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Recent toxicity studies of stormwater runoff implicated N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-quinone) as the contaminant responsible for the mass mortality of coho salmon (Oncorhynchus kisutch). In the wake of this discovery, 6PPD-quinone has been measured in waterways around urban centers, along with other tire wear leachates like hexamethoxymethylmelamine (HMMM). The limited data available for 6PPD-quinone have shown toxicity can vary depending on the species. In this study we compared the acute toxicity of 6PPD-quinone and HMMM to Brook trout (Salvelinus fontinalis) fry and fingerlings. Our results show that fry are ∼3 times more sensitive to 6PPD-quinone than fingerlings. Exposure to HMMM ≤ 6.6 mg/L had no impact on fry survival. These results highlight the importance of conducting toxicity tests on multiple life stages of fish species, and that relying on fingerling life stages for species-based risk assessment may underestimate the impacts of exposure. 6PPD-quinone also had many sublethal effects on Brook trout fingerlings, such as increased interlamellar cell mass (ILCM) size, hematocrit, blood glucose, total CO2, and decreased blood sodium and chloride concentrations. Linear relationships between ILCM size and select blood parameters support the conclusion that 6PPD-quinone toxicity is an outcome of osmorespiratory challenges imposed by gill impairment.

This study investigates the effect of taxifolin and arabinogalactan premixed with dihydroquercetin (Lavitol V) at different concentrations on the quality changes of trout soup at 4 ± 1°C for 31 days. Shelf life studies included physiochemical, sensory, and microbiological quality measures. The shelf lives of the fish soups were extended for 2–4 and 7–10 days with taxifolin and Lavitol V, respectively, with significant variations (p < 0.05), the longest shelf life corresponding to Lavitol V for 31 days. The highest TBA and TVB-N were obtained for the control as 3.72 mg MA/kg and 11.21 mg/100 g, respectively. Therefore, Lavitol V has a good potential for future applications in seafood preservation. [ABSTRACT FROM AUTHOR]

The Lake Huron fish community is comprised of many non-native species, including the piscivorous Pacific salmonids chinook salmon Oncorhynchus tshawtscha, coho salmon Oncorhynchus kisutch, and rainbow trout Oncorhynchus mykiss. The only abundant native piscivorous salmonid is the lake trout Salvelinus namaycush. Since 1980, there has been a steady decline in the biomass of the prey fishes these salmonids consume. Considering the collapse of alewife Alosa pseudoharengus in 2003, there has been growing concern that lake trout will be outcompeted by the non-native salmonids. Paramount to understanding this concern is determining the diet overlap between salmonids and how the overlap has shifted with changes in prey abundance. Here, stable isotope analyses (δ13C, δ15N) from lipid-extracted muscle tissues were compared among salmonids revealing large percentages of lake-wide isotopic niche overlap. Comparisons of these isotopes from salmonid scale samples taken before and after the alewife collapse revealed a shift in the diets of chinook salmon that now overlap with lake trout. Given the strong competitiveness of chinook salmon, this result is concerning for the management of the native lake trout. [ABSTRACT FROM AUTHOR]

In Québec, Canada, brook charr (Salvelinus fontinalis) is the most sought-after species for recreational fisheries, which makes it economically important. To improve population monitoring and better anticipate climate change impacts on brook charr, bioenergetics models can be useful. The objective of this research was to evaluate the performance of a resident brook charr Wisconsin Energy Budget (WEB) model applied to an anadromous strain under two salinity treatments. Growth and food consumption were predicted by the model and compared to the observed values obtained after a 60 day experiment in the laboratory on fish reared in fresh or brackish water. Predictions for fish reared in fresh water better estimated growth rate and consumption than for fish reared in brackish water, for which growth was overestimated and consumption was underestimated. Overall, these results suggest that there is a difference for the WEB model's predictions depending on the salinity and that observed food consumption is predicted more accurately than growth. [ABSTRACT FROM AUTHOR]

Salmonid fishes provide an important indicator of climate change given their reliance on cold water. We evaluated temporal changes in the density of stream-dwelling brook trout (Salvelinus fontinalis) from surveys conducted over a 36-year period (1988–2023) by the Maryland Department of Natural Resources in Eastern North America. Nonparametric trend analyses revealed decreasing densities of adult fish (age 1+) in 19 sites (27%) and increases in 5 sites (7%). In contrast, juvenile fish (age 0) densities decreased in 4 sites (6%) and increased in 10 sites (14%). Declining adult brook trout trends were related to atmospheric warming rates during the study period, and this relationship was stronger than the effects of land use change or non-native brown trout. In contrast, juvenile fish trends generally increased with elevation but were not related to air temperature trends or land use change. Our analysis reveals significant changes in several brook trout populations over recent decades and implicates warming atmospheric conditions in population declines. Our findings also suggest the importance of temperature for adult survival rather than recruitment limitation in brook trout population dynamics.

The Journal of Antimicrobial Chemotherapy published an article titled "Acknowledgement of referees," expressing gratitude to numerous individuals who assisted in assessing manuscripts over the past year. The list includes a diverse range of names from various cultural backgrounds, reflecting the global nature of the journal's contributors and reviewers. The document highlights the collaborative effort of these individuals in maintaining the quality and integrity of the journal's content. [Extracted from the article]

Simple Summary: We provide the first (preliminary) characterization of an immune-related gene (MHC-DAB) in trouts from Albania, an area harboring ecologically and genetically rich Salmonid diversity, including endemisms valuable for conservation. By genotyping 36 trout samples, we revealed generally high sequence/allelic polymorphism and remarkable distinctiveness (34 different sequences in total, most of which were exclusive to a taxon or population), also finding expected signals of historical positive selection. Interestingly, samples of lacustrine Belvica trout (Salmo ohridanus) showed contrasting results compared to other examined trout (S. trutta complex and S. letnica). Further investigations will provide a deeper understanding of the evolutionary mechanisms yielding the observed pattern of MHC-DAB diversity. Beyond evolutionary genetics, our outcomes offer useful information (namely immune-related adaptive genetic diversity) for conservation programs aimed at preserving the long-term viability of threatened wild populations. Due to their involvement in pathogen-mediated immune responses, the hypervariable genes of the Major Histocompatibility Complex (MHC) have become a paradigm for investigating the evolution and maintenance of genetic (adaptive) diversity, contextually providing insight into the viability of wild populations, which is meaningful for conservation. Here, we provide the first preliminary characterization of MHC polymorphism and evolution in trouts from Albania, a known hotspot of Salmonid diversity harboring ecologically and phylogenetically distinct native (threatened) taxa. Overall, 36 trout—including Lake Ohrid-endemic Salmo ohridanus and S. letnica, and both riverine and lacustrine native brown trout (the S. trutta complex) from the Drin-Skadar drainage—were genotyped at the MHC-DAB locus through next-generation amplicon sequencing. We identified 34 alleles (including 30 novel alleles), unveiling remarkable population/taxon MHC-DAB distinctiveness. Despite apparent functional (supertype) similarity, S. letnica and the S. trutta complex showed MHC-typical high sequence/allele diversity and evidence of global/codon-specific positive selection, particularly at antigen-binding sites. Conversely, deep-water-adapted S. ohridanus revealed unexpectedly reduced allelic/supertype diversity and relaxed selection. Evolution by reticulation and signals of trans-species polymorphism emerged from sequence genealogies. Further investigations and increased sampling will provide a deeper understanding of the evolutionary mechanisms yielding the observed pattern of MHC diversity across Albanian trout taxa and populations. [ABSTRACT FROM AUTHOR]

Fish stocking has been utilized for over a century to offset extirpations or declines in abundance of many native species. These historical declines and hatchery contributions have led to uncertainty surrounding whether many contemporary populations are native, introgressed with hatchery sources, or entirely of hatchery origin. Such uncertainty is problematic for the conservation of native biodiversity as it hampers management agencies' ability to prioritize the conservation of indigenous locally adapted populations. Fortunately, genetic and genomic tools have allowed researchers to investigate these questions, often through the use of clustering or assignment approaches that are predicated on identifiable and consistent divergence between native populations and hatchery sources. Here, we apply these methods to restriction‐site associated DNA (RAD) data from 643 brook trout (Salvelinus fontinalis) originating from 13 wild populations and an exogenous hatchery strain to investigate the extent of historical extirpations, hatchery contributions, and processes affecting population structure in a small area of the previously unglaciated Driftless Area of Wisconsin, USA. The results from these analyses suggest that wild populations in this region are genetically distinct even at small spatial scales, lack strong hydrologically associated population structure, rarely exchange gene flow, and have small effective population sizes. Furthermore, wild populations are substantially diverged from known hatchery strains and show minimal evidence of introgression in clustering analyses. However, we demonstrate through empirically informed simulations that distinct wild populations may potentially be hatchery‐founded and have since diverged through rapid genetic drift. Collectively, the apparent lack of hydrological population structure and potential for rapid drift in the Driftless Area suggest that many native populations may have been historically extirpated and refounded by stocking events. If this is the case, then commonly used genomic clustering methods and their associated model selection criteria may result in underestimation of hatchery introgression in the face of rapid drift. [ABSTRACT FROM AUTHOR]

Salmonid fishes provide an important indicator of climate change given their reliance on cold water. We evaluated temporal changes in the density of stream-dwelling brook trout (Salvelinus fontinalis) from surveys conducted over a 36-year period (1988–2023) by the Maryland Department of Natural Resources in Eastern North America. Nonparametric trend analyses revealed decreasing densities of adult fish (age 1+) in 19 sites (27%) and increases in 5 sites (7%). In contrast, juvenile fish (age 0) densities decreased in 4 sites (6%) and increased in 10 sites (14%). Declining adult brook trout trends were related to atmospheric warming rates during the study period, and this relationship was stronger than the effects of land use change or non-native brown trout. In contrast, juvenile fish trends generally increased with elevation but were not related to air temperature trends or land use change. Our analysis reveals significant changes in several brook trout populations over recent decades and implicates warming atmospheric conditions in population declines. Our findings also suggest the importance of temperature for adult survival rather than recruitment limitation in brook trout population dynamics. [ABSTRACT FROM AUTHOR]

River classification is a necessary starting point for understanding river ecosystems and developing management guidelines. Using GIS to analyse an Andean river basin, we compare the application of two geomorphic classification methods at the segment scale: The Geomorphic Units Survey Classification System (GUS) and the Functional Process Zones (FPZ). Segment definition follows a manual procedure in GUS and a semi‐automated procedure in FPZ. Our objective was to assess the relationship between geomorphology and fish assemblages' structure. Fish sampling was carried out in collaboration with participants from local indigenous Mapuche‐Pewenche communities. Non‐parametric multivariate statistical analyses were conducted in order to quantify and describe geomorphic patterns and whether fish assemblages responded consistently with river classifications. Both classifications give insight into the physical characteristics of rivers, such as slope and floodplain width, that make habitat available for different fish assemblages. The two methods provide results that consistently coincide in their identification of geographic distribution and main geomorphic variables of different river types (geomorphic types) throughout the river network. The variation of different river geomorphologies was associated with variation in fish assemblage structure. Geomorphic variables that best characterize the distribution pattern of fish assemblages were elevation, confinement and valley floor width. Confined rivers accommodated highly similar fish assemblages dominated by invasive trout (Salmo trutta and Oncorhynchus mykiss). Unconfined rivers located at higher elevations had greater temporal variability and were mainly composed of trout and native catfish Trichomycterus areolatus. Semiconfined rivers presented the highest geomorphic variability and were associated with high spatial and temporal variability of fish assemblages characterized by both native and non‐native species. The association between fish assemblages and fluvial geomorphology could help in prioritizing rivers for exotic fish species control. These findings should aid in restoring highly intervened Andean rivers and improving management techniques in basins with a variety of human activities. [ABSTRACT FROM AUTHOR]

Signs of early maturation have been revealed in 50% of underyearling males of brown trout from the Alatsoya River in Karelia: spermatocytes of the first- and second-orders and spermatids were observed in their testes. Precociously mature males began to be formed as early as the first summer of their life. Signs of early maturation have not been observed in females at age 0+. Gonads contained germ cells of opposite sexes in a very small number of individuals. [ABSTRACT FROM AUTHOR]

ABSTRACT Rainbow trout have been translocated from North America worldwide for more than 150 years, but have not reproduced in the wild in Europe in the last 100 years. In recent decades, several examples of successful reproduction have become public. This study reports scientific evidence of natural reproduction of North American rainbow trout (Oncorhynchus mykiss) in three alpine rivers in Bavaria, Germany. Eggs collected from spawning redds were determined to be rainbow trout in all study rivers. In the river Leitzach, where spawning was exclusively observed in spring, electrofishing revealed a balanced length‐frequency distribution with a high abundance of rainbow trout and a high proportion of individuals < 10 cm. In the rivers Isar and Traun, spawning was observed in winter and supposedly also in spring, according to local reports. Rainbow trout < 10 cm were also observed in these two rivers during electrofishing surveys but were less abundant than in the river Leitzach. Genetic factors and river‐specific environmental and climatic conditions may have contributed to the success or failure of rainbow trout reproduction. Effects of rainbow trout on native fish vary widely, from severe negative impacts to minimal niche overlap, so further studies of genetic and environmental factors that determine rainbow trout naturalisation are needed to better inform fisheries management. [ABSTRACT FROM AUTHOR]

The recent revision of Italian legislation on nature conservation has highlighted the pressing necessity of elucidating the native distribution range of managed species. A recent study by Antognazza et al. (Current and Historical Genetic Variability of Native Brown Trout Populations in a Southern Alpine Ecosystem: Implications for Future Management. Fishes 2023, 8, 411) provides insights into the native status of brown trout in the Lombardy Prealps, northern Italy, and advocates urgent conservation measures. However, the possible effect of historical and recent anthropogenic impacts was dismissed in the paper. Here, we present how human-mediated activities plausibly might contribute to the observed distribution of population genetic variation, considering both the available literature and ongoing "Mediterranean trout" stocking activities in the region. Implementing management strategies without clear scientific evidence poses significant risks to native biodiversity conservation. [ABSTRACT FROM AUTHOR]

The geographic ranges of slimy (Uranidea cognata) and mottled (Uranidea bairdii) sculpin overlap broadly across cool and coldwater streams and rivers in North America, where they can serve very important roles in fish community dynamics. The diet diversities of slimy and mottled sculpin were examined in early March (late winter) during eight out of nine years after the August 2007 catastrophic flooding in four streams to assess potential diet shifts as benthic invertebrate prey communities recovered post-flood. In total, 10,823 prey items, representing 39 invertebrate taxa and three fish taxa were identified from the stomachs of 532 slimy sculpins (present in Garvin Brook, Gilmore Creek, and Trout Run) and 179 mottled sculpins (present in Middle Fork Whitewater River). Only four prey taxa were consumed by sculpin in all streams: midge larvae and pupae (Diptera: Chironomidae), blackfly larvae and pupae (Diptera: Simuliidae), Hydropsyche caddisfly larvae (Trichoptera: Hydropsychidae), and Baetis mayfly nymphs (Ephemeroptera: Baetidae). Midges dominated diets of both slimy (61% of prey by number) and mottled (76%) sculpin across all years. Consequently, Shannon diversities of diets were typically low across all years and streams for slimy sculpin (annual site range 0.07–0.83) and across years for mottled sculpin (annual range 0.11–0.46). Diversities and taxa richness of slimy sculpin diets increased in Garvin Brook and Trout Run across the study years (driven by significant declines in midge dominance) but remained relatively unchanged for slimy sculpin in Gilmore Creek and mottled sculpin in the Middle Fork. Individual slimy and mottled sculpin differed significantly both in the numbers of taxa consumed per fish (<2 versus 2.5 taxa/fish, respectively) and in the numbers of individual prey per fish (11 versus 26 prey, respectively). Slimy sculpin in two streams displayed modest shifts in diets as benthic prey communities recovered during the 9-year period post-flood, whereas slimy and mottled sculpin in other streams displayed little to no changes in diets. Differing flood severity among streams may have produced the different responses observed in sculpin diets. [ABSTRACT FROM AUTHOR]

The 10th International Charr Symposium was held in Nikko, Japan, bringing together researchers from 11 countries to discuss the ecological and evolutionary studies of charr species, such as Arctic charr and lake charr. The symposium covered various topics, including migration patterns, feeding habits, and habitat differences among charr species. Researchers emphasized the importance of conservation and management of charr species worldwide, especially in the face of anthropogenic stressors like climate change and development. The symposium aimed to foster collaboration and knowledge-sharing among scientists to deepen our understanding of charr biology and contribute to their conservation. [Extracted from the article]

One of the greatest challenges for researchers today is understanding climate-change impacts on fish populations, particularly in vulnerable and understudied ecosystems such as the Canadian Arctic. Among other impacts, northern fishes will undergo thermal stress as atmospheric and sea surface temperatures are projected to rise globally. Models that consider how both environmental factors such as temperature and potential species interactions will impact population extirpation and species' range contraction can help project the future distribution of a species in the face of a warming climate. Here, we investigate the climate-change impacts of rising temperatures and the potential northward distributional shift of brook charr (Salvelinus fontinalis) on Arctic charr (Salvelinus alpinus), Canada's northernmost freshwater fish species. Specifically, we used a logistic regression model to establish baseline relationships between the current distribution of Arctic charr and the variables, degree-days (a key climate variable), geographical location, and brook charr occurrence. We developed the model applying the expected changes in degree-days to 2050 (25–50% increase from the average of 1976–2005) and 2080 (50–100% increase) while incorporating the historical distribution of Arctic charr to estimate the change in Arctic charr distribution over that time. We found that growing degree-days, longitude, latitude, and brook charr occurrences correctly classified 93% of Arctic charr historical occurrences in Canada. We estimate that in a high-carbon scenario, where degree-days are expected to increase by 50 to 100%, Arctic charr range is projected to decrease by 18% in Canada by 2051–2080 and decrease even further by 3% with the presence of brook charr. The Canadian high Arctic may provide refuge for Arctic charr, likely maintaining temperatures optimal for species persistence. Regardless, management that considers the climate stresses on Arctic charr populations will be important to preserve this highly valued resource that is pivotal for food security and traditional ways of life for northerners. [ABSTRACT FROM AUTHOR]

Migrations between spawning, growth and refuge habitats are critical for many fish species. Partially migratory populations of brook charr Salvelinus fontinalis (known as brook trout in the United States), in which a portion of the population migrates, were once widespread in the Great Lakes region of North America, but are now scarce and a rehabilitation priority. Great Lakes fishery managers lack a simple, non-lethal means to determine whether a large brook charr caught in a Great Lakes accessible stream reach represents a stream-resident fish or migrant that previously spent time foraging and growing in Great Lakes waters. We explored a relatively inexpensive and non-lethal stable isotope approach for documenting lake to stream movements of brook charr, using fin clips from brook charr captured in streams in fall prior to spawning. Using fin tissue from juvenile and adult coho salmon captured in Michigan tributaries to Lake Superior, we confirmed distinct stable isotope signatures indicative of prior stream and Lake Superior foraging. We identified brook charr from tributaries accessible to Lake Superior whose stable isotope signatures were similar to those of lake-captured brook charr, lake charr and splake (a brook charr–lake charr hybrid) and distinct from stable isotope signatures of brook charr in streams inaccessible to Lake Superior fishes, suggestive of an adfluvial migratory pattern. Brook charr from two streams had elevated δ15N values, indicative of previous residency in a downstream lake receiving water from a sewage treatment facility. Our findings demonstrate the utility of stable isotope analysis as a non-lethal technique for confirming adfluvial movements of brook charr from Lake Superior to streams. [ABSTRACT FROM AUTHOR]

Objective: Brook Trout Salvelinus fontinalis often outcompete and displace native salmonids in western North America. Due to the limitations of traditional removal methods, managers are implementing the Trojan Y Chromosome approach to extirpate nonnative Brook Trout populations. However, there are uncertainties of the comparative performance (i.e., survival, reproductive success) of YY‐male (MYY) fish and their wild counterparts. In addition, it is unclear how effective YY‐female (FYY) fish compare with MYY fish for extirpation of wild Brook Trout. To address these uncertainties, we modeled the time to extirpation of wild Brook Trout using 5 years of empirical data, assuming introductions of either MYY or FYY fish. Methods: Our simulations assumed varying stocking (0% to 100%) and removal (0% to 90%) scenarios. In addition, we evaluated model sensitivity to changes in the reproductive success and survival of MYY fish. Result: The simulations suggest that the average time to extirpation would be 14 years using MYY fish and 8 years for FYY fish, assuming 50% annual removal and 50% initial stocking of the wild Brook Trout abundance. Increasing removal and/or stocking levels resulted in reductions in extirpation times using either MYY or FYY fish. Sensitivity analyses indicated that the model was relatively insensitive to changes in the reproductive success and survival of MYY Brook Trout. Conclusion: Our results suggest that either MYY or FYY fish can be used to eradicate wild Brook Trout populations, but FYY fish are likely the most efficient means of eradicating nonnative Brook Trout in streams typical of western North America. Impact statementTrojan Y Chromosome fish show promising results as an additional control method for eradicating nonnative Brook Trout in southern Rocky Mountain streams. [ABSTRACT FROM AUTHOR]

A recent spontaneous return of a native brown trout population in Lake Laka and its tributaries followed the gradual recovery of the Bohemian Forest (Czechia) from atmospheric acidification. The lake had hosted a vibrant brown trout population in the first half of the 20th century, which then became extinct around the 1960s due to strong atmospheric acidification, peaking in the 1980s. However, since the 1990s, a gradual reversibility in acidification has occurred. This positive trend was delayed after tree dieback in the lake catchment in the 2000s. The following detailed monitoring showed recurrent critical periods of low pH and ANC, and elevated concentrations of ionic Al. This was especially in spring, lasting until the late 2010s. Electrofishing from 2020 to 2022 indicated suitable conditions for permanent fish populations. In comparison to previous electrofishing (2005–2010), brown trout colonised Lake Laka and formed a stable population in the lake outflow. Downstream of the lake, the fish abundance remained similar to those some ten years earlier. In contrast to the brown trout, the bullhead was only found in the stream below the lake, as it was unable to migrate to the upper areas due to natural barriers. The recovery of the brown trout population in Lake Laka after the acidification phase is an example of the successful restoration of a disturbed aquatic ecosystem under pristine conditions. [ABSTRACT FROM AUTHOR]

Among salmonids, brook charr, Salvelinus fontinalis has been gaining popularity in aquaculture. However, major limitations associated with opportunistic diseases that result from unstable egg and fry‐rearing conditions are experienced under intensive rearing conditions. Great losses in brook charr culture result from viral (e.g., infectious pancreatic necrosis, viral hemorrhagic septicemia virus), fungal (e.g., saprolegniosis), and bacterial (e.g., furunculosis, cold water disease, columnaris) diseases. Unfortunately, there is no effective treatment for viral diseases for brook charr, and the chemical disinfectants and antibiotics commonly used against bacterial and fungal infections are reaching their limits (pathogen resistance, microbial community disruption), making alternative and more sustainable rearing approaches essential to bolster aquaculture. In this regard, recent studies show that many microbial species (bacteria, archaea, viruses, eukaryotes‐like protozoa, and unicellular fungi) are essential from the earliest life stages for the proper development and growth of fish. Based on ecological theory and work on marine fish, it has been hypothesized that current aquaculture practices favor r‐strategic, opportunistic microbes that are detrimental to fish health and development. Consequently, to ensure the success and sustainability of brook charr farming, a new aquaculture paradigm involving recirculating aquaculture systems (RAS) that select a K‐enriched, specialized microbial community as a preventive measure against those microbial diseases is a very promising avenue. In this review, after introducing brook charr biology, the role of microbes in brook charr rearing and the general problems of disease and low fry survival due to an imbalance in the microbial community will be discussed. Various curative and prophylactic treatment methods currently used to control these diseases and their impact on microbial ecology will be covered, and we will conclude with the rationale of microbial ecology management and its effectiveness in promoting fry survival through disease prevention. To our knowledge, this is the first literature review addressing the promises of managing microbial ecology in a sustainable way in the brook char industry. [ABSTRACT FROM AUTHOR]

Hybridisation is a complex process that begins with mating. Females have more to lose with each hybrid fertilisation than males, so they should avoid it. Even if females choose con‐specific males as preferred mates, they often cannot control which additional males release sperm during spawning. Polyandry is ubiquitous and may result in hetero‐specific sperm competition between males of different species. In such cases, cryptic female choice (the ability to bias paternity towards certain males under sperm competition) is the last line of defence to prevent hybridisation of her eggs and is highly adaptive if it enables con‐specific sperm preference. Such seems to be the case with the hybridisation of Atlantic salmon (Salmo salar) and brown trout (S. trutta) in their native Europe. Under hetero‐specific sperm competition, hybrid fertilisations in these fish are reported to be reduced via ovarian fluid‐mediated cryptic female choice. It is not known, however, whether the strength of this mechanism is dependent on reinforcement and thus, the historical sympatry/allopatry of hybridising populations. Brown trout are one of the world's worst invasive species. Ecological impacts arise through competition with other species (e.g. Galaxids in the southern hemisphere, Oncorhynchus in western North America). Eastern North America contains native salmonids that evolved in the absence of brown trout but have gametes that are compatible. The 140 ‐year‐old brown trout invasion of Newfoundland is ground zero to study these potential interactions. Their relatively low spread rate across the island may be the result of inherent poor productivity, but data suggest it could also be a function of hybridisation with native Atlantic salmon and brook char (Salvelinus fontinalis). [ABSTRACT FROM AUTHOR]

The recent miniaturisation of implantable temperature recording tags has made measuring the water temperatures fish experience in the wild possible, but there may be a body size‐dependent delay in implanted tag response time to changes in external temperature. To determine whether fish body size affects the response rate of implanted temperature tags, we implanted 20 Salvelinus fontinalis (127–228 mm fork length (FL), 15.1–120.4 g) with temperature recording tags and subjected them to rapid temperature changes (±8°C in less than 2 seconds) in the laboratory. We found that thermal transfer rates, and the lag in temperature tag response rate, was positively correlated with fish size, but the direction of temperature change (colder or warmer) had no significant effect. In fish exposed to a slower rate of temperature change (2°C h−1) implanted tags did not show a response lag. Understanding the limitations of this important technology is crucial to determining the utility of the data it produces and its ability to accurately measure fish thermal experience in the wild. [ABSTRACT FROM AUTHOR]

Introduced species may exhibit variations in their preferred climatic niches between their native and introduced ranges, which can have important implications for the transferability of distribution models. In the Himalayan ecoregion, little is known about the geographic distribution and climatic niche overlap between native and introduced cold‐water species. Here, we used the COUE (centroid shift, overlap, unfilling, and expansion) framework to explore the invasive potential of rainbow (Oncorhynchus mykiss) and brown (Salmo trutta fario) trout and corresponding climatic niche overlap with native snow trout (Schizothorax plagiostomus and Schizothorax richardsonii) in the Indus and Ganges River basins. Although we found more stability in the climatic niche for O. mykiss (93%) than S. trutta (58%), both species do not conserve their climatic niches in this region (p > 0.05). S. trutta has expanded more toward new environmental conditions (42%) compared to O. mykiss (7%). However, there are still available environmental gaps that O. mykiss and S. trutta can potentially occupy in the future. There was a higher overlap in climatic niches between S. plagiostomus and O. mykiss and between S. richardsonii and S. trutta. Observed shifts in climatic niches of these introduced species can negatively affect the transferability of distribution models, which may underestimate the assessments of habitat suitability for introduced trout in the Himalayas. Our study demonstrates that the information on climatic niche dynamics can inform the model‐building process and improve the transferability and predictive performance to better assess vulnerability of sensitive habitats to introduced species in the Himalayas and elsewhere. [ABSTRACT FROM AUTHOR]

Unprecedented warm river temperatures in July 2023 in Labrador, a subarctic region of Canada, were the highest since monitoring began (1994–2023) and ranged from 19.4°C (Hunt River) to 22.5°C (Eagle River). Incipient lethal water temperatures were exceeded for adult Atlantic salmon and brook trout (≥25°C) on 14 days in five of seven rivers and Arctic charr (≥24°C) on 17 days in six of seven rivers. Consequently, Labrador had the greatest number of angling restrictions and closures in 2023. Recent warming serves as a warning to fishery managers of regions historically unaffected by heat waves of the need to prepare action plans that mitigate the effects of a warming climate on fishes. [ABSTRACT FROM AUTHOR]

The spatial configuration of thermal habitats constrains the thermoregulatory performance of ectotherms. Thermal landscapes also vary through time, which is particularly relevant in seasonal environments such as temperate lakes. Indeed, elevated temperatures in the epilimnion of dimictic lakes during summer could substantially reduce the use of this habitat by cold‐stenothermic fish during the stratified period. The main objective of this study was to evaluate whether thermal habitat fragmentation in stratified lakes modulates accessibility to resources that brook charr, Salvelinus fontinalis, which is a mobile consumer, can track across seasons. More specifically, we hypothesize that reduced access to the littoral habitat during summer enhances foraging opportunities in this habitat during winter. We used an automatic acoustic telemetry system offering full coverage of the lake to continuously record brook charr locations across seasons, and we estimated zoobenthos abundances in the littoral habitat using image processing and semi‐automatic classification. While brook charr concentrate in the metalimnion of the pelagic habitat in summer, most individuals in winter shift to a shallow bay that is unexploited in summer due to thermal constraints. In this habitat, zoobenthos abundance is more than twice as high at the end of the summer compared to littoral habitats close to the thermal refuge in the pelagic habitat. Surprisingly, brook charr showed strong within‐lake site fidelity between two consecutive summers, which suggests that spatial memory could be a key driver of seasonal habitat use in this lacustrine population. Overall, our results suggest that thermal barriers create fragmentation between littoral and pelagic habitats that in turn produces resource opportunities that brook charr can track across seasons. [ABSTRACT FROM AUTHOR]

Brook Trout (Salvelinus fontinalis) populations have experienced marked declines throughout their native range and are presently threatened due to isolation in small habitat fragments, land use changes, and climate change. The existence of numerous, spatially distinct populations poses substantial challenges for monitoring population status (e.g., abundance, recruitment, or occupancy). Genetic monitoring with estimates of effective number of breeders (Nb) provides a potentially powerful metric to complement existing population monitoring, assessment, and prioritization. We estimated Nb for 71 Brook Trout habitat units in mid‐Atlantic region of the United States and obtained a mean Nb of 73.2 (range 6.90–493). Our modeling approach tested whether Nb estimates were sensitive to differences in habitat size, presence of non‐native salmonids, base flow index, temperature, acidic precipitation, and indices of anthropogenic disturbance. We found significant support for three of our hypotheses including the positive influences of available habitat and base flow index and negative effect of temperature. Our results are consistent with presently observed and predicted future impacts of climate change on populations of this cold‐water fish. Importantly, these findings support the use of Nb in population assessments as an index of relative population status. [ABSTRACT FROM AUTHOR]

Slow and sustainable intermittent swimming has recently been described in several Centrarchid fishes, such as bluegill and largemouth bass. This swimming behavior involves short periods of body‐caudal fin undulation alternating with variable periods of coasting. This aerobic muscle powered swimming appears to reduce energetic costs for slow, sustainable swimming, with fish employing a "fixed‐gear" or constant tailbeat frequency and modulating swimming speed by altering the length of the coasting period. We asked if this swimming behavior was found in other fish species by examining volitional swimming by brook trout in a static swimming tank. Further, we employed muscle mechanics experiments to explore how intermittent swimming affects muscle power output in comparison to steady swimming behavior. Brook trout regularly employ an intermittent swimming form when allowed to swim volitionally, and consistently showed a tailbeat frequency of ~2 Hz. Coasting duration had a significant, inverse relationship to swimming speed. Across a range of slow, sustainable swimming speeds, tailbeat frequency increased modestly with speed. The duration of periods of coasting decreased significantly with increasing speed. Workloop experiments suggest that intermittent swimming reduces fatigue, allowing fish to maintain high power output for longer compared to continuous activity. This study expands the list of species that employ intermittent swimming, suggesting this behavior is a general feature of fishes. Research Highlights: This is the first analysis of muscle function during intermittent swimming in a salmonid. Intermittent muscle activity reduces fatigue during extended bouts of aerobic, sustained swimming. [ABSTRACT FROM AUTHOR]

Objective: Native inland trout conservation efforts rely on physical barriers to exclude nonnative salmonids from target habitats. We used genetic techniques to evaluate a series of natural waterfalls for their potential to serve as barriers to prevent nonnative salmonids from entering a proposed reintroduction area for federally threatened Greenback Cutthroat Trout Oncorhynchus virginalis stomias. Methods: Genetic samples were collected from nonnative Brook Trout Salvelinus fontinalis at 11 sampling reaches above and below natural waterfalls (height: ~1–3 m under base flow conditions) along a 33‐km segment of Colorado's upper Cache la Poudre River near the outflow of the proposed reintroduction area. To evaluate whether upstream movement of Brook Trout is restricted by any of these waterfalls, we characterized longitudinal trends in genetic diversity along the river corridor and examined patterns of genetic differentiation and population structure in relation to waterfall locations using a panel of microsatellites. Result: We found no evidence that the waterfalls served as complete movement barriers for nonnative Brook Trout based on genetic clustering analyses, estimates of population differentiation, and longitudinal genetic patterns. Our multilocus assessment did not identify alleles restricted to downstream reaches, and the river segment was genetically homogenized. Conclusion: Our evaluation suggests that the existing waterfalls do not fully prevent upstream movement by nonnative Brook Trout, and thus barrier modification would be needed to establish an isolated Greenback Cutthroat Trout population in the proposed wilderness area. Impact statementGenetic analyses suggested that a series of natural waterfalls do not act as sufficient barriers for isolating a proposed Greenback Cutthroat Trout reintroduction area in Colorado, USA. Barrier modification or construction would be necessary to prevent invasion by nonnative salmonids. [ABSTRACT FROM AUTHOR]

Water temperature is recognised as a crucial variable in lotic ecosystems affecting the metabolism of aquatic organisms, with extremely high‐temperature events increasing the risk of mortality of various species. Impounding rivers to regulate flow and generate electricity is one of the causes of altered thermal regimes in river systems. This paper presents the results of a study to simulate the impact of reservoirs on downstream temperatures of the Tobique River, New Brunswick, Canada. CEQUEAU, a hydrological and water temperature model, was used to simulate and assess the flow and water temperature of the Tobique River from 1997 to 2020. It was coupled to a statistical model to generate water temperature at different depths in the reservoir. Results show that the CEQUEAU model was successfully calibrated for water temperature with an overall root mean square error of 1.7°C. Based on the results, when water is drawn from the lower parts of the reservoir, the mean water temperature downstream of the dam increases in winter and spring by ~1°C. The results of this paper provide insight into how dams can affect the incubation time of cold‐water species in eastern Canada. We calculated the hatching degree days of Atlantic salmon and Brook trout to evaluate the impact of dams on fry emergence. Results indicated that the hatching period of Atlantic salmon and Brook trout downstream of reservoirs may shorten under the influence of dams. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to assess the microbiological quality of rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis) from aquaculture farms located within the "Dolina Słupi" (Slupia Valley) Landscape Park, with a focus on regional sustainability practices. The research aims to evaluate water hygiene, the microbiological quality of feed, the prevalence of antibiotic-resistant bacteria, and their impact on the final quality of the farmed trout. This study seeks to contribute to the broader discourse on sustainable aquaculture by highlighting the importance of quality and risk management practices in maintaining food safety and environmental stewardship. Design/methodology/approach: The research employed a comprehensive microbiological analysis of samples collected from trout farms, including external and internal parts of trout, viscera, water, and feed. The study focused on identifying the presence of specific pathogens, such as Staphylococcus aureus, Escherichia coli, Salmonella spp., methicillin-resistant S. aureus, and vancomycin-resistant Enterococcus spp. The approach combined field sampling with laboratory testing to assess the hygienic conditions of the aquaculture environment and the quality of the final fish products. The research focuses on evaluating the microbiological quality of trout from aquaculture farms, with particular attention to local practices and their alignment with sustainability goals. Findings: The study revealed that the trout from the examined farms generally met good microbiological quality standards. Specifically, no methicillin-resistant S. aureus or vancomycin-resistant E. faecium and E. faecalis were detected, indicating effective risk management. However, Salmonella spp. were present in 30.5% of water samples, yet their presence did not significantly affect the contamination levels in fish samples. The highest S. aureus count was found on the skin of rainbow trout (1.5±101 cfu/g), while E. coli was detected on brook trout skin and viscera (11%). Enterococcus spp. were found in 17% of feed samples, but at low concentrations (<10 cfu/g). These results suggest that while overall microbiological quality is satisfactory, ongoing monitoring and adherence to good management practices are crucial for maintaining safety and quality in aquaculture. Research limitations/implications: One limitation of the research is the geographical focus on aquaculture farms within the "Dolina Słupi" Landscape Park, which may limit the generalizability of the findings to other regions or types of aquaculture systems. Future research could expand the scope to include a broader range of aquaculture environments and examine the long-term impact of sustainability practices on fish quality. Practical implications: The research underscores the critical role of continuous monitoring and rigorous quality management practices in aquaculture. The findings indicate that by implementing effective hygiene protocols and risk management strategies, aquaculture farms can achieve high safety standards for their fish products. These practices not only ensure product quality and consumer safety but also support the sustainability and economic viability of the aquaculture industry. Social implications: The study demonstrates that sustainable aquaculture enhances food security and environmental conservation. By promoting effective practices, it builds public trust in farmed fish, potentially influencing consumer behavior and supporting more sustainable industry practices. Originality/value: This paper contributes to the existing body of knowledge on sustainable aquaculture by providing empirical evidence on the microbiological quality of trout from farms in a specific regional context. It offers practical insights for industry professionals and consumers on optimizing quality and risk management to ensure safe and sustainable fish production. [ABSTRACT FROM AUTHOR]

This article presents the first recorded instance of Sphaerothecum destruens infection in a native North American fish species, the warpaint shiner. S. destruens is a pathogen that has been linked to disease in salmonids in North America and has spread to European cyprinids through the introduction of the invasive topmouth gudgeon. The parasite can have significant impacts, causing deaths in salmonids and leading to population declines in susceptible wild fish species. The article provides details on the microscopic characteristics of the infection in the warpaint shiner and raises concerns about the health of native cyprinid populations in North America. Further research is needed to understand the distribution and host range of S. destruens in freshwater fish in North America. [Extracted from the article]

Warming water temperatures as a result of climate change pose a major threat to coldwater organisms. However, the rate of warming is not spatially uniform due to surface‐ground‐water interactions and stream and watershed characteristics. Coldwater habitats that are most resistant to warming serve as thermal refugia and identifying their locations is critical to regional aquatic conservation planning. We quantified the thermal sensitivity of 203 streams providing current and potential habitat for brook trout (Salvelinus fontinalis) across nearly 1000 linear km of their native range in the southern and central Appalachian Mountains region, USA, and characterized their spatial variability with landscape variables available in the National Hydrography Dataset. Using the Bayesian framework, we calculated the maximum slope of the logistic function relating paired weekly mean air temperature and stream temperature as an index of stream thermal sensitivity. Streams differed greatly in thermal sensitivity and those with more resistant water temperature regimes (i.e., thermal refugia) were consistently characterized by southerly latitudes and groundwater input. Landscape variables derived from a principal component analysis explained 16% of the variation in thermal sensitivity, indicating that the existing landscape variables were modestly successful in explaining spatial thermal heterogeneity. Using our model and spatial interpolation, we predicted thermal sensitivity at 8695 stream segments potentially suitable for brook trout in the study region. Thermal refugia were more common southward presumably due to higher elevations, but elsewhere they were also clustered at finer spatial scales. Our analysis informs prioritizing habitat conservation and restoration of this native salmonid and other aquatic organisms that depend on coldwater habitats in a warming world. [ABSTRACT FROM AUTHOR]

Since the last century, the aquatic ecosystems of Tierra del Fuego have been impacted by the introduction of exotic species, among which the North American beaver Castor canadensis and salmonids stand out for their dispersion and abundance. This study is part of the project Strengthening Governance for the Protection of Biodiversity Through the Formulation and Implementation of the National Strategy on Invasive Alien Species, for the eradication of C. canadensis from the Isla Grande de Tierra del Fuego (IGTdF). This work aimed to evaluate the effect of beaver plantation removal on different aspects of the ichthyofauna of the IGTdF. Ichthyological sampling was carried out before and after the beaver ponds in six sites spread across the island. Three species of salmonids (Salmo trutta, Oncorhynchus mykiss and Salvelinus fontinalis) were captured, and an average increase of 43% in their abundance, changes in their diet, and differences in their energy density (higher or lower depending on the species) was observed after the removal of the beaver ponds. No native fish species were recorded before or after the removal of the beaver pond. The results suggest that the beaver ponds impact positively salmonid populations. [ABSTRACT FROM AUTHOR]

The microsomal metabolism of phenol (11 °C) over an annual reproductive cycle from June to December was studied using fall spawning adult brook trout (Salvelinus fontinalis). Hepatic microsomes were isolated from three male and three female fish each month. Incubations were optimized for time, cofactor concentration, pH, and microsomal protein concentration. The formation of phase I ring-hydroxylation metabolites, i.e., hydroquinone (HQ) and catechol (CAT), was quantified by HPLC with dual-channel electrochemical detection. Sample preparation and chromatographic conditions were optimized to achieve the separation and sensitivity required for the analysis of these labile products. Biotransformation of phenol over a range of substrate concentrations (1 to 150 mM) was quantified for the calculation of Michaelis–Menten constants (Km and Vmax) for each month. Results indicate a nearly equal production of HQ and CAT among males and females in late June. At the peak of maturity in October, there was an approximate ten-fold greater production of ring-hydroxylation metabolites noted in females in comparison with males on a total liver basis. In vitro phase II biotransformation of phenol glucuronidation was assessed by determining the Michaelis–Menten constants (Km, Vmax) using brook trout hepatic microsomes over a range of substrate concentrations (1 to 60 mM). Initially, there were no significant differences in the glucuronide rate of formation (pmol/min/mg protein) or total capacity (nmol/min/liver) between females and males. At the peak of maturation, the maximum rate of glucuronide formation was 4-fold less in females; however, the total capacity was 2-fold less in females due to the increased liver size in the females. The alterations in biotransformation coincided with increases in the hepatic and gonadal somatic indices and with changes in plasma hormone concentrations. These experiments provide insight into the metabolic deactivation of xenobiotics and to provide data for the prediction of altered hepatic biotransformation rates and pathways during the reproductive cycle. [ABSTRACT FROM AUTHOR]

Objective: Hybridization between native and nonnative fishes represents a global threat to biodiversity. Understanding how hybridization changes in response to management actions is critical to evaluating the efficacy of conservation efforts. Methods: We quantified changes in levels of hybridization between Yellowstone Cutthroat Trout Oncorhynchus virginalis bouvieri and Rainbow Trout Oncorhynchus mykiss in the South Fork Snake River watershed, where a multipronged approach has been implemented to protect the evolutionary distinctiveness of one of the last remaining large‐river populations of Yellowstone Cutthroat Trout. Result: Over a 20‐year period, we observed an increase in the number of sample reaches without hybrids in the South Fork Snake River watershed; however, contrasting patterns were noted in main‐stem and tributary reaches. Through time, hybrid abundance increased at main‐stem reaches of the South Fork Snake River below Palisades Dam but decreased in tributaries. Efforts to reduce hybridization in spawning tributaries, including both suppression and selective passage weirs, were effective at preventing the expansion of hybridization in resident and migratory populations. Multimodel inference was used to understand factors affecting levels of hybridization, and year, sampling reach, and the interaction thereof was identified as the best‐fit model but explained only a small percentage of the overall variation, suggesting that other factors not captured in our model were driving patterns in hybridization. Conclusion: Changes in hybridization in the South Fork Snake River watershed are likely the result of multiple processes, namely management actions to reduce Rainbow Trout and hybrids in tributaries, as well as demographic changes in Rainbow Trout in the main‐stem river below Palisades Dam. Our results suggest that Yellowstone Cutthroat Trout populations in the South Fork Snake River watershed have not experienced widespread interspecific hybridization with Rainbow Trout but that proactive management will be necessary to ensure long‐term conservation. Impact statementOver the past 20 years, hybridization between introduced Rainbow Trout and native Yellowstone Cutthroat Trout in the South Fork Snake River watershed has declined in spawning tributaries because of management actions but increased in select main‐stem river reaches because of Rainbow Trout population growth. [ABSTRACT FROM AUTHOR]

Wildlife reintroduction is an important conservation tool for threatened species, yet identifying appropriate source populations poses a challenge. In particular, the possibility of outbreeding depression is cited as a constraint limiting the range of candidate source populations for translocation. When multiple source lineages are mixed during reintroduction, genetic monitoring is necessary to evaluate whether sources contribute equally to subsequent generations and whether they are interbreeding as expected. Moreover, statistical analysis of genetic data should account for complex life histories that might affect the timescale of admixture and genetic drift. Here, we use samples collected over a 23-year period and a stochastic age-structured model to analyze the genetic mixing process in reintroduced Brook Trout (Salvelinus fontinalis) populations in the Southern Appalachians. Each restored population was seeded with two to three source populations. Previous research inferred reproductive isolation between source populations leading to a proposal of splitting the species into multiple taxa. In contrast, we found patterns of ancestry that were consistent with random mating and no advantage for one source lineage over any other. Brook Trout from different source streams are mixing as expected in the restoration sites. This result does not support the hypothesis that Brook Trout in the Southern Appalachian Mountains includes several distinct species. Mixing different sources from the same watershed seems to be an effective way to increase genetic diversity of reintroduced populations while minimizing risk to source populations. [ABSTRACT FROM AUTHOR]

In Japan, stocked chum salmon (Oncorhynchus keta) fry may have become the perfect prey for non-native brown trout (Salmo trutta), which are popular targets of anglers. If this is the case, fry stocking which is intended to boost commercial fishing may be helping to sustain the populations of an invasive predator. We used dietary and biochemical analyses to examine whether brown trout quickly restore their nutritional status following wintertime declines by preying upon chum salmon fry that are stocked in spring. We targeted six rivers in Hokkaido, Japan, three with fry stocking and three without. Changes in brown trout condition factor, triglyceride contents in muscle and serum, serum insulin-like growth factor-1 (IGF-1; an indicator of short-term growth), and docosahexaenoic acid (DHA; an essential fatty acid abundant in fish) content in muscle were examined between before stocking and during the stocking period in the six rivers. Dietary analysis showed that brown trout preyed on fry during the stocking period in all stocked rivers. Their nutritional status tended to be higher during the stocking period than before stocking in stocked rivers, but not in unstocked rivers. These results suggest that the massive stocking of chum salmon fry provides brown trout with the perfect prey to quickly restore their nutritional status and fuel increased growth; this may therefore be a controversial issue among stakeholders. [ABSTRACT FROM AUTHOR]

The in vitro biotransformation of phenol at 11 °C was studied using pre-spawn adult rainbow (Oncorhynchus mykiss) (RBT), brook (Salvelinus fontinalis) (BKT), and lake trout (Salvelinus namaycush) (LKT) hepatic microsomal preparations. The incubations were optimized for time, cofactor concentration, pH, and microsomal protein concentration. Formation of Phase I ring-hydroxylation and Phase II glucuronidation metabolites was quantified using HPLC with dual-channel electrochemical and UV detection. The biotransformation of phenol over a range of substrate concentrations (1 to 180 mM) was quantified, and the Michaelis–Menten kinetics constants, Km and Vmax, for the formation of hydroquinone (HQ), catechol (CAT), and phenylglucuronide (PG) were calculated. Species differences were noted in the Km values for Phase I enzyme production of HQ and CAT, with the following rank order of apparent enzyme affinity for substrate: RBT > BKT = LKT. However, no apparent differences in the Km for Phase II metabolism of phenol to PG were detected. Conversely, while there were no apparent differences in Vmax between species for HQ or CAT formation, the apparent maximum capacity for PG formation was significantly less in LKT than that observed for RBT and BKT. These experiments provide a means to quantify metabolic activation and deactivation of xenobiotics in fish, to compare activation and deactivation reactions across species, and to act as a guide for future predictions of new chemical biotransformation pathways and rates in fish. These experiments provided the necessary rate and capacity (Km and Vmax) inputs that are required to parameterize a fish physiologically based toxicokinetic (PB-TK) model for a reactive chemical that is readily biotransformed, such as phenol. In the future, an extensive database of these rate and capacity parameters on important fish species for selected chemical structures will be needed to allow the effective use of predictive models for reactive, biotransformation chemicals in aquatic toxicology and environmental risk assessment. [ABSTRACT FROM AUTHOR]

Brook trout (Salvelinus fontinalis) are a highly prized species found in lakes and streams throughout Ontario. A broadscale monitoring program (BsM) has been conducted in lakes throughout the province, in 5‐year cycles, which targets Salvelinus fontinalis populations. The objective of this study was to use the data gained from the BsM and establish a contemporary baseline on the variation of relative abundance and demographics of natural lake populations of S. fontinalis in Ontario. Additionally, given the variability in environmental conditions across the landscape, an objective was to assess the factors, abiotic and biotic, that influence relative abundance among waterbodies. Over the three BsM cycles (2008–2022), 273 S. fontinalis waterbodies were assessed, some multiple times, and 124 were unique populations. S. fontinalis were sampled in 112 of these unique lakes. In total, 7487 S. fontinalis were caught and 5372 were fully sampled (length, weight, and age assessed). The mean catch‐per‐unit‐effort (CPUE) in all waterbodies was 1.4 (0.12 standard error) S. fontinalis per net gang. There was not a significant trend in CPUE over the three BsM cycles nor did CPUE vary significantly among BsM cycles at the provincial scale, but CPUE varied significantly among fisheries management zones (FMZs). Multiple variables were examined to explain the variation in CPUE across the province; a negative association with species diversity was the only variable considered significant. Furthermore, S. fontinalis were more associated with the relative abundance of small cyprinids (i.e., chubs and shiners) and negatively associated with centrarchids, smelt, and other game species. Mean growth potential was greater for males than females but not significantly, whereas longevity favored females. Growth potential and parameters were similar between sexes within FMZs but varied among FMZs. Mean survival among these populations was 25.7%, ranging from 15.2% to 45.6%, with a mean instantaneous mortality of 1.41. This study provided a contemporary assessment of the current range and variability in relative abundance population dynamics of S. fontinalis in lakes within Ontario. This provides a benchmark to assess changes with the pending stressors of climate change and human expansion across the landscape. [ABSTRACT FROM AUTHOR]

Understanding recruitment, the process by which individuals are added to a population or to a fishery, is critical for understanding population dynamics and facilitating sustainable fisheries management. Important variation in recruitment dynamics is observed among populations, wherein some populations exhibit asymptotic productivity and others exhibit overcompensation (i.e., compensatory density‐dependence in recruitment). Our ability to understand this interpopulation variability in recruitment patterns is limited by a poor understanding of the underlying mechanisms, such as the complex interactions between density dependence, recruitment, and environment. Furthermore, most studies on recruitment are conducted using an observational design with long time series that are seldom replicated across populations in an experimentally controlled fashion. Without proper replication, extrapolations between populations are tenuous, and the underlying environmental trends are challenging to quantify. To address these issues, we conducted a field experiment manipulating stocking densities of juvenile brook trout Salvelinus fontinalis in three wild populations to show that these neighboring populations—which exhibit divergent patterns of density dependence due to environmental conditions—also have important differences in recruitment dynamics. Testing against four stock‐recruitment models (density independent, linear, Beverton‐Holt, and Ricker), populations exhibited ~twofold variation in asymptotic productivity, with no overcompensation following a Beverton‐Holt model. Although environmental variables (e.g., temperature, pH, depth, substrate) correlated with population differences in recruitment, they did not improve the predictive power in individual populations. Comparing our patterns of recruitment with classic salmonid case studies revealed that despite differences in the shape and parameters of the curves (i.e., Ricker vs. Beverton‐Holt), a maximum stocking density of about five YOY fish/m2 emerged. Higher densities resulted in very marginal increases in recruitment (Beverton‐Holt) or reduced recruitment due to overcompensation (Ricker). [ABSTRACT FROM AUTHOR]

The European Commission requested scientific and technical assistance in the preparation of a EU‐wide baseline survey of antimicrobial resistance (AMR) in bacteria from aquaculture animals. It is recommended that the survey would aim at estimating the occurrence of AMR in Aeromonas spp. isolated from Atlantic Salmon (Salmo salar), European seabass (Dicentrarchus labrax) and trout (Salmo trutta, Salvelinus fontinalis, Oncorhynchus mykiss) intended to consumption, at harvesting (at farm/slaughter), at the EU level and in addition, at estimating the occurrence and diversity of AMR of Escherichia coli, Enterococcus faecium, Enterococcus faecalis, Vibrio parahaemolyticus and Vibrio alginolyticus in blue mussel (Mytilus edulis) and Mediterranean mussel (Mytilus galloprovincialis) from production areas and at dispatch centres at the EU level. These technical specifications define the target populations, the sample size for the survey, sample collection requirements, the analytical methods (for isolation, identification, phenotypic susceptibility testing and further genotypic analysis of some of the bacteria targeted) and the data reporting requirements. The data to be reported by the EU Member States to support this baseline survey are presented in three data models. The results of the survey should be reported using the EFSA reporting system. This publication is linked to the following EFSA Journal article: http://onlinelibrary.wiley.com/doi/10.2903/j.efsa.2024.8896/full [ABSTRACT FROM AUTHOR]

Stream dewatering is expected to become more prevalent due to climate change, and we explored the potential consequences for brook trout (Salvelinus fontinalis) within a temperate forest ecosystem in eastern North America.We estimated fish density within stream pools (n = 386) from electrofishing surveys over 10 years (2012–2021) to compare a stream that exhibits episodic dewatering (Paine Run) against a stream of similar size that remains flow‐connected (Staunton River) within Shenandoah National Park, Virginia (U.S.A.). Annual surveys encompassed fluvial distances ranging from 2.6 to 4.4 km in each stream.Mean annual fish density (fish/pool m2) was not different between streams for juvenile or adult age classes, but spatial variation in density was greater in Paine Run for both age classes of fish. Paine Run also included a greater proportion of unoccupied pools than Staunton River and exhibited stronger spatial autocorrelation in fish density among nearby pools, suggesting dispersal limitation due to surface flow fragmentation.Fish density in pools increased during years with low summer precipitation, and this effect was observed in both streams but was stronger in Paine Run than Staunton River, further indicating the importance of fish movement into pools in response to low‐flow thresholds.Our results indicate the importance of pools as ecological refuges during low‐flow conditions and that episodic dewatering may affect extirpation risks for brook trout by sequestering more fish into fewer areas. Our findings also highlight the importance of hydrological variation within stream networks because downstream river gages could not predict the observed spatial heterogeneity in fish density or pool occupancy. [ABSTRACT FROM AUTHOR]

Population models are increasingly used to predict population‐level effects of chemicals. For trout, most toxicity data are available on early‐life stages, but this may cause population models to miss true population‐level effects. We predicted population‐level effects of copper (Cu) on a brook trout (Salvelinus fontinalis) population based on individual‐level effects observed in either a life‐cycle study or an early‐life stage study. We assessed the effect of Cu on predicted trout densities (both total and different age classes) and the importance of accounting for effects on the full life cycle compared with only early‐life stage effects. Additionally, uncertainty about the death mechanism and growth effects was evaluated by comparing the effect of different implementation methods: individual tolerance (IT) versus stochastic death (SD) and continuous versus temporary growth effects. For the life‐cycle study, the same population‐level no‐observed‐effect concentration (NOECpop) was predicted as the lowest reported individual‐level NOEC (NOECind; 9.5 µg/L) using IT. For SD, the NOECpop was predicted to be lower than the NOECind for young‐of‐the‐year and 1‐year‐old trout (3.4 µg/L), but similar for older trout (9.5 µg/L). The implementation method for growth effects did not affect the NOECpop of the life‐cycle study. Simulations based solely on the early‐life stage effects within the life‐cycle study predicted unbounded NOECpop values (≥32.5 µg/L), that is, >3.4 times higher than the NOECpop based on all life‐cycle effects. For the early‐life stage study, the NOECpop for both IT and SD were predicted to be >2.6 times higher than the lowest reported NOECind. Overall, we demonstrate that effects on trout populations can be underestimated if predictions are solely based on toxicity data with early‐life stages. Environ Toxicol Chem 2024;43:1662–1676. © 2024 SETAC [ABSTRACT FROM AUTHOR]

Understanding patterns of species abundance is essential for planning landscape‐level conservation. The complex hierarchies of dendritic ecosystems result in different levels of heterogeneity at distinct geographic scales. Species responses to dynamic environmental drivers may also vary spatially depending on their interactions with landscape features. Monitoring abundance by explicitly quantifying their spatial and temporal variation is important for strategic management.We analysed brook trout (Salvelinus fontinalis) count data collected from 173 sites in western North Carolina between 1989 and 2015. We developed a Bayesian hierarchical model that used single‐ and multi‐pass electro‐fishing data and characterized their respective capture probabilities. We quantified spatial variation using a multi‐scale process model representative of the nested stream habitats, and we investigated differences in population temporal trends and responses to seasonal weather patterns by space and life stage.Trout abundance was lower on the Atlantic slope of the Eastern Continental Divide than in the interior, on average, and the Atlantic slope juveniles were more adversely affected by high winter flows. However, Atlantic slope populations of both lifestages demonstrated positive temporal trends, whereas Interior juveniles demonstrated a negative trend. We found higher spatial variation than temporal variation in abundance when conditioned on the covariates, where the primary source of spatial heterogeneity was revealed at the segment level, compared to watershed or network levels.Our multi‐scale spatial model outperformed simpler models in abundance estimation and out‐of‐sample prediction. The inferred per‐pass capture probabilities indicated that single‐pass surveys were as efficient as multi‐pass surveys.Synthesis and applications. Our study suggested conservation priority should involve multiple criteria, including present‐day abundance, temporal trend and sensitivity to environmental drivers. Based on the inferred scale‐specific variations in trout abundance, we recommend that future surveys strategically combine single‐pass surveys with multi‐pass surveys to optimize abundance estimation. Our approach is widely applicable to other species and ecosystems occupying dendritic habitats. [ABSTRACT FROM AUTHOR]

Objective: Our objective was to compare wild and hatchery sourced Brook Trout Salvelinus fontinalis to determine the importance of source population on routine respiration rate (RRR), the major cost term in bioenergetic models. Methods: We evaluated intraspecific variation in RRRs of one hatchery and four wild Brook Trout populations. Hatchery fish were obtained from the Bowden State Fish Hatchery in Elkins, West Virginia, and were the basis for the previously published bioenergetics model for the species. Wild fish were obtained from four headwater streams in West Virginia. Using intermittent respirometry, we measured and analyzed RRRs sequentially at 20, 16, and 12°C. Measures on hatchery fish were censored to restrict the dataset to similar sizes and temperatures as used with the wild populations. We used a suite of mixed effects models and one linear model to compare RRRs of hatchery fish with wild fish, as well as to determine whether wild populations differed. Result: We found that the RRR of hatchery fish was double that of wild fish over the range of 12–20°C. Within the wild populations, the RRR of the Potomac drainage fish was lower than two of the three Ohio drainage populations despite all steams falling within 55 km of each other. Conclusion: Our findings suggest that selective pressures at the hatchery, as well as factors that influence thermal regimes in wild populations, likely influence RRR in Brook Trout. More research is needed to identify correlates related to intraspecific variation in fish respiration rates. Most fish bioenergetics models are not based on, or calibrated to, the specific population to which they are applied. Therefore, we encourage greater efforts be expended to calibrate and validate such models in the future. Impact statementBioenergetic models are widely used in fisheries management and science but are often not based on underlying measures for the fish population to which they are applied. Our results show differences in the primary cost term (respiration) among Brook Trout from hatchery and wild populations, as well as differences among wild populations over small spatial scales. Given their importance and widespread use in fisheries, we encourage greater efforts be expended to calibrate and validate bioenergetic models in the future. [ABSTRACT FROM AUTHOR]