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Partial migration is common in a variety of taxa and has important ecological and evolutionary implications, yet the underlying factors that lead to different migratory strategies are not clearly understood. Given the importance of temperature in serving as a cue for migration, along with its role in regulating metabolism, growth, reproduction, and survival, we examined how intraspecific variation in critical thermal maximum (CTmax) values influenced migratory strategy (residency vs. migration), timing of migration, growth, and predation vulnerability in a wild population of partially anadromous juvenile brown trout (Salmo trutta). Using passive integrated transponder telemetry and mark-recapture techniques, we identified individuals that out-migrated to sea, assumed residency, and were predated by cormorants several months later. Acute thermal stress induced by conducting CTmax trials did not affect the final fate of assayed fish compared with controls. We found that mass and body condition predicted CTmax and migration timing, but CTmax failed to predict migratory strategy or timing, growth (of resident fish), or predation vulnerability. Although there may be links between mass, thermal tolerance, and migration strategy, the relationship between CTmax and migration remains unclear. The role of upper thermal tolerance in influencing life-history strategies should not be neglected, however, as alternative indicators of thermal tolerance could be further explored. The high degree of variation in CTmax estimates warrants additional investigation of how increasingly prevalent high-temperature events might drive selection toward thermally tolerant extremes, which is particularly relevant in a rapidly warming world.

In recent years, the numbers of native brown trout caught by anglers has declined throughout the Czech Republic. In this study, we focus on individual factors potentially related to this negative trend, based primarily on long-term angling catch data (2000-2020) for twenty fishing grounds of the Czech and Moravian angling unions covering twelve upland trout streams. The results indicate that angling pressure, expressed as annual number of attendances, is the most important factor in the decline of trout populations, with drought caused by climate change as a secondary factor. There is a clear need for changes in current fisheries management practice, using new sustainable development scenarios, in order to protect and improve unfavourable conditions for natural brown trout populations.

The behavior of organisms can be subject to human‐induced selection such as that arising from fishing. Angling is expected to induce mortality on fish with bold and explorative behavior, which are behaviors commonly linked to a high standard metabolic rate. We studied the transgenerational response of brown trout (Salmo trutta) to angling‐induced selection by examining the behavior and metabolism of 1‐year‐old parr between parents that were or were not captured by experimental fly fishing. We performed the angling selection experiment on both a wild and a captive population, and compared the offspring for standard metabolic rate and behavior under predation risk in common garden conditions. Angling had population‐specific effects on risk taking and exploration tendency, but no effects on standard metabolic rate. Our study adds to the evidence that angling can induce transgenerational responses on fish personality. However, understanding the mechanisms of divergent responses between the populations requires further study on the selectivity of angling in various conditions., Angling‐induced divergent responses on a wild and a hatchery population of brown trout, making hatchery population juveniles from low‐vulnerability parents more explorative than offspring from high‐vulnerability parents, but having no effect on juveniles from the wild population. Our results imply that angling selection may lead to accumulating behavioral changes across generations. Whether this will manifest as increased shyness, as has been predicted, can depend on the background of the population or the ecological conditions during angling.

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 × 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-summer-autumn 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.

For successful evaluation of the overall effects of salmon louse infestation on brown trout population dynamics, it is crucial to have a realistic understanding of how lice infestation distributions are generated and how they should be interpreted. Here, we simulated the potential effects of spatio-temporal variance in lice larvae densities, temporal variance in sea trout marine migration timing and spatial variance in marine habitat use on lice infestation distributions. We show that, when sampling populations with individual variation in marine behaviour, e.g. from post-smolts to veteran migrants, we must expect multi-modal mixture lice infestation distributions. Applying standard statistical distributions, such as the Poisson, negative binomial or zeroinflated distributions, can be too simplistic and give biased results. Temporary increases in salmon lice load in a given area may have inconsistent effects among individuals of a population and may be critical for vulnerable groups such as post-smolts, dependent on timing. For many analyses, it will be necessary to resolve the contributions from groups of fish with different lice infestation expectations due to spatio-temporal differences in habitat use within the overall mixture distribution. Another consequence is that different data sources, obtained by different methods or sampled at different locations and periods, must be expected to give different lice infestation distributions, even when sampling the same population. We also discuss additional factors that may complicate the interpretation of salmon lice infestation distributions on sea trout, such as lice-induced mortality, and behavioural changes, such as premature return to less saline water for delousing. Salmo trutta · Lepeophtheirus salmonis · Anadromy · Marine migration · Aquaculture · Negative binomial distribution · Zero-inflated models © The authors 2020. Open Access under Creative Commons by Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited.

We used microsatellite markers to investigate levels and structuring of genetic diversity in trout (Salmo trutta L.) sampled from 16 rivers along the south coast of Cornwall in southwest England. This region is characterized by many small coastal streams with a few larger catchments. At a regional level, genetic structuring of contemporary populations has been influenced by a combination of events, including the last Ice Age and also more recent human activities over the last millennium. All populations are shown to have gone through strong genetic bottlenecks, coinciding with increased exploitation of mineral resources within catchments, beginning during the Medieval period. At more local levels, contemporary human‐induced habitat fragmentation, such as weir and culvert construction, has disproportionally affected trout populations in the smaller catchments within the study area. However, where small catchments are relatively unaffected by such activities, they can host trout populations with diversity levels comparable to those found in larger rivers in the region. We also predict significant future loses of diversity and heterozygosity in the trout populations inhabiting small, isolated catchments. Our study highlights how multiple factors, especially the activity of humans, have and continue to affect the levels and structuring of genetic diversity in trout over long timescales., Structuring and levels of genetic diversity in brown trout populations along the south Cornwall stretch has been influenced by multiple natural and anthropogenic factors. At a regional scale, factors since the last glacial maximum have left their imprint. At finer local scales, the main driver of evolutionary change appears to be human activity. This area of southwest Britain has a long history of mining for metal ores. This mining would have affected fish populations in many ways, including the construction of weirs to divert water to ore processing mills and the release of mine water contaminated with heavy metals into rivers.

We used the distribution of stream-dwelling brown trout (Salmo trutta) in a 67 km2 boreal catchment to explore the importance of environmental organizing factors at a range of spatial scales, including whole-catchment characteristics derived from map data, and stream reach chemical and physical characteristics. Brown trout were not observed at any sites characterized by pH < 5.0 during the spring snowmelt episode, matching published toxicity thresholds. Brown trout distributions were patchy even in less acidic regions of the stream network, positively associated with glaciofluvial substrate and negatively associated with fine sand/silty sediments. A multivariate model including only whole-catchment characteristics explained 43% of the variation in brown trout densities, while models with local site physical habitat characteristics or local stream chemistry explained 33 and 25%, respectively. At the stream reach scale, physical habitat apparently played a primary role in organizing brown trout distributions in this stream network, with acidity placing an additional restriction by excluding brown trout from acidic headwater streams. Much of the strength of the catchment characteristics-fish association could be explained by the correlation of catchment-scale landscape characteristics with local stream chemistry and site physical characteristics. These results, consistent with the concept of multiple hierarchical environmental filters regulating the distribution of this fish species, underline the importance of considering a range of spatial scales and both physical and chemical environments when attempting to manage or restore streams for brown trout.

Variations in behavioral traits are widely recognized to drive animal behaviors exhibited within a population. However, information on how behavior traits influence behavior in anthropogenically modified habitats is lacking. Many habitats have become highly fragmented as a result of human processes. To mitigate this and improve habitat connectivity, wildlife passes are increasingly employed, with the aim of enabling animals to move freely between habitats. However, wildlife passes (e.g., fishways) are not always effective in achieving passage and it remains uncertain what factors play a role in an individual's likelihood of passing successfully. This study measured three behavioral traits (boldness, exploration, and activity) in juvenile brown trout (Salmo trutta; n = 78) under field conditions within a river and tested whether these behavior traits influenced both the passage success and the behaviors exhibited during upstream fishway passage attempts. Although behavioral traits were found and collapsed into two behavioral trait dimensions, behavioral traits had low repeatability and so did not contribute to a personality spectrum. Boldness was found to negatively influence the number of passage attempts carried out by an individual and to positively influence passage success, with bolder individuals carrying out fewer attempts and having an increased probability of passage success. No behavioral traits were found to be related to other passage metrics (passage success, Time until First Attempt, and Passage Duration) during the first passage. But all three behavioral traits were significantly negatively related to the changes in passage behaviors at consecutive, successful passage attempts, with bolder, more exploratory and more active individuals passing through a fishway quicker on the second passage than on the first. This study suggests that bolder and more active individuals may perform better during fishway passage attempts, particularly within rivers where multiple barriers to movement exist., Information on how behavior traits influence behavior in anthropogenically modified habitats is lacking. We show that an individual's boldness influences the interactions fish have with fishways (wildlife passes) and that boldness, exploration, and activity influence interactions at multiple fishways. These interactions may lead to fitness consequences and may result in selection for specific behavioral and physiological characteristics.

A new record of a marble trout mtDNA haplotype known to be restricted to Adriatic basin (called marmoratus lineage within Salmo trutta complex) has been reported from Eşen Stream in the Aegean Sea basin of southeastern Turkey, based on sequence data of the mitochondrial DNA control region. The results of this study showed a single unique haplotype from this population, called MATR1. Phylogenetic analyses of this haplotype along with other haplotypes belonging to different mitochondrial DNA lineages of the S. trutta complex confirmed the existence of the marmoratus lineage in Turkey, suggesting a possible river capture between the Adriatic and Aegean Sea basins until the last (Würmian) marine regression.

This paper reports heavy metal and metalloid accumulation in wild brown trout (Salmo trutta L., 1758 complex) raised in freshwater and uncontaminated Sardinia system (Italy). Metals are widespread pollutants of aquatic systems, and their contamination can originate from anthropogenic activities such as industrial waste, agricultural and domestic environments, and geochemical release. Fish has a relevant position within the human diet; moreover, fishes can accumulate metals, making them a valuable tool as biomarkers for risk assessment studies. The concentration of 22 metals and metalloids after chemical digestion was assessed by inductively coupled plasma-optic emission spectroscopy (ICP-OES) in both the guts and the edible part (EP, muscle + skin) of brown trout. The results, expressed as μg g−1, showed different levels of accumulation in the EP and guts, following the series Cu > Zn > Ba > Al > Sr > Fe > Pb and Fe > Al > Hg > As > Mn > Cu > Ba > B > Zn > Pb, respectively. PCA analysis showed a fairly good correlation between the total lipid and SAFA content and Cd, Hg, and Pb accumulation in the gut. Non-carcinogenic risk assessment, expressed as THQ (target hazard quotient), showed values far below 1 for all metals in muscles, while high As and Hg contamination of the gut draws attention to possible health risks which should be discarded from the fish before consumption. TR (target cancer risk) values showed alarmingly high values for As and Cd when the fish were consumed entirely (gut + EP), while Pb levels were far below the safety levels.

Species–environment relationships were studied between the occurrence of 13 fish and lamprey species and 9 mainly map‐based environmental variables of Finnish boreal small streams. A self‐organizing map (SOM) analysis showed strong relationships between the fish species and environmental variables in a single model (explained variance 55.9%). Besides basic environmental variables such as altitude, catchment size, and mean temperature, land cover variables were also explored. A logistic regression analysis indicated that the occurrence probability of brown trout, Salmo trutta L., decreased with an increasing percentage of peatland ditch drainage in the upper catchment. Ninespine stickleback, Pungitius pungitius (L.), and three‐spined stickleback, Gasterosteus aculeatus L., seemed to benefit from urban areas in the upper catchment. Discovered relationships between fish species occurrence and land‐use attributes are encouraging for the development of fish‐based bioassessment for small streams. The presented ordination of the fish species in the mean temperature gradient will help in predicting fish community responses to climate change., Species–environment relationships were studied between the occurrence of 13 fish and lamprey species and 9 mainly map‐based environmental variables of Finnish boreal small streams. Modelling fish species occurrence in streams with a logistic regression and self‐organizing map indicated clear species–environment relationships. The results support the development of fish‐based bioassessment for small streams and help in predicting fish assemblage changes in a warming climate.

Nodular Gill Disease (NGD) in highly intensive farming systems plays a major role in production losses and its outbreaks can result in cumulative mortality exceeding 60%, especially during the winter months and early spring. NGD was described in rainbow trout farms of North America and Europe and appears to be caused by different species of amoebae, for example both testate (Roghostoma minus) and naked amoebae belonging to five genera. In the last few years, NGD is widespread in rainbow trout farms of northern and central Italy. In March 2017, during the epidemiological investigations into NGD in salmonid farms of northern Italy, the first cases of branchitis referable to amoebic infection in juvenile brown trout (Salmo trutta L.) were observed. Twenty‐five live and moribund brown trout from each tank were collected at monthly intervals from March to May 2017 for a total of 150 fish. The samples were subjected to necropsy, parasitological analysis, histology and bacteriological and virological examinations for diagnostic purposes. Histological examination of gills from diseased and moribund brown trout showed characteristic pathological signs of NGD infection. The most significant change was the development of heavy gill lesions with variable degrees of lamellar fusion, especially in the distal part of filaments (clubbing), with obliteration of interlamellar spaces. A limited number of amoebae were detected along the surface of the gills. The lesions observed in fresh mounts and in histological sections obtained from the gills of the infected brown trout confirmed to be less serious than those detected in affected rainbow trout of the same farm. Therefore, this investigation, which reports for the first time NGD in brown trout, has shown that S. trutta would be less susceptible to this pathology than rainbow trout.

International audience; The introduction of the use of molecular data has caused debates on the taxonomy of Corsican and Sardinian trouts, also referred to as Tyrrhenian trouts (i.e. Salmo trutta, Salmo macrostigma, Salmo cettii). A recent study by Delling et al. (2020) (Morphologic and genetic characterization of Corsican and Sardinian trout with comments on Salmo taxonomy. Knowl Manage Aquat Ecosyst 421: 21) introduces important evidence regarding the taxonomy of these populations. However, their subsequent denomination as Salmo sp., that is, an undefined taxon, could have serious consequences on their future conservation management plans. Considering their threatened status, the Tyrrhenian trouts should be referred to as Salmo trutta until the ongoing taxonomic uncertainty can be unambiguously resolved. These populations must then be treated as an Evolutionary Significant Unit (ESU) or as an Operational Conservation Unit (OCU) for further conservation managements plans, as already done for other Mediterranean trout lineages.; La taxonomie des truites corses et sardes, également appelées truites tyrrhéniennes (i.e. Salmo trutta, Salmo macrostigma, Salmo cettii) a fait l'objet de débats depuis l'utilisation des premières données moléculaires. Une étude récente de Delling et al. (2020) (Morphologic and genetic characterization of Corsican and Sardinian trout with comments on Salmo taxonomy. Knowl Manage Aquat Ecosyst 421: 21) a présenté des éléments importants sur la taxonomie de ces populations. Cependant, leur dénomination comme Salmo sp. – i.e. espèce non déterminée − qui s'ensuivit, pourrait avoir de graves conséquences en terme de gestion future de la conservation de ces populations. Compte tenu de leur statut menacé, les truites tyrrhéniennes devraient être appelées Salmo trutta jusqu'à ce que l'incertitude taxonomique actuelle puisse être résolue sans ambiguïté. Ces populations doivent ensuite être traitées comme une Unité Évolutive Importante (ESU) ou comme une Unité Opérationnelle de Conservation (OCU) pour les futures gestions de conservation, comme c'est déjà le cas pour d'autres lignées de truites méditerranéennes.

Individual growth of juvenile offspring of anadromous and freshwater resident brown trout Salmo trutta and crosses between the two from the River Imsa, Norway was estimated. The juveniles were incubated until hatching at two temperatures (±SD), either 4.4 ± 1.5 °C or 7.1 ± 0.6 °C. Growth rate was estimated during 22 days in August-September when the fish on average were about 8 g in wet mass, and the estimates were standardized to 1 g fish dry mass. Offspring of anadromous S. trutta grew better at both 15 and 18 °C than offspring of freshwater resident S. trutta or offspring of crosses between the two S. trutta types. This difference appears not to result from a maternal effect because anadromous S. trutta grew better than the hybrids with anadromous mothers. Instead, the difference appears to be an inherited difference between the anadromous and the freshwater resident fish lending support to the hypothesis that anadromous and freshwater resident S. trutta in this river differ in genetic expression. Egg incubation temperature of S. trutta appeared not to influence later growth as earlier reported from studies of Atlantic salmon Salmo salar. This article is protected by copyright. All rights reserved.

Background In species showing partial migration, as is the case for many salmonid fishes, it is important to assess how anthropogenic pressure experienced by migrating individuals affects the total population. We focused on brown trout (Salmo trutta) from the Guddal River in the Norwegian Hardanger Fjord system, which encompasses both resident and anadromous individuals. Aquaculture has led to increased anthropogenic pressure on brown trout during the marine phase in this region. Fish traps in the Guddal River allow for sampling all ascending anadromous spawners and descending smolts. We analyzed microsatellite DNA markers from all individuals ascending in 2006–2016, along with all emigrating smolts in 2017. We investigated (1) if there was evidence for declines in census numbers and effective population size during that period, (2) if there was association between kinship and migration timing in smolts and anadromous adults, and (3) to what extent resident trout were parents of outmigrating smolts. Results Census counts of anadromous spawners showed no evidence for a decline from 2006 to 2016, but were lower than in 2000–2005. Estimates of effective population size also showed no trends of declines during the study period. Sibship reconstruction of the 2017 smolt run showed significant association between kinship and migration timing, and a similar association was indicated in anadromous spawners. Parentage assignment of 2017 smolts with ascending anadromous trout as candidate parents, and assuming that unknown parents represented resident trout, showed that 70% of smolts had at least one resident parent and 24% had two resident parents. Conclusions The results bear evidence of a population that after an initial decline has stabilized at a lower number of anadromous spawners. The significant association between kinship and migration timing in smolts suggests that specific episodes of elevated mortality in the sea could disproportionally affect some families and reduce overall effective population size. Finally, the results based on parentage assignment demonstrate a strong buffering effect of resident trout in case of elevated marine mortality affecting anadromous trout, but also highlight that increased mortality of anadromous trout, most of which are females, may lower overall production in the system.

Freshwater acidification is characterised by elevated concentrations of aqueous aluminium. Global emissions of acidifying agents are reduced due to international agreements, and freshwater acidification has shifted from chronic to a more episodic character. The recovery of fish populations in acidified areas is likely to depend on the individual’s ability to recover from short-time aluminium exposures. We exposed brown trout (Salmo trutta) to an Al-rich medium, nominal concentration 600 µg L–1, for 0.5, 2, 6, 8 and 11 hours, before transfer to circumneutral Al-poor water for recovery. As controls, fish were either exposed for 11 hours to an acidified Al-poor medium or to untreated water. Some mortality during the first 24 hours of the recovery period occurred in fish exposed for 11, 8 and 6 hours to aluminium. No mortality during recovery was observed in the remaining groups. Aluminium exposure led to increased haematocrit and plasma lactate concentration, decreased plasma chloride concentration, deposition of aluminium on gill surfaces, and morphological alteration of the gill structures. The responses depended on exposure time. Aluminium deposited on the gill disappeared and plasma lactate levels were at control levels after 1 day in the recovery water, while haematocrit and plasma chloride levels were at control levels after 14 days of recovery. Gills in fish exposed to aluminium for 11 hours were almost fully recovered after 14 days. We conclude that the toxic response in brown trout exposed to an acutely toxic aluminium challenge is reversible. Moreover, the first 24 hours after aluminium exposures is the most critical period for the fish recovery. Further, it takes no more than 14 days for brown trout to fully recover from an acute toxic aluminium exposure, and only 1 day if the aluminium challenge is moderate.

Biological invasions are important causes of biodiversity loss, particularly in remote islands. Brown trout (Salmo trutta) have been widely introduced throughout the Southern Hemisphere, impacting endangered native fauna, particularly galaxiid fishes, through predation and competition. However, due to their importance for sport fishing and aquaculture farming, attempts to curtail the impacts of invasive salmonids have generally been met with limited support and the best prospects for protecting native galaxiids is to predict where and how salmonids might disperse. We analysed 266 invasive brown trout from 14 rivers and ponds across the Falkland Islands as well as 32 trout from three potential source populations, using a panel of 592 single nucleotide polymorphisms (SNPs) and acoustic tagging, to ascertain their origins and current patterns of dispersal. We identified four genetically distinct clusters with high levels of genetic diversity and low admixture, likely reflecting the different origins of the invasive brown trout populations. Our analysis suggests that many trout populations in the Falklands may have originated from one of the donor populations analysed (River Wey). The highest genetic diversity was observed in the rivers with the greatest number of introductions and diverse origins, while the lowest diversity corresponded to a location without documented introductions, likely colonized by natural dispersal. High levels of gene flow indicated widespread migration of brown trout across the Falkland Islands, likely aided by anadromous dispersal. This is supported by data from acoustically tagged fish, three of which were detected frequently moving between two rivers ~26 km apart. Our results suggest that, without containment measures, brown trout may invade the last remaining refuges for the native endangered Aplochiton spp. We provide new insights into the origin and dispersal of invasive brown trout in the Falkland Islands that can pave the way for a targeted approach to limit their impact on native fish fauna.

Long-term data from marked animals provide a wealth of opportunities for studies with high relevance to both basic ecological understanding and successful management in a changing world. The key strength of such data is that they allow us to quantify individual variation in vital rates (e.g. survival, growth, reproduction) and then link it mechanistically to dynamics at the population level. However, maintaining the collection of individual-based data over long time periods comes with large logistic efforts and costs and studies spanning over decades are therefore rare. This is the case particularly for migratory aquatic species, many of which are in decline despite their high ecological, cultural and economical value. This paper describes two unique publicly available time series of individual-based data originating from a 51-year mark-recapture study of a land-locked population of large-sized migratory brown trout (Salmo trutta) in Norway: the Hunder trout. In the period 1966-2015, nearly 14,000 adult Hunder trout have been captured and individually marked during their spawning migration from Lake Mjøsa to the river Gubrandsdalslågen. Almost a third of those individuals were later recaptured alive during a later spawning run and/or captured by fishermen and reported dead or alive. This has resulted in the first data series: a mark-recapture-recovery dataset spanning half a century and more than 18,000 capture records. The second data series consists of additional data on juvenile and adult growth and life-history schedules from half of the marked individuals, obtained by means of scale-sample analysis. The two datasets offer a rare long-term perspective on individuals and population dynamics and provide unique opportunities to gain insights into questions surrounding management, conservation and restoration of migratory salmonid populations and freshwater ecosystems.

Water temperature is one of the most important abiotic parameters in rivers having direct and indirect effects on fish. Especially cold-water species like the brown trout (Salmo trutta) are limited by high temperatures. Beside direct physiological stress, higher water temperatures also reinforce the emergence of diseases. In this study we investigate thermal regimes of rivers based on a large-scale dataset covering Austria (approximately 70,000 km²). The analyses aim to clarify to what extent water temperatures support the emergence of proliferative kidney disease (PKD) and assemble physiological stress for brown trout under current and future climate conditions. Data from 274 gauging stations at 184 rivers were used to calibrate a water temperature model and to investigate critical water temperature thresholds. Therefore, we developed a risk assessment scheme to identify river reaches that already have or will develop critical thermal regimes for brown trout in respect of PKD emergence and thermal physiological stress. The results revealed severe changes in the thermal regimes of the investigated rivers under climate change. Furthermore, the variable characterising riparian vegetation played a vital role to explain cooling of the water in downstream direction. In respect of PKD, the amount of river reaches having unlikely outbreaks of PKD decreased from 72.6 % under current conditions to 37.7 % in the far future RCP8.5 scenario. Within small rivers that currently showed optimal thermal regimes over large extents (10,244 km), the habitat suitability will be reduced by combined effects of PKD and physiological stress to 6,554 km. In general, suitable habitats of S. trutta will shift upstream, thus to higher altitudes, and to smaller, alpine rivers in Austria. The warming leads to physiological stress that induces a diminished growth due to the non-positive transition of caloric values to growth as well as cardiac dysfunction in brown trout. These factors will further restrict the distribution of brown trout. However, the results also underline the enormous importance of the alpine region as a future refuge for brown trout in Central Europe. Thus, this study will help to inform managers to timely develop robust conservation strategies.

Changes in abiotic and biotic factors between seasons in subarctic lake systems are often profound, potentially affecting the community structure and population dynamics of parasites over the annual cycle. However, few winter studies exist and interactions between fish hosts and their parasites are typically confined to snapshot studies restricted to the summer season whereas host‐parasite dynamics during the ice‐covered period rarely have been explored. The present study addresses seasonal patterns in the infections of intestinal parasites and their association with the diet of sympatric living Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) in Lake Takvatn, a subarctic lake in northern Norway. In total, 354 Arctic charr and 203 brown trout were sampled from the littoral habitat between June 2017 and May 2018. Six trophically transmitted intestinal parasite taxa were identified and quantified, and their seasonal variations were contrasted with dietary information from both stomachs and intestines of the fish. The winter period proved to be an important transmission window for parasites, with increased prevalence and intensity of amphipod‐transmitted parasites in Arctic charr and parasites transmitted through fish prey in brown trout. In Arctic charr, seasonal patterns in parasite infections resulted mainly from temporal changes in diet toward amphipods, whereas host body size and the utilization of fish prey were the main drivers in brown trout. The overall dynamics in the community structure of parasites chiefly mirrored the seasonal dietary shifts of their fish hosts., Seasonal variation in prevalence and intensity of trophically transmitted intestinal parasites hosted by Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) in high‐latitude lakes is linked to dietary shifts occurring throughout the seasons. Winter proved to be an important transmission window, with increased prevalence and intensity of amphipod‐transmitted parasites in Arctic charr and parasites transmitted through piscivory in brown trout. In Arctic charr, seasonal patterns in intestinal parasite infections resulted mainly from temporal changes in diet towards amphipods, whereas host body size and the utilization of fish prey were the main drivers in brown trout.

Previous studies with olfactory-disturbing pesticides resulted after exposure in disturbed behavior and physiology in fish. In the present experiment, reproductive behavior and milt volumes of precocious brown trout (Salmo truttaL.) male parr were studied in a large stream aquarium after exposure to the olfactory-disturbing fungicide 15 μg l−1IPBC (iodocarb; 3-iodo-2-propynyl butyl carbamate) for 96 h. The statistical analyses did not reveal any significant differences for time attending females between controls and IPBC-exposed males. Furthermore, there were no significant differences in milt volumes. However, when taking all fish into consideration, there were significant differences in milt volumes between parr that had been attending females and those had not been attending females. Controls that had attended females had significantly higher milt volumes than controls or IPBC-exposed males that had not attended females. Taking all control and IPBC parr into consideration, there was a statistically significant positive correlation between time attended females and volume of milt and gonadosomatic index (GSI), respectively. In summary, 15 μg l−1IPBC did not have any significant effects on mature male parr reproductive behavior and milt volumes.

With rapid global change, organisms in natural systems are exposed to a multitude of stressors that likely co‐occur, with uncertain impacts. We explored individual and cumulative effects of co‐occurring environmental stressors on the striking, yet poorly understood, phenomenon of facultative migration. We reared offspring of a brown trout population that naturally demonstrates facultative anadromy (sea migration), under different environmental stressor treatments and measured life history responses in terms of migratory tactics and freshwater maturation rates. Juvenile fish were exposed to reduced food availability, temperatures elevated to 1.8°C above natural conditions or both treatments in combination over 18 months of experimental tank rearing. When considered in isolation, reduced food had negative effects on the size, mass and condition of fish across the experiment. We detected variable effects of warm temperatures (negative effects on size and mass, but positive effect on lipids). When combined with food restriction, temperature effects on these traits were less pronounced, implying antagonistic stressor effects on morphological traits. Stressors combined additively, but had opposing effects on life history tactics: migration increased and maturation rates decreased under low food conditions, whereas the opposite occurred in the warm temperature treatment. Not all fish had expressed maturation or migration tactics by the end of the study, and the frequency of these ‘unassigned’ fish was higher in food deprivation treatments, but lower in warm treatments. Fish showing migration tactics were smaller and in poorer condition than fish showing maturation tactics, but were similar in size to unassigned fish. We further detected effects of food restriction on hypo‐osmoregulatory function of migrants that may influence the fitness benefits of the migratory tactic at sea. We also highlight that responses to multiple stressors may vary depending on the response considered. Collectively, our results indicate contrasting effects of environmental stressors on life history trajectories in a facultatively migratory species.

Individual fish identification and recognition is an important step in the conservation and management of fisheries. One of most frequently used methods involves capturing and tagging fish. However, these processes have been reported to cause tissue damage, premature tag loss, and decreased swimming capacity. More recently, marine video recordings have been extensively used for monitoring fish populations. However, these require visual inspection to identify individual fish. In this work, we proposed an automatic method for the identification of individual brown trouts, Salmo trutta. We developed a deep convolutional architecture for this purpose. Specifically, given two fish images, multi-scale convolutional features were extracted to capture low-level features and high-level semantic components for embedding space representation. The extracted features were compared at each scale for capturing representation for individual fish identification. The method was evaluated on a dataset called NINA204 based on 204 videos of brown trout and on a dataset TROUT39 containing 39 brown trouts in 288 frames. The identification method distinguished individual fish with 94.6% precision and 74.3% recall on a NINA204 video sequence with significant appearance and shape variation. The identification method takes individual fish and is able to distinguish them with precision and recall percentages of 94.6% and 74.3% on NINA204 for a video sequence with significant appearance and shape variation.

Saprolegnia infections are among the main parasitic diseases affecting farmed salmonids. The distribution and potential transfer of Saprolegnia spp. between farms and the natural environment has been scarcely investigated. Therefore, this work aimed to study the diversity and abundance of oomycete species in salmonid farms, tributary water, and effluent water systems. Four trout farms in Italy and two Atlantic salmon farms in Scotland were considered. In Italian farms, 532 isolates of oomycetes were obtained from fish and water, at upstream, inside, and downstream the farms. In Scottish farms, 201 oomycetes isolates were obtained from water outside the farm and from fish and water inside the farming units. Isolates were identified to the species level through amplification and sequencing of the ITS rDNA region. In Italy, S. parasitica was significantly more present in farmed than in wild fish, while in water it was more frequently isolated from the wild, particularly in effluent systems, not associated with more frequent isolation of S. parasitica in wild fish downstream the farm. In Scotland, S. parasitica was the most prevalent species isolated from fish, while isolates from water were mostly Pythium spp. with few S. parasitica isolates from upstream and downstream the farms., European Union’s Horizon 2020 research and innovation programme under grant agreement No. 634429

Phenotypic plasticity can be viewed as the first level of defense of organism homeostasis against environmental stress and therefore represents the potential to deal with rapid environmental changes. Transitions between low complexity, artificial environments and complex, natural habitats can promote phenotypic plasticity. Here, we conducted an experimental introduction with juvenile brown trout to evaluate the plasticity of shape in response to a transition between contrasting environments. We released 202 juvenile trout reared under hatchery conditions in a natural stream and analyzed changes in shape and morphological variability after 5 months. A geometric morphometrics approach based on 14 landmarks was used to compare changes in body shape for 37 fish recaptured at the end of the experiment. A similar number of hatchery and wild fish caught at the receptor stream were used as controls for shape in the two environments. After 5‐months, fish showed significant change in shape, shifting from elongated to robust shapes, and affecting to the relative position of the caudal peduncle. These new shapes were closer to wild than to the hatchery shapes, suggesting a process of rapid phenotype change. Moreover, these changes were concomitant with a marked increase in morphological variability. Our results support the hypothesis that phenotypic plasticity is a major potential for adjustment to environmental change but not the idea that shape can be constrained by initial shapes. We confirmed the “increased” variance hypothesis and phenotype convergence with wild morphs. This has important implications because stresses the role of phenotypic plasticity as a buffer that allows organisms to cope with important environmental discontinuities at time scales that preclude the onset of adaptive adjustments. We suggest that environmental conditioning and shape plasticity can overcome both reduced morphological diversity and phenotype uncoupling with habitat characteristics resulting from initial rearing in low complexity artificial environments.

International audience; Gathering information on both individual movement and gene flow is rarely possible when studying dispersal among populations in fish species. It is, however, possible to assess both at a reasonable cost in Salmo trutta L. on the Atlantic coast of Europe where the facultative anadromous species is composed of discrete populations of brown trout residents occupying distinct river systems, but exchanging phenotypically distinguishable sea trout migrants. We performed two kinds of genetic analyses using individual microsatellite genotypes: the stock identification of sea trout entering each corridor and the estimates of effective dispersal through each corridor. We observed that individual movement (nonlocal individuals of each source population ranging from 4% to 35% of the sea trout run) never translates into effective dispersal except in one of four migratory corridors examined. The likely origin of this uniquely detected gene flow event is discussed in the light of well-documented migratory fish management actions undertaken in the past in the studied area.

Purpose. To study food resources, feeding conditions and trophic relationships of the brown trout (Salmo trutta morpha fario), rainbow trout (Oncorhynchus mykiss), and European grayling (Thymallus thymallus) in a Transcarpatioan river. Methodology. The material on the food resources and feeding of the brown trout, rainbow trout, and European grayling was collected in summer period of 2012 on the Shypit river. The study was performed on two different sites of the river: the first one was located on the middle pre-mountain reach of the river (upstream of the Hydroelectric power plant), the second one – on the mountain reach of the river (near tourist base) on typical biotopes: I – with boulders and riffles with fast current; II – with medium size stones and low riffles with moderate current; III – with small stones, sand and slow current. The material was collected and processed according to standard and unified hydrological, ichthyological, and trophological methods. Findings. We studied the level of macrozoobenthos development and obtained data on feeding and trophic relationships among brown trout, rainbow trout, and European grayling on different biotopes on pre-mountain and mountain reaches of the Shypit river. The number of “soft” macrozoobenthos on different biotopes varied from 972 to 2576 ind./m2 with biomasses from 6.3 to 121.8 g/m2. Total diet overlap index (DOI) between brown trout and rainbow trout on the biotope with boulders and fast current in the pre-mountain reach was 32.4% by number and 20.3% by biomass, while that on the mountain reach was 49.6% and 52.9%, respectively. On the biotope with medium size stones and moderate current, the diet overlap index between rainbow trout and European grayling in the pre-mountain reach was 19.0% by number and 27.9% by biomass. Originality. First study of the diet and tropic relationships of the brown trout, rainbow trout, and еuropean grayling on different reached of the Shypit river. Practical value. The results of this work can be used when calculating the amounts of brown trout, rainbow trout, and European grayling to be stocked into rivers of the Transcarpathian region.

Despite that the study of individual repeatability is a common topic in behavioral ecology, virtually nothing is known about inter-annual variability in the marine migratory behavior of iteroparous salmonids that can complete multiple feeding migrations in their lifespan. Behavioral data from 38 anadromous brown trout (Salmo trutta), tracked by acoustic telemetry in 2–3 consecutive marine feeding migrations in two Norwegian fjord systems, were analyzed for intra-individual repeatability in key aspects of their marine migration. Individual brown trout displayed significant inter-annual consistency in marine area use and in the timing of marine exit (i.e. when they returned to spawning rivers), but not in the timing of marine entry or the time spent in the marine environment each year. Our study raises new questions about how anadromous brown trout respond to changing conditions and anthropogenic factors in the marine environment. Intra-individual repeatability of brown trout linked to changing environmental conditions should therefore be a focus for future studies. Copyright © 2019 Eldøy, Bordeleau, Crossin and Davidsen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY)

Many species are capable of facultative migration, but the relative roles of extrinsic versus intrinsic factors in generating diverse migratory tactics remain unclear. Here we explore the proximate drivers of facultative migration in brown trout in an experimental laboratory setting. The effects of reduced food, as a putative environmental cue, were examined in two populations: one that exhibits high rates of anadromy (sea-migration) in nature, and one that does not exhibit anadromy in nature. Juveniles derived from wild-caught parents were reared for two years under four environmental treatments: low food in years 1 and 2 (Low-Low); high food in years 1 and 2 (High-High), low food in year 1 and high in year 2 (Low-High), and vice versa (High-Low). Food restriction had a significant effect on migratory tactics, with the frequency of smolts (juveniles choosing migration) highest in the Low-Low treatment in both populations. No individuals became smolts in the High-High treatment, and intermediate smolting rates were observed in the Low-High and High-Low treatments. Higher overall smolting rates in the naturally anadromous population suggested an inherited component to anadromy/migration decisions, but both populations showed variability in migratory tactics. Importantly, some fish from the naturally non-anadromous population became smolts in the experiment, implying the capacity for migration was lying ‘dormant’, but they exhibited lower hypo-osmoregulatory function than smolts from the naturally anadromous population. Tactic frequencies in the naturally anadromous population were more affected by food in the 2nd year, while food in the 1st year appeared more important for the naturally non-anadromous population. Migratory tactics were also related to sex, but underpinned in both sexes by growth in key periods, size and energetic state. Collectively these results reveal how migration decisions are shaped by a complex interplay between extrinsic and intrinsic factors, informing our ability to predict how facultatively migratory populations will respond to environmental change.

This study investigated the influence of temperature (4, 8 and 12 degrees C) on development and survival of brown trout (Salmo trutta) fry. The three aims of this study were: (a) to propose a typology of malformations; (b) to compare malformation types between live and dead fry and (c) to establish relationships between temperature and malformation occurrences. It was found 20 single malformations and 39 combinations of two or more malformations. Comparison between dead and live fry at different development stages (hatching, emergence and first food intake) showed that malformations of yolk sac were predominant at hatching and then decreased, while malformations of skeleton or multiple malformations were higher thereafter. All dead fry, and only 14% of live fry were malformed. Dead fry were mainly characterized by yolk sac malformations and multiple malformations whatever the temperature. Live fry showed a higher rate of skeleton malformations at 12 degrees C, and the different types of malformations were equally represented at two other temperatures (4 and 8 degrees C). To conclude, it is suggested that some malformations (yolk sac at hatching, yolk sac associated with skeleton malformations at emergence and skeleton at first food intake or combinations of malformations at all stages) might be lethal as they were founding dead fry and that temperature influences differently the occurrence of malformations.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples; International audience; Investigating the variables driving synchrony in populations and the spatial scales at which they operate is worthwhile for both a basic understanding of population dynamics and for management. Various environmental classifications have been developed to group sites according to predefined similarities in abiotic variables (with spatial and/or temporal components) and to explain population dynamics in running waters. These classifications may be useful to managers and decision makers, as studies have shown relationships between time-dependent population variability and environmental classifications on different spatial scales. We investigated whether synchrony among brown trout (Salmo trutta) populations could be explained by three regional (hydro-ecoregions, hydrological units, and natural flow regime classification) and one local environmental classification and their associated variables. We first analysed whether densities of two size classes (0+ and >0+ fish) varied over a large spatial scale (i.e. 112 sites spread throughout France sampled for >11 years). We then determined whether the degree of synchrony matched the spatial patterns defined by the environmental classifications. Finally, we investigated whether variables such as river distance between sites, hydrology, and temperature were associated with patterns of synchrony. Overall, relationships observed between synchronies in environmental variables and trout population densities were weak. Synchrony was best explained by the classification based on hydrological units, defined as discrete physical units that provided boundaries with real biological significance for river assemblages (12% for 0+ density and 9% for >0+ density and total densities). However, when considering environmental variables alone, synchrony in trout populations was mainly associated (from 11% to 23%) with seasonal flow variables such as high flows during reproductive and emergence periods. Temperature and river distance did not explain synchrony between trout populations. High flows during emergence appear to be a key driver of brown trout population dynamics. Floods during the reproductive period could explain synchrony among brown trout populations, although the effect was weaker than that of high flows during the emergence period. We concluded that existing physical, morphological, and biogeographical classifications at regional spatial scales were not sufficiently integrative to account for environmental drivers (such as flow variables) that were most associated with the spatiotemporal patterns of synchrony in trout populations. Flow explained synchrony better than classifications did. Further investigations should focus on the spatial patterns of flow variations during the emergence and reproductive periods to derive geographical areas that best capture synchrony patterns in trout dynamics. This approach could be extended to other freshwater fish species for which climatic drivers are important, and may help to explain the distributional changes of exotic species, the propensity of populations to fluctuate synchronously and the scale of synchrony patterns under different scenarios of climate change, or the threat of extinction of native species if the Moran effect is high. © 2019 John Wiley and Sons Ltd.

International audience; Growth is a fundamental ecological process of stream-dwelling salmonids which is strongly interrelated to critical life history events (emergence, mortality, sexual maturity, smolting, spawning). The ability to accurately model growth becomes critical when making population predictions over large temporal (multi-decadal) and spatial (meso) scales, e.g., investigating the effect of global change. Body length collection by removal sampling is a widely-used practice for monitoring fish populations over such large scales. Such data can be efficiently integrated into a Hierarchical Bayesian Model (HBM) and lead to interesting findings on fish dynamics. We illustrate this approach by presenting an integrated HBM of brown trout (Salmo trutta) growth, population dynamics, and removal sampling data collection processes using large temporal and spatial scales data (20 years; 48 sites placed along a 100 km latitudinal gradient). Growth and population dynamics are modelled by ordinary differential equations with parameters bound together in a hierarchical structure. The observation process is modelled with a combination of a Poisson error, a binomial error, and a mixture of Gaussian distributions. Absolute fit is measured using posterior predictive checks, which results indicate that our model fits the data well. Results indicate that growth rate is positively correlated to catchment area. This result corroborates those of other studies (laboratory, exploratory) that identified factors besides water temperature that are related to daily ration and have a significant effect on stream-dwelling salmonid growth at a large scale. Our study also illustrates the value of integrated HBM and electrofishing removal sampling data to study in situ fish populations over large scales.

Background Enormous variability in skin colour and patterning is a characteristic of teleost fish, including Salmonidae fishes, which present themselves as a suitable model for studying mechanisms of pigment patterning. In order to screen for candidate genes potentially involved in the specific skin pigment pattern in marble trout (labyrinthine skin pattern) and brown trout (spotted skin pattern), we conducted comparative transcriptome analysis between differently pigmented dermis sections of the adult skin of the two species. Results Differentially expressed genes (DEGs) possibly associated with skin pigment pattern were identified. The expression profile of 27 DEGs was further tested with quantitative real-time PCR on a larger number of samples. Expression of a subset of ten of these genes was analysed in hybrid (marble x brown) trout individuals and compared with the complexity of their skin pigment pattern. A correlation between the phenotype and the expression profile assessed for hybrid individuals was detected for four (gja5, clcn2, cdkn1a and tjp1) of the ten candidate genes tested. The potential role of these genes in skin pigment pattern maintenance is discussed. Conclusions Our results indicate that the maintenance of different pigment patterns in trout is dependent upon specific communication—involving gap junctions, tight junctions and ion channels—between chromatophores present in differentially pigmented skin regions. Electronic supplementary material The online version of this article (10.1186/s12864-019-5714-1) contains supplementary material, which is available to authorized users.

Proliferative kidney disease (PKD) is an emerging disease of salmonids caused by the myxozoan parasite Tetracapsuloides bryosalmonae, which plays a major role in the decrease of wild brown trout (Salmo trutta) populations in Switzerland. Strong evidence demonstrated that water temperature modulates parasite infection. However, less knowledge exists on how seasonal water temperature fluctuations influence PKD manifestation under field conditions, how further environmental factors such as water quality may modulate the disease, and whether these factors coalesce with temperatures role possibly giving rise to cumulative effects on PKD. The aims of this study were to (1) determine the correlation between seasonal course of water temperature and PKD prevalence and intensity in wild brown trout populations, (2) assess if other factors such as water quality or ecomorphology correlate with the infection, and (3) quantitatively predict the implication of these factors on PKD prevalence with a statistical model. Young-of-the-year brown trout were sampled in 45 sites through the Canton of Vaud (Switzerland). For each site, longitudinal time series of water temperature, water quality (macroinvertebrate community index, presence of wastewater treatment plant effluent) and ecomorphological data were collected and correlated with PKD prevalence and intensity. 251 T. bryosalmonae-infected trout of 1,118 were found (overall prevalence 22.5%) at 19 of 45 study sites (42.2%). Relation between PKD infection and seasonal water temperature underlined that the mean water temperature for June and the number of days with mean temperature ≥15°C were the most significantly correlated parameters with parasite prevalence and intensity. The presence of a wastewater treatment plant effluent was significantly correlated with the prevalence and infection intensity. In contrast, macroinvertebrate diversity and river ecomorphology were shown to have little impact on disease parameters. Linear and logistic regressions highlighted quantitatively the prediction of PKD prevalence depending on environmental parameters at a given site and its possible increase due to rising temperatures. The model developed within this study could serve as a useful tool for identifying and predicting disease hot spots. These results support the importance of temperature for PKD in salmonids and provides evidence for a modulating influence of additional environmental stress factors.

Due to the ecological concerns and preservation of genetic resources, the characterization of genetic structure of the brown trout (Salmo trutta) was carried out on the "Braduljica" fish farm. DNA was isolated from fin clips of 10 individuals, and after that molecular PCR-RFLP methods were used for distinguishing between Atlantic and Danubian lineages based on control region of the mitochondrial DNA (CR mtDNA) and lactate dehydrogenase gene of the nuclear DNA (LDH nDNA). Based on phenotypic characteristics it was estimated that out of 10 individuals included in this study five belonged to the allochtonous Atlantic lineage and remaining five belonged to the native Danubian lineage of brown trout. However, results of molecular analyses showed a high percentage of allochthonous genes among the individuals, which confirms the hybridization between these two lineages. Also, the results showed that the selection based on the phenotype is not adequate. In order to continue with proper broodstock management, it is necessary to eliminate allochtonous individuals of the Atlantic lineage from the broodstock.

International audience; Inland and diadromous fish stocks can support important ecological, social and cultural functions. However, many of these stocks are data-limited and do not have formal state assessments or management reference points. Empirical surveillance indicators of relative abundance and population size-structure may provide an accessible first-step for monitoring such stocks. These indicators could be informed and interpreted via expert knowledge of specific systems and stock histories. The current study focused on an international scientific working group that met in 2017-2019. The group collated long-term monitoring data for sea trout Salmo trutta from six salmonid 'index rivers' in France, Ireland, Wales, Northern Ireland and Sweden. Indicators were selected, and time series of abundance-and length-based metrics for each river were presented on a new visual indicator plot. Expert knowledge from each system was elicited through one-to-one interviews to provide a corresponding stock narrative, in which indicator trends reflected known historical pressure-state events. The accessible presentation of simple empirical indicators supports elicitation of local expert knowledge, and provides an accessible framework for surveillance and reference-direction assessment of data-limited sea trout stocks. This approach could be applied to inland or diadromous stocks where available data are restricted to estimates of relative abundance and size-structure.

International audience; Individual interactions are crucial to many ecological processes but are difficult to quantify for long periods in aquatic animals. In this study, we applied a digital proximity logging device recently developed for terrestrial animals to a freshwater fish, the brown trout (Salmo trutta L.). After preliminary calibration and quantification of detection errors, we recorded the interactions occurring between five male and four female brown trout in an artificial channel during one week of the spawning season. The 55,637 logs recorded allowed us to describe the encounter network and its fine scale evolution. In particular, the time spent with females varied a lot across males, from two to 24 h in a five-day period, and the males, which spent the most time with females tended to mate more. At the individual level, the temporal distribution of encounters reflected shifts in dominance status, with males sequentially taking over exclusive proximity with females before spawning. Beyond sexual encounters, the method presented here could be applied to many processes interesting to fish ecologists, such as predator-prey interactions, intra and interspecific competition or disease transmission

Accepted manuscript version. Published version available in Effects of fish species composition on Diphyllobothrium spp. infections in subarctic brown trout - is three-spined stickleback a key species? (2016) 39(11), s.1313-1323. . Subarctic populations of brown trout (Salmo trutta) are often heavily infected with cestodes of the genus Diphyllobothrium, assumedly because of their piscivorous behavior. This study explores possible associations between availability of fish prey and Diphyllobothrium spp. infections in lacustrine trout populations. Trout in i) allopatry (group T); ii) sympatry with Arctic charr (Salvelinus alpinus) (group TC); and iii) sympatry with charr and three-spined stickleback (Gasterosteus aculeatus) (group TCS) were contrasted. Mean abundance and intensity of Diphyllobothrium spp. were higher in group TCS compared to group TC and group T. Prevalence however was similarly higher in group TCS and group TC compared to group T. Zero-altered negative binomial modelling identified lowest probability of infection in group T and similar probabilities of infection in group TC and group TCS, whereas the highest intensity was predicted in group TCS. Evidently, the most infected trout were from the group co-occurring with stickleback (TCS), assumedly due to a high availability of suitable prey fishes. In conclusion, our study demonstrates elevated Diphyllobothrium spp. infections in lacustrine trout populations where fish prey are available, and suggests that highly available and easily caught stickleback prey may play a key role in the transmission of Diphyllobothrium spp. parasite larvae.

The aims of this study were to determine the prevalence and phylogenetic relationship of motile Aeromonas spp. that might be pathogenic species for rainbow trout in infected/mix infection cases (based upon different outbreaks on fish farms). A total of 99 motile Aeromonas isolates (and three reference strains) were analysed that were isolated from four different fish species in different sizes of fish (0.1-3,000 g), different months and water temperatures (6.1-21.2 degrees C). The biochemical characteristics of the isolates were determined using conventional tests and a rapid test kit. Additionally, molecular identification was performed using the gyrB housekeeping gene region and with glycerophospholipid-cholesterol acyltransferase polymerase chain reaction (GCAT-PCR). The sequencing results obtained from the gyrB gene region were deposited in the GenBank database, and phylogenetic relationships were determined with the BioNumerics 7.6 database. Nearly half of the Aeromonas isolates that were isolated from rainbow trout showing signs of disease were determined to be possible infectious agents. Aeromonas species exhibit biochemical variability for many characters, so some Aeromonas species tested negative for GCAT-PCR despite that this test was created especially for Aeromonas identification. The phylogenetic tree based upon gyrB contained 10 different phylogroups that were based on 96% cut-off value in gyrB gene region. Ministry of Food, Aqriculture and Animal Husbandry (TAGEM/14/AR-GE/26)

Body composition (total crude protein, lipid, ash, dry matter and moisture) and fatty acid profiles were compared between wild and farmed brown trout and between farmed rainbow trout. Farmed brown trout contained the highest amount of crude protein (18.39%), whereas farmed rainbow trout contained higher levels of crude lipid (2.35%). Thirty six fatty acids were found, including sixteen saturated fatty acids (SFA), nine monounsaturated fatty acids (MUFA) and eleven polyunsaturated fatty acids (PUFA). The most abundant SFA in all fish were palmitic acid and stearic acid. However, the most abundant fatty acids in all trout samples were MUFA and PUFA. MUFA were the most abundant fatty acid in farmed brown trout because of high abundance of oleic acid in this samples (35.46g / 100g fatty acids). PUFA were predominating in the samples of wild brown trout and of rainbow trout 56.16 and 56.29g/100g fatty acids, respectively). Linoleic acid was the most abundant fatty acid reported in the rainbow trout (47.17g/100g fatty acids). Significantly higher amounts of docosahexaenoic acid, α-linolenic acid, arachidonic acid and eicosapentaenoic acid were observed in the wild trout samples. Wild brown trout contained significantly more docosahexaenoic acid, α-linolenic acid, Eicosapentaenoic acidArachidonic acid. Sensory quality evaluation, by a consumers’ panel, revealed all samples were equally well accepted. A composição corporal (teores de proteína, gordura total, cinzas, matéria seca e humidade) e os perfis de ácidos gordos da trutafário (selvagem e proveniente de aquacultura) e da truta-arco-íris (cultivada) foram comparados. A truta-fário cultivada continha a maior quantidade de proteína bruta (18,39%), enquanto a truta arco-íris possuía teores mais elevados de lípidos (2,35%). Foram detectados 36 ácidos graxos, incluindo 16 ácidos graxos saturados (SFA), nove ácidos graxos monoinsaturados (MUFA) e 11 ácidos graxos poliinsaturados (PUFA). Os SFA mais abundantes foram o ácido palmítico e o ácido esteárico. No entanto, os ácidos graxos mais abundantes em todas as amostras de truta foram os MUFA e os PUFA. A grande abundância de ácido oleico existente nas amostras de truta-fário cultivada (35,46g/100g de ácidos graxos) faz com que os MUFA sejam os ácidos graxos mais abundantes nesta variedade de truta (42,43g/100g de ácidos graxos) Nas amostras de truta-fário selvagem e nas de truta arco-íris predominaram os PUFA (56,16 e 56,29g/100g de ácidos graxos, respetivamente), sendo o ácido linoleico o mais abundante na truta-arco-íris (47,17g/100g de ácidos graxos). Nas amostras trutafário selvagem foram observadas quantidades significativamente mais elevadas de ácido docosahexaenóico, ácido α-linolênico, ácido acidoaraquidônico e ácido eicosapentaenóico. Todas as amostras foram igualmente bem aceitas por um painel de consumidores. info:eu-repo/semantics/publishedVersion

Large and long-lived piscivorous brown trout, Salmo trutta, colloquially known as ferox trout, have been described from a number of oligotrophic lakes in Britain and Ireland. The "ferox" life history strategy is associated with accelerated growth following an ontogenetic switch to piscivory and extended longevity (up to 23 years in the UK). Thus, ferox trout often reach much larger sizes and older ages than sympatric lacustrine invertebrate-feeding trout. Conventional models suggest that S. trutta adopting this life history strategy grow slowly before a size threshold is reached, after which, this gape-limited predator undergoes a diet switch to a highly nutritional prey source (fish) resulting in a measurable growth acceleration. This conventional model of ferox trout growth was tested by comparing growth trajectories and age structures of ferox trout and sympatric invertebrate-feeding trout in multiple lake systems in Scotland. In two of the three lakes examined, fish displaying alternative life history strategies, but living in sympatry, exhibited distinctly different growth trajectories. In the third lake, a similar pattern of growth was observed between trophic groups. Piscivorous trout were significantly older than sympatric invertebrate-feeding trout at all sites, but ultimate body size was greater in only two of three sites. This study demonstrates that there are multiple ontogenetic growth pathways to achieving piscivory in S. trutta and that the adoption of a piscivorous diet may be a factor contributing to the extension of lifespan.

Juvenile salmonids experience high mortality when negotiating lentic waters during their downstream migration to the sea. The development of artificial lakes and wetlands in streams has become a widely used management tool to reduce nutrient load to coastal areas. Such wetlands may threaten anadromous populations. In this study we quantify net ground speed of downstream migrating brown trout Salmo trutta smolts in equally long stream and lake sections in a Danish lowland stream and artificial lake. This was done by passive integrated transponder telemetry in 2016 and 2017. Mean net ground speed in the stream section was 36.58 km day-1 and 0.8 km day-1 in the lake section. This decrease of net ground speed through the lake may lead to prolonged exposure to predators and probably contributes to high mortalities threatening anadromous populations.

There is considerable variation in glucocorticoid (GC) baseline status and stress responses of individuals, yet the cause and consequence of this variation remains ambiguous. Attempts to relate GC levels to fitness and life-history trade-offs have yielded variable results. In this study, we evaluated whether baseline and poststressor GC hormone concentrations predicted migration strategy (i.e., resident or migrant) and successful seaward migration in a partially migrating population of juvenile brown trout (Salmo trutta Linnaeus, 1758). Baseline (N = 99) or poststressor (N = 102) plasma cortisol concentrations were obtained from brown trout and they were tagged with passive integrated transponder (PIT) and released in a natural Danish stream. Subsequently, fish were tracked with PIT reader systems and the stream was resampled for resident individuals. GC levels were not found to be associated with recapture of resident individuals or migration propensity to our first tracking station (S1), but increased baseline (and not poststressor) GC levels were associated with increased passage from S1 to our second tracking station, which anecdotally was an area of high predation or challenge. Our study found no evidence to suggest that cortisol regulates the migration life history in juvenile brown trout, but intermediate increases in baseline GC (and not poststressor GC) levels may favor migration performance.

International audience; While there is a long-history of biological invasions and their ecological impacts have been widely demonstrated across taxa and ecosystems, our knowledge on the temporal dynamic of these impacts remains extremely limited. Using a meta-analytic approach, we investigated how the ecological impacts of non-native brown trout (Salmo trutta), a model species with a 170-year-long and well-documented history of intentional introductions across the globe, vary with time since introduction. We first observed significant negative ecological impacts immediately after the species introduction. Second, we found that the negative ecological impacts decrease with time since introduction and that the average ecological impacts become nonsignificant more than one century after introduction. This pattern was consistent across other ecological contexts (i.e., geographical location, levels of biological organization, and methodological approach). However, overall negative ecological impacts were more pronounced at the individual and population levels and in experimental studies. While the mechanisms leading to this decrease remain to be determined, our results indicate that rapid response of native organisms (e.g. adaptation, but also local extinction) may play an important role in this dynamic. Changes in native species traits and local extinction can have important conservation implications. Therefore, we argue that the decline of the negative ecological impacts over time should not be used as an argument to neglect the negative impacts of biological invasions

International audience; Brown trout (Salmo trutta L.) was voluntarily introduced in some rivers of the Kerguelen Islands in the 1950s–1960s. Fish originating from hatcheries rapidly colonized other streams, thanks to the early occurrence of anadromous (i.e., migratory) form. Getting insight into the success of colonization requires investigating fitness-related traits such as growth and reproductive investment. In particular, increased growth and body size—traits that are broadly related to dispersal ability—are predicted on colonization front, to the possible detriment of reproductive ability. We here report such investigation on early data following the first natural reproductions in the founder populations of Kerguelen, from 1971 to 1994, assessing the main characteristic on growth at sea and reproductive investment for both sexes. Our results reveal that growth of sea trout is excellent with individuals fully benefiting from their relatively short period of growth at sea, sizes and weights ranking among the highest recorded to date. During the reproduction period, males lose on average 15–21% of their weight, whereas females lose 18–19% of their weight. Although a trade-off between growth and reproduction may arise at marginal distribution of invasive species, our study indicates that any potential advantages arising from increased growth and therefore potential dispersal ability may not be directly balanced by reduced reproductive investment, with respect to other published studies. Results overall shed light on intrinsic invasiveness of the brown trout in a post-glacial landscape with barely any interaction with human activities.

The biological and anthropogenic (management) factors that may contribute to the expansion of non-native lineages in managed fish have been studied in this work taking brown trout (Salmo trutta) as a model species. The changes of users’ opinion about stocking was studied employing social science methodology (surveys). The evolution of hatchery stocks together with the outcome of stocking were analysed with two genetic tools: the LDH-C1* locus (marker of non-native stocks) and six microsatellite loci (for assignment of wild trout to the natural population or putative hatchery stocks). Consulted stakeholders were convinced of the correctness of releasing only native stocks, although in practice the hatcheries managed by them contained important proportions of non-native gene carriers. Our results suggest that allochthonous individuals perform better and grow faster in hatchery conditions than the native ones. We also find a dilution of the impact of this kind of suplementation in wild conditions. The use of only native individuals as hatchery breeders tested for the presence of non-native alleles previously to the artificial crosses must be a priority. Surveys can help steer policy making toward decisions that will be followed by the public, but they should not be used to justify science.

International audience; Intraspecific diversity can be strongly impacted by the dynamics of reproductive isolation during secondary contacts. The high levels of hybridisation and introgression between Atlantic and Mediterranean lineages in contemporary populations of brown trout in the Northern part of the French Alps are a good case in point. After a long period of allopatry, which one assumes has facilitated their divergent phenotypic and genetic evolution, man has removed a geographical reproductive barrier via stocking the Atlantic lineage in the Mediterranean area, thereby potentially enabling gene flow between native and non native populations. We investigate how much a prezygotic reproductive behaviour, that is female preference for male phenotype, can influence hybridisation in natural environments, using subaquatic video recording of reproduction. Our statistical model indicates that female preference appears to be largely heterogamous: females tend to select dissimilar males with respect to their own phenotype; thus, rather than acting as a barrier to gene flow, female preference is favouring gene flow between lineages that have been artificially placed in sympatry. This finding based on observational data is in agreement with previously reported genetic data, high levels of hybridisation between the lineages. We suggest that a knowledge of reproductive behaviour in natural environments is an essential tool for biodiversity managers to assess the potential risks associated with the introduction into recipient populations of non-native lineage fish at the intraspecific level

Stocking with eggs has been widely used as a management measure to support degraded salmonid stocks. In Finland, Atlantic salmon and both sea-migrating and lake-migrating brown trout are stocked as eggs, alevins, fry, parr, and smolt, whereas trout are also stocked as mature fish. The aim of this stocking is to improve catches and to support collapsed spawning stocks. We assessed the success of stocking with brown trout eggs in a study of 17 Finnish boreal forest rivers, of which 9 were subject to egg stocking. All rivers contained some naturally spawning trout. In 16 rivers, including non-stocking years and unstocked rivers, egg stocking did not increase the total (wild and stocked) density of 0-year-old parr. However, those rivers with higher existing trout densities in non-stocking years seemed to benefit most from stocking, suggesting some role of river-specific extrinsic factors affecting egg-to-parr survival. In one river monitored for 14 years, only a weak correlation was found between the total density of 0-year-old parr and the number of eggs stocked. However, in nine parr samples from five rivers, the mean proportion of parr derived from stocked eggs was 40%. The mean survival to first autumn parr of egg-stocked and wild individuals was 1.0 and 3.3%, respectively. Probable reasons for the detected low to moderate impact of egg-stocking are (i) large variation in total parr density between years and rivers, (ii) small number of stocked eggs, (iii) placing egg boxes and egg pockets in unsuitable microhabitats, and (iv) unsuitable emergence time of egg-stocked individuals, or other extrinsic factors creating extra mortality. We recommend field and laboratory experiments to improve and standardize stocking methods, and monitoring the connection of wild spawning stocks and parr recruitment. Finally, we encourage fishery authorities to create clear management goals for threatened wild salmonid stocks.

The aim of the study was to assess the growth and development of sea trout, Salmo trutta L., fry obtained from frozen, thawed semen after the fish had been released into the wild and were feeding there. The semen was cryopreserved with either methanol (MeOH) or dimethyl sulfoxide (DMSO). Fresh eggs were collected and fertilized with the thawed semen. The control was eggs fertilized with fresh semen that had been kept on ice. The eggs were incubated and reared in a closed recirculating system. The fertilized eggs were counted for visible eye pigment. After rearing, three groups of fish were tagged and stocked into a stream. The fish aged 6 months were caught from the stream. The fish were measured, weighed, identified to which experimental variant they belonged, and their survival rate was estimated. No significant differences in survival rate, length, weight, or condition factor among the control, DMSO, and MeOH groups were noted during larval development in a closed recirculating system. These parameters were also similar in the control and experimental groups after the fish had grow in a natural stream. The use of frozen semen to fertilize fresh sea trout eggs resulted in a normal incubation process, larval stage, and regular fry growth and survival, both under laboratory conditions, and, most importantly, in the wild. The results indicate it is possible to use frozen semen for fry production and the restoration of wild fish populations.

High-density linkage maps are valuable tools for conservation and eco-evolutionary issues. In salmonids, a complex rediploidization process consecutive to an ancient whole genome duplication event makes linkage maps of prime importance for investigating the evolutionary history of chromosome rearrangements. Here, we developed a high-density consensus linkage map for the brown trout (Salmo trutta), a socio-economically important species heavily impacted by human activities. A total of 3,977 ddRAD markers were mapped and ordered in 40 linkage groups using sex- and lineage-averaged recombination distances obtained from two family crosses. Performing map comparison betweenS. truttaand its sister speciesSalmo salarrevealed extensive chromosomal rearrangements. Strikingly, all of the fusion and fission events that occurred after theS.salar/S.truttaspeciation happened in the Atlantic salmon branch, whereas the brown trout remained closer to the ancestral chromosome structure. Using the strongly conserved synteny within chromosome arms, we aligned the brown trout linkage map to the Atlantic salmon genome sequence to estimate the local recombination rate inS.truttaat 3,721 loci. A significant positive correlation between recombination rate and within-population nucleotide diversity (π) was found, indicating that selection constrains variation at linked neutral sites in brown trout. This new high density linkage map provides a useful genomic resource for future aquaculture, conservation and eco-evolutionary studies in brown trout.