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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]

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]

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]

Evaluating the efficacy of the use of Trojan male brook trout with two Y chromosomes (MYY) requires a better understanding of reproductive performance. We measured the reproductive performance of hatchery age-0 and age-1 MYY brook trout compared to hatchery XY males using laboratory crosses. Offspring of XY males had higher survival than offspring of age-1 MYY 1-day post-fertilization, but not offspring of age-0 MYY. We found no detectable differences in survival from eyed-egg to the juvenile-fry stage. However, size-at-age differed, where offspring of age-0 MYY were 3.6% smaller in length and 25.2% smaller in weight than those of XY males. For crosses fertilized by both MYY and XY males, we found that a significantly higher proportion of offspring within families were sired by MYY versus XY males. These results show, under controlled conditions, evidence for possible fitness advantage for MYY under sperm competition, but a possible fitness disadvantage associated with early growth of their offspring. Overall, our results hold promise for the use of MYY brook trout to serve as an effective eradication tool. [ABSTRACT FROM AUTHOR]

We applied an ensemble of climate warming models to an iconic protected landscape (Algonquin Park, Ontario) and the seasonal temperature profile model for lakes to assess changes in brook trout (Salvelinus fontinalis) thermal habitat volume (THV) among lakes of different sizes in 30-year periods under two climate warming scenarios (RCP 4.5 and 8.5). Bayesian beta regression models show that lake size (surface area) and morphometry (dynamic lake ratio) are important factors in THV loss. THV loss increases as a function of the dynamic lake ratio (transition from bowl-shaped to dish-shaped lakes). The magnitude of this effect depends on the lake size category and the RCP scenario. Small (<100 ha) and medium (100–500 ha) dish-shaped lakes are projected to have greater THV loss in 2071–2100 (60%–100% of brook trout THV under RCP 8.5; 40%–70% under RCP 4.5) than large lakes (>500 ha) of similar shape. Climate warming projections for the balance of this century, regardless of the RCP category, will result in the loss of brook trout THV in lakes that range widely in size and morphometry. [ABSTRACT FROM AUTHOR]

Brook charr is a cold-water species which is highly sensitive to increased water temperatures, such as those associated with climate change. Environmental variation can potentially induce phenotypic changes that are inherited across generations, for instance, via epigenetic mechanisms. Here, we tested whether parental thermal regimes (intergenerational plasticity) and offspring-rearing temperatures (within-generational plasticity) modify the brain transcriptome of Brook charr progeny (fry stage). Parents were exposed to either cold or warm temperatures during final gonad maturation and their progeny were reared at 5 or 8 °C during the first stages of development. Illumina Novaseq6000 was used to sequence the brain transcriptome at the yolk sac resorption stage. The number of differentially expressed genes was very low when comparing fry reared at different temperatures (79 differentially expressed genes). In contrast, 9,050 differentially expressed genes were significantly differentially expressed between fry issued from parents exposed to either cold or warm temperatures. There was a significant downregulation of processes related to neural and synaptic activity in fry originating from the warm parental group vs fry from the cold parental one. We also observed significant upregulation of DNA methylation genes and of the most salient processes associated with compensation to warming, such as metabolism, cellular response to stress, and adaptive immunity. [ABSTRACT FROM AUTHOR]

In the context of climate change, it is crucial to understand whether animals that have been domesticated and (or) selected maintain their abilities to adapt to changes in their thermal environment. Here, we tested how selection for absence of early sexual maturation combined with better growth performance may have impacted thermal resistance and gene expression response in the presence of thermal stress in brook charr Salvelinus fontinalis (Mitchill, 1814). We performed temperature challenge tests on brook charr 0+ juveniles and studied the expression of genes involved in the response to oxidative stress, in synthesis of heat shock proteins, or involved in regulation of apoptosis, in heart and liver tissues. Juveniles from the selected lineage had a higher thermal resistance than controls and a loss of equilibrium occurred on average 1 °C above what was observed for the controls. The relative expressions of catalase and HSP70 were significantly higher in juveniles from the selection program. Overall, thermally sensitive fish were characterized by low mass and length and lower relative expressions of genes associated with stress response. Our results indicate that selection for traits of interests may be indirectly related to the significant lineage effect on growth in early stages of development. [ABSTRACT FROM AUTHOR]

Invasion of non-native fishes threatens freshwater biodiversity worldwide. Yet, detailed estimates of population demography for invasive species, such as population size and body size, are rarely integrated in evaluating aquatic community responses. Our study capitalised on detailed brook trout population demographic data collected for a replicated whole lake ecosystem experiment involving experimental harvesting of exotic brook trout in nine mountain lakes. We applied environmental DNA (eDNA) metabarcoding and morphological taxonomy to examine the response of crustacean zooplankton and macroinvertebrate communities to gradients in brook trout effective density and lake elevation. Density-dependent effects of brook trout on crustacean zooplankton and macroinvertebrate communities were detected even decades after their first introductions (between 1926 & 1980). However, they were moderated by environmental factors such as elevation, lake maximum depth and dissolved organic carbon. Elevation was important in structuring crustacean zooplankton and macroinvertebrate community composition. While there were differences in explanatory variables when describing communities characterized by eDNA metabarcoding and morphological taxonomy, the principal environmental factors that structured the communities were similar. Our paper highlights persisting density-dependent impacts of exotic trout on invertebrate communities even decades after first introduction, and it considers the conservation implications for lake restoration. [ABSTRACT FROM AUTHOR]

Understanding rain, ground, and surface water interactions in riparian zones is essential for hydrologic and environmental management. The novelty of this study lies in its revelation of isotopic shifts and consequent evaluation of hydrologic pathways and processes within the forested riparian zones of three distinct streams, valleys, and riparian systems in a carbonate-sandstone incipient karst landscape. We collected water samples from three southeastern Minnesota catchments: Trout Brook, Crystal Creek, and Bridge Creek. A Picarro L2130i was used to measure δ18O for oxygen, and δD for deuterium in units of ‰ (per mil). We estimated the global meteoric line for the study sites, built upon aquifer age dating, and explored aquifer transit time for the study sites using a simple seasonal amplitude model. The results showed small amplitudes for 2020 and 2021, suggesting that bedrock aquifer water was the primary source water with a mean core transit time greater than 10 years. All three catchments were different but had similar bedrock valley types and riparian sediment. The primary driving factor was the seasonal precipitation input mixing with existing water. In a normal to wetter year, the isotopic data showed larger amplitude shifts between seasons with trendlines that adjusted depending on the temperature of the new water additions. The proposed approach is valuable in revealing complex hydrologic processes and pathways and can contribute extensively to the planning and management of karst riparian systems. [ABSTRACT FROM AUTHOR]

Critical thermal maximum (CTmax) is widely used to measure upper thermal tolerance in fish but is rarely examined in embryos. Upper thermal limits generally depend on an individual's thermal history, which molds plasticity. We examined how thermal acclimation affects thermal tolerance of brook trout (Salvelinus fontinalis) embryos using a novel method to assess CTmax in embryos incubated under three thermal regimes. Warm acclimation was associated with an increase in embryonic upper thermal tolerance. However, CTmax variability was markedly higher than is typical for juvenile or adult salmonids. [ABSTRACT FROM AUTHOR]

Salmonids have been introduced globally as a food source and recreational fishing target. In Japan, brown trout (Salmo trutta) and brook trout (Salvelinus fontinalis) were introduced in the 19th century and have since spread. In many headwater streams, native white‐spotted charr (Salvelinus leucomaenis) are thought to be experiencing negative impacts from these species. The current study examined foraging behavior, microhabitat use, and diet overlap of these three species in Kamikochi, Nagano Prefecture: one of Japan's premier mountain areas. In Kamikochi, many spring‐fed headwater streams are currently dominated by these invasive salmonids and white‐spotted charr have declined drastically over the last half century. Underwater video analysis revealed that while total foraging rates and foraging modes were similar between the three species, brook trout and white‐spotted charr foraged benthically more frequently than brown trout. Microhabitat water depth and flow velocity were similar between species, and fish size had a positive effect on water depth and flow velocity in all three species. Diet analysis indicated that brook trout and white‐spotted charr diets were nearly identical, comprised primary of aquatic invertebrates, while brown trout preyed on a mix of terrestrial and aquatic invertebrates, as well as amphibians and fish. These results indicate that in Kamikochi, the decline of white‐spotted charr is likely most influenced by direct competition with brook trout for prey resources. However, brown trout likely also predate on juvenile white‐spotted charr, while also possibly causing a foraging niche shift of white‐spotted charr, and have ecosystem‐level impacts due to predation on terrestrial prey. [ABSTRACT FROM AUTHOR]

Understanding how metabolic costs change in relation to increasing temperature under future climate changes is important to predict how ectotherms will be affected across the globe. In fish, whole body respiration is traditionally used to estimate aerobic performance via an organism's minimum and maximum oxygen consumption rates. However, mitochondria play a crucial role in the aerobic cascade and may be a useful surrogate of aerobic performance. To test whether whole body oxygen consumption and mitochondrial capacity are correlated, we estimated whole body metabolic and mitochondrial respiration rates (using permeabilized red muscle fibres) in brook trout (Salvelinus fontinalis (Mitchill, 1814)) at 10, 15, and 20 °C. Standard metabolic rate increased with acclimation temperature, while maximum rates were less sensitive. All mitochondrial respiration rates increased with acclimation temperature, suggesting that red muscle mitochondrial preparations may correlate to the minimal metabolic demands in this species. When expressed as relative rates of electron flow, the red muscle fibres showed no effect of temperature on mitochondrial coupling efficiency. However, there was a pattern of declining capacity to augment respiration via complex II with increasing temperature with a concomitant increase in the capacity of the phosphorylating system relative to maximal rates of mitochondrial electron flow. [ABSTRACT FROM AUTHOR]

Climate‐induced expansion of invasive hybridization (breeding between invasive and native species) poses a significant threat to the persistence of many native species worldwide. In the northern U.S. Rocky Mountains, hybridization between native cutthroat trout and non‐native rainbow trout has increased in recent decades due, in part, to climate‐driven increases in water temperature. It has been postulated that invasive hybridization may enhance physiological tolerance to climate‐induced thermal stress because laboratory studies indicate that rainbow trout have a higher thermal tolerance than cutthroat trout. Here, we assessed whether invasive hybridization improves cardiac performance response to acute water temperature stress of native wild trout populations. We collected trout from four streams with a wide range of non‐native admixture among individuals and with different temperature and streamflow regimes in the upper Flathead River drainage, USA. We measured individual cardiac performance (maximum heart rate, "MaxHR", and temperature at arrhythmia, "ArrTemp") during laboratory trials with increasing water temperatures (10–28°C). Across the study populations, we observed substantial variation in cardiac performance of individual trout when exposed to thermal stress. Notably, we found significant differences in the cardiac response to thermal regimes among native cutthroat trout populations, suggesting the importance of genotype‐by‐environment interactions in shaping the physiological performance of native cutthroat trout. However, rainbow trout admixture had no significant effect on cardiac performance (MaxHR and ArrTemp) within any of the three populations. Our results indicate that invasive hybridization with a warmer‐adapted species does not enhance the cardiac performance of native trout under warming conditions. Maintaining numerous populations across thermally and hydrologically diverse stream environments will be crucial for native trout to adapt and persist in a warming climate. [ABSTRACT FROM AUTHOR]

Complexity of addressing cumulative effects that vary in space and time, especially for species occupying large ranges, makes conservation and recovery of populations difficult. In Alberta, declines of all three native stream trout species led to them being listed as species at risk. We developed a novel, semi‐quantitative cumulative effects modelling process to quantify threats using stressor‐response curves with a single common response scale, wherein inputs were determined for each population, and outputs were used to create population‐specific recovery action hypotheses to inform management. Using a case study of bull trout recovery in Rocky Creek, Alberta, we tested these hypotheses using a before–after control‐impacted design. Recovery actions positively affected bull trout, and the modelling approach provided insight into threats (sedimentation and angling effort) that most likely limited the population. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The taxonomic status of native trout species of the Marmara and Aegean Sea drainages is evaluated and three species, Salmo duhani, S. coruhensis and S. brunoi sp. nov. , are recognized. Salmo brunoi, a new species, is described from the Nilüfer River, a tributary of the Susurluk River. It is distinguished by a general brownish body color in life; few black spots (fewer than 60) on the body, generally scattered on the back and the upper part of the flank, rarely in the median part; few (fewer than 40) and small (smaller than pupil) red spots on the body, scattered on the median part and lower half of the flank; a number of black and red spots not increasing with size in both sexes; a long adipose fin (adipose-fin height 8–9% SL); a short distance between adipose-fin and caudal-fin (12–14% SL); and a short anal fin (anal-fin height 12–15% SL). Salmo brunoi sp. nov. is separated from the rest of the Marmara and Aegean trouts of Anatolia based on genome-wide distributed 187.385 unlinked SNP markers. According to the best of the authors' knowledge, whole genome data is used for the first time here to characterize a new species of trout. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Climate change is increasing global atmospheric temperatures, which can reduce abundance and cause range shifts in species that are sensitive to warming. However, fine‐scale thermal heterogeneity can drive highly variable local responses to climate change, especially in freshwater environments that differ in groundwater inputs and geomorphology.We used temperature data collected during 2012–2021 from 10 small, pristine streams in eastern Canada to characterise thermal variation at a small spatial scale (~25 km2). We then used relationships between daily air and stream temperatures to reconstruct stream temperature since 1980, and assessed how thermal variation influenced the phenology and growth of brook trout (Salvelinus fontinalis).Air–stream temperature relationships varied considerably among streams despite their close proximity, with predicted summer temperatures differing up to 9.5°C between warmer rainfall‐dominated streams and cooler groundwater‐dominated streams. Rainfall‐dominated streams warmed more than twice as fast as groundwater‐dominated streams across all seasons since 1980, with nearly four‐fold differences in rates of warming evident during summer months. Fine‐scale thermal heterogeneity also shaped brook trout phenology, as juveniles in rainfall‐dominated streams were estimated to hatch and emerge much later (~70 and 40 days, respectively) and experience faster phenological shifts than in groundwater‐dominated streams. Relationships between juvenile brook trout size and accumulated degree‐days were positive, but slopes differed over two‐fold and did not vary systematically based on stream hydrology, suggesting more idiosyncratic impacts of warming on early growth.Collectively, our study illustrates how species responses to climate change in freshwater environments can be consistent in direction but vary substantially in magnitude owing to the influence of groundwater. Future climate change is likely to increase the thermal stress experienced by brook trout populations in warmer rainfall‐dominated streams, while potentially benefiting those in groundwater‐dominated streams where current temperatures are often suboptimal.Observed differences in the rates and ecological impacts of warming among streams suggest that fine‐scale thermal variation must be considered when forecasting effects of future climate change on stream fish population dynamics. [ABSTRACT FROM AUTHOR]

An analysis of multidecadal (1994–2021) temperature and dissolved oxygen profiles revealed a generally consistent pattern of response to climate change among oligotrophic lakes in the Adirondack Mountain region. Regional increases in annual average air temperature (0.34 ± 0.09 °C per decade) were accompanied by warming and thinning of epilimnia, cooling and expansion of hypolimnia, and declining hypolimnetic dissolved oxygen. Lakes in this region are recovering from acidification and we hypothesize that associated increases in dissolved color have caused greater heat trapping in the surface layer and earlier onset of stratification. The combined effects of increasing air temperature and declining water clarity resulted in stronger thermal stratification and greater oxygen depletion in bottom waters. Although the lakes were clustered in a relatively small geographic region, we found considerable interlake variability in trends for epilimnetic temperature (−0.06 to 0.66 °C decade−1), hypolimnetic temperature (−0.44 to 0.31 °C decade−1), and hypolimnetic oxygen (−55 to 0.7 µg L−1 year−1). Lake bathymetry was a key variable determining the sensitivity of lakes to climate effects on oxygen resources. Lakes with thin hypolimnia exhibited low dissolved oxygen concentrations, which were exacerbated by strengthening of vertical temperature gradients and earlier onset of stratification. Photic depths are decreasing faster than mixing depths such that declines in photosynthesis may contribute to lower dissolved oxygen in deeper layers. We predict that with climate warming, fewer Adirondack lakes will provide suitable habitat for cold water fisheries such as brook trout due to decreasing hypolimnetic oxygen. [ABSTRACT FROM AUTHOR]

Many salmonid species are particularly susceptible to chronic and acute temperature changes caused by global warming. We aimed to study the differences in metabolic and transcriptomic responses of a chronic heat stress on a control and selected (absence of early sexual maturation and growth) line of brook charr Salvelinus fontinalis (Mitchill, 1814). We exposed individuals to different temperatures for 35 days (15, 17, and 19 °C). High temperature reduced the growth rate (in length) and the Fulton condition factor. Both maximal metabolic rate and the aerobic scope were higher in fish reared at 17 °C, while they decreased in fish maintained at 19 °C. The relative gene expression of cytochrome c oxidase was lower at 19 °C than at 15 °C. The relative gene expressions of both liver and gill hsp90 was higher at the highest temperature. The standard metabolic rate, while not affected by temperature, was higher for the control line over the selected line. Only in the control line, the relative expression of catalase and of receptor of insulin-like growth factor-1 increased at 19 °C. Our results showed that the selected line was able to cope more effectively with the oxidative stress caused by the rise in temperature. [ABSTRACT FROM AUTHOR]

While it is well‐accepted that predation plays a key role in shaping both size structure and species composition in natural ecosystems, fine‐scale variation in predation risk within ecosystems has been largely neglected. The objective of this study was to use normalised size spectra (NSS) to investigate whether small‐scale spatial variation in predation risk (by fish) can modulate zooplankton community structure at the within‐lake level in a small temperate lake.We tested the difference in the NSS between two hydrologically well‐connected basins of a lake exhibiting contrasting thermal regimes. The first is a well‐mixed shallow basin (max. depth 2.5 m) that is inaccessible to brook charr (Salvelinus fontinalis) during summer because the temperature is too warm. The second is a deeper basin (max. depth 18 m) offering a thermal refuge during summer because of lake stratification. As a consequence of these differences in fish accessibility, the fishless basin should contain larger and more abundant zooplankters, inducing a change in NSS slope and height.Our results showed that both the zooplankton size structure and taxonomic composition were distinct in the two basins, with a higher proportion of small individuals and a higher abundance of zooplankton in the shallow basin compared to the deep one. Furthermore, following cooling of the epilimnion in late summer, the zooplankton communities of both basins exhibited a clear shift in size structure and species composition: in autumn, there were smaller individuals and larger proportions of Bosminidae and Daphniidae compared to colonial rotifers than in summer. These results suggest a potential effect of the change in the spatial distribution of brook charr which feed preferentially on large individuals, reducing the average body size of the zooplankton community.Our results show that predation risk by fish can induce a spatial and temporal variation in zooplankton community structure within small temperate lake ecosystems exhibiting contrasted thermal regimes. Other potential predators also influenced the zooplankton community structure, creating a complex interplay that has to be taken into account to disentangle ecological processes and predict their future changes. [ABSTRACT FROM AUTHOR]

The impact of rising atmospheric CO2 (pCO2atm) from anthropogenic activities on pH, dissolved inorganic carbon, carbonate mineral saturation, and aluminum (Al) speciation is evaluated for 18 northeastern USA lakes using polythermal, sliding activity reaction path models. pCO2atm was forced using two scenarios from the IPCC's Sixth Assessment Report in which pCO2atm attains either 600 or 1,100 ppm in 2,100. Results suggest pH will decrease 0.15 and 0.32 pH units, aCO32− ${a}_{\mathrm{C}{\mathrm{O}}_{3}^{2-}}$ will decrease 24% and 49%, and Ωaragonite will decrease 21% and 45%, respectively. These changes are of the same magnitude as those expected for the oceans. The effects of rising pCO2atm on sub‐lethal 20% effect concentrations (i.e., EC20) of Al for brook trout (Salvelinus fontinalis) are evaluated with the biotic ligand model, which indicates Al toxicity effects will increase as pH decreases. These changes could reverse gains in water quality and fisheries health achieved since implementation of the Clean Air Act. Plain Language Summary: Fossil fuel consumption, deforestation, and changing land use are all contributing to rising CO2 concentrations in the atmosphere. In addition to atmospheric warming and climate impacts, rising atmospheric CO2 will also promote acidification of ocean surface waters, which is expected to have detrimental effects on marine ecosystems. Much less is known about how rising atmospheric CO2 will impact terrestrial freshwaters such as lakes and streams. We developed reaction path models for 18 lakes from northeastern USA to investigate possible impacts of rising atmospheric CO2 and temperature on these systems. The models indicate that acidification of these lakes could be of similar magnitude to ocean acidification. The saturation state of these lakes with respect to the mineral aragonite, which is important for calcifying organisms, will also decrease. Finally, acidification will alter aluminum (Al) speciation, which could augment toxic effects from this metal on important sport fish like brook trout, possibly reversing gains made in water quality since implementation of the Clean Air Act decreased the input of strong acids via acid rain. Key Points: Rising atmospheric CO2 from anthropogenic activities will lead to acidification of lakes in the northeastern USA during the 21st centuryAcidification will alter Al speciation and lower concentrations required to cause a sub‐lethal response in 20% of the resident brook troutAnthropogenic‐sourced CO2 could reverse gains in lake water quality realized since implementation of the Clean Air Act [ABSTRACT FROM AUTHOR]

Salvelinus namaycush (Lake Trout) occur in the Canadian Maritime Provinces of New Brunswick and Nova Scotia, and are absent in Prince Edward Island. Lake Trout are assumed to be native in parts of New Brunswick, but their ancestry in Nova Scotia is unknown. Starting in 1886, stocking was used to spread Lake Trout across lakes in the Maritime Provinces to bolster existing populations and to create new fishing opportunities. The success of most stocking efforts was not well documented, and it is presumed that many of these efforts failed. After the early stocking from which some populations persist, little effort has been made to understand the distribution, stock structure, or ancestry of Lake Trout in this region. This review is a synthesis of Lake Trout distribution in the Canadian Maritime Provinces, including a comprehensive account of stocking history, proposed native population occurrence, and identification of populations with variable ancestry. At present, Lake Trout occur in 20 lakes in New Brunswick (19 confirmed and 1 potential), and 4 lakes in Nova Scotia (2 confirmed and 2 potential). Native Lake Trout may persist in 12 of 15 New Brunswick lakes and 3 of 9 Nova Scotia lakes that historically contained ancestral Lake Trout populations. Of these lakes with historical populations that persist to this day, 10 in New Brunswick and 1 in Nova Scotia were supplemented with introduced stock; therefore, only 2 lakes in New Brunswick and 2 in Nova Scotia are likely to still contain purely native Lake Trout. By improving the understanding of population structure and origins, this synthesis provides information that is critical for the effective management and conservation of native Lake Trout in the eastern Maritime region. [ABSTRACT FROM AUTHOR]

Insufficient knowledge about the occurrence and spread of non‐native fish in mountain regions has impeded effective management strategies worldwide. To address this gap, this study analysed over 1300 electrofishing surveys across 650 sites, encompassing a vast 7400 km2 area in the Eastern Alps. The primary objectives were to quantify the occurrence of non‐native species and predict their spread in different river types. Furthermore, the study estimated population sizes and biomass trends for over 150 sites that were surveyed multiple times between 2000 and 2020. Out of the 42 fish species in the study region, 11 were identified as non‐native. Notably, two invasive species of Union concern, Lepomis gibbosus and Pseudorasbora parva, increased their population sizes by 8% and 9% per year, over the past decades, supposedly supported by increasing water temperatures. Among the non‐native species relevant for recreational fishing, Oncorhynchus mykiss populations showed a significant increase of approximately 7% per year, Salmo trutta populations remained stable, and Salvelinus fontinalis populations experienced a notable decline of approximately 7.4% per year. These varying population trends may be attributed to disparities in stocking intensities, with S. fontinalis receiving minimal stocking compared to the other species. This study revealed that non‐native and invasive fish species are a relevant part of fish communities in mountain rivers. Non‐salmonid non‐natives thrive in warm rivers at lower elevations, whereas salmonid non‐natives consolidate in steeper habitats. Because rising temperatures in mountain rivers will accelerate the spread and growth of these species, this first quantification of the current extent will improve fish management strategies in mountainous areas. [ABSTRACT FROM AUTHOR]

Non-native species have numerous and significant, often negative, effects on amphibians, but that threat may be ameliorated if the native species is able to respond behaviourally to the non-native predators. We experimentally compared the behavioural response of tadpoles of the Ridged Tree Frog, Dryophytes plicatus , to cues from non-native Rainbow Trout, Oncorhynchus mykiss , to those to a native predator, the Short-tail Alpine Garter Snake, Thamnophis scaliger. Dryophytes plicatus tadpoles did not alter activity in response to cues from O. mykiss but increased activity in the presence of cues from T. scaliger , although it is possible this increase is related, at least in part, to the order of the presentation of the cues. The activity of D. plicatus tadpoles was higher in the absence of the vegetation than in its presence when exposed to predator cues, both T. scaliger and O. mykiss , but not in the control. In conclusion, our results show D. plicatus tadpoles alter their overall activity when exposed to cues from a native predator, T. scaliger , but not the non-native O. mykiss. These results may explain, in part, why D. plicatus can co-occur with T. scaliger but not O. mykiss. [ABSTRACT FROM AUTHOR]

In this paper, we review and synthesize trout management philosophy and policies for Black Hills streams in the states of South Dakota and Wyoming through the roles of hatcheries, fish stocking, and natural production from 1883 to 2023. We identified three specific fisheries management time periods (eras) in the Black Hills: (1) the early management–fry stocking era (pre‐1950), (2) the catchable‐trout stocking era (1950s to mid‐1990s), and (3) the integrated management era (mid‐1990s to present). The first era emphasized juvenile trout stocking, with little evaluation of effectiveness in terms of return to creel. The second era was characterized by greater emphasis on stocking catchable‐sized trout and a substantial increase in hatchery rearing capabilities. In the first two eras, instead of fish stocking being one of many potentially useful tools for managers of Black Hills streams, stocking was the dominant activity—leading and directing fisheries management rather than supporting it. By the third era, trout management began to embody a more encompassing and complex national ideology and philosophy that more fully considered ecology, including habitat improvement, natural reproduction of trout, defining the role of fish stocking, and understanding the relationship of trout to the depauperate native (nongame) fish fauna. We also discuss the three eras in the Black Hills in relation to national trends in trout management. In contrast to many other localities, the lack of any native salmonids and the lack of native game fish species have facilitated the development of valuable, self‐sustaining recreational fisheries in streams that support trout, with less concern for native species than in many areas with harvestable native fish species. The cultural ideology that brought western expansion of settlers to the Black Hills in search of gold, land, freedom, and prosperity was emboldened by a science‐based belief and confidence in technology and industry to rapidly shape lands and waters to improve the human condition. In part, the sculpting and shaping of Mount Rushmore symbolize that ideology. In the context of fisheries management in the Black Hills, the introduction of trout, development of stream fisheries, and investment in hatchery technology to produce catchable trout for an expanding tourist economy also exemplify that prevailing ideology, modulated by improved ecological understanding and an accompanying shift toward a more ecological management philosophy. [ABSTRACT FROM AUTHOR]

Urban streams are impacted by multiple anthropogenic environmental stressors that exert considerable pressure on resident fish populations. Species such as brook trout (Salvelinus fontinalis) are particularly vulnerable because urban environments typically limit the cold oxygenated water required by all life stages. To understand factors associated with native brook trout movement in urban streams, we monitored 20 radio-tagged individuals from late summer through the spawning season in autumn, and modelled how movement was influenced by body size and habitat. Tracking occurred in two adjacent streams that differed in forest cover and channelization. In both streams, brook trout mainly travelled upstream, particularly at the onset of the autumn spawning season. Larger individuals exhibited greater movements, and habitat complexity imposed stronger effects in larger individuals. Greater movements were made into locations of shallower depth and lower conductivity, although these factors were conflated with movement into upstream locations. This study addresses a fundamental knowledge gap in urban stream ecology by providing detailed information on the movement of a key indicator species of aquatic ecosystem health. [ABSTRACT FROM AUTHOR]

Fish invasions threaten native freshwater ecosystems worldwide, yet methods to map biodiversity in data-deficient regions are scarce. Rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta fario) have been introduced to the Himalayan ecoregion where they are sympatric with vulnerable native snow trout Schizothorax plagiostomus and Schizothorax richardsonii. We aim to evaluate potential habitat overlap among snow trout and non-native trout in the Indus and Ganges River basins, Himalayan ecoregion. We transferred maximum entropy (MaxEnt) models developed with spatially continuous freshwater-specific environmental variables to map the distribution of potentially suitable habitats for rainbow and brown trout in the Himalayas. We adopted a similar procedure to map suitable habitats for snow trout species. There were substantial habitat overlaps (up to 96%) among snow trout and non-native trout. Yet, the physiography of receiving basins could play a role minimizing the impacts of each non-native trout on native snow trout. We generate high-resolution classified stream suitability maps as decision support tools to help managers in habitat allocation and policy formation to balance recreational fisheries with conservation of snow trout. Our workflow can be transferred to other basins and species for mapping freshwater biodiversity patterns in species-rich yet data-poor regions of the world. [ABSTRACT FROM AUTHOR]

Smoking represents one of the oldest thermic processing methods of fish, and it was originally used to preserve fish for later meals, delaying spoiling. The objective of this study was to analyze the physicochemical and microbiological safety and quality of two traditionally smoked trout species (Oncorhynchus mykiss and Salvelinus fontinalis). We analyzed the effect of trout processed by traditional smoking, characterizing the samples according to the relationships existing between classical microbial analysis, physicochemical parameters, and the content of polycyclic aromatic hydrocarbons (PAHs). The microbial activity of the smoked fish was very low. Although traditional smoking implies high temperatures and direct exposure to the smoke, Benzo[a]pyrene, Benzo[b]fluoranthene, Benzo[k]fluoranthene, Dibenzo[a,h]anthracene, Benzo[g,h,i]perylene, and Indeno [1,2,3-cd]pyrene compounds had undetectable levels in the samples. The products obtained in this study did not exceed the maximum values imposed by EU legislation regarding the TVB-N values during the 30 days of the experiment. We conclude that traditionally smoked trout has many advantages in terms of quality and safety of the products. Thus, the obtained products are safe for consumption for at least 30 days after processing. [ABSTRACT FROM AUTHOR]

The highly polymorphic taxon European brown trout (genus Salmo) has high phenotypic plasticity, displaying a complex pattern of morphological and life-history variation, contributing to taxonomic confusion. Three main mitochondrial lineages (Adriatic, Mediterranean, and marmoratus) developed during the Pleistocene climatic events in the southern Alpine ecosystem. Here, the natural distribution of native brown trout S. trutta is controversial, complicated by introductions of the Atlantic strain. By investigating museum vouchers, this study aimed to retrace the historical presence of brown trout in the southern Alpine ecosystem before the beginning of mass introductions, which occurred since the middle of the 19th century. By examining the combination of historical and current genetic variability, this study aims to depict the actual impact of introductions of the introduced strain, increasing knowledge and informing conservation strategies and future management plans. The molecular approaches selected were: (i) sequencing of the mitochondrial control region and (ii) genotyping of the nuclear gene LDH-C1*. Vouchers dated the presence of the native Adriatic strain since 1821, while current genetic variability showed the widespread signature of introgression, a consequence of several decades of introductions. Focused plans to preserve local lineages are urgently needed, including short-term solution to avoid complete pauperization of this ecosystem. [ABSTRACT FROM AUTHOR]

Polyandrous mating systems result in females mating with multiple males, generating opportunities for strong pre‐mating and post‐mating sexual selection. Polyandry also creates the potential for unintended matings and subsequent sperm competition with hybridizing species. Cryptic female choice allows females to bias paternity towards preferred males under sperm competition and may include conspecific sperm preference when under hybridization risk. The potential for hybridization becomes particularly important in context of invasive species that can novelly hybridize with natives, and by definition, have evolved allopatrically. We provide the first examination of conspecific sperm preference in a system of three species with the potential to hybridize: North American native Atlantic salmon (Salmo salar) and brook char (Salvelinus fontinalis), and invasive brown trout (Salmo trutta) from Europe. Using naturalized populations on the island of Newfoundland, we measured changes in sperm swimming performance, a known predictor of paternity, to determine the degree of modification in sperm swimming to female cues related to conspecific sperm preference. Compared to water alone, female ovarian fluid in general had a pronounced effect and changed sperm motility (by a mean of 53%) and swimming velocity (mean 30%), but not linearity (mean 6%). However, patterns in the degree of modification suggest there is no conspecific sperm preference in the North American populations. Furthermore, female cues from both native species tended to boost the sperm of invasive males more than their own. We conclude that cryptic female choice via ovarian fluid mediated sperm swimming modification is too weak in this system to prevent invasive hybridization and is likely insufficient to promote or maintain reproductive isolation between the native North American species. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are predominant pollutants in the aquatic environment that can cause a variety of potentially toxic effects, affecting the entire ecosystem. PAHs were evaluated following the application of different heat treatments to fish meat by liquid chromatography (HPLC). The following polycyclic aromatic hydrocarbons were determined: acenaphthene, anthracene, benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(gy)pyrylene, chrysene, dibenzo(a,h)anthracene, phenanthrene, fluorene, fluoranthene, indeno(1,2,3-cd)pyrene, naphthalene and pyrene. The samples analyzed were from raw trout (Salvelinus fontinalis); fried in sunflower oil; fried in olive oil; fried with rapeseed oil; baked in the oven and fried in lard. The brook trout (Salvelinus fontinalis) was harvested from the Mărișel area, Cluj county. The highest values for the hydrocarbons analyzed from raw fish were for naphthalene (5.51±0.21) and benzo(a)anthracene (2.47±0.06). The trout fried in sunflower oil showed the highest values for anthracene (10.34±0.09) and pyrene (10.24±0.30) and Indeno(1,2,3-cd)pyrene was <0.05. Trout fried with rapeseed oil showed the highest values for anthracene (10.34±0.09), followed by pyrene (10.24±0.30) and indeno(1,2,3-cd)pyrene was below <0.05. Trout fried in olive oil showed very high values for pyrene (51.37±0.63) and fluoranthene (20.36±0.89) and dibenzo(a,h)anthracene was <0.05. According to this study, fish meat has the highest percentage of PAHs following the frying process. These compounds play a very important role in the ecosystem, therefore the most affected is the consumer due to the carcinogenic effect they can cause on the body. [ABSTRACT FROM AUTHOR]

Simple Summary: This study explores the use of alternative and non-harmful methods for monitoring endangered Mediterranean trout in small intermittent streams. Specifically, two visual survey techniques were compared: a visual survey from streambanks and an underwater visual survey using underwater cameras. The main objective was to assess the effectiveness of detecting patterns in fish occupancy in relation to a set of environmental factors. The comparison revealed that underwater camera surveys performed similarity to visual surveys from streambanks during low-flow regimes. However, visual surveys from streambanks were less effective during the highest flow regimes. The volume of pools and the percentage cover of submerged macrophytes were found to be significant environmental variables affecting fish detection probability using underwater cameras. On the other hand, the analysis of data from visual observations from streambanks indicated a clear impact of high turbulence rates on pool occupancy. In conclusion, these findings demonstrate the utility of visual methods in describing the occupancy patterns of Mediterranean trout in small streams. Monitoring the conservation status of endangered freshwater fish using less invasive methods poses challenges for ecologists and conservationists. Visual surveys have been proposed as an alternative to electrofishing, which is a standard methodology that can cause injuries, physiological stress and post-release mortality in organisms. To test the efficacy of visual methods, a study was conducted in an intermittent stream of Sardinia (Italy). Two visual methods were employed: a visual survey from streambanks (VSS) and an underwater visual survey (UVS) using cameras. The aims of this study were (1) to compare the effectiveness of these methods in detecting patch occupancy patterns and (2) to investigate the effect of environmental variables on the detection probability of Mediterranean native trout. Environmental variables characterizing pool habitats were recorded, and generalized linear models (GLMs) were employed to assess the correlation between these variables and trout presence/absence. GLM analysis revealed that UVS had higher detection probability with larger pool volume, whereas submerged macrophytes negatively affected detection probability. Detection from streambanks (VVS) was negatively affected by a high turbulence rate. In conclusion, our study suggests the utility of visual methods to describe patterns of patch occupancy of Mediterranean trout. However, methods can be differently affected by environmental variables. Therefore, monitoring programs using these methods should consider these factors to ensure a reliable description of within-stream trout distribution in intermittent streams. [ABSTRACT FROM AUTHOR]

Sustainable harvesting of wild populations relies on evidence‐based knowledge to predict harvesting outcomes for species and the ecosystems they inhabit. Although harvesting may elicit compensatory density‐dependence, it is generally size‐selective, which induces additional pressures that are challenging to forecast. Furthermore, responses to harvest may be population‐specific and whether generalizable patterns exist remains unclear.Taking advantage of Parks Canada's mandate to remove introduced brook trout Salvelinus fontinalis to restore alpine lakes in Canadian parks, we experimentally applied standardized size‐selective harvesting rates (the largest ~64% annually) for three consecutive summers in five populations with different initial size structures. Four unharvested populations were used as controls.At reduced densities, harvested and control populations exhibited similar density‐dependent increases in specific growth, juvenile survival and earlier maturation. However, size‐selective harvesting simultaneously induced changes to size and age structure that contrasted among harvested populations. Average body length decreased in three of five harvested populations, whereas it tended to increase in control populations over the 3 years. We also detected contrasting, population‐specific changes in body length variability and ultimately in length‐ and age‐at‐harvest in harvested populations but not controls.Overall, populations with smaller, more homogeneous body sizes, and living at high densities were most resilient to size‐selective harvesting, exhibiting the smallest change in size‐at‐age. In contrast, large‐bodied populations exhibited more substantial size‐structure changes following selective harvesting: large‐bodied populations experienced either stabilizing or disruptive pressures, when initial length variability was high or low, respectively.Synthesis and application. Our results show that within species, size‐selective harvesting inherently leads to more risk and uncertainty when harvesting populations with larger and more varied body sizes than smaller‐bodied populations with less range in body size. Our study supports prioritizing regulations that protect harvested populations with larger and more varied body sizes. Such a management strategy would reduce the likelihood of eliciting unpredictable or undesirable demographic changes to fish populations with these attributes. [ABSTRACT FROM AUTHOR]

A fundamental assumption of mark‐recapture studies is that individuals do not lose their marks or tags, because tag loss can lead to biased parameter estimates. Retention of 8‐mm full‐duplex and 12‐mm half‐duplex passive integrated transponder (PIT) tags implanted in the abdomen, opercular musculature, and dorsal sinus of age‐0+ hatchery male brook trout (Salvelinus fontinalis) was evaluated in the laboratory. Treatments included single‐ and double‐tagged fish. Survival, growth, and tag retention were monitored for 181–187 days for 640 tagged fish and 80 untagged controls. Survival to 180 days ranged 95%–100% and was not affected by tagging. PIT‐tagging caused a short‐term reduction in growth rates. Tag retention to 180 days was 100% for dorsal implantation, 83.0% with 8‐mm tags in the operculum, 97.5% with 8‐mm tags in the abdomen, and 99.6% with 12‐mm tags in the abdomen. Retention of opercular tags was positively related to size at tagging. Tag loss was independent of whether fish were single‐ or double‐tagged. Double tagging with one full‐ and one half‐duplex PIT tag in different body locations would hedge against data loss relative to single tagging, especially for longer‐lived and iteroparous species where tag loss through time is more likely. [ABSTRACT FROM AUTHOR]

Lotic systems in mountain regions have historically provided secure habitat for native fish populations because of their relative isolation from human settlement and lack of upstream disturbances. However, rivers of mountain ecoregions are currently experiencing heightened levels of disturbance due to the introduction of nonnative species impacting endemic fishes in these areas. We compared the fish assemblages and diets of mountain steppe fishes of the stocked rivers in Wyoming with rivers in northern Mongolia where stocking is absent. Using gut content analysis, we quantified the selectivity and diets of fishes collected in these systems. Nonnative species had more generalist diets with lower levels of selectivity than most native species and native species had high levels of dietary specificity and selectivity. High abundances of nonnative species and high levels of dietary overlaps in our Wyoming sites is a cause of concern for native Cutthroat Trout and overall system stability. In contrast, fish assemblages characterizing Mongolia mountain steppe rivers were composed of only native species with diverse diets and higher selectivity values, suggesting low probability for interspecific competition. [ABSTRACT FROM AUTHOR]

Brook trout populations have been declining throughout their native range in the east coast of the United States. Many populations are now distributed in small, isolated habitat patches where low genetic diversity and high rates of inbreeding reduce contemporary viability and long‐term adaptive potential. Although human‐assisted gene flow could theoretically improve conservation outcomes through genetic rescue, there is widespread hesitancy to use this tool to support brook trout conservation. Here, we review the major uncertainties that have limited genetic rescue from being considered as a viable conservation tool for isolated brook trout populations and compare the risks of genetic rescue with other management alternatives. Drawing on theoretical and empirical studies, we discuss methods for implementing genetic rescue in brook trout that could yield long‐term evolutionary benefits while avoiding negative fitness effects associated with outbreeding depression and the spread of maladapted alleles. We also highlight the potential for future collaborative efforts to accelerate our understanding of genetic rescue as a viable tool for conservation. Ultimately, while we acknowledge that genetic rescue is not without risk, we emphasize the merits that this tool offers for protecting and propagating adaptive potential and improving species' resilience to rapid environmental change. [ABSTRACT FROM AUTHOR]

Higher temperatures are now observed in several ecosystems and act as new selective agents that shape traits and fitness of individuals. Transgenerational effects may be important in modulating adaptation of future generations and buffering negative impacts of temperature changes. The potential for these effects may be important in freshwater fish species, as temperature is a key abiotic component of their environment. Yet, still, relatively few studies have assessed the presence and importance of transgenerational effects under natural conditions. The purpose of this study was to test how parental thermal conditions influenced offspring growth and survival following stocking in Brook charr (Salvelinus fontinalis). To do so, part of the breeders were exposed to a "cold" treatment while others were exposed to a "warm" treatment during the final steps of gonad maturation (constant 2°C difference between treatments along the seasonal temperature decrease). The impact on offspring of a selection treatment targeting production traits of interest (absence of sexual maturation at 1+, combined with increased growth) in breeders was also evaluated. After 7–8 months of growth in captivity, offspring were stocked in natural lakes. Their growth and survival were assessed about a year later. Offspring from "cold" breeders showed lower survival than those from "warm" breeders and the selection treatment had no effect on survival. However, the selection treatment was linked to lower Fulton's condition index, which, in turn, was positively correlated to survival in lakes. This study highlights the importance of working in ecological/industrial context to fully assess the different impacts of transgenerational effects on traits and survival. Our results also have important implications for stocking practices used to support the sport fishing industry. [ABSTRACT FROM AUTHOR]

In external fertilizer fish, ovarian fluid (OF) seems to play a key role in fertilization success, improving spermatozoa swimming performance. These OF/sperm interaction mechanisms are frequently species-specific and/or population-specific and could decrease the risk of genetic introgression of wild populations from introduced or escaped zootechnical individuals. The Mediterranean brown trout (Salmo cettii) is threatened by genetic introgression with strains of domestic brown trout (Salmo trutta) that were introduced for recreational purposes. The aim of our study was to test if native S. cettii females, rather than zootechnical S. trutta, produce OF with a greater ability to upregulate the sperm motility of conspecific males. Thus, we compared the sperm swimming performances of males inhabiting the Biferno River (Molise region—Southern Italy) activated in native S. cettii vs. zootechnical S. trutta female's OFs. In our study, native females' OFs (20% diluted), compared to spring water, has the ability to significantly boost the sperm performance of the autochthonous males, while zootechnical S. trutta fails. These preliminary results suggest that OF-sperm interactions could potentially influence or direct the hybridization mechanisms involving the native Mediterranean trout inhabiting the Biferno River and the domestic lineage of brown trout introduced in the past. [ABSTRACT FROM AUTHOR]

Environmental stressors associated with a changing climate and non‐native fish, individually, represent significant threats to native fish conservation. These threats can exacerbate risks to native fishes when conditions interact at the trailing edge of a population's distribution. We collected capture–mark–recapture data for Rio Grande cutthroat trout (RGCT, Oncorhynchus clarkii virginalis) at the trailing edge of all cutthroat trout distributions from eight northern New Mexico populations. We used a factorial sampling design from streams characterised as "cool" or "warm" and whether RGCT were sympatric with non‐native brown trout (Salmo trutta). We tested competing hypotheses that warm temperatures, reduced flows, high densities and sympatry with brown trout would negatively impact RGCT apparent survival rates. We found the strongest evidence for a non‐native trout interaction with total trout density affecting RGCT apparent survival rates. Our results are consistent with patterns observed in northern cutthroat trout populations where non‐native salmonids negatively impacted apparent survival rates. We also found that a negative density effect was observed on allopatric RGCT and sympatric brown trout apparent survival, but a positive density effect was observed for sympatric RGCT. These results suggest higher density populations of RGCT may be more resilient to displacement by non‐native trout than low‐density populations. [ABSTRACT FROM AUTHOR]

Behaviour observations of the endangered native marble trout (Salmo marmoratus, Cuvier, 1829) and introduced rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) in the laboratory and in a tributary to the Idrijca River in Slovenia were combined to study the movements and dominance relationships between individuals of the two species in an open field test. Under laboratory conditions, no difference between the species was detected for neither time spent actively or distance moved. In species paired tests, rainbow trout initiated more aggressive behaviours towards marble trout than vice versa, and rainbow trout were clearly the dominant individuals. After simultaneous release in the river, marble trout immediately left the release area and spent twice as long time as rainbow trout until they settled in an area of the river; therefore, the release site was immediately occupied exclusively by rainbow trout. Thus, the dominant and aggressive behaviour of rainbow trout seen in the laboratory before release might have influenced marble trout's subsequent behaviour in the river, by marble trout leaving the areas occupied by rainbow trout and moving to locations further away from the release site. In the field, the marble trout occupied sites individually, whereas rainbow aggregated at a few locations. Rainbow trout showed higher movement activity in the morning compared to marble trout. There was a positive correlation between swimming speed in the laboratory and movement in the field for marble trout but not for rainbow trout. In conclusion, the results in this study support the need to end stocking of rainbow trout in rivers with native marble trout. To better understand the interaction between the species, and to develop efficient management plans to protect the native marble trout, reference behaviours should first be understood, and future research in sites where the two species do not co‐exist is needed. This is especially important for marble trout for which behavioural research and data are lacking. [ABSTRACT FROM AUTHOR]

Schooling in fish is linked to a number of factors such as increased foraging success, predator avoidance, and social interactions. In addition, a prevailing hypothesis is that swimming in groups provides energetic benefits through hydrodynamic interactions. Thrust wakes are frequently occurring flow structures in fish schools as they are shed behind swimming fish. Despite increased flow speeds in these wakes, recent modeling work has suggested that swimming directly in-line behind an individual may lead to increased efficiency. However, only limited data are available on live fish interacting with thrust wakes. Here we designed a controlled experiment in which brook trout, Salvelinus fontinalis, interact with thrust wakes generated by a robotic mechanism that produces a fish-like wake. We show that trout swim in thrust wakes, reduce their tail-beat frequencies, and synchronize with the robotic flapping mechanism. Our flow and pressure field analysis revealed that the trout are interacting with oncoming vortices and that they exhibit reduced pressure drag at the head compared to swimming in isolation. Together, these experiments suggest that trout swim energetically more efficiently in thrust wakes and support the hypothesis that swimming in the wake of one another is an advantageous strategy to save energy in a school. [ABSTRACT FROM AUTHOR]

The study presents the outline review of fish species in the flooded area and the recent development of ichthyocenosis in the water reservoir. The resources for the information have been the results of our own research undertaken in the period from 1983 to 2014. The results indicate that the Šance water reservoir has been colonised, approximately during the last 30 years, by the fish community predominated by carp species and the relatively high share of predatory fishes. In the monitored period, there have been 25 fish species well documented in the area of Šance water reservoir raise. Before the reservoir fill up, they were Salmo trutta, Oncorhynchus mykiss, Thymallus thymallus, Squalius cephalus, Phoxinus phoxinus, Barbatula barbatula, and Cottus poecilopus. The reservoir has been then successively colonised by introduced species Salvelinus fontinalis, Hucho hucho, Esox lucius, Aspius aspius, Silurus glanis, Lota lota, and Sander lucioperca. We could not find trustworthy information about the way how some other species occurred in the reservoir and we thus consider them alien. Specifically, they are Rutilus ruitilus, Abramis brama, Carassius gibelio, Cyprinus carpio, Alburnus alburnus, Gobio gobio, Tinca tinca, Leuciscus leuciscus, Scardinius erythrophthalmus, Perca fluviatilis, and Gymnocephalus cernnus. In 2014, the biggest numbers occurring in gillnets belonged to Perca fluviatilis (36.01%), Alburnus alburnus (29.2%), Rutilus ruitilus (15%), and Gymnocephalus cernnus (11.9%). The catch biomass showed mostly Rutilus ruitilus (35.9%), Silurus glanis (16.8%), Perca fluviatilis (15.2%), and Alburnus alburnus (10.4%). The share of predatory fishes (28.2%) putting the effective pressure on individuals of smaller carp species has been undoubtedly positive. [ABSTRACT FROM AUTHOR]

As air temperature increases, it has been suggested that smaller individual body size may be a general response to climate warming. However, for ectotherms inhabiting cold, highly seasonal environments, warming temperatures may increase the scope for growth and result in larger body size.In a long‐term study of individual brook trout Salvelinus fontinalis and brown trout Salmo trutta inhabiting a small stream network, individual lengths increased over the course of 15 years. As size‐selective gains and losses to the population acted to reduce body sizes and mean body size at first tagging in the autumn (<60 mm) were not observed to change substantially over time, the increase in body size was best explained by higher individual growth rates.For brook trout, increasing water temperatures during the spring (when both trout species accomplish most of their total annual growth) was the primary driver of growth rate for juvenile fish and the environmental factor which best explained increases in individual body size over time.For brown trout, by contrast, reduction in and subsequent elimination of juvenile Atlantic salmon Salmo salar midway through the study period explained most of the increases in juvenile growth and body size.In addition to these major trends, a considerable amount of interannual variation in trout growth and body size was explained by other abiotic (stream flow) and biotic (population density) factors with the direction and magnitude of these effects differing by season, age‐class and species. For example, stream flow was the dominant growth rate driver for adult fish with strong positive effects in the summer and autumn, but flow variation could not explain increases in body size as we observed no trend in flow.Overall, our work supports the general contention that for high‐latitude ectotherms, increasing spring temperatures associated with a warming climate can result in increased growth and individual body size (up to a point), but context‐dependent change in other factors can substantially contribute to both interannual variation and longer‐term effects. [ABSTRACT FROM AUTHOR]

Brook trout (Salvelinus fontinalis) are an iconic freshwater salmonid native to northeastern North America. They prefer cold, clean rivers and lakes, and have been culturally, socially and economically valued for decades. Overharvest and deforestation associated with European settlement in southern Ontario, Canada led to notable declines in brook trout abundance in rivers and streams by the late 1800s. Today, they are threatened by further habitat degradation, non‐native species, and climate change. In this study, we document brook trout occupancy in rivers and streams of the Mixedwood Plains Ecozone in southern Ontario, between 1970–1980 and 2000–2010. We used generalised linear models to determine occupancy variation between the two time periods at five spatial scales spanning multiple watershed levels. We detected a decline in occupancy between time periods for the tertiary (from 23% to 17%) and quaternary (from 35% to 22%) watershed scales. In the Credit River‐Sixteen Mile Creek watershed, mean occupancy decreased to a third of past estimate (from 31% to 10%). For a subset of 86 sites with overlapping sampling in both periods no temporal trend was detected, but a post‐hoc analysis indicated low statistical power (0.07), which suggested that more intensive sampling would be needed to better quantify brook trout occupancy changes at this scale. The occupancies quantified for the past period in our study may serve as benchmarks for brook trout restoration efforts. [ABSTRACT FROM AUTHOR]

Success of stream restoration can be difficult to define because many interacting abiotic and biotic factors across spatio‐temporal scales can have measurable effects. Consequently, failure in habitat restoration to achieve targeted biological goals may reflect interactions of habitat restoration with unaccounted risks that have yet to be addressed on the landscape. This is particularly true within invaded landscapes, where habitat restoration can benefit non‐native competitors as much as the native fishes for which restoration is designed. We tested for interacting effects of a reach scale habitat restoration effort and non‐native trout competition on habitat use by a brook trout (Salvelinus fontinalis) metapopulation within a productive main stem corridor of the Shavers Fork watershed, West Virginia. We used a joint species occupancy model within a BACI sampling design to show that brook trout occupancy of main stem habitat was highest post‐restoration within restored sampling reaches, but this benefit to native brook trout was conditional on brown trout (Salmo trutta) not being present within the main stem habitat. Collectively these results indicate that habitat restoration was only beneficial for native brook trout when non‐native trout were absent from the restored sampling area. Proactive approaches to restoration will be integral for supporting resilient ecosystems in response to future anthropogenic threats (e.g. climate change), and we have shown that such actions will only be successful if non‐native competitors do not also benefit from the restoration actions. [ABSTRACT FROM AUTHOR]

Widespread extirpation of native fish populations has led to a rise in species reintroduction efforts worldwide. Most efforts have relied on demographic data alone to guide project design and evaluate success. However, the genetic characteristics of many imperiled fish populations including low diversity, local adaptation, and hatchery introgression emphasize the importance of genetic data in the design and monitoring of reintroduction efforts. Focusing on a case study of brook trout (Salvelinus fontinalis) in North Carolina, we show how the combined use of genetic and demographic data can support reintroduction efforts by improving source population selection and providing opportunities to evaluate genetic viability and adaptive potential in restored populations. Using this combined approach, we reintroduced brook trout into a restored stream from two source populations and monitored changes in genetic diversity and population size in source and recipient populations. Three years after the initial translocation, the reintroduced population had comparable density, but higher genetic diversity, than either source population. This study demonstrates the utility of genetic and demographic data for reintroduction efforts, particularly when extant populations are genetically depauperate and maintaining adaptive potential is a primary restoration goal. However, we emphasize the value of continued monitoring at longer temporal and spatial scales to determine the effects of stochastic process on the long‐term adaptive capacity and persistence of reintroduced populations. Overall, inclusion of genetic data in reintroduction efforts offers increased ability to meet project goals while simultaneously conserving critical sources of adaptive variation that exist across the landscape. [ABSTRACT FROM AUTHOR]