Consistent Negative Correlations between Parasite Infection and Host Body Condition Across Seasons Suggest Potential Harmful Impacts of Salmincola markewitschi on Wild White-Spotted Charr, Salvelinus leucomaenis.

Assessing the impacts of parasites on wild fish populations is a fundamental and challenging aspect of the study of host-parasite relationships. Salmincola, a genus of ectoparasitic copepods, mainly infects salmonid species. This genus, which is notorious in aquaculture, damages host fishes, but its impacts under natural conditions remain largely unknown or are often considered negligible. In this study, we investigated the potential impacts of mouth-attaching Salmincola markewitschi on white-spotted charr (Salvelinus leucomaenis) through intensive field surveys across four seasons using host body condition as an indicator of harmful effects. The prevalence and parasite abundance were highest in winter and gradually decreased in summer and autumn, which might be due to host breeding and/or wintering aggregations that help parasite transmissions. Despite seasonal differences in prevalence and parasite abundance, consistent negative correlations between parasite abundance and host body condition were observed across all seasons, indicating that the mouth-attaching copepods could reduce the body condition of the host fish. This provides field evidence suggesting that S. markewitschi has a potential negative impact on wild white-spotted charr.

Fine scale diversity in the lava: genetic and phenotypic diversity in small populations of Arctic charr Salvelinus alpinus.

BACKGROUND: A major goal in evolutionary biology is to understand the processes underlying phenotypic variation in nature. Commonly, studies have focused on large interconnected populations or populations found along strong environmental gradients. However, studies on small fragmented populations can give strong insight into evolutionary processes in relation to discrete ecological factors. Evolution in small populations is believed to be dominated by stochastic processes, but recent work shows that small populations can also display adaptive phenotypic variation, through for example plasticity and rapid adaptive evolution. Such evolution takes place even though there are strong signs of historical bottlenecks and genetic drift. Here we studied 24 small populations of the freshwater fish Arctic charr (Salvelinus alpinus) found in groundwater filled lava caves. Those populations were found within a few km2-area with no apparent water connections between them. We studied the relative contribution of neutral versus non-neutral evolutionary processes in shaping phenotypic divergence, by contrasting patterns of phenotypic and neutral genetic divergence across populations in relation to environmental measurements. This allowed us to model the proportion of phenotypic variance explained by the environment, taking in to account the observed neutral genetic structure. RESULTS: These populations originated from the nearby Lake Mývatn, and showed small population sizes with low genetic diversity. Phenotypic variation was mostly correlated with neutral genetic diversity with only a small environmental effect. CONCLUSIONS: Phenotypic diversity in these cave populations appears to be largely the product of neutral processes, fitting the classical evolutionary expectations. However, the fact that neutral processes did not explain fully the phenotypic patterns suggests that further studies can increase our understanding on how neutral evolutionary processes can interact with other forces of selection at early stages of divergence. The accessibility of these populations has provided the opportunity for long-term monitoring of individual fish, allowing tracking how the environment can influence phenotypic and genetic divergence for shaping and maintaining diversity in small populations. Such studies are important, especially in freshwater, as habitat alteration is commonly breaking populations into smaller units, which may or may not be viable.

Association of ectoparasite Lepeophtheirus salmonis counts on farmed Atlantic salmon and wild sea trout in Scotland.

Parasitic sea lice (Copepoda: Caligidae) colonising marine salmonid (Salmoniformes: Salmonidae) aquaculture production facilities have been implicated as a possible pressure on wild salmon and sea trout populations. This investigation uses monitoring data from the mainland west coast and Western Isles of Scotland to estimate the association of the abundance of adult female Lepeophtheirus salmonis (Krøyer) colonising farmed Atlantic salmon Salmo salar L. with the occurrence of juvenile and mobile L. salmonis on wild sea trout, anadromous S. trutta L. The associations were evaluated using generalised linear mixed models incorporating farmed adult female salmon louse abundances which are temporally lagged relative to dependent wild trout values. The pattern of lags, which is consistent with time for L. salmonis development between egg and infective stage, was evaluated using model deviances. A significant positive association is identified between adult female L. salmonis abundance on farms and juvenile L. salmonis on wild trout. This association is consistent with a causal relationship in which increases in the number of L. salmonis copepodids originating from lice colonising farmed Atlantic salmon cause an increase of L. salmonis abundance on wild sea trout.

Towards a comprehensive understanding of the muscle proteome in Schizothorax labiatus: Insights from seasonal variations, metabolic responses, and reproductive signatures in the River Jhelum.

Proteomics is a very advanced technique used for defining correlations, compositions and activities of hundreds of proteins from organisms as well as effectively used in identifying particular proteins with varying peptide lengths and amino acid counts. In the present study, an endeavour has been put forth to create muscle proteome expression of snow trout, Schizothorax labiatus. Liquid chromatography-mass spectrometry (LC-MS) using label free quantification (LFQ) technique has extensively been carried out to explore changes in protein metabolism and its composition to discriminate across species, clarify functions and pinpoint protein biomarkers from organisms. In LFQ technique, the abundances of proteins are determined based on the signal intensities of their corresponding peptides in mass spectrometry. The main benefit of using this method is that it doesn't require pre-labelling proteins with isotopic tags, which streamlines the experimental procedure and gets rid of any bias that might have been caused by the labelling process. LFQ techniques frequently offer a wider dynamic range, making it possible to detect and quantify proteins over a broad range of abundances obtained from the complex biological materials including fish muscle. The results of proteomic analysis could provide an insight in understanding about how various proteins are expressed in response to environmental challenges. For proteomic study, two different weight groups of S. labiatus were taken from River Jhelum based on biological, physiological and logistical factors. These groups corresponded to different life stages, such as younger size and adults/brooders in order to capture potential variations in the muscle proteome related to growth and development. The proteomic analysis of S. labiatus depicted that an overall of 220 proteins in male and 228 in female fish of group 1 were noted. However, when male and female S. labiatus were examined based on spectral count and peptide abundance using ProteinLynx Global Software, a total of 10 downregulated and 32 upregulated proteins were found. In group 2 of S. labiatus, a total of 249 proteins in male and 301 in female fish were documented. When the two genders of S. labiatus were likened to one another by LFQ technique, a total of 41 downregulated and 06 upregulated proteins were identified. The variability in the protein numbers between two fish weight groups reflected biological differences, influenced by factors such as age, developmental stages, physiological condition and reproductive activities. During the study, it was observed that S. labiatus exhibited downregulated levels of proteins that were involved in feeding and growth. The contributing factors to this manifestation could be explained by lower feeding and metabolic activity of fish and decreased food availability during winter in River Jhelum. Contrarily, the fish immune response proteins were found to be significantly over-expressed in S. labiatus, indicating that the environment was more likely to undergo increased microbial infection, pollution load and anthropogenic activities. In addition, it was also discovered that there was an upregulated expression of the reproductive proteins in S. labiatus, which could be linked to the fish's pre-spawning time as the fish used in this study was collected in the winter season which is the pre-spawning period of the fish. Therefore, the present study would be useful in obtaining new insights regarding the molecular makeup of species, methods of adaptation and reactions to environmental stresses. This information contributes to our understanding of basic science and may have applications in environmental monitoring, conservation and preservation of fish species.

Genomic underpinnings of head and body shape in Arctic charr ecomorph pairs.

Across its Holarctic range, Arctic charr (Salvelinus alpinus) populations have diverged into distinct trophic specialists across independent replicate lakes. The major aspect of divergence between ecomorphs is in head shape and body shape, which are ecomorphological traits reflecting niche use. However, whether the genomic underpinnings of these parallel divergences are consistent across replicates was unknown but key for resolving the substrate of parallel evolution. We investigated the genomic basis of head shape and body shape morphology across four benthivore-planktivore ecomorph pairs of Arctic charr in Scotland. Through genome-wide association analyses, we found genomic regions associated with head shape (89 SNPs) or body shape (180 SNPs) separately and 50 of these SNPs were strongly associated with both body and head shape morphology. For each trait separately, only a small number of SNPs were shared across all ecomorph pairs (3 SNPs for head shape and 10 SNPs for body shape). Signs of selection on the associated genomic regions varied across pairs, consistent with evolutionary demography differing considerably across lakes. Using a comprehensive database of salmonid QTLs newly augmented and mapped to a charr genome, we found several of the head- and body-shape-associated SNPs were within or near morphology QTLs from other salmonid species, reflecting a shared genetic basis for these phenotypes across species. Overall, our results demonstrate how parallel ecotype divergences can have both population-specific and deeply shared genomic underpinnings across replicates, influenced by differences in their environments and demographic histories.

Characterization of gill bacterial microbiota in wild Arctic char (Salvelinus alpinus) across lakes, rivers, and bays in the Canadian Arctic ecosystems.

Teleost gill mucus has a highly diverse microbiota, which plays an essential role in the host's fitness and is greatly influenced by the environment. Arctic char (Salvelinus alpinus), a salmonid well adapted to northern conditions, faces multiple stressors in the Arctic, including water chemistry modifications, that could negatively impact the gill microbiota dynamics related to the host's health. In the context of increasing environmental disturbances, we aimed to characterize the taxonomic distribution of transcriptionally active taxa within the bacterial gill microbiota of Arctic char in the Canadian Arctic in order to identify active bacterial composition that correlates with environmental factors. For this purpose, a total of 140 adult anadromous individuals were collected from rivers, lakes, and bays belonging to five Inuit communities located in four distinct hydrologic basins in the Canadian Arctic (Nunavut and Nunavik) during spring (May) and autumn (August). Various environmental factors were collected, including latitudes, water and air temperatures, oxygen concentration, pH, dissolved organic carbon (DOC), salinity, and chlorophyll-a concentration. The taxonomic distribution of transcriptionally active taxa within the gill microbiota was quantified by 16S rRNA gene transcripts sequencing. The results showed differential bacterial activity between the different geographical locations, explained by latitude, salinity, and, to a lesser extent, air temperature. Network analysis allowed the detection of a potential dysbiosis signature (i.e., bacterial imbalance) in fish gill microbiota from Duquet Lake in the Hudson Strait and the system Five Mile Inlet connected to the Hudson Bay, both showing the lowest alpha diversity and connectivity between taxa.IMPORTANCEThis paper aims to decipher the complex relationship between Arctic char (Salvelinus alpinus) and its symbiotic microbial consortium in gills. This salmonid is widespread in the Canadian Arctic and is the main protein and polyunsaturated fatty acids source for Inuit people. The influence of environmental parameters on gill microbiota in wild populations remains poorly understood. However, assessing the Arctic char's active gill bacterial community is essential to look for potential pathogens or dysbiosis that could threaten wild populations. Here, we concluded that Arctic char gill microbiota was mainly influenced by latitude and air temperature, the latter being correlated with water temperature. In addition, a dysbiosis signature detected in gill microbiota was potentially associated with poor fish health status recorded in these disturbed environments. With those results, we hypothesized that rapid climate change and increasing anthropic activities in the Arctic might profoundly disturb Arctic char gill microbiota, affecting their survival.

Balancing risks and rewards of alternate strategies in the seaward extent, duration and timing of fjord use in contemporary anadromy of brown trout (Salmo trutta).

BACKGROUND: Anadromy comprises a successful life-cycle adaptation for salmonids, with marine migration providing improved feeding opportunities and thus improved growth. These rewards are balanced against costs from increased energy expenditure and mortality risk. Anthropogenic-induced environmental changes that reduce benefits and/or increase costs of migration e.g., aquaculture and hydropower, may therefore result in adaptations disfavouring anadromy. We tagged brown trout (Salmo trutta) smolts (N = 175) and veteran migrants (N = 342), from five adjacent riverine populations located in Sognefjorden, the longest Norwegian fjord-system supporting anadromous brown trout populations (209 km). Over four years, 138 acoustic telemetry receivers were deployed to track migrations of tagged individuals from freshwater and throughout Sognefjorden. Detected movements were used to fit migration models and multi-state mark-recapture models of survival and movement for each life-stage. Seaward migration distance was modelled to examine the fitness consequences from alternate migration strategies, with these models used to simulate the extent of fjord-use by individuals and accompanying growth, fecundity and survival consequences. We compared these findings with mark-recapture data collected prior to aquaculture and hydropower development. RESULTS: The telemetry data revealed that the outermost-fjord region was utilised by all populations albeit by few individuals. However, historical recaptures were located at a greater distance from the river mouth (87.7 ± 70.3 km), when compared to maximum migration distances of present-day counterparts (58.6 ± 54.9 km). River of origin influenced observed migratory behaviour and differential survival was estimated for each population and life-stage. The simulations based on telemetry-data models revealed a 30% and 23% difference in survival among populations for smolts and veteran migrants, respectively. At the individual-level, a long-distance migration strategy was rewarded with enhanced fecundity. However, the main contribution to population-level fecundity was overwhelmingly derived from middle-distance migrants, due to higher mortality rates and limited numbers of long-distant migrants. CONCLUSIONS: We conclude that present-day anadromy is precarious, but potential risk varies considerably between life-stages and populations, even within a single fjord system. Our findings suggest that selection for extended migration is under pressure, we therefore stress the importance of monitoring and management actions to secure genetic variation pertinent to preserve fitness gains of anadromy.

Sex-specific effects of inbreeding in juvenile brown trout.

Inbreeding depression, that is, the reduction of health and vigour in individuals with high inbreeding coefficients, is expected to increase with environmental, social, or physiological stress. It has therefore been predicted that sexual selection and the associated stress usually lead to higher inbreeding depression in males than in females. However, sex-specific differences in life history may reverse that pattern during certain developmental stages. In some salmonids, for example, female juveniles start developing their gonads earlier than males who instead grow faster. We tested whether the sexes are differently affected by inbreeding during that time. To study the effects of inbreeding coefficients that may be typical for natural populations of brown trout (Salmo trutta), and also to control for potentially confounding maternal or paternal effects, we sampled males and females from the wild, used their gametes in a block-wise full-factorial breeding design to produce 60 full-sib families, released the offspring as yolk-sac larvae into the wild, sampled them 6 months later, identified their genetic sex, and used microsatellites to assign them to their parents. We used whole-genome resequencing to calculate the kinship coefficients for each breeding pair and hence the expected average inbreeding coefficient per family. Juvenile growth could be predicted from these expected inbreeding coefficients and the genetic sex: Females reached lower body sizes with increasing inbreeding coefficient, while no such link could be found in males. This sex-specific inbreeding depression led to the overall pattern that females were on average smaller than males by the end of their first summer.

Smaller body size under warming is not due to gill-oxygen limitation in a cold-water salmonid.

Declining body size in fishes and other aquatic ectotherms associated with anthropogenic climate warming has significant implications for future fisheries yields, stock assessments and aquatic ecosystem stability. One proposed mechanism seeking to explain such body-size reductions, known as the gill oxygen limitation (GOL) hypothesis, has recently been used to model future impacts of climate warming on fisheries but has not been robustly empirically tested. We used brook trout (Salvelinus fontinalis), a fast-growing, cold-water salmonid species of broad economic, conservation and ecological value, to examine the GOL hypothesis in a long-term experiment quantifying effects of temperature on growth, resting metabolic rate (RMR), maximum metabolic rate (MMR) and gill surface area (GSA). Despite significantly reduced growth and body size at an elevated temperature, allometric slopes of GSA were not significantly different than 1.0 and were above those for RMR and MMR at both temperature treatments (15°C and 20°C), contrary to GOL expectations. We also found that the effect of temperature on RMR was time-dependent, contradicting the prediction that heightened temperatures increase metabolic rates and reinforcing the importance of longer-term exposures (e.g. >6 months) to fully understand the influence of acclimation on temperature-metabolic rate relationships. Our results indicate that although oxygen limitation may be important in some aspects of temperature-body size relationships and constraints on metabolic supply may contribute to reduced growth in some cases, it is unlikely that GOL is a universal mechanism explaining temperature-body size relationships in aquatic ectotherms. We suggest future research focus on alternative mechanisms underlying temperature-body size relationships, and that projections of climate change impacts on fisheries yields using models based on GOL assumptions be interpreted with caution.

Heat shocks during egg incubation led to developmental, morphological, and behavioral differences in Arctic charr (Salvelinus alpinus).

Temperature variation is affecting fish biodiversity worldwide, causing changes in geographic distribution, phenotypic structure, and even species extinction. Incubation is a critical stage for stenothermic species, which are vulnerable to large temperature fluctuations, and its effects on the phenotype at later developmental stages are understudied, despite the fact that the phenotype being essential for organism ecology and evolution. In this study, we tested the effects of heat shocks during the embryonic period on the phenotype of Arctic charr (Salvelinus alpinus). We repeatedly quantified multiple phenotypic traits, including morphology, development, and behavior, over a period of 4 months, from hatching to juvenile stage in individuals that had experienced heat shocks (+ 5°C on 24 h, seven times) during their embryonic stage and those that had not. We found that heat shocks led to smaller body size at hatching and a lower sociability. Interestingly, these effects weakened throughout the development of individuals and even reversed in the case of body size. We also found an accelerated growth rate and a higher body condition in the presence of heat shocks. Our study provides evidence that heat shocks experienced during incubation can have long-lasting effects on an individual's phenotype. This highlights the importance of the incubation phase for the development of ectothermic organisms and suggests that temperature fluctuations may have significant ecological and evolutionary implications for Arctic charr. Given the predicted increase in extreme events and the unpredictability of temperature fluctuations, it is critical to further investigate their effects on development by examining fluctuations that vary in frequency and intensity.

Non-lethal detection of Eubothrium crassum (Cestoda) in farmed Atlantic salmon, Salmo salar, using anal swabs and real-time PCR.

Detection of intestinal parasites in fish typically requires autopsy, resulting in the sacrifice of the fish. Here, we describe a non-lethal method for detecting the tapeworm Eubothrium crassum in fish using anal swabs and real-time PCR detection. Two assays were developed to detect cytochrome oxidase I (COI) mitochondrial DNA and 18S ribosomal DNA sequences of E. crassum, respectively. The assays were tested on swab samples from confirmed pathogen free Atlantic salmon (Salmo salar L.) and on samples from farmed Atlantic salmon, where the presence and intensity of parasites had been established through autopsy. The COI assay was shown to be specific to E. crassum, while the 18S assay also amplified the closely related E. salvelini, a species infecting Arctic charr (Salvelinus alpinus L.) in freshwater. The COI assay detected E. crassum in all field samples regardless of parasite load while the 18S assay failed to detect the parasite in two samples. The results thus demonstrates that this non-lethal approach can effectively detect E. crassum and can be a valuable tool in assessing the prevalence of infection in farmed salmon, aiding in treatment decisions and evaluating treatment effectiveness.

Effects of pre-winter cortisol exposure on condition, diet, and morphology of wild juvenile brown trout (Salmo trutta).

Winter is an energetically challenging period for many animals in temperate regions because of the relatively harsh environmental conditions and reduction in food availability during this season. Moreover, stressors experienced by individuals in the fall can affect their subsequent foraging strategy and energy stores after exposure has ended, referred to as carryover effects. We used exogenous cortisol manipulation of wild juvenile brown trout (Salmo trutta) in the fall to simulate a physiological stress response and then investigated short-term (2 weeks) and long-term (4 months) effects on condition metrics (hepatosomatic index and water muscle content), diet (stomach contents and stable isotopes), and morphology during growth in freshwater. We revealed some short-term impacts, likely due to handling stress, and long-term (seasonal) changes in diet, likely reflecting prey availability. Unfortunately, we had very few recaptures of cortisol-treated fish at long-term sampling, limiting detailed analysis about cortisol effects at that time point. Nonetheless, the fish that were sampled showed elevated stable isotopes, suggestive of a cortisol effect long after exposure. This is one of few studies to investigate whether cortisol influences foraging and morphology during juvenile growth, thus extending the knowledge of proximate mechanisms influencing ecologically-relevant phenotypes.

Neurotransmitter norepinephrine regulates chromatosomes aggregation and the formation of blotches in coral trout Plectropomus leopardus.

Color changes and pattern formations can represent strategies of the utmost importance for the survival of individuals or of species. Previous studies have associated capture with the formation of blotches (areas with light color) of coral trout, but the regulatory mechanisms link the two are lacking. Here, we report that capture induced blotches formation within 4-5 seconds. The blotches disappeared after anesthesia dispersed the pigment cells and reappeared after electrical stimulation. Subsequently, combining immunofluorescence, transmission electron microscopy and chemical sympathectomy, we found blotches formation results from activation of catecholaminergic neurons below the pigment layer. Finally, the in vitro incubation and intraperitoneal injection of norepinephrine (NE) induced aggregation of chromatosomes and lightening of body color, respectively, suggesting that NE, a neurotransmitter released by catecholaminergic nerves, mediates blotches formation. Our results demonstrate that acute stress response-induced neuronal activity can drive rapid changes in body color, which enriches our knowledge of physiological adaptations in coral reef fish.

Concurrent warming and browning eliminate cold-water fish habitat in many temperate lakes.

Cold-water species in temperate lakes face two simultaneous climate-driven ecosystem changes: warming and browning of their waters. Browning refers to reduced transparency arising from increased dissolved organic carbon (DOC), which absorbs solar energy near the surface. It is unclear whether the net effect is mitigation or amplification of climate warming impacts on suitable oxythermal habitat (<20 °C, >5 mgO/L) for cold-loving species because browning expands the vertical distribution of both cool water and oxygen depletion. We analyzed long-term trends and high-frequency sensor data from browning lakes in New York's Adirondack region to assess the contemporary status of summertime habitat for lacustrine brook trout. Across two decades, surface temperatures increased twice as fast and bottom dissolved oxygen declined >180% faster than average trends for temperate lakes. We identify four lake categories based on oxythermal habitat metrics: constrained, squeezed, overheated, and buffered. In most of our study lakes, trout face either seasonal loss (7 of 15) or dramatic restriction (12 to 21% of the water column; 5 of 15) of suitable habitat. These sobering statistics reflect rapid upward expansion of oxygen depletion in lakes with moderate or high DOC relative to compression of heat penetration. Only in very clear lakes has browning potentially mitigated climate warming. Applying our findings to extensive survey data suggests that decades of browning have reduced oxythermal refugia in most Adirondack lakes. We conclude that joint warming and browning may preclude self-sustaining cold-water fisheries in many temperate lakes; hence, oxythermal categorization is essential to guide triage strategies and management interventions.

A shift in habitat use patterns of brown trout (Salmo trutta): A behavioural response to macrophyte removal.

Mass development of macrophytes is an increasing problem worldwide and they are frequently removed where they are in conflict with local waterway users. Yet, macrophytes can provide important refuge and nursery habitats for fish. Little is known about the consequences of macrophyte removal for fish behavioural space use and habitat selection. We hypothesised that macrophyte removal would affect brown trout (Salmo trutta) movement during the partial removal of the aquatic plant Juncus bulbosus (L.) in an oligotrophic impounded Norwegian river.We tagged 94 brown trout and tracked them using passive acoustic telemetry for 10 months and mapped the cover of J. bulbosus. Trout behavioural patterns were quantified as space use (utilisation areas 50% and 95%) which was linked to habitat use and selection for J. bulbosus. Removal of J. bulbosus influenced space use of brown trout by reducing the core utilisation area by 22%. Habitat use and selection were likewise influenced by removal with increased use and selection of areas with low J. bulbosus cover (<25%) with corresponding reduction in high J. bulbosus cover (>25-75%). Finally, diurnal differences in space use and habitat use were found, with 19% larger utilisation areas at night and higher use of areas with low J. bulbosus during daytime. Yet, all effect sizes were relatively small compared to the size of the study area. This research provides a detailed case study on the effects of macrophyte removal on fish behavioural patterns in a section of a large Norwegian river with macrophyte mass development. We found no large effects of removal on trout behaviour but noted an increased use of areas with low macrophyte cover. This research is relevant for water managers and policy makers of freshwater conservation and provides a template for using acoustic telemetry to study the effects of macrophyte removal on fish.

Male lake char release taurocholic acid as part of a mating pheromone.

The evolutionary origins of sexual preferences for chemical signals remain poorly understood, due, in part, to scant information on the molecules involved. In the current study, we identified a male pheromone in lake char (Salvelinus namaycush) to evaluate the hypothesis that it exploits a non-sexual preference for juvenile odour. In anadromous char species, the odour of stream-resident juveniles guides migratory adults into spawning streams. Lake char are also attracted to juvenile odour but have lost the anadromous phenotype and spawn on nearshore reefs, where juvenile odour does not persist long enough to act as a cue for spawning site selection by adults. Previous behavioural data raised the possibility that males release a pheromone that includes components of juvenile odour. Using metabolomics, we found that the most abundant molecule released by males was also released by juveniles but not females. Tandem mass spectrometry and nuclear magnetic resonance were used to identify the molecule as taurocholic acid (TCA), which was previously implicated as a component of juvenile odour. Additional chemical analyses revealed that males release TCA at high rates via their urine during the spawning season. Finally, picomolar concentrations of TCA attracted pre-spawning and spawning females but not males. Taken together, our results indicate that male lake char release TCA as a mating pheromone and support the hypothesis that the pheromone is a partial match of juvenile odour.

First report of Myxobolus neurofontinalis (Bivalvulida: Myxobolidae) infecting anadromous Brook Trout from Prince Edward Island, Canada.

OBJECTIVE: During routine histological examination of tissues from mortality events of anadromous Brook Trout Salvelinus fontinalis from Prince Edward Island (PEI), Canada, myxospores consistent with Myxobolus were observed infecting the central nervous system. The objective of this study was to identify the species of Myxobolus infecting the nervous system of anadromous Brook Trout from PEI, Canada. METHODS: Myxospore morphology, small subunit (SSU) ribosomal DNA (rDNA) sequence data, and histology were used to identify myxospores isolated from infected Brook Trout. RESULT: Myxospore measurements from the PEI samples matched those reported in the description of Myxobolus neurofontinalis from North Carolina. A 1057-bp fragment of the SSU rDNA from myxospores collected from Brook Trout in PEI was identical to an isolate of M. neurofontinalis (MN191598) collected previously from the type locality, New River basin, North Carolina. Histological sections confirmed infections were intercellular in the central nervous system. Minimal host response was observed, with only sparse mononuclear inflammatory infiltrates present at the periphery of and within dispersed myxospores, suggesting that infections are not pathogenic to Brook Trout. CONCLUSION: Myxospores were identified as M. neurofontinalis, which was previously described from the central nervous system of Brook Trout from the New River basin, North Carolina, USA. This constitutes the first time M. neurofontinalis has been documented outside of the New River basin in North Carolina.

Environmental variation associated with overwintering elicits marked metabolic plasticity in a temperate salmonid, Salvelinus fontinalis.

Poleward winters commonly expose animals, including fish, to frigid temperatures and low food availability. Fishes that remain active over winter must therefore balance trade-offs between conserving energy and maintaining physiological performance in the cold, yet the extent and underlying mechanisms of these trade-offs are not well understood. We investigated the metabolic plasticity of brook char (Salvelinus fontinalis), a temperate salmonid, from the biochemical to whole-animal level in response to cold and food deprivation. Acute cooling (1°C day-1) from 14°C to 2°C had no effect on food consumption but reduced activity by 77%. We then assessed metabolic performance and demand over 90 days with exposure to warm (8°C) or cold winter (2°C) temperatures while fish were fed or starved. Resting metabolic rate (RMR) decreased substantially during initial cooling from 8°C to 2°C (Q10=4.2-4.5) but brook char exhibited remarkable thermal compensation during acclimation (Q10=1.4-1.6). Conversely, RMR was substantially lower (40-48%) in starved fish, conserving energy. Thus, the absolute magnitude of thermal plasticity may be masked or modified under food restriction. This reduction in RMR was associated with atrophy and decreases in in vivo protein synthesis rates, primarily in non-essential tissues. Remarkably, food deprivation had no effect on maximum oxygen uptake rates and thus aerobic capacity, supporting the notion that metabolic capacity can be decoupled from RMR in certain contexts. Overall, our study highlights the multi-faceted energetic flexibility of Salvelinus spp. that likely contributes to their success in harsh and variable environments and may be emblematic of winter-active fishes more broadly.

Mechanisms of PVP-functionalized silver nanoparticle toxicity in fish: Intravascular exposure disrupts cardiac pacemaker function and inhibits Na+/K+-ATPase activity in heart, but not gill.

Polyvinylpyrrolidone-functionalized silver nanoparticles (nAgPVP) are popular in consumer products for their colloidal stability and antimicrobial activity. Whole lake additions of nAgPVP cause long term, ecosystem-scale changes in fish populations but the mechanisms underlying this effect are unclear. We have previously shown that in fish, nAgPVP impairs cardiac contractility and Na+/K+-ATPase (NKA) activity in vitro, raising the possibility that heart dysfunction could underlie population-level exposure effects. The goal of this study was to determine if nAgPVP influences the control of heart rate (fh), blood pressure, or cardiac NKA activity in vivo. First, a dose-response curve for the effects of 5 nm nAgPVP on contractility was completed on isometrically contracting ventricular muscle preparations from Arctic char (Salvelinus alpinus) and showed that force production was lowest at 500 µg L-1 and maximum pacing frequency increased with nAgPVP concentration. Stroke volume, cardiac output, and power output were maintained in isolated working heart preparations from brook char (Salvelinus fontinalis) exposed to 700 µg L-1 nAgPVP. Both fh and blood pressure were elevated after 24 h in brook char injected with 700 µg kg body mass-1 nAgPVP and fh was insensitive to modulation with blockers of ß-adrenergic and muscarinic cholinergic receptors. Na+/K+-ATPase activity was significantly lower in heart, but not gill of nAgPVP injected fish. The results indicate that nAgPVP influences cardiac function in vivo by disrupting regulation of the pacemaker and cardiomyocyte ionoregulation. Impaired fh regulation may prevent fish from appropriately responding to environmental or social stressors and affect their ability to survive.

Spatial asynchrony and cross-scale climate interactions in populations of a coldwater stream fish.

Climate change affects populations over broad geographic ranges due to spatially autocorrelated abiotic conditions known as the Moran effect. However, populations do not always respond to broad-scale environmental changes synchronously across a landscape. We combined multiple datasets for a retrospective analysis of time-series count data (5-28 annual samples per segment) at 144 stream segments dispersed over nearly 1,000 linear kilometers of range to characterize the population structure and scale of spatial synchrony across the southern native range of a coldwater stream fish (brook trout, Salvelinus fontinalis), which is sensitive to stream temperature and flow variations. Spatial synchrony differed by life stage and geographic region: it was stronger in the juvenile life stage than in the adult life stage and in the northern sub-region than in the southern sub-region. Spatial synchrony of trout populations extended to 100-200 km but was much weaker than that of climate variables such as temperature, precipitation, and stream flow. Early life stage abundance changed over time due to annual variation in summer temperature and winter and spring stream flow conditions. Climate effects on abundance differed between sub-regions and among local populations within sub-regions, indicating multiple cross-scale interactions where climate interacted with local habitat to generate only a modest pattern of population synchrony over space. Overall, our analysis showed higher degrees of response heterogeneity of local populations to climate variation and consequently population asynchrony than previously shown based on analysis of individual, geographically restricted datasets. This response heterogeneity indicates that certain local segments characterized by population asynchrony and resistance to climate variation could represent unique populations of this iconic native coldwater fish that warrant targeted conservation. Advancing the conservation of this species can include actions that identify such priority populations and incorporate them into landscape-level conservation planning. Our approach is applicable to other widespread aquatic species sensitive to climate change.