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Many studies have investigated the loss of adaptive potential in endangered or exploited species experiencing recent population declines. Less research has studied adaptive genomic variation in small populations known to have persisted for long periods, despite the unique contribution that such populations provide for determining mechanisms underlying population persistence in evolutionary and conservation modeling. Small populations of Brook trout (Salvelinus fontinalis) have persisted in Cape Race, Newfoundland for >12 000 years. We used genotyping-by-sequencing data to investigate the demographic history and adaptive genomic variation of 26 populations with effective population sizes (Ne) ranging from 11 to 442, and to explore mechanisms underlying long-term persistence. We show that all populations experienced demographic declines following postglacial colonization but have remained in their current, small Ne state for thousands of years. We also reveal greater homozygosity in adaptive alleles within the smallest populations and found signatures of adaptive divergence in small populations relating to several abiotic and biotic factors. Our study illustrates how the demographic history of a species can influence the adaptive dynamics of small populations persisting over long time periods. [ABSTRACT FROM AUTHOR]

ABSTRACT Island ecosystems, particularly vulnerable to environmental challenges, host many endangered native species. Diadromous fish, in particular, are threatened throughout their marine and freshwater habitats. The conservation of these species requires an in‐depth understanding of their genetic diversity and structure, to better understand their adaptive potential. We investigated fine‐scale population diversity and structure in native brook charr (Salvelinus fontinalis) by genotyping 10 microsatellite loci in 244 individuals at three spatial scales in Saint‐Pierre and Miquelon, France. We found limited genetic variability across the archipelago, with particularly low genetic diversity in one island, Langlade. A significant difference in allelic richness was also detected among the three islands, indicating a difference in genetic composition across the archipelago, probably induced by historical stocking actions on both Saint‐Pierre and Miquelon. Finally, a strong genetic structure was detected across the archipelago among hydrosystems (overall FST = 0.19) and even within several of them. The presence of predominant interisland gene flow combined with complete genetic isolation from certain hydrosystems suggests that this contemporary genetic structure is the result of both natural demographic processes during the species postglacial colonization and recent restocking actions. The complex genetic structure of such isolated brook charr subpopulations highlights the importance of considering fine‐scale genetic structure in conservation management.

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]

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]

Individual- and population-level responses to thermal change will be pivotal for species' resilience and adaptive responses to climate change. Thermal tolerance of ectotherms has been extensively studied under laboratory conditions, but comparatively few studies have assessed intra- and interpopulation variation under natural conditions or in situ. We measured field critical thermal maximum (CTmax) of brook trout (Salvelinus fontinalis) populations at twenty sites across Ontario, Canada, to assess their thermal tolerance in situ and examine potential factors underlying intraspecific variation in thermal performance. We modelled CTmax as a function of acclimation using short-term stream temperature data to assess interpopulation variation, and used full-season stream temperatures to calculate thermal safety margins (TSM) for each population. CTmax ranged between 27.41 and 30.46°C and acclimation periods between 4 and 40 days were strong predictors of site CTmax, aligning closely with lab-based studies. Seasonal temperature profiles varied substantially among sites, with mean 30-day stream temperature accounting for 66% of the among-site variation in CTmax. TSMs ranged between 0.51 and 15.51°C and reflected differences among site thermal regimes. Streams in watersheds with more urban or agricultural development had the lowest TSMs in addition to those that were fed by lake surface water. This work emphasizes the importance of locally based conservation and management practices that act at or below the population level, as local factors beyond acclimation temperature were partly responsible for variation in thermal tolerance and thus dictate the resiliency of brook trout under climate change. [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]

In many freshwater ecosystems, carbon dioxide (CO2) is increasing. Unknown are the risks that high CO2 poses for freshwater organisms, especially fish. The objective of this study was to determine how CO2 may influence the growth rate, metabolic rate, feeding rate, and volitional behaviour of young-of-year Arctic charr (Salvelinus alpinus (Linnaeus, 1758)), brook charr (Salvelinus fontinalis (Mitchill, 1814)), and rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)). For this study, fish stayed in control (1100 microatmospheres (µatm)) or elevated (5236 µatm) CO2 levels for 15 days. During this time, metabolic rate and behavioural tests were conducted on alternating days for each treatment. Weight and length of each fish were taken on days 0, 7, and 15. There was no evidence that elevated CO2 affected the growth rate, feeding rate, or behaviour in any of these species. The standard metabolic rate in Arctic charr differed based on CO2 exposure. Therefore, salmonids can withstand short periods of elevated CO2 under these conditions. By comparing closely related species, the implications of this work are more ecologically relevant and will also help industry quantify the effects of high CO2 on young salmonids. [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]

Microplastic (MP) pollution is a major environmental concern for mountain ecosystem and for high-mountain lakes in particular, which are recognized indicators of global change. In this study, the presence of MPs was assessed in abiotic (water and sediment) and biotic (zooplankton, tadpoles, fish) compartments of two high-mountain lakes (Upper Lake Balma and Lower Lake Balma) in the Cottian Alps (northwest Italy). No MPs were found in water and zooplankton samples, whereas the mean MPs in sediment samples was 1.33 ± 0.67 items/m3 and 1.75 ± 0.62 items/m3 in Lower and Upper Lake Balma, respectively. The mean MPs in tadpoles of Rana temporaria was 0.33 ± 0.58 items/individual and 0.66 ± 0.58 items/individual in Lower and Upper Lake Balma, respectively. The mean number of MPs items found in the gastrointestinal tract (GIT) of fish (Salvelinus fontinalis) was considerably higher in specimens from the Lower (0.45 items/g GIT) than in those from the Upper Lake (0.20 items/g GIT). There was a negative relationship between fish size (weight and age) and MPs abundance in the GIT of fish, indicating that young fish accumulated more MP items probably due to the high prey ingestion rate compared to adults. The same MPs color (blue, white, black), shape (fibers and fragments), and chemical type (polypropylene and polyethylene) were found in the compartments of both lakes. Our findings suggest the use of S. fontinalis as an indicator of MP pollution in high-mountain lakes. Further studies are needed to better understand the sources and the effects of MPs in these remote ecosystems.

Brook trout are a species of conservation concern in Southwestern Ontario, Canada, and effective monitoring of their populations is crucial for making informed management decisions. Electrofishing is a traditional, yet invasive, method that allows for fish abundance estimation. Environmental DNA (eDNA) is an emerging molecular tool that presents a non-invasive alternative to electrofishing. This study was a collaborative effort between researchers in academia, industry, and an NGO, with the following objectives: 1) compare eDNA detections with electrofishing when monitoring brook trout populations in a site of known occupancy, 2) compare existing eDNA collection methods, and 3) extend eDNA surveys to regions of unknown occupancy that could be of conservation concern (Hanlon Creek and Twelve Mile Creek, Ontario). First, eDNA sampling methods were validated with standard electrofishing. Water samples were filtered in tandem at each site using two commercially available eDNA samplers. The results suggest a significant difference in total eDNA capture and incidence of PCR inhibitors between the two autosamplers. Brook trout eDNA was detected at all locations in Hanlon Creek in September and November, as well as 5/6 sampling locations in Twelve Mile Creek. Brook trout signal in Hanlon Creek was stronger in November compared to September 2019, suggesting possible spawning activity. Brook trout eDNA was also detected in Twelve Mile Creek where brook trout were previously unreported. This study provides a technical validation for the use of eDNA in brook trout monitoring and illustrates the opportunity to use eDNA surveys in regulated settings to complement and improve conventional biomonitoring methods for the management of elusive species. [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]

Throughout their range, Brook Trout (Salvelinus fontinalis) occupy thousands of disjunct drainages with varying levels of disturbance, which presents substantial challenges for conservation. Within the southern Appalachian Mountains, fragmentation and genetic drift have been identified as key threats to the genetic diversity of the Brook Trout populations. In addition, extensive historic stocking of domestic lineages of Brook Trout to augment fisheries may have eroded endemic diversity and impacted locally adapted populations. We used 12 microsatellite loci to describe patterns of genetic diversity within 108 populations of wild Brook Trout from Tennessee and used linear models to explore the impacts of land use, drainage area, and hatchery stockings on metrics of genetic diversity, effective population size, and hatchery introgression. We found levels of within-population diversity varied widely, although many populations showed very limited diversity. The extent of hatchery introgression also varied across the landscape, with some populations showing high affinity to hatchery lineages and others appearing to retain their endemic character. However, we found relatively weak relationships between genetic metrics and landscape characteristics, suggesting that contemporary landscape variables are not strongly related to observed patterns of genetic diversity. We consider this result to reflect both the complex history of these populations and the challenges associated with accurately defining drainages for each population. Our study highlights the importance of genetic data to guide management decisions, as complex processes interact to shape the genetic structure of populations and make it difficult to infer the status of unsampled populations. [ABSTRACT FROM AUTHOR]

Abstract Understanding the drivers of successful species invasions is important for conserving native biodiversity and for mitigating the economic impacts of introduced species. However, whole‐genome resolution investigations of the underlying contributions of neutral and adaptive genetic variation in successful introductions are rare. Increased propagule pressure should result in greater neutral genetic variation, while environmental differences should elicit selective pressures on introduced populations, leading to adaptive differentiation. We investigated neutral and adaptive variation among nine introduced brook trout (Salvelinus fontinalis) populations using whole‐genome pooled sequencing. The populations inhabit isolated alpine lakes in western Canada and descend from a common source, with an average of ~19 (range of 7–41) generations since introduction. We found some evidence of bottlenecks without recovery, no strong evidence of purifying selection, and little support that varying propagule pressure or differences in local environments shaped observed neutral genetic variation differences. Putative adaptive loci analysis revealed nonconvergent patterns of adaptive differentiation among lakes with minimal putatively adaptive loci (0.001%–0.15%) that did not correspond with tested environmental variables. Our results suggest that (i) introduction success is not always strongly influenced by genetic load; (ii) observed differentiation among introduced populations can be idiosyncratic, population‐specific, or stochastic; and (iii) conservatively, in some introduced species, colonization barriers may be overcome by support through one aspect of propagule pressure or benign environmental conditions.

Understanding the drivers of successful species invasions is important for conserving native biodiversity and for mitigating the economic impacts of introduced species. However, whole‐genome resolution investigations of the underlying contributions of neutral and adaptive genetic variation in successful introductions are rare. Increased propagule pressure should result in greater neutral genetic variation, while environmental differences should elicit selective pressures on introduced populations, leading to adaptive differentiation. We investigated neutral and adaptive variation among nine introduced brook trout (Salvelinus fontinalis) populations using whole‐genome pooled sequencing. The populations inhabit isolated alpine lakes in western Canada and descend from a common source, with an average of ~19 (range of 7–41) generations since introduction. We found some evidence of bottlenecks without recovery, no strong evidence of purifying selection, and little support that varying propagule pressure or differences in local environments shaped observed neutral genetic variation differences. Putative adaptive loci analysis revealed nonconvergent patterns of adaptive differentiation among lakes with minimal putatively adaptive loci (0.001%–0.15%) that did not correspond with tested environmental variables. Our results suggest that (i) introduction success is not always strongly influenced by genetic load; (ii) observed differentiation among introduced populations can be idiosyncratic, population‐specific, or stochastic; and (iii) conservatively, in some introduced species, colonization barriers may be overcome by support through one aspect of propagule pressure or benign environmental conditions. [ABSTRACT FROM AUTHOR]

Optimality theory is useful for modeling habitat use in animals, although many models have not been rigorously tested. We evaluated the ability of the Grossman et al. net‐energy‐intake (NEI) optimal foraging model for drift‐feeding stream fishes, to predict the holding velocity (microhabitat) of native brook charr (BC; Salvelinus fontinalis) inhabiting a southern Appalachian stream. This model postulates that fish choose holding velocities that maximize their NEI, and is broadly applicable to stream fishes, many of which are drift‐feeders. We used laboratory prey capture success versus water velocity data to quantify the relationship between prey capture success, water velocity, and holding velocity of BC (N = 21, mean standard length = 147 mm ± 14 sd). Parameterization of the Grossman et al. model yielded an optimal holding velocity prediction of 18.5 cm·s−1. Based on fitting criteria from previous work, the model prediction was successful because it fell within the 95% confidence interval (13.5–20.5 cm·s−1) of mean holding velocities (17.0 cm·s−1, N = 26) of BC in Lynn Camp Prong, Tennessee. Consequently, NEI maximization likely is a causal factor affecting BC habitat choice. Our result argues strongly for the general usefulness of this model. [ABSTRACT FROM AUTHOR]

Adfluvial brook trout Salvelinus fontinalis populations in the Lake Superior basin have suffered declines over the last century due to habitat degradation and exploitation. Natural resources agencies throughout the basin have restored habitat and implemented restrictive angling regulations as tools to protect remnant coaster brook trout populations, but the success of these practices is unknown in some locations. We used electrofishing and passive integrated transponder (PIT) tag movement data from 2008 to 2020 to describe population characteristics, temporal trends, and adfluvial life history of coaster brook trout in Washington Harbor, Isle Royale National Park, Lake Superior after implementation of catch-and-release regulations in 2004. Our results document the presence of an adfluvial coaster brook trout population in Washington Harbor, Isle Royale. Temporal trends indicate that brook trout abundance and distribution in Washington Harbor increased since earlier observations in the late 1990s and early 2000s likely due to enactment of protective regulations, and increased stream flows and water levels observed in recent years in both Washington Creek and Lake Superior, respectively. Annual tag detection of Washington Harbor brook trout in Washington Creek at the antenna arrays varied from 25% in 2009 to 100% in 2011 and 2013, and averaged 60.7% throughout the study. Peak in adfluvial brook trout use of Washington Creek was from August – October with few detections occurring outside of the presumed spawning period. This study provides valuable insight into the population characteristics, movement patterns, and temporal increase in abundance of an adfluvial brook trout population in Lake Superior. [ABSTRACT FROM AUTHOR]

This paper reports the occurrence of three new fish species, extremely rare in the Baltic Sea, and provides new data on their parasite fauna. The fish collected were Barbus barbus (Linnaeus, 1758), Salvelinus fontinalis (Mitchill, 1814), and Scophthalmus rhombus (Linnaeus, 1758). Their taxonomic identity was confirmed through genetic analyses using DNA extracted from fin clips. The stomach contents were examined, and age was determined by otolith or scale readings. Parasitological examinations focused on the skin, vitreous humour, eye lenses, mouth and nasal cavities, gills, gonads, viscera, and muscles. Furthermore, the changes of fish species composition over 20 years in Pomeranian Bay were analysed. The sequence comparisons against GenBank records revealed that sequences obtained for B. barbus and S. rhombus from Pomeranian Bay represent new rhodopsin barcodes. Record of the juvenile B. barbus in this study is the first in the Baltic Sea. Scophthalmus rhombus is a new host for the ciliate Trichodina jadranica, while Neogobius melanostomus (Pallas, 1814) is a new food item in the diet of S. rhombus in the Baltic Sea. Acanthocephalan Pomphorhynchus laevis found in the adult specimen of B. barbus and myxozoan Myxobolus musculi, noted in the juvenile specimen, have not been recorded previously in this fish species in Polish waters. Species collected as bycatch can potentially be used for monitoring potential changes in the overall fish community structure and biodiversity.

Indicators of the condition factor, growth rate, and quality of the final products of cultivated objects are important parameters for the effective management of cold-water fish farming. These indicators are also used as a way to control the impact of environmental factors on fish, which requires constant research in the context of intensification of the aquaculture sector. The research is aimed at determining the condition factor and the amino acid composition of muscle tissues of Salmo trutta fario (Linnaeus, 1758), Oncorhynchus mykiss (Walbaum, 1792) and Salvelinus fontinalis (Mitchill, 1814) under the conditions of the western region of Ukraine. The results of the condition factor showed that, S. fontinalis had the highest value with 1.52±0.0340, and O. mykiss and S. trutta showed the lowest value with 1.33±0.0361 and 1.26±0.0181, respectively. Food conversion ratios were similar for S. fontinalis and O. mykiss (1.0), whereas S. trutta showed higher values (1.4). The specific growth rate was higher for rainbow trout (1.4) compared to the brook trout (1.32) and brown trout (1.28). The maximum content of protein, total amino acids (TAA), total essential amino acids (TEAA) and nonessential amino acids (TNEAA) were recorded in the brook trout. The muscle tissue of the investigated fish species is a well-balanced source of the nutrition energy in terms of the ratio of total essential to total nonessential amino acids (TEAA:TNEAA ratio). [ABSTRACT FROM AUTHOR]

Brook Trout Salvelinus fontinalis in southern Appalachian Mountains streams of the United States occur at the southernmost portion of their native range, and occupy small, isolated, and low-productivity headwater streams. The existing standard weight (Ws) equation is applicable only to Brook Trout > 120 mm total length (TL), but many individuals in the region are smaller than this minimum size threshold due to their habitat characteristics. Here, we developed a new Ws equation for Brook Trout in southern Appalachian Mountains streams using length–weight data on 72,502 individuals. The weighted quadratic empirical-percentile method minimized length-related bias in relative weight compared to the regression-line-percentile and weighted linear empirical-percentile methods. The proposed Ws equation was: log10W = −3.364 + 1.378 × log10L + 0.397 × (log10L)2, where W was weight (g) and L was TL (mm). The new equation characterized body condition of Brook Trout in southern Appalachian Mountains streams more accurately than the existing equation. [ABSTRACT FROM AUTHOR]

A survey of trout species was carried out to assess the trout stocks' quality inhabiting the Palena River Basin, one of the most important rivers for recreational angling in Chilean Patagonia. Six sampling campaigns were carried out over 16 selected stretches of the river between February 2012 and June 2013. A total of 912 trout were collected, 57% rainbow trout (Oncorhynchus mykiss), 33.3% brown trout (Salmo trutta), and 9.6% brook trout (Salvelinus fontinalis). Also, one tiger trout (Salmo trutta X Salvelinus fontinalis) (a hybrid between brown and brook trout) was recorded. Results showed that both rainbow trout and brown trout shared the same reaches of the river, with very similar feeding habits, while brook trout inhabited smaller and more enclosed streams. Maturity stages (V-VI) were recorded from the fish sampled over the period spring-summerautumn in the case of rainbow trout; autumn-winter for brook trout, and summer-autumn for brook trout. One of the study's most notable features was the small size of the mature brook trout, reaching 17.5 cm in length for gravid females and 12.4 cm for mature males at age 2+. The maximum age recorded for rainbow and brown trout was 6+, with a maximum length of 69.8 and 58.5cm, respectively, while for brook trout, the maximum age recorded was 3+ for a female with a length of 29.9 cm length and 2+ for a male of 16.6 cm. [ABSTRACT FROM AUTHOR]

Hematological parameters of fish are useful for diagnosing pathophysiological conditions associated with metabolic perturbations in fish and therefore act as a non-specific biomarker of acute and chronic stress in the natural habitat and in aquaculture. Salmonid fish are of great importance in aquaculture; however, hematological studies of these species are scarce. This study presents the first set of data for the complete hematological profile of brook trout (Salvelinus fontinalis, Salmonidae). In total, seven blood cell types were identified and their characterization, range, size/surface area, and the leukocyte differential count are presented. Large numbers of immature erythrocytes and two subtypes of thrombocytes (round and prolate) were present in blood. Lymphocytes were the dominant leukocytes, followed by segmented neutrophils. Total leukocyte and segmented neutrophil counts were higher in the blood of male than female fish (P < 0.05). Here we describe, for the first time, basophilic cells in salmonid fish species. Blood cell types present in brook trout were similar to mammalian blood cells, but their morphology, number, size, and subtypes were unique to this fish species. The established reference model indicates differences in comparison with the cyprinid fish. The hematological profile described in this study will serve as an important model for examining comparative physiology of blood cells in other salmonid fish and will provide useful diagnostic criteria in aquaculture for the detection and mitigation of different pathological outcomes. [ABSTRACT FROM AUTHOR]

Spermatozoa movement in many aquatic animals with external fertilization is directly related to the external aqueous environment. In particular, environmental toxic metals can cause harmful effects and impair sperm cell functions. The high concentrations of copper (Cu) may be harmful for aquatic animals, while low levels are required for metabolic interactions. Herein, we investigated the effect of different copper concentration [0 mg L−1 (Control),.5 mg L−1, 1 mg L–1, and 2 mg L−1] on spermatozoa of brook trout Salvelinus fontinalis. Motility and survival of sperm cells were assessed. Our results indicated that Cu exposure caused to an evident decrease in motility and longevity of spermatozoa with increasing concentrations (p <.05). Overall, we showed that Cu exposure can impair sperm motility of S. fontinalis. Our study suggested that sperm motility has the potential to be a sensitive bioindicator of freshwater environmental pollution. [ABSTRACT FROM AUTHOR]

The nonconsumptive effects of predators on prey include behavioral, physiological, and life-history changes that reduce the risk of predation but have associated energetic or fitness costs to prey individuals and populations. Biologists have documented such changes for a wide array of predator–prey interactions in a variety of ecosystems; however, the energetic cost of nonconsumptive effects to prey populations has rarely been measured directly. Using a reach-scale manipulation of a naturally-fishless stream, we added chemical cues produced by live Brook Trout (Salvelinus fontinalis Mitchill, 1814) to simulate the presence of trout predation risk, and we quantified the impact of nonconsumptive effects on the secondary production of mayfly prey in the stream. The addition of trout chemical cues reduced the secondary production of larval Baetis mayflies in the treatment reach by 17% compared to an upstream, unmanipulated reference reach. This reduction was driven by smaller body size and earlier emergence of mayflies from the reach with added predator cues. The nonconsumptive effects of a predator can consequently reduce the flux of energy through a dominant stream invertebrate by altering individual life-history and development patterns. Furthermore, quantifying the population-level impact of nonconsumptive effects enables understanding the extent to which these widespread predator effects shape food-web dynamics and ecosystem processes. [ABSTRACT FROM AUTHOR]

The use of Trojan Y chromosomes (TYC) for controlling invasive species involves manipulating the sex chromosomes of captive‐raised individuals. Following release, the offspring of these individuals consist of only one sex, thereby skewing the sex ratio of the invasive population and potentially leading to eradication. Simulation models are needed that can inform managers about how to maximize the likelihood of invasive species eradication, since implementation of this novel management approach in the field is still rare.Here, we present the first spatially explicit, mechanistic simulation model of a real‐world TYC program for invasive species eradication. Using a brook trout Salvelinus fontinalis system model, we investigated the effects of competitive and reproductive fitness of the captive‐raised YY males, dispersal behaviour upon their release and landscape heterogeneity on eradication success.Likelihood of eradication was dependent on both the competitive and reproductive fitness of the Trojan individuals. Competitive fitness (i.e. survival) had a higher threshold for eradication, below which the invasive populations were not eradicated.Movement ecology of both the wild and YY male populations was important for eradication. Under a restricted dispersal scenario for YY males following their release, the wild population was not extirpated but maintained a stable, yet reduced, population size. Analysis of landscape configuration indicated that time to eradication of local patches increased with greater connectivity within the stream network.In addition to sex ratio distortion, density‐dependent mortality resulting from outplantings made an important contribution to population decline and therefore may also affect native competitors.Synthesis and applications. The use of Trojan sex chromosomes to skew population sex ratios is a novel method for the suppression and eradication of aquatic invasive species. Results from our modelling work indicate that while eradication is possible, maximizing its likelihood requires an understanding of the fitness and movement ecology of both the wild and YY male populations of the invasive species. Both our model and the principles derived from this study related to fitness and behavioural landscape ecology can be broadly applied to other invaded species and systems. [ABSTRACT FROM AUTHOR]

Maturation of salmonid species reduces growth, flesh quality and immunocompetency and has inhibited, in part, the commercial production of brook trout in Tasmania. Photoperiod manipulation is routinely used to inhibit or reduce the incidence of maturation in salmonids, so an experimental adaptation of this approach was trialled experimentally for brook trout. Mixed-sex fish (age = 14 months) were subjected to simulated natural photoperiod (NP), advanced photoperiod (AP) and continuous photoperiod (CP) to investigate the response of endogenous circannual rhythm upon sexual maturity in this species. Light treatments commenced on the first day of the last month of the southern hemisphere's winter and concluded towards the end of autumn when fish were ovulating. Maturation was observed in 100% of females and 96% of males held under NP. Fish exposed to AP corrected their maturation cycle by advanced phase shift of their endogenous rhythm for eight weeks and achieved final maturation during March–April. Plasma profiles of testosterone and oestradiol-17β were also adjusted according to advancement of photoperiod. Exposure to AP inhibited maturation by 6% and 8% in males and females, respectively. CP treatment for 10 consecutive months failed to inhibit gonadal development; however, this regime did delay or inhibit spermiation and ovulation. Early maturation in males, and maturation overall, compromises the growth and immunocompetency in brook trout. Exposure of fish to eight weeks advanced photoperiod reduces the number of the finally mature fish while continuous photoperiod failed to inhibit or reduce maturation in brook trout. It can be concluded that control of maturation in brook trout by photoperiod manipulation can affect maturation if further refined. Photo by Ryan Wilkinson. [ABSTRACT FROM AUTHOR]

In 2018, Vagococcus salmoninarum was isolated from two lots of broodstock "coaster" brook trout (Salvelinus fontinalis) containing ~1,500 fish at the Iron River National Fish Hatchery, at which time it was identified as the causative agent of a chronic coldwater streptococcosis epizootic. Clinical signs included exophthalmia, lethargy, erratic swimming and loss of equilibrium. Female fish experienced disproportionately higher morbidity and mortality than male co‐inhabitants, and routinely retained eggs following spawning. The most consistent gross clinical sign was heart pallor and turbid pericardial effusion. An attempted treatment using florfenicol was ineffective at halting the epizootic, which spanned more than a year and resulted in >50% mortality before remaining fish were culled. As there is no previous documentation of V. salmoninarum at this hatchery or in this species, it is still unclear what circumstances led to this epizootic. The inability to treat this chronic disease led to the loss of valuable broodstock, hampering ongoing fishery conservation efforts in the Great Lakes Basin. [ABSTRACT FROM AUTHOR]

Important variation in the shape and strength of density‐dependent growth and mortality is observed across animal populations. Understanding this population variation is critical for predicting density‐dependent relationships in natural populations, but comparisons amongst studies are challenging as studies differ in methodologies and in local environmental conditions.Consequently, it is unclear whether: (a) the shape and strength of density‐dependent growth and mortality are population‐specific; (b) the potential trade‐off between density‐dependent growth and mortality differs amongst populations; and (c) environmental characteristics can be related to population differences in density‐dependent relationships.To elucidate these uncertainties, we manipulated the density (0.3–7 fish/m2) of young‐of‐the‐year brook trout (Salvelinus fontinalis) simultaneously in three neighbouring populations in a field experiment in Newfoundland, Canada. Within each population, our experiment included both spatial (three sites per stream) and temporal (three consecutive summers) replication.We detected temporally consistent population variation in the shape of density‐dependent growth (negative linear and negative logarithmic), but not for mortality (positive logarithmic). The strength of density‐dependent growth across populations was reduced in sections with a high percentage of boulder substrate, whereas density‐dependent mortality increased with increasing flow, water temperature and more acidic pH. Neighbouring populations exhibited different mortality‐growth trade‐offs: the ratio of mortality‐to‐growth increased linearly with increasing density at different rates across populations (up to 4‐fold differences), but also increased with increasing temperature.Our results are some of the first to demonstrate temporally consistent, population‐specific density‐dependent relationships and trade‐offs at small spatial scales that match the magnitude of interspecific variation observed across the globe. Furthermore, key environmental characteristics explain some of these differences in predictable ways. Such population differences merit further attention in models of density dependence and in science‐based management of animal populations. [ABSTRACT FROM AUTHOR]

Context: Preservation of genetic diversity is a commonly cited, yet under-evaluated aspect of species conservation plans. Understanding the influence of human-mediated translocations and habitat constraints on landscape patterns of genetic structure in threatened fish species is essential to maintaining biodiversity and adaptive potential. Objectives: We evaluated the degree of influence from supplemental stocking, assessed the spatial population genetic structure, and examined the potential relationship between hybridization and ecology for Brook Trout (Salvelinus fontinalis) in the Black River watershed in New York State, USA. Methods: We used 13 microsatellite loci from over 450 fish at 18 sampling locations to map genetic structure and diversity, estimate the level of influence from stocked conspecifics, and model the relationship between hybridization and ecological characteristics. Results: We found widespread genetic introgression attributable to state-based stocking activities and a pattern of hierarchical genetic diversity across the landscape, which has additionally been influenced by geography. Site-specific fish assemblage variables appear to be unrelated to introgressive hybridization from stocked conspecifics, and only one hydrochemical variable, SO42−, exhibited strong explanatory power in predicting hybridization between wild and supplemented fish. A single locality exhibited genetic structure consistent with no history of introgression potentially associated with differences in elevation, and thus contributed disproportionately to the level of genetic diversity observed across the landscape. Conclusions: When examining genetic structure in fluvial riverine networks, it is important to consider the combined and interacting effects of both hybridization and habitat, which may result in augmented genetic structure not predictable from any single factor. [ABSTRACT FROM AUTHOR]

Introductions of non-native fish have the potential to cause substantial economic and ecological losses. In the western United States, non-native brook trout (Salvelinus fontinalis) are widely established and pose a threat to the persistence of bull trout (Salvelinus confluentus), a native char listed as threatened under the US Endangered Species Act, due to competition and hybridization. With brook trout identified as a factor limiting the recovery of ESA-listed bull trout in the Malheur Watershed of eastern Oregon, managers are pursuing brook trout eradication efforts. Key to the eradication efforts is reliable monitoring to ensure success. Traditional monitoring practices have included mechanical sampling methods such as seining, netting, and electrofishing, all of which are labor intensive and limited in reliability. Environmental DNA (eDNA) is genetic material naturally shed by organisms that can be found in bulk environmental samples without isolating individual organisms. Sampling for eDNA can often be done with less time and expense than traditional methods, making it ideal for effectiveness monitoring following fish eradication efforts. This study placed a single fish in a live-car where the species was not otherwise present and used eDNA sampling to infer the likelihood of detection downstream. Results suggest that a single fish can be detected reliably up to 500 m downstream when multiple samples are taken. This eDNA sampling method provides managers with the ability to conduct eradication effectiveness monitoring reliably and rapidly and may also be used to detect new fish invasions as well as rare or cryptic species. [ABSTRACT FROM AUTHOR]

Individual aggression and thermal refuge use were monitored in brook trout Salvelinus fontinalis in a controlled laboratory to determine how fish size and personality influence time spent in forage and thermal habitat patches during periods of thermal stress. On average, larger and more exploratory fish initiated more aggressive interactions and across all fish there was decreased aggression at warmer temperatures. Individual personality did not explain changes in aggression or habitat use with increased temperature; however, larger individuals initiated comparatively fewer aggressive interactions at warmer temperatures. Occupancy of forage patches generally declined as ambient stream temperatures approached critical maximum and fish increased thermal refuge use, with a steeper decline in forage patch occupancy observed in larger fish. These findings suggest that larger individuals may be more vulnerable to stream temperature rise. Importantly, even at thermally stressful temperatures, all fish periodically left the thermal refuge to forage. This indicates that the success of refugia at increasing population survival during periods of stream temperature rise may depend on the location of thermal refugia relative to forage locations within the larger habitat mosaic. These results provide insights into the potential for thermal refugia to improve population survival and can be used to inform predictions of population vulnerability to climate change. [ABSTRACT FROM AUTHOR]

Manual removal of non-native brown trout (Salmo trutta) led to increased abundance and improved size structure of a native brook trout (Salvelinus fontinalis) population. Reproductive dynamics of brook trout in response to release from this competitor were quantified using 14 microsatellite DNA loci to estimate effective population sizes, family sizes, and parentage across five cohorts. We hypothesized that brown trout removal allowed more brook trout to reproduce and distribute reproductive success more evenly among individuals, thereby increasing generational effective population size (Ne) and cohort effective number of breeders (Nb). However, N ^ e varied little (27–32), but was estimated for only one generation before and after removals began. Similarly, N ^ b differed little between pre-removal (21–25) and post-removal (19–23) cohorts, because increased numbers of reproductively successful adults were offset by highly skewed family sizes. Variance in family size increased following brown trout removal, but was uncorrelated with brook trout abundance across all years. Although most individuals matured at a small size, reproductive success increased with length. Increased abundance of adult brook trout has not increased N ^ b and N ^ e remains low. Managers should consider moving adults from nearby populations to increase genetic diversity of this isolated population. [ABSTRACT FROM AUTHOR]

We reviewed the literature pertaining to Brook Charr thermal habitat, one of Fry's original species used in developing his scope for activity, to determine what guidance may be established for defining thermal habitat from the literature. The literature was surprisingly large, with 53 publications estimating Brook Charr thermal habitat. The laboratory-based optimal temperature estimates varied widely but were far more consistent when only acclimation-controlled studies were considered. Acclimation-controlled estimates of optimal temperature matched the peak of the aerobic scope curve published nearly 70 years ago. Confidence in defining optimal thermal habitat is strengthened for Brook Charr based on this match because the peak in aerobic scope has strong mechanistic links between physiology and thermal ecology. However, laboratory-based studies used only sub-adult Brook Charr and may underrepresent Brook Charr thermal habitat in nature due to ontogenetic differences in thermal preference. Optimal temperature estimates from aerobic scope or acclimation-controlled studies should be used to define thermal habitat boundaries for fish but should be treated with caution if based on sub adults. Population level sampling is needed to determine the generality of these literature-derived boundaries among Brook Charr populations. [ABSTRACT FROM AUTHOR]

We used direct observation via snorkeling surveys to quantify microhabitat use by native brook (Salvelinus fontinalis) and non‐native brown (Salmo trutta) and rainbow (Onchorynchus mykiss) trout occupying natural and restored pool habitats within a large, high‐elevation Appalachian river, United States. Permutational multivariate analysis of variance (PERMANOVA) and subsequent two‐way analysis of variance (ANOVA) indicated a significant difference in microhabitat use by brook and non‐native trout within restored pools. We also detected a significant difference in microhabitat use by brook trout occupying pools in allopatry versus those occupying pools in sympatry with non‐native trout—a pattern that appears to be modulated by size. Smaller brook trout often occupied pools in the absence of non‐native species, where they used shallower and faster focal habitats. Larger brook trout occupied pools with, and utilized similar focal habitats (i.e. deeper, slower velocity) as, non‐native trout. Non‐native trout consistently occupied more thermally suitable microhabitats closer to cover as compared to brook trout, including the use of thermal refugia (i.e. ambient–focal temperature >2°C). These results suggest that non‐native trout influence brook trout use of restored habitats by: (1) displacing smaller brook trout from restored pools, and (2) displacing small and large brook trout from optimal microhabitats (cooler, deeper, and lower velocity). Consequently, benefits of habitat restoration in large rivers may only be fully realized by brook trout in the absence of non‐native species. Future research within this and other large river systems should characterize brook trout response to stream restoration following removal of non‐native species. [ABSTRACT FROM AUTHOR]

The influence of timing of extended photoperiods on growth and maturity of brook trout was investigated in a 112‐day experiment. The fish with mean initial weight of ~192 g were reared under four light regimes: one control group with natural ambient photoperiod and three groups exposed to an 18L:6D regime initiated at days 1, 23 or 46 of the growth trial. Light‐emitting diodes, with intensity of 250–1000 lux, depending on the distance from the light source, were used for extending light periods. There was a positive effect of prolonged day length on fish growth (p < 0.05), and a delay in gonad development and sexual maturity. Significantly higher numbers of sexually mature fish were found among controls groups, regardless of sex. Survival rate was not affected by light regime. This study demonstrated that the short‐term expansion of the photo period delayed maturation and increased the growth rate of brook trout. [ABSTRACT FROM AUTHOR]

Stream connectivity promotes resilience and population viability of aquatic organisms. Landscape genetic approaches, traditionally applied to terrestrial systems, may reveal important watershed‐level dynamics that influence connectivity. Additional validation would improve understanding of how the models perform when gene flow is constrained to dendritic networks. The objectives of this study were to use simulations to assess the utility of landscape genetics analyses in dendritic stream networks and investigate riverscape variables influencing gene flow among brook trout Salvelinus fontinalis populations in headwater streams.We used an individual‐based simulation program to simulate different dispersal scenarios and used combinations of landscape genetic models, model selection methods, and genetic metrics to determine the best combination for riverscape systems. We also sampled brook trout from 76 headwater streams in two watersheds (c. 1,000 km2) in Connecticut, U.S.A. to assess connectivity and riverscape influences on genetic structuring.Gravity models with Bayesian information criterion (BIC) selection were the most accurate (>85%) landscape genetic models that consistently identified the correct simulated gene flow barrier. However, all models performed poorly when unidirectional barriers were simulated without a distance‐based dispersal limitation. Excluding this scenario, model accuracy for the gravity models using BIC selection was >90% across multiple genetic metrics, validating the application of landscape genetic models to riverscape systems.We found highly variable levels of brook trout genetic connectivity (FST range 0.01–0.19) at the watershed level (5–15 river km). Gravity models identified increases in upstream impervious surfaces and decreases in riparian tree canopy cover as riverscape variables associated with increases in genetic differentiation in one watershed, while the other watershed was consistent with an isolation by distance pattern.In this study we used demogenetic (i.e. combined demographic and genetic) simulations to demonstrate the utility of landscape genetics techniques in dendritic river networks. Our empirical genetic study documented gene flow among headwater populations of brook trout at the watershed level and also suggested connectivity can be limited by watershed development. Incorporating the heterogeneity of riverscapes into connectivity‐focused conservation planning is essential to the development of effective restoration actions, and landscape genetics approaches can be useful tools to identify watershed‐level connectivity in stream systems. [ABSTRACT FROM AUTHOR]

The purpose of this study was to establish physiologic reference values for intraocular pressure (IOP) in clinically healthy trout (Salvelinus fontinalis). The study population consisted of 15 adult brook trout (14 male, 1 female); body weight ranged from 0.47 to 1.15 kg; length from 33.5 to 45.2 cm; and eye diameter from 11 to 14 mm. Animals were anesthetized, and a preliminary ophthalmic exam was performed. IOP was then measured by rebound tonometer. Three values were obtained for each eye. The animals were subsequently euthanized, and postmortem IOP was measured by the same method. A standard necropsy was performed on each fish to determine sex and to examine it for gross lesions. Premortem results (mm Hg) of measurements in the right eyes (n = 15) were 8.82 ± 2.45 mm Hg (minimum–maximum [min/max], 5–14 mm Hg; median, 8.33 mm Hg), and postmortem results were 6.31 ± 2.31 mm Hg (min/max, 3–11 mm Hg; median, 6 mmHg). Premortem results (mm Hg) of measurements in the left eyes (n = 15) were 9.20 ± 1.91 mm Hg (min/max, 5.33–12.33 mm Hg; median, 10 mm Hg), and postmortem results were and 9.81 ± 2.19mm Hg (min/max, 5–13 mmHg; median, 10.17mm Hg). A Mann-Whitney U-test was performed and revealed no significant difference within an eye under both pre- and postmortem conditions, and no significant difference between eyes between pre- and postmortem conditions. Rebound tonometry is a practical and efficient means of determining IOP in freshly euthanized fish or in anesthetized fish, where it requires minimal anesthetic and restraint time; it could potentially serve as a useful diagnostic tool when evaluating ophthalmic health. [ABSTRACT FROM AUTHOR]

The aim of the present study was to assess the effects of a prolonged photoperiod on growth rate and sexual maturation in brook trout Salvelinus fontinalis. The task of the experiment was to determine the most effective light regimen capable to minimizing the effects of puberty, including impairment of somatic growth and further general characteristics. In this regard, the studied fish were reared under three photoperiod regimens in which fish were exposed to 24 h continuous light alternating with 24 or 48 h under the ambient photoperiod or 48 h continuous light alternating with a 24 h ambient photoperiod. A control group was reared under the natural ambient photoperiod. Four-hundred and fifty fish with an average initial body weight of 101.3 ± 1.2 g were used for each experimental group (three replicates of each treatment plus control). A statistically lower growth rate showed control groups in both sexes. At the end of the study, control males had an average body weight of 226.6 ± 39.8 g and control females a body weight of 199.8 ± 12.2 g. At the same period, a significantly higher average body weight was found in groups reared 24 h under ambient photoperiod alternating with a 48 h continuous light regime (2CP:1AP) in both sexes (296.56 ± 62.5 g—males, and 239.9 ± 19.2 g—females, respectively). A significantly higher percentage of sexually mature fish was observed in the control group (80% of males and 29% of females, respectively). We found significantly fewer sexually mature females compared to males. The lowest survival was observed in group 2CP:1AP at 92%. It was concluded that regimen under which fish was exposed to 48 h of natural ambient photoperiod alternating with 24 h of constant light (1CP:2AP) lead to the successful delay of gonad development and onset of puberty and increased somatic growth in both sexes.

The effects of an artificially prolonged photoperiod on growth, survival rate, colouration, and sexual maturation in brook trout Salvelinus fontinalis during pre‐ and post‐spawning periods from 21 June to 06 November were investigated. Fish of mean initial weight ˜150 g were reared at ambient photoperiod as well as with an artificially prolonged photoperiod produced by either a light‐emitting diode or a metal‐halide light. The fish groups subjected to a prolonged period of artificial light grew significantly larger and had a higher survival rate (p < 0.05), regardless of sex, and showed lower occurrence of fungal disease compared to controls reared in the natural photoperiod. We found a significantly higher number of sexually mature fish in the control groups compared with experimental groups. The increased photoperiod effectively delayed gonad development and increased somatic growth in both male and female brook trout, and also increased resistance to fungal disease. The increased photoperiod produced an observable difference in fish colouration, with control groups exhibiting more intensive spawning colouration. [ABSTRACT FROM AUTHOR]

This paper reports the occurrence of three new fish species, extremely rare in the Baltic Sea, and provides new data on their parasite fauna. The fish collected were Barbus barbus (Linnaeus, 1758), Salvelinus fontinalis (Mitchill, 1814), and Scophthalmus rhombus (Linnaeus, 1758). Their taxonomic identity was confirmed through genetic analyses using DNA extracted from fin clips. The stomach contents were examined, and age was determined by otolith or scale readings. Parasitological examinations focused on the skin, vitreous humour, eye lenses, mouth and nasal cavities, gills, gonads, viscera, and muscles. Furthermore, the changes of fish species composition over 20 years in Pomeranian Bay were analysed. The sequence comparisons against GenBank records revealed that sequences obtained for B. barbus and S. rhombus from Pomeranian Bay represent new rhodopsin barcodes. Record of the juvenile B. barbus in this study is the first in the Baltic Sea. Scophthalmus rhombus is a new host for the ciliate Trichodina jadranica, while Neogobius melanostomus (Pallas, 1814) is a new food item in the diet of S. rhombus in the Baltic Sea. Acanthocephalan Pomphorhynchus laevis found in the adult specimen of B. barbus and myxozoan Myxobolus musculi, noted in the juvenile specimen, have not been recorded previously in this fish species in Polish waters. Species collected as bycatch can potentially be used for monitoring potential changes in the overall fish community structure and biodiversity. [ABSTRACT FROM AUTHOR]

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As anthropogenic impacts accelerate changes to landscapes across the globe, understanding how genetic population structure is influenced by habitat features and dispersal is key to preserving evolutionary potential at the species level. Furthermore, knowledge of these interactions is essential to identifying potential constraints on local adaptation and for the development of effective management strategies. We examined these issues in Brook Trout (Salvelinus fontinalis) populations residing in the Upper Hudson River watershed of New York State by investigating the spatial genetic structure of over 350 fish collected from 14 different sampling locations encompassing three river systems. Population genetic analyses of microsatellite data suggest that fish in the area exhibit varying degrees of introgression from nearby State‐directed supplementation activities. Levels of introgression in these populations correlate with water‐way distance to stocking sites, although genetic population structure at the level of individual tributaries as well as their larger, parent river systems is also detectable and is dictated by migration and influenced by habitat connectivity. These findings represent a significant contribution to the current literature surrounding Brook Trout migration and dispersal, especially as it relates to larger interconnected systems. This work also suggests that stocking activities may have far‐reaching consequences that are not directly limited to the immediate area where stocking occurs. The framework and data presented here may aid in the development of other local aquatic species‐focused conservation plans that incorporate molecular tools to answer complex questions regarding diversity mapping, and genetically important conservation units. As anthropogenic impacts accelerate changes to landscapes across the globe, understanding how genetic population structure is influenced by habitat features and dispersal is key to preserving evolutionary potential at the species level. We examined these issues in Brook Trout (Salvelinus fontinalis) populations residing in the Upper Hudson River watershed of New York State by investigating the spatial genetic structure of over 350 fish collected from 14 different sampling locations encompassing three river systems. The methods and data presented here may aid in the development of other fisheries‐focused conservation plans that incorporate a molecular perspective. [ABSTRACT FROM AUTHOR]

Due to increased anthropogenic pressures on many fish populations, supplementing wild populations with captive‐raised individuals has become an increasingly common management practice. Stocking programs can be controversial due to uncertainty about the long‐term fitness effects of genetic introgression on wild populations. In particular, introgression between hatchery and wild individuals can cause declines in wild population fitness, resiliency, and adaptive potential and contribute to local population extirpation. However, low survival and fitness of captive‐raised individuals can minimize the long‐term genetic consequences of stocking in wild populations, and to date the prevalence of introgression in actively stocked ecosystems has not been rigorously evaluated. We quantified the extent of introgression in 30 populations of wild brook trout (Salvelinus fontinalis) in a Pennsylvania watershed and examined the correlation between introgression and 11 environmental covariates. Genetic assignment tests were used to determine the origin (wild vs. captive‐raised) for 1,742 wild‐caught and 300 hatchery brook trout. To avoid assignment biases, individuals were assigned to two simulated populations that represented the average allele frequencies in wild and hatchery groups. Fish with intermediate probabilities of wild ancestry were classified as introgressed, with threshold values determined through simulation. Even with reoccurring stocking at most sites, over 93% of wild‐caught individuals probabilistically assigned to wild origin, and only 5.6% of wild‐caught fish assigned to introgressed. Models examining environmental drivers of introgression explained <3% of the among‐population variability, and all estimated effects were highly uncertain. This was not surprising given overall low introgression observed in this study. Our results suggest that introgression of hatchery‐derived genotypes can occur at low rates, even in actively stocked ecosystems and across a range of habitats. However, a cautious approach to stocking may still be warranted, as the potential effects of stocking on wild population fitness and the mechanisms limiting introgression are not known. [ABSTRACT FROM AUTHOR]

We conducted a large-scale assessment of unconventional oil and gas (UOG) development effects on brook trout ( Salvelinus fontinalis ) distribution. We compiled 2231 brook trout collection records from the Upper Susquehanna River Watershed, USA. We used boosted regression tree (BRT) analysis to predict occurrence probability at the 1:24,000 stream-segment scale as a function of natural and anthropogenic landscape and climatic attributes. We then evaluated the importance of landscape context (i.e., pre-existing natural habitat quality and anthropogenic degradation) in modulating the effects of UOG on brook trout distribution under UOG development scenarios. BRT made use of 5 anthropogenic (28% relative influence) and 7 natural (72% relative influence) variables to model occurrence with a high degree of accuracy [Area Under the Receiver Operating Curve (AUC) = 0.85 and cross-validated AUC = 0.81]. UOG development impacted 11% ( n = 2784) of streams and resulted in a loss of predicted occurrence in 126 (4%). Most streams impacted by UOG had unsuitable underlying natural habitat quality ( n = 1220; 44%). Brook trout were predicted to be absent from an additional 26% ( n = 733) of streams due to pre-existing non-UOG land uses (i.e., agriculture, residential and commercial development, or historic mining). Streams with a predicted and observed (via existing pre- and post-disturbance fish sampling records) loss of occurrence due to UOG tended to have intermediate natural habitat quality and/or intermediate levels of non-UOG stress. Simulated development of permitted but undeveloped UOG wells ( n = 943) resulted in a loss of predicted occurrence in 27 additional streams. Loss of occurrence was strongly dependent upon landscape context, suggesting effects of current and future UOG development are likely most relevant in streams near the probability threshold due to pre-existing habitat degradation. [ABSTRACT FROM AUTHOR]

This research presents an ecological assessment, based on the structure of natural biotope elements, anthropogenic elements and fish fauna of the salmonids sector of Bâlea River, situated in the Făgăraş Mountains. The research highlights the importance of all three of these categories for the composition and distribution of fish fauna. The presence or absence of the local fish species Salmo trutta fario, Salvelinus fontinalis, and Cottus gobio gobio in some of the Bâlea Stream sectors, can be explained mainly due to natural factors. Additionally, some anthropogenic factors identified in the area of interest were found as being responsible too. [ABSTRACT FROM AUTHOR]

Ecosystem impacts due to invasive species continue to attract significant conservation effort worldwide. In aquatic ecosystems, physical interventions such as suppression and eradication of non-native species are typically expensive, long-term commitments, with few examples of lasting success in the absence of significant ongoing effort. Control of non-native species is a major conservation and restoration challenge, as a species' demographic resilience and connectivity within networks can limit the ability of suppression or eradication efforts to influence populations. Simulation tools can provide valuable insights for the management of these systems - from evaluation of tradeoffs between time and effort to prediction of relative success rates of alternative strategies in changing environments. In the Pacific Northwest region of the U.S., the eastern brook trout (EBT; Salvelinus fontinalis ) is a non-native invasive species that competes with native fish species across a wide spatial scale due to extensive human-mediated introduction starting in the early 20th century. The goal of this study was to simulate the individual movement and demographics of EBT before, during, and following implementation of control efforts in tributaries within the Pend Oreille River watershed. The ultimate purpose of the model was to inform mitigation decisions through the investigation of alternative management actions in an adaptive management framework. Our results indicate that eradication of EBT is improbable in large systems via electrofishing, but suppression is a viable alternative given sustained management efforts. Changes to scheduling, effort, and length of electrofishing suppression treatments had minimal effects on EBT population recovery times. We reproduced the effects of compensatory responses to control treatments, including increases in juvenile survival and emigration rates, and demonstrated that these mechanisms are likely drivers of recovery following treatment. Our study highlights the many benefits of incorporating spatially explicit, individual-based models into management plans for the control of invasive species. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome sequence of the hybrid fish Salvelinus fontinalis (♀) × Salvelinus malma sp. (♂) was sequenced. It was 16,623-nucleotide in length and consisted of 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes, and 2 non-coding regions (L-strand replication origin and control region), showing conserved gene arrangement with most vertebrates. The phylogenetic tree showed the hybrid salmon to be one of the Salvelinus and the relationships of S. fontinalis were closer. The complete mitochondrial genome sequence of S. fontinalis (♀) × S. malma sp. (♂) provided an important dataset for a better understanding of the mitogenomic diversities and evolution in salmon fish as well as novel genetic markers for studying population genetics and species identification.