Behaviour-Genetics of Lake Charr (Salvelinus namaycush) and Brook Charr (S. fontinalis): Observation of Backcross and F2 Generations

Brook charr (Salvelinus fontinalis) defend territories and show high levels of agonistic behaviour. In contrast, lake charr (S. namaycush) are non-territorial and rarely show any agonistic behaviour. The genetic determinance of behavioural differences between these species was confirmed by the behavioural similarity of brook charr backcross hybrids and brook charr and a significant maternal effect on hybrid behavioural phenotypes. Backcross and F₂ generations showed either one of two distinct behavioural strategies, one aggressive and territorial and the other non-aggressive and non-territorial. It seems most likely that these strategies are conditional on individual phenotypes, such as size of nearby conspecifics. However, precise measurements of costs and benefits of each strategy are required to distinguish between these alternate hypotheses for either species. Each action pattern was an independent pattern of variation and a distinct behavioural unit. However, patterns were coordinated with all other patterns at a higher hierarchical level (corresponding to the particular behavioural strategy). It seems most likely that these strategies would be controlled by a polygenic system, even though the nature of our data does not allow us to make firm conclusions in this regard.     

Behavioural plasticity of lake charr (Salvelinus namaycush) x brook charr (S. fontinalis) F1 hybrids in response to varying social environment

Lake x brook F₁ hybrid charr were observed in heterogeneous groups with lake charr or brook charr to assess the effects of different species on hybrid social behaviour. Levels of behavioural plasticity were low in relation to the behavioural differences between the parental and hybrid types. Feeding behaviour showed the most dramatic change, with higher levels in the lake charr treatment and lower levels in the brook charr treatment than controls, suggesting social facilitation. Even though only two measures varied significantly between treatments, there was a tendency for the frequencies and durations of all agonistic measures to increase in the presence of lake charr and decrease with brook charr. A cost-benefit argument is presented to account for this trend.     

Hybridization between native white-spotted charr and nonnative brook trout in the upper Sorachi River,Hokkaido, Japan

Invasion status and impacts of nonnative brook trout (Salvelinus fontinalis) in a Hokkaido stream were investigated with field surveys and genetic analyses. Nonnative brook trout was detected in nine (41 %) of the 22 sampled reaches in three tributaries of the Sorachi River, Hokkaido, Japan. Based on the external pigmentation, twelve putative hybrids between brook trout and native white-spotted charr (Salvelinus leucomaenis) were collected in two reaches. Microsatellite and mitochondrial DNA data established that 58% of these hybrids were first-generation (F₁) progenies between male brook trout and female white-spotted charr. Our results suggest potential negative impacts of nonnative brook trout on native charr populations in Hokkaido through interspecific interactions.     

Comparative ontogeny of photobehavioural responses of charrs (Salvelinus species)

Synopsis The development of photobehavioural responses in brook (Salvelinus fontinalis) and lake (S. namaycush) charr was studied by monitoring the intrasubstrate movements and concurrent photoresponse behaviour of incubated embryos and alevins. Photoresponse behaviour of both F-1 hybrids of the parent species was also recorded. All embryos initially moved downward in the substrate, however brook charr descended farther and faster into the substrate than did lake charr. Photoresponse tests demonstrated a similar pattern of photoresponse transformation from a photonegative to a photopositive state in both species. However, photoresponse reversal was faster, more extensive and occurred later in brook charr than in lake charr. Patterns of photoresponse change in F-1 hybrids were intermediate between those of the parent species. Photoresponse shifts preceded the onset of alevin emergence in both species. occurring when differential development of various morphological characters existed. Developmental states of characters were synchronously maximal towards the end of alevin emergence. Intermediate measures of morphological development were observed for F-1 hybrids. Possible functions and mechanisms of photoresponse transitions are discussed in relation to ecological differences between the species.     

Induction of androgenetic development of the brook charr (Salvelinus fontinalis) × Arctic charr (Salvelinus alpinus) hybrids in eggs derived from the parental species

Failure of interspecific androgenesis between brook charr (Salvelinus fontinalis, Mitchill 1814) and Arctic charr (Salvelinus alpinus, L.) has been attributed to the conflict between the egg cytoplasm of one species and the sperm nucleus of the other species. To overcome this incompatibility, sperm derived from the brook charr × Arctic charr hybrid male was used to induce androgenetic development in eggs originating from the parental species as well as their hybrids. The eggs were subjected to 420 Gy of X-radiation to damage the maternal nuclear DNA and inseminated with untreated sperm. Haploid zygotes were exposed to high hydrostatic pressure shock (7000 psi for 4 min), which was applied 420 min after insemination to inhibit the first cell cleavage and recover the diploid state of the zygote. The androgenetic diploid offspring that hatched from the brook charr, the Arctic charr and the hybrids eggs had survival rates of 4.7 ± 0.6%, 1.2 ± 0.4% and 16.8 ± 0.5%, respectively. Drastic mortality among the hatched androgenetic individuals was observed within the first five months of rearing. Cytogenetic analysis of the androgenetic progenies exhibited residues of the irradiated maternal nuclear genome in the form of radiation-induced chromosome fragments in 47% of the specimens that were examined. Interactions between the egg cytoplasm and the sperm nucleus, the low quality of the gametes, the expression of homozygous paternal lethal alleles and the incomplete inactivation of the maternal chromosomes were identified as factors responsible for the large mortality among androgenetic embryos and hatchlings.     

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.     

Chemical Alarm Signals Enhance Survival of Brook Charr (Salvelinus fontinalis) During Encounters with Predatory Chain Pickerel (Esox niger)

A diversity of aquatic organisms release chemical alarm signals when attacked or captured by a predator. These alarm signals are thought to warn other conspecifics of danger and, consequently, may benefit receivers by increasing their survival. Here we experimentally investigated the differences in behaviour and survival of hatchery-reared juvenile brook charr Salvelinus fontinalis that had been exposed to either brook charr skin extract (experimental treatment) or a control of swordtail skin extract (control treatment). Charr exposed to conspecific skin extract exhibited a significant reduction in movement and/or altered their foraging behaviour in the laboratory when compared with charr exposed to swordtail skin extract. We also exposed charr to either water conditioned by a single brook charr disturbed by a predatory bird model or water conditioned by a single undisturbed brook charr. Charr exposed to disturbance signals reduced activity significantly more than charr exposed to chemical stimuli from undisturbed charr. These results demonstrate the existence of both damage-released alarm signals and disturbance signals in brook charr. Wild brook charr also responded to damage-released alarm cues under natural conditions. Charr avoided areas of a stream with minnow traps labelled with conspecific alarm cues vs. control cues. During staged encounters with chain pickerel Esox niger in the laboratory, predator-naive charr fry were better able to evade the predator if they were previously warned by an alarm signal, thus suggesting a survival benefit to receivers. Collectively, these results demonstrate that the presence of alarm signals in brook charr has important implications for understanding predator–prey interactions.     

Genetic Diversity and Hybridisation between Native and Introduced Salmonidae Fishes in a Swedish Alpine Lake

Understanding the processes underlying diversification can aid in formulating appropriate conservation management plans that help maintain the evolutionary potential of taxa, particularly under human-induced activities and climate change. Here we assessed the microsatellite genetic diversity and structure of three salmonid species, two native (Arctic charr, Salvelinus alpinus and brown trout, Salmo trutta) and one introduced (brook charr, Salvelinus fontinalis), from an alpine lake in sub-arctic Sweden, Lake Ånn. The genetic diversity of the three species was similar and sufficiently high from a conservation genetics perspective: corrected total heterozygosity, H’_T = 0.54, 0.66, 0.60 and allelic richness, A_R = 4.93, 5.53 and 5.26 for Arctic charr, brown trout and brook charr, respectively. There were indications of elevated inbreeding coefficients in brown trout (G_IS = 0.144) and brook charr (G_IS = 0.129) although sibling relationships were likely a confounding factor, as a high proportion of siblings were observed in all species within and among sampling locations. Overall genetic structure differed between species, Fst = 0.01, 0.02 and 0.04 in Arctic charr, brown trout and brook charr respectively, and there was differentiation at only a few specific locations. There was clear evidence of hybridisation between the native Arctic charr and the introduced brook charr, with 6% of individuals being hybrids, all of which were sampled in tributary streams. The ecological and evolutionary consequences of the observed hybridisation are priorities for further research and the conservation of the evolutionary potential of native salmonid species.     

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.     

Emergence chronology of brook charr,Salvenus fontinalis,alevins in an acidic stream

Synopsis The emergence chronology of brook charr alevins in the Chikanishing River, Ontario, Canada and the concurrent changes in stream chemistry resulting from acidic snowmelt runoff were examined during the spring, 1986–1988. Emergence patterns were similar among years with the most intense emergence (> 70%) occurring during the declining stream discharge following the spring flood. This period coincided with stream pH depressions (minimum pH 5.2) in 2 of 3 years, suggesting emergence behaviour frequently subjects the earliest free-swimming life interval of brook charr to episodic acidification events.     

Diel locomotor activity of brook charr, as determined by radiotelemetry

Locations by radiotelemetry during eight 24–h sampling periods in 1991, 1992, and 1993 were used to evaluate the diel activity patterns of adult brook charr Salvelinus fontinalis in two lakes of the Laurentian Shield (Québec, Canada). Based on the minimum distance travelled between two consecutive locations, adult brook charr were more active at dusk and at night than during the day. During daylight periods, individual fish displayed strong site selection, remaining in the same area along the shore from day to day. The fish left their inshore position at dusk, were highly mobile during the night, and returned to their focal point at sunrise, exhibiting diel homing behaviour. These results are supported by an increase in gillnet captures of adult brook charr in Lac Melchior at night. Data obtained by gillnet fishing in lakes Bondi and Simpson showed that juvenile (1+) brook charr were active throughout the diel cycle and that young-of-the-year were active mainly during the day, suggesting that there is an ontogenetic change in the diel activity of brook charr. Despite its limitations (restrictions on the number and size of tracked individuals, post-manipulation mortality, lifetime of transmitter battery), radiotelemetry allows for collection of multiple behavioural observations (distances travelled, instantaneous activity, site selection and homing) during the activity cycle of individual fish, and thus provides a finer degree of spatial resolution than alternative methods such as gillnetting.     

Influence of spring and summer water temperature on brook charr, Salvelinus fontinalis, growth and age structure in the Ford River, Michigan

Synopsis The influence of late spring and summer water temperatures on brook charr, Salvelinus fontinalis, growth and age structure was evaluated from 1984 to 1991 in the Ford River, Michigan. Temperature was monitored and brook charr sampled for vital statistics from late May through September using fyke nets and weirs at four locations within a 25.8 km section of stream. Scale analysis was used to determine captured brook charr age, past length at age and relative annual growth rates. Late spring and summer water temperature patterns varied between years with the greatest variability occurring in May and June. Age and size structure also varied between years and was significantly related to temperature. Years with cooler late spring and summer temperature patterns were dominated by older (age 2 and 3), larger brook charr, while years with warmer spring and summer temperature patterns were dominated by younger (age 1), smaller brook charr. Spring and summer temperature did not appear to have a significant effect on the growth of age 0 or age 1 brook charr. However, temperature was negatively related to brook charr growth from age 2 on. As spring and summer water temperatures are critical to brook charr growth and survival, it is important that a streams thermal regime be considered when establishing management goals for this species.     

Environmental influences on territoriality of juvenile brook charr,Salvelinus fontinalis,in a stream environment

Synopsis Juvenile brook charr, Salvelinus fontinalis, defending territories in a laboratory stream channel changed their defensive tactics when fish numbers or water current velocity were increased. The associated increase in energy costs of territorial defense were apparently reduced by using relatively more lateral displays and fewer chases to repel intruders, and by decreasing territory size. Territory size tended to increase with food ration, although levels of aggression were not affected. These results emphasize the importance of energetic considerations in territoral defense in these fish, and are discussed in terms of current hypotheses regarding the resource base for territoriality.     

The most variable vertebrate on Earth

In the search for the most variable non-human vertebrate on Earth, intraspecific variation of ten variable traits was compared among ten highly variable species. Mammals, birds and many reptiles, amphibians and fishes were excluded because most of the variation is among, and not within species. The focus was on northern fishes, where high intraspecific variation is well documented. The ten selected species were European whitefish Coregonus lavaretus, chinook salmon Oncorhyncus tshawytscha, sockeye salmon O. nerka, rainbow trout O. mykiss, atlantic salmon Salmo salar, brown trout S. trutta, arctic charr Salvelinus alpinus, brook charr S. fontinalis, dolly varden charr S. malma and threespine stickleback Gasterosteus aculeatus. Variation included not only size and phenotype, but also ecology, behaviour and life history. The traits were geographic range, migration, habitat, adult size, colour, body form, polymorphism, diet, reproduction and genetics. Arctic charr came on top in the final ranking, followed by dolly varden charr and rainbow trout. The two least variable were chinook salmon and threespine stickleback. It is proposed that arctic charr, which is also the northernmost fish on Earth, has evolved its unique variability in range, size, phenotype, ecology and life history by adapting to the extreme and highly unpredictable ecological conditions of arctic and other northern lakes for many glacial periods.     

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.     

Spatial patterns of hybridization between bull trout, <Emphasis Type="Italic">Salvelinus confluentus</Emphasis>, and brook trout, <Emphasis Type="Italic">Salvelinus fontinalis</Emphasis> in an Oregon stream network

Hybridization with introduced species represents a serious threat to the persistence of many native fish populations. Brook trout (Salvelinus fontinalis) have been introduced extensively throughout the native range of bull trout (S. confluentus) and hybridization has been documented in several systems where they co-exist and is seen as a significant threat to the persistence of bull trout populations. We identified a group of diagnostic microsatellite loci to differentiate bull trout and brook trout and then used these loci to examine the spatial distribution of hybrids in the Malheur River basin, Oregon USA. In random samples of approximately 100 fish from each of three creeks we identified 181 brook trout, 112 bull trout and 14 hybrids. Although bull trout, brook trout and hybrids were found in all three creeks, they were not evenly distributed; brook trout were primarily found in the lower sections of the creeks, bull trout further upstream, and hybrids in the areas of the greatest overlap. One creek with a population of brook trout in a headwater lake provided an exception to this pattern; brook trout were found distributed throughout the creek downstream of the lake. Several post-F1 hybrids were identified suggesting that hybrids are reproducing in the Malher River Basin. Mitochondrial DNA analysis indicated that both female bull trout and brook trout are involved in hybridization events. Analysis of population structure suggested that brook trout have established multiple spawning populations within the Malheur system. Data presented in this study suggest that relative abundance of brook trout and habitat quality are important factors to consider when evaluating the threat of hybridization to bull trout populations.     

The influence of groundwater withdrawal and land use changes on brook charr (<Emphasis Type="Italic">Salvelinus fontinalis</Emphasis>) thermal habitat in two coldwater tributaries in Michigan,U.S.A.

Brook charr (Salvelinus fontinalis) is a sentinel fish species which requires clean, cold water habitats. As such, many jurisdictions in the United States where brook charr are present use this species as an indicator of ecosystem health. In Michigan, groundwater-dominated streams are currently being impacted by increased groundwater withdrawal and land use/land cover changes which alter stream temperatures and their flow, and thus have the potential to significantly influence brook charr production and behavior. We quantified the influence of groundwater withdrawal and land use alteration on thermal habitat availability for brook charr using a groundwater modeling tool that estimated changes in baseflow to a stream segment based on changes to the groundwater system due to groundwater withdrawal and changes in rates of recharge related to landscape changes within a watershed. Projected stream temperature changes were calculated using a stream temperature modeling tool and compared to the range of temperature preferenda for brook charr in order to evaluate the potential impact of policy decisions regarding water extraction and land use/cover changes. The models predicted relatively small changes in both stream baseflow and consequently, stream temperature, with increased groundwater withdrawal rates. Land use/land cover alterations which we analyzed were shown to either mitigate or enhance the loss of brook charr thermal habitat as a result of groundwater withdrawal, depending on its relationship to recharge dynamics. This study emphasizes the importance of collaboration between water, land, and fisheries managers to ensure brook charr population viability, productivity, and sustainability in the face of environmental change, increasing water use and development in the watershed.     

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.     

Attraction of slimy sculpins to chemical cues of brook charr eggs

In a laboratory study to examine the responses of slimy sculpin Cottus cognatus to chemical cues of brook charr Salvelinus fontinalis eggs, water that held freshly laid eggs (<20 min old), water-hardened eggs (i.e. eggs >4 h old) or injured eggs was collected and used in a series of two-choice tests. Slimy sculpin were exposed to paired stimuli of (1) hard egg water v . control water, (2) fresh egg water v . control water, (3) hard egg water v . injured egg water or (4) hard egg water v . fresh egg water. Sculpin spent considerably more time on the side of the tank with hard egg water and fresh egg water v . control water and injured egg water v . hard egg water. Sculpin did not show a preference for hard egg water v . fresh egg water. In a field study, brook charr were attracted to chemical cues from brook charr eggs, suggesting that brook charr eggs produce sufficient odour to attract some species under natural conditions.     

Fish mercury levels in relation to characteristics of hydroelectric reservoirs in Newfoundland, Canada

Mercury levels in fish have been demonstrated to increase after impoundment with augmented levels of mercury predicted to decline as the reservoir ages. Previous research in Newfoundland predicted return rates in the order of 10 to 12 years for landlocked Atlantic salmon or ouananiche (Salmo salar) and 7 years for brook trout (Salvelinus fontinalis). In order to test the validity of these predictions on a broader spatial and temporal scale, and develop more generally predictive models, mercury levels in three fish species were studied in 16 older Newfoundland hydroelectric reservoirs of various age (32 to 95 years) and area flooded (21 to 13,000 ha).Mercury concentrations were standardized to fish length and correlated with physical, chemical, and biological characteristics of the sampling sites. Standard length mercury levels ranged from 0.23 to 0.86 ppm in ouananiche, 0.13 to 0.59 ppm in brook trout, and 0.22 to 0.72 in arctic charr (Salvelinus alpinus). Fish in excess of the Canadian Safety Limit (0.5 ppm) were collected from 14 of 16 sites for ouananiche, 8 of 17 sites for brook trout, and 3 of 7 sites for arctic charr, including control lakes. Standard length fish mercury levels were correlated with reservoir age and (log₁₀) area flooded for ouananiche and with pH for arctic charr. A multiple regression model was developed relating standard length mercury in ouananiche with reservoir age and log₁₀ of the flooded area. There were no apparent relationship between reservoir characteristics and brook trout mercury concentrations. Based on this analysis, it is not possible, at present, to develop generally predictive models for all species found in Newfoundland impoundments.