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.     

Growth and food of young-of-the-year brook charr,Salvelinus fontinalis,in lake and creek environments

Synopsis Growth and diet of brook charr,Salvelinus fontinalis, during their first weeks of exogenous feeding were compared between the nearshore zone of a central Ontario lake and its small, inlet creeks. Food selection was related to size and age of charr and possibly availability of food items. Mean growth was similar between habitats despite differences in consumed food types and caloric values. Differences in social behaviour may have been responsible for different patterns of growth between habitats. The importance of creek habitats to the dynamics and fitness of lake populations of brook charr are suggested.     

Loss of genetic integrity correlates with stocking intensity in brook charr (Salvelinus fontinalis)

Supportive breeding and stocking performed with non‐native or domesticated fish to support sport fishery industry is a common practice throughout the world. Such practices are likely to modify the genetic integrity of natural populations depending on the extent of genetic differences between domesticated and wild fish and on the intensity of stocking. The purpose of this study is to assess the effects of variable stocking intensities on patterns of genetic diversity and population differentiation among nearly 2000 brook charr (Salvelinus fontinalis) from 24 lakes located in two wildlife reserves in Québec, Canada. Our results indicated that the level of genetic diversity was increased in more intensively stocked lakes, mainly due to the introduction of new alleles of domestic origin. As a consequence, the population genetic structure was strongly homogenized by intense stocking. Heavily stocked lakes presented higher admixture levels and lower levels of among lakes genetic differentiation than moderately and un‐stocked lakes. Moreover, the number of stocking events explained the observed pattern of population genetic structure as much as hydrographical connections among lakes in each reserve. We discuss the implications for the conservation of exploited fish populations and the management of stocking practices.     

Genetically based population divergence in overwintering energy mobilization in brook charr (Salvelinus fontinalis)

Investigating the nature of physiological traits potentially related to fitness is important towards a better understanding of how species and/or populations may respond to selective pressures imposed by contrasting environments. In northern species in particular, the ability to mobilize energy reserves to compensate for the low external energy intake during winter is crucial. However, the phenotypic and genetic bases of energy reserve accumulation and mobilization have rarely been investigated, especially pertaining to variation in strategy adopted by different populations. In the present study, we documented variation in several energy reserve variables and estimated their quantitative genetic basis to test the null hypothesis of no difference in variation at those traits among three strains of brook charr (Salvelinus fontinalis) and their reciprocal hybrids. Our results indicate that the strategy of winter energy preparation and mobilization was specific to each strain, whereby (1) domestic fish accumulated a higher amount of energy reserves before winter and kept accumulating liver glycogen during winter despite lower feeding; (2) Laval fish used liver glycogen and lipids during winter and experienced a significant decrease in condition factor; (3) Rupert fish had relatively little energy reserves accumulated at the end of fall and preferentially mobilized visceral fat during winter. Significant heritability for traits related to the accumulation and use of energy reserves was found in the domestic and Laval but not in the Rupert strain. Genetic and phenotypic correlations also varied among strains, which suggested population-specific genetic architecture underlying the expression of these traits. Hybrids showed limited evidence of non-additive effects. Overall, this study provides the first evidence of a genetically based—and likely adaptive—population-specific strategy for energy mobilization related to overwinter survival.     

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).     

Water temperature, light intensity and zooplankton density and the feeding activity of juvenile brook charr (Salvelinus fontinalis)

SUMMARY 1. The objective of this study was to evaluate the effects of zooplankton biomass (as a measure of density), fish biomass, light intensity and water temperature on the attack rate and swimming characteristics (i.e. swimming speed and angle of turn) of juvenile (1+) brook charr (Salvelinus fontinalis) in field enclosures. We used a portable underwater camera system in a series of pelagic enclosures to quantify the feeding behaviour of brook charr over a gradient of natural conditions. 2. In simple linear or non‐linear regression models we found (i) that attack rate and angle of turn were positively related to water temperature, (ii) that attack rate and swimming speed were positively related to zooplankton biomass and light intensity and (iii) that attack rate was positively related to swimming speed. In multiple regression models, fish biomass, light intensity and variance of the angle of turn accounted for 87% of the variation in attack rate. Light intensity and water temperature accounted for 86% of the variation in swimming speed. Fish gut fullness and attack rate accounted for 83% of the variation in the variance of the angle of turn executed by fish. 3. The increase in the number of attacks as zooplankton biomass increases conforms to the general positive functional response observed in other fish species. Our results also support the hypothesis that swimming speed increases with prey biomass. We did not observe a plateau in attack rate as zooplankton biomass increased. As our experiments were performed under natural biotic and abiotic conditions, factors other than zooplankton biomass might affect or limit this response, such as water temperature and light intensity. 4. Because zooplankton biomass was correlated with water temperature and light intensity, it was not possible to evaluate the independent contribution of these factors on the attack rate and swimming characteristics (swimming speeds and angle of turn) of brook charr. However, this study highlighted the impact of these factors on the feeding behaviour of juvenile brook charr when feeding in the pelagic habitat under natural conditions, and their importance in future models of optimal foraging and fish habitat quality.     

Hydrography and population genetic structure in brook charr (Salvelinus fontinalis, Mitchill) from eastern Canada

Despite the abundance of studies of genetic diversity in freshwater fishes, few have specifically addressed the role of habitat structure in partitioning genetic variance within and among populations. In this study, we analysed the variability of six microsatellite loci among 24 brook charr population samples in order to correlate hydrographic structure with genetic organization. These populations originated from three Canadian National parks (Kouchibouguac, Fundy and Forillon) that showed distinct hydrographic structure. Considering the general characteristics of these habitats, we formulated specific hypotheses in regard to genetic structure, which were principally based on the potential for gene flow and population size associated with each habitat. The hierarchical analysis of molecular variance and the genetic distances computed among populations revealed that habitat structure analyses constitute an important, but insufficient, predictor of genetic structure. We discuss the importance of habitat complexity on genetic structure in the context of management and conservation.     

The rise and fall of isolation by distance in the anadromous brook charr (Salvelinus fontinalis Mitchill)

Geographic patterns of genetic diversity depend on a species' demographic properties in a given habitat, which may change over time. The rates at which patterns of diversity respond to changes in demographic properties and approach equilibrium are therefore pivotal in our understanding of spatial patterns of diversity. The brook charr Salvelinus fontinalis is a coastal fish exhibiting limited marine movements, such that a stable one-dimensional isolation-by-distance (IBD) pattern should be observed over the whole range. Its range, however, recently shifted northward such that northern populations may still be in the process of reaching equilibrium. We investigated variation in IBD patterns, genetic divergence, and allelic richness at six microsatellite markers in 2087 anadromous brook charr from 59 rivers along the most likely postglacial colonization route. We observed a decrease in allelic richness, together with an increase in differentiation and a decrease in IBD in the most recently colonized northern populations, as expected following recent colonization. Contrary to expectation, however, similar patterns were also observed at the southernmost part of the range, despite the fact that these populations are not considered to be newly colonized. We propose that the loss of dispersal capabilities associated with anadromy may have caused the southernmost populations to evolve relatively independently of one another. This study thus demonstrated that changes in a species' geographic range and dispersal capabilities may contribute to shaping geographic patterns of genetic diversity.     

Occurrence of Salmincola sp. on brook charr Salvelinus fontinalis in Lake Superior

Hydrobiologia - Salmincola sp. infect fishes of the family Salmonidae and can negatively affect host health. The parasite–host relationship was examined between Salmincola sp. and a remnant...     

Seawater acclimation of diploid and triploid brook charr (Salvelinus fontinalis), diploid Arctic charr (Salvelinus alpinus), and their diploid and triploid hybrids

Seawater acclimation of diploid (FF) and triploid (F2F) brook charr Salvelinus fontinalis , diploid (AA) Arctic charr Salvelinus alpinus , and diploid (FA) and triploid (F2A) hybrids between female brook charr and male Arctic charr was investigated. Triploidization of brook charr and the hybrid did not have any effect on the acclimation. Seawater acclimation of the hybrid was achieved during the experimental period and was comparable to that observed in brook charr. Acclimation could not be ascertained in Arctic charr since the level of cortisol, a stress indicator, was still high at the end of the experiment. No relationship between either length or condition factors and plasma osmolality was observed. Elevated plasma cortisol concentrations in Arctic charr and in diploid or triploid hybrids, both in fresh water and sea water, indicate more favourable rearing conditions for brook charr.     

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.     

Pyloric caecal morphology of brook charr,Salvelinus fontinalis,in relation to diet

Synopsis Brook charr, Salvelinus fontinalis, shifts its diet from zoobenthos to pelagic prey when living sympatrically with white sucker, Catostomus commersoni, in lakes of the Laurentian Shield. We tested the hypothesis that this diet difference would have a significant impact on their pyloric caecal morphology in 5 lakes containing allopatric brook charr populations and 6 other lakes containing both brook charr and white sucker. We observed that the mean length of the most posterior caecum of charr was significantly greater in sympatry than in allopatry (X ± 1 SD: 9.91 ± 1.12 mm versus 8.44 ± 0.67 mm). This is equivalent to an increase of 18% of total pyloric caecal mass (dry weight) in sympatric brook charr. These results indicate that this response to differences in diet, well known in birds, also occurs in fish.     

Neutral and selective processes shape MHC gene diversity and expression in stocked brook charr populations (Salvelinus fontinalis)

The capacity of an individual to battle infection is an important fitness determinant in wild vertebrate populations. The major histocompatibility complex (MHC) genes are crucial for a host's adaptive immune system to detect pathogens. However, anthropogenic activities may disrupt natural cycles of co‐evolution between hosts and pathogens. In this study, we investigated the dynamic sequence and expression variation of host parasite interactions in brook charr (Salvelinus fontinalis) in a context of past human disturbance via population supplementation from domestic individuals. To do so, we developed a new method to examine selection shaping MHC diversity within and between populations and found a complex interplay between neutral and selective processes that varied between lakes that were investigated. We provided evidence for a lower introgression rate of domestic alleles and found that parasite infection increased with domestic genomic background of individuals. We also documented an association between individual MHC alleles and parasite taxa. Finally, longer cis‐regulatory minisatellites were positively correlated with MHC II down‐regulation and domestic admixture, suggesting that inadvertent selection during domestication resulted in a lower immune response capacity, through a trade‐off between growth and immunity, which explained the negative selection of domestic alleles at least under certain circumstances.     

A comparative mitogenomic analysis of the potential adaptive value of Arctic charr mtDNA introgression in brook charr populations (Salvelinus fontinalis Mitchill)

Wild brook charr populations (Salvelinus fontinalis) completely introgressed with the mitochondrial genome (mtDNA) of arctic charr (Salvelinus alpinus) are found in several lakes of northeastern Québec, Canada. Mitochondrial respiratory enzymes of these populations are thus encoded by their own nuclear DNA and by arctic charr mtDNA. In the present study we performed a comparative sequence analysis of the whole mitochondrial genome of both brook and arctic charr to identify the distribution of mutational differences across these two genomes. This analysis revealed 47 amino acid replacements, 45 of which were confined to subunits of the NADH dehydrogenase complex (Complex I), one in the cox3 gene (Complex IV), and one in the atp8 gene (Complex V). A cladistic approach performed with brook charr, arctic charr, and two other salmonid fishes (rainbow trout [Oncorhynchus mykiss] and Atlantic salmon [Salmo salar]) revealed that only five amino acid replacements were specific to the charr comparison and not shared with the other two salmonids. In addition, five amino acid substitutions localized in the nad2 and nad5 genes denoted negative scores according to the functional properties of amino acids and, therefore, could possibly have an impact on the structure and functional properties of these mitochondrial peptides. The comparison of both brook and arctic charr mtDNA with that of rainbow trout also revealed a relatively constant mutation rate for each specific gene among species, whereas the rate was quite different among genes. This pattern held for both synonymous and nonsynonymous nucleotide positions. These results, therefore, support the hypothesis of selective constraints acting on synonymous codon usage.     

Quantitative field investigations of feeding and territorial behaviour of young-of-the-year brook charr,Salvelinus fontinalis

Synopsis Direct observations of young-of-the-year brook charr, Salvelinus fontinalis, in a second-order woodland stream indicated that most of their feeding effort was directed toward sub-surface, drifting prey (83% of feeding time). Feeding from the substrate and water surface was much less frequent (17% of feeding time). Comparisons of gut contents to drift net and substrate fauna samples corroborated that the most commonly consumed prey (chironomid and trichopteran larvae, ostracods, and ephemeropteran nymphs) were captured primarily from sub-surface, invertebrate drift. The disproportionate numbers of some prey species in the guts of several fish indicate that some prey selection occurred. Territories appeared to be cardioid-shaped, and were often contiguous, with dominance hierarchies evident among the residents. Agonistic interactions were frequent. Charges and chases predominated (91% of interactions) while lateral displays were infrequent (9% of interactions). Overall, these fish spent most of the daylight hours station-holding (77%) and feeding (18%). While only 3% of total time was spent in aggression, this amounted to 14% of the time a fish spent away from its station. There was some indication that territories were defended at a cost of feeding time.     

The disruption of sodium balance in brook charr, Salvelinus fontinalis (Mitchill), by manganese and iron

A primary toxic action of manganese to brook charr, Sulvelinusjonfinalis, at concentrations near or above the 96 h LC₅₀ was the disruption of sodium regulation. Body and plasma sodium concentrations of brook charr declined by 52 and 40%, respectively, during exposure to 10.9 mM manganese (in 250 PM CaCI), and all fish died within 36 h. Sodium balance was less severely affected by 2.7 and 5.5 mM manganese. An increase in the external calcium concentration from 0.05 to 1.0 mM raised the LC₅₀ for manganese from 4.9 to 5.8 mM, and a further increase to 2.5 mM calcium almost doubled it to 10.2 mM. An examination of stable manganese uptake by the gills revealed that accumulation was inversely correlated with body sodium concentration (r =−0.77). Radioactive J4Mn entered the bloodstream in low levels and accumulated in the liver. Thus manganese may have systemic effects as well as those attributable to surface binding on the gill. Studies of the mechanism ofdissolved iron toxicity were less conclusive, but it did not appear to involve extensive disruption of sodium balance. There was about a 15% drop in body sodium concentration when the trout were exposed for 48 h to the 96 h LC₅₀ level of iron, but plasma sodium was unaffected. Also, an iron concentration at twice the LC₅₀ did not escalate the loss of body sodium, and increasing the water calcium concentration did not raise the LC₅₀.     

Dynamics of introgressive hybridization assessed by SNP population genomics of coding genes in stocked brook charr (Salvelinus fontinalis)

Salmonid fishes rank among species being most severely affected by introgressive hybridization as a result of a long tradition of stocking with hatchery-reared conspecifics. The objectives of this study were (i) to evaluate the genetic consequences of stocking and resulting introgression rates on the genetic integrity of natural populations of brook charr, (ii) to identify genomic regions potentially associated with adaptation to natural and artificial rearing environments, and (iii) to test the null hypothesis that introgression from domesticated brook charr into wild populations is homogeneous among loci. A total of 336 individuals were sampled from nine lakes, which were stocked at different intensities with domestic fish. Individuals were genotyped at 280 SNPs located in transcribed regions and developed by means of next-generation sequencing. As previously reported with microsatellites, we observed a positive relationship between stocking intensity and genetic diversity among stocking groups, and a decrease in population differentiation. Individual admixture proportions also increased with stocking intensity. Moreover, genomic cline analysis revealed 27 SNPs, seven of which were also identified as outliers in a genome scan, which showed an introgression rate either more restricted or enhanced relative to neutral expectations. This indicated that selection, mainly for growth-related biological processes, has favored or hampered the introgression of genomic blocks into the introgressed wild populations. Overall, this study highlights the usefulness of investigating the impact of stocking on the dynamics of introgression of potentially adaptive genetic variation to better understand the consequences of such practice on the genomic integrity of wild populations.