this CMA(3)-positive region was flanked by telomeric sequences. Previously, the subterminal position of interstitial telomeric sequences located in the vicinity of the CMA(3)-positive guanine-rich chromatin have been described in two other Salvelinus species, brook trout ( Salvelinus fontinalis ) and lake trout ( Salvelinus namaycush ). Moreover, multichromosomal location and variation in size of CMA(3) bands have been observed in various Salvelinus taxa, including fishes with internally located telomeric sequences. These results suggest that relocation of CMA(3)-positive chromatin segments in these species may be facilitated by flanking interstitial telomeric sequences (ITSs).     

Piscivory by brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.) in Norwegian lakes

Size and frequency of occurrence of prey of brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.) were recorded in 13 Norwegian lakes during 1973–1990. Piscivores usually comprised less than 5% of the total population. Arctic charr were less piscivorous than brown trout. Trout and charr became piscivorous at 13 and 16 cm length, respectively. These size thresholds were similar to those of other facultative piscivorous freshwater fish species. When present, three-spined sticklebacks, Gasterosteus aculeatus (L.), were preferred by all length groups of piscivorous brown trout and Arctic charr. Length of prey increased with increasing predator length, and the mean body length of prey was about 33 and 25% of predator length for trout and charr, respectively. Yearlings of charr were not recorded as prey.     

Lake enrichment and the status of Windermere charr, Salvelinus alpinus (L.)

All English populations of Arctic charr, Salvelinus alpinus (L.), are found in the Lake District (northwest England). There are at least four races of charr in Windermere, the largest lake in England; the North and South basins of the lake each contain two distinct races that spawn in autumn and spring respectively. The spring spawners in both basins probably represent less than 15% of the total population in the lake.
Changes in the population density of charr in the lake are described briefly and examined in relation to the trophic status of the lake. Other factors that could possibly affect the charr population are reviewed, especially the influence of climate change.     

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

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

Development of a species-specific fractionation equation for Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis> (L.)): an experimental approach

A species-specific fractionation equation for Arctic charr (Salvelinus alpinus (L.)) was developed experimentally for use in ecological studies of temperature-driven phenologies for the species. Juvenile Arctic charr were reared in controlled conditions at different temperatures (2–14°C), with three replicates of each temperature. Otoliths from the fish and water samples from the chambers were analysed for oxygen isotope composition and used to estimate temperature-dependent fractionation equations relating the isotopic ratio to rearing temperature. A linear and a second order polynomial relationship were estimated and validated using comparable Arctic charr data from another study. Temperatures predicted using the polynomial equation were not significantly different from recorded experimental temperatures, whereas with the linear equation there were significant differences between the predicted and measured temperatures. The polynomial equation also showed the least bias as measured by mean predictive error. Statistical comparisons of the polynomial fractionation equation to a similarly estimated equation for brook charr (Salvelinus fontinalis (Mitchill)) indicated significant differences. Results imply the need for species-specific fractionation equations, even for closely related fish. Results further suggest the polynomial form of the fractionation equation will facilitate more accurate characterisation of water temperatures suitable for use in ecological studies of temperature-driven phenologies of Arctic charr.     

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.     

In vivo effects of the steroid analogue RU486 on some aspects of intermediary and thyroid metabolism of brook charr, Salvelinus fontinalis.

The glucocorticoid analogue RU486 was administered by intraperitoneal injection to brook charr (Salvelinus fontinalis) to further explore the role of cortisol on aspects of intermediary and thyroid hormone metabolism of the species. RU486 significantly elevated the hepatosomatic index, hepatic G3PDH activity, and hepatic glycogen content, but was without effect on hepatic protein content, hepatic FPBase activity, or plasma glucose concentration. However, the stressor-related increase in plasma glucose concentration that was evident in brook charr 24 h following handling and injection was suppressed in RU486-treated groups. The distribution volume, turnover rates, and metabolic clearance rates of [3H]cortisol were similar in RU486- and vehicle-treated groups. Plasma T3 and T4 concentrations were similar in RU486- and vehicle-treated groups, but hepatic T3 production and hepatic T3 content were lower in RU486-treated fish; TSH had no effect on hepatic T3 content of vehicle-treated brook charr but significantly increased T3 content in the RU486-treated group. These observations support the concept of a role of cortisol in the control of peripheral monodeiodination of T4 in salmonid fish and suggest that RU486 may be a useful drug for evaluating the role of cortisol in fish in vivo.     

Early microhabitat use by age 0 year brook charr Salvelinus fontinalis in lakes

The early habitat use of age 0 year brook charr Salvelinus fontinalis in three north temperate lakes which differ in terms of shoreline physical habitat is described. In the two lakes, which contained abundant shoreline woody debris and inundated vegetation, brook charr were observed in extremely close proximity with these habitat features, near shore and near the surface. Fish were absent from open areas away from shore unless in close proximity with fallen floating logs near the surface, extending offshore. In a third lake that had no woody debris or inundated shoreline vegetation, brook charr were observed exclusively in close proximity with the shoreline itself, and near the surface. In all three lakes, fish were most closely associated with the shoreline and with woody debris and inundated vegetation (when present) shortly after emergence, and significantly farther from shore and deeper in the water column thereafter.