The passage efficiency of downstream migrating brown trout (Salmo trutta) smolts past two hydropower plants in the River Emån, southeastern Sweden, was evaluated by telemetry. From 26 April to 17 May 2005, 40 wild brown trout smolts were radio-tagged, and their positions were recorded daily until 14 June. Approximately 45% of the individuals passed both power plants, and 15% made it to the sea, some 28 km downstream of the power plants. About 20% of the individuals ceased migrating, residing in a lotic habitat. Mortality due to predation was 33%, and the predation rate was higher in the power plant dams than it was downstream of the power plants. Turbine-induced mortality was greater in the upper power plant (40%) than in the lower one (13%). Fish that chose the alternative routes, through the gates, swam past the upper dam faster than fish that swam through the turbines. The results confirm previous work in the river, namely that measures need to be taken to improve passage efficiency past the power plants, particularly passage of the upper power plant. Such measures are of crucial importance if the nature-like bypass channels at the power plants in Finsjö are going to have any long-term effects on the brown trout population. / Passageeffektiviteten för nedströms vandrande havsöringssmolt (Salmo trutta) förbi två vattenkraftverk i Emån, i sydöstra Sverige, utvärderades med telemetri. Från 26 april till och med 17 maj 2005 märktes 40 vilda havsöringssmolt med radiosändare och de positionsbestämdes dagligen till och med 14 juni. Ungefär 45% av individerna passerade båda kraftverken, och 15% klarade sig till havet, cirka 28 km nedströms kraftverken. Omkring 20% av individerna avbröt vandringen och stannade i ett lotiskt habitat. Mortalitet på grund av predation uppgick till 33%, och predationshastigheten var högre i kraftverksdammarna än nedströms kraftverken. Den turbininducerade mortaliteten var högre i det övre kraftverket (40%) än i det nedre (13%). Det gick fortare att passera den övre kraftverksdammen för fisk som valde de alternativa rutterna, genom dammluckorna, jämfört med att passera genom turbinerna. Dessa resultat bekräftar tidigare studier i ån, nämligen att åtgärder krävs för att förbättra passageeffektiviteten förbi kraftverken, i synnerhet passagen av det övre kraftverket. Sådana åtgärder är av avgörande betydelse om de naturlika fiskvägarna vid kraftverken i Finsjö ska få några långsiktiga effekter på havsöringspopulationen.

Les anàlisis realitzades en cent deu poblacions de truita comuna (Salmo trutta) que abarquen el seu rang natural de distribució indiquen que el patró filogenètic es relaciona amb les tres grans vessants on es troba distribuïda l'espècie: ponto-càspia, atlàntica i mediterrània. Aquesta diferenciació estaria associada a l'aïllament de les vessants durant el Quaternari. L'origen de l'espècie es relaciona amb la vessant ponto-càspia, d'acord amb els models biogeogràfics que postulen l'origen asiàtic de la ictiofauna europea. S'ha detectat també un segon nivell de divergència dins de cada vessant que dóna com a resultat l'existència de sis llinatges evolutius: Atlàntic i Duero a la vessant atlàntica, els llinatges Adriàtic, Mediterrani i Marmoratus als rius mediterranis, i el llinatge Danubi a la zona ponto-càspia.Les glaciacions del Pleistocè han modificat profundament el rang de distribució de la truita comuna, especialment a la vessant atlàntica, on s'han proposat quatre grans refugis glacials: a l'est de la capa de gel, a Europa central, a l'entorn del canal de la Mànega i a l'entorn del golf de Biscaia; tot i que només els tres primers haurien participat en la recolonització del nord d'Europa al final de l'última glaciació. El quart refugi, que inclou el sud de França i el Cantàbric hauria estat l'origen de l'expansió cap al sud durant el Pleistocè Superior d'un grup de poblacions distribuïdes actualment a la vessant atlàntica ibèrica, i també hauria servit de base per a l'expansió cap al nord d'altres grups de truita durant interglacials anteriors.A la vessant atlàntica de la peninsula Ibèrica, l'estructura poblacional es troba associada a la xarxa hidrogràfica i es determinen fins a cinc unitats poblacionals: les truites dels rius Cantàbrics, les del Miño, les del Duero, les del Tajo i les del Guadalquivir. Les poblacions del Guadalquivir pertanyerien a un grup d'influència mediterrània. Els marcadors d'al·lozims i de DNA mitocondrial es troben fortament correlacionats en aquesta vessant, on apunten cap als mateixos grups de poblacions. Per contra, els rius de la vessant mediterrània haurien estat colonitzats pels llinatges Adriàtic i Mediterrani i s'hauria produït una intensa intergradació secundària entre aquests llinatges durant els períodes glacials a partir de l'expansió de les poblacions retingudes a les capçaleres durant els interglacials. Els grups de hibridació, l'aïllament i la deriva en el període interglacial fa que els grups de poblacions identificats pels marcadors d'al·lozims i de DNA mitocondrial no coincideixin. / The analyses performed in one hundred and ten brown trout (Salmo trutta) populations that cover its native European distribution, shows that the phylogenetic pattern is associated with the three major basins occupied by the species: Ponto-Caspian, Atlantic and Mediterranean. This differentiation is related with basin isolations during the Quaternary. The origin of the species is placed in the Ponto-Caspian region, in clear agreement with biogeographic models that postulates the Asian origin of European ichthyofauna. Further divergence occurred in the mid-lower Pleistocene generated the actual lineages: Atlantic and Duero in the Atlantic basin, Adriatic, Mediterranean and Marmoratus lineages in the Mediterranean rivers and the Danubian lineage in the Ponto-Caspian area.Pleistocene glacial periods have deeply modified the distribution range of brown trout, mainly in the Atlantic basin, where four major glacial refugia have been proposed: (i), at the East side of the ice sheet, (ii), in Central Europe, (iii), around the English Channel and (iv), around the Bay of Biscay. Only the three first seem to be involved in the recolonization of North Europe at the end of the last glacial period. The fourth glacial refugia, placed in Southern France and the Cantrabrian Sea area, would have been the origin of a southern expansion during Late Pleistocene. Nowadays, those trout populations are distributed in the Atlantic basin of the Iberian Peninsula. This glacial refugia could also be involved in older recolonizations of North-Europe previous to last glacial process.Brown trout population structure in areas at the Atlantic basin of the Iberian Peninsula is associated with river network. Thus, five trout population groups could be determined: trout from the Cantabrian Rivers, from the Miño River, from the Duero River, from the Tajo River and trout populations from the Guadalquivir basin. These last populations show a strong Mediterranean influence. In this basin, comparisons involving allozyme and mitochondrial DNA data are strongly correlated and points towards the same population groups. The rivers in the Mediterranean basin have been colonized by Adriatic and Mediterranean lineages, and strong secondary intergradations are reported among them during glacial periods. Population groups identified by allozyme and mitochondrial DNA do not agree as a consequence of this intergradation, as well as isolation and genetic drift during interglacial periods.

Diss. (sammanfattning). Umeå : Sveriges lantbruksuniv. / Härtill 6 uppsatser.

Freshwater sport fisheries contribute substantially to the economies of England and Wales. However, many trout fisheries rely partly or entirely on stocking farmed trout to maintain catches within freshwater fisheries. Farmed trout often differ genetically from their wild counterparts and wild trout could be at risk of reduced fitness due to interbreeding or competition with farmed fish. Therefore, to protect remaining wild brown trout (Salmo trutta L) populations and as a conservation measure, stocking policy has changed. Legislation introduced by the Environment Agency (EA, 2009) will now only give consent to stocking of rivers and some stillwaters with sterile, all-female triploid brown trout. There are reliable triploidy induction protocols for some other commercially important salmonid species however; there is limited knowledge on triploid induction in brown trout. Previously, triploid brown trout have been produced by heat shocks although reduced survivals were obtained suggesting that an optimised heat shock had not been identified, or that heat shock gives less consistent success than hydrostatic pressure shock (HP), which is now recognised as a more reliable technique to produce triploid fish. Thus the overall aim of this thesis was to conduct novel research to support the aquaculture and freshwater fisheries sector within the United Kingdom by optimising the production and furthering the knowledge of triploid brown trout. Firstly, this PhD project investigated an optimised triploidy induction protocol using hydrostatic pressure (Chapter 2). In order to produce an optimised hydrostatic pressure induction protocol three experiments were conducted to (1) determine the optimal timing of HP shock application post-fertilisation, (2) define optimal pressure intensity and duration of the HP shock and (3) study the effect of temperature (6-12 °C) on triploid yields. Results indicated high survival to yolk sac absorption stage (69.2 - 93.6 %) and high triploid yields (82.5 - 100 %) from the range of treatments applied. Furthermore, no significant differences in triploid rates were shown when shock timings and durations were adjusted according to the temperature used. In all treatments deformity prevalence remained low during incubation (<1.8 %) up to yolk sac absorption (~550 degree days post hatch). Overall, this study indicated that the optimised pressure shock for the induction of triploidy in brown trout delivering high survival and 100 % triploid rate (a prerequisite to brown trout restocking) is a shock with a magnitude of 689 Bar applied at 300 Centigrade Temperature Minutes (CTM) for 50 CTM duration. Regarding the assessment of triploid status, the second experimental chapter tested the accuracy and efficacy of three ploidy verification techniques (Chapter 3). Techniques studied were erythrocyte nuclei measurements (Image analysis), flow cytometry (Becton Dickinson Facscalibur flow cytometer) and DNA profiling (22 polymorphic microsatellite loci) to assess the effectiveness of triploidy induction in brown trout. Results indicated the validity of using erythrocyte indices major nuclear axis measurements, flow cytometric DNA distributions expressed as relative fluorescence (FL2-Area), and polymorphic microsatellite loci (Ssa410UOS, SSa197, Str2 and SsaD48) for assessing ploidy status in brown trout. Accuracy of each technique was assessed and indicated that all techniques correctly identified ploidy level indicating 100 % triploid rate for that commercial batch of brown trout. These techniques may be utilised within aquaculture and freshwater fisheries to ensure compliance with the legislation introduced by the EA. As a result of the legislation introduced by the Environment Agency triploid brown trout will freely interact with diploid trout therefore there is a need to assess feeding response and behavioural differences between diploid and triploid trout prior to release. Therefore, in the third experimental chapter (Chapter 4) diploid and triploid brown trout were acclimated for six weeks on two feeding regimes (floating/sinking pellet). Thereafter, aggression and surface feeding response was compared between pairs of all diploid, diploid and triploid and all triploid brown trout in a semi natural stream (flume). In each pairwise matching, fish of similar size were placed in allopatry and rank determined by the total number of aggressive interactions initiated. Dominant individuals initiated more aggression than subordinates, spent more time defending a territory and positioned themselves closer to the food source (Gammarus pulex) whereas subordinates occupied the peripheries. When ploidy was considered, diploid trout were more aggressive than triploid, and dominated their siblings when placed in pairwise matchings. However, surface feeding did not differ statistically between ploidy irrespective of feeding regime. Triploids adopted a sneak feeding strategy while diploids expended more time defending a territory. In addition, an assessment of whether triploids exhibited a similar social dominance to diploids when placed in allopatry was conducted. Although aggression was lower in triploid pairs than in the diploid/triploid pairs, a dominance hierarchy was observed between individuals of the same ploidy. Dominant triploid fish were more aggressive and consumed more feed items than subordinate individuals. Subordinate fish displayed a darker colour index than dominant fish suggesting increased stress levels. However, dominant triploid fish seemed more tolerant of subordinate individuals and did not display the same degree of invasive aggression as observed in the diploid/diploid or diploid/triploid matchings. These novel findings suggest that sterile triploid brown trout feed similarly but are less aggressive than diploid trout and therefore may provide freshwater fishery managers an alternative to stocking diploid brown trout. In addition to research at the applied level in triploid brown trout, this thesis also examined the fundamental physiological effects of ploidy in response to temperature regime. Triploid salmonids have been shown to differ in their tolerance to environmental temperature. Therefore the fourth experimental chapter (Chapter 5) investigated whether temperature tolerance affected feed intake and exercise recovery. Diploid and triploid brown trout were exposed to an incremental temperature challenge (10 and 19 °C) and subsequent survival and feed intake rates were monitored. Triploids took longer to acclimate to the increase in temperature however feed intake were significantly greater in triploids at high temperature. In a follow on study, we investigated post-exercise recovery processes under each temperature regime (10 and 19 °C). Exhaustion was induced by 10 minutes of forced swimming, with subsequent haematological responses measured to determine the magnitude of recovery from exercise. Plasma parameters (alkaline phosphatase, aspartate aminotransferase, calcium, cholesterol, triglycerides, phosphorous, total protein, lactate, glucose, pH, magnesium, osmolality, potassium, sodium, chloride, lactate dehydrogenase) were measured for each ploidy. Basal samples were taken prior to exercise and then at: 1; 4, and 24 hours post-exercise. Contrary to previous studies, there was no triploid mortality during or after the exercise at either temperature. Although diploid and triploid brown trout responded metabolically to the exercise, the magnitude of the response was affected by ploidy and temperature. In particular, triploids had higher levels of plasma lactate, osmolality, and lower pH than diploids at 1 hour post exhaustive exercise. By 4 hours post-exercise plasma parameters analysed had returned to near basal levels. It was evident that the magnitude of the physiological disturbance post-exercise was greater in triploids than diploids at 19 °C. This may have implications where catch and release is practiced on freshwater fisheries. Overall, this work aimed to develop and/or refine current industry induction and assessment protocols while better understand the behaviour and physiology of diploid and triploid brown trout. The knowledge gained from this work provides aquaculture and freshwater fisheries with an optimised protocol, which delivers 100 % triploid rates and profitability without compromising farmed trout welfare, thus ultimately leading towards a more sustainable brown trout industry within the United Kingdom.

I Österdalälven har mängden Siljansöring (Salmo trutta) minskat avsevärt på grund av kraftverk som stoppar fiskens vandringsvägar. För att lyckas med att stärka beståndet krävs en fördjupad kunskap kring fiskens beteendemönster, bland annat rörelser i samband med uppströms lekvandring. Denna studie är ett försök att ge en överblick av den lekmogna Siljansöringens uppströmsvandring i Österdalälven och se om det föreligger några skillnader mellan odlad/vild öring respektive hanar/honor. Genom akustisk telemetri har 18 Siljanöringars rörelser längs en begränsad älvsträcka registrerats under 56 dagar. Analys har gjorts för hitta variationer både rumsligt och tidsmässigt samt mellan odlade/vilda Siljansöringar respektive honor/hanar, likväl som skillnader avseende rörelser, tim- och dygnsaktivitet och benägenhet att söka sig uppströms till det definitiva vandringshindret Spjutmo kraftverk. Siljansöringarna rörde sig mer under dagen jämfört med natt vilket skulle kunna kopplas till påverkan från elproduktion och vattenströmmar som skapas vid Spjutmo kraftverks turbinutlopp och/eller att dagsljuset är en fördel då de använder sig av synintryck för att kunna navigera. Skillnader (dock ej statistiskt säkerställda) kunde urskiljas mellan odlade och vilda fiskar och hanar/honor, såsom exempelvis att vild fisk simmade längre sträckor än odlad. Studier som denna är viktiga för att kunna få en helhetsbild kring livsvillkor och beteendemönster för Siljansöring och därigenom lyckas med framtida förvaltnings- och åtgärdsarbeten. / The number of Siljan trout (Salmo trutta) in the River Österdalälven has declined due to hydropower development. To restore the river information about the behavioural patterns of the trout, such as upstream migration, are needed. The aim of this study is to describe the upstream movements of tagged Siljan trout as well as to identify differences between hatchery-reared and wild trout and between males and females. During 56 days, 18 individuals tagged with acoustic telemetry transmitters were registered in a section of the River Österdalälven. The data were analysed to identify variation in time and space as well as differences between origin (hatchery-reared vs wild trout) and sex. Analyses were also performed on hourly and diel movement patterns and if the fish swam upstream to the first migration barrier, the power station in Spjutmo. Variation in diurnal activity was identified, with higher activity during daytime compared to night, which might be related to power production in relation to currents flowing from turbine outlets and/or the importance of daylight for effective navigation. There were no significant differences identified between hatchery-reared and wild trout, respectively, nor were there any sex-related differences. Information obtained from this study is important to understand the situation for Siljan trout, to help in future management and restoration of this valuable stock of trout.

Many populations of salmonids are threatened by fragmentation and degradation of spawning habitats. Common remedial measures are habitat restoration and stocking of hatchery fish to support degraded wild populations. Many populations of brown trout in Sweden have been extirpated. The restoration plan for the endangered brown trout in Lake Siljan started decades ago and involves releases of hatchery produced trout. A decline of the spawning run of hatchery fish has been observed. In this study, wild and hatchery fish were tagged and monitored using hydroacustic telemetry during May-October, 2018. Movement patterns were studied to detect potential differences between wild and hatchery fish during lake and spawning migration. The results showed a difference of preferred territories between the groups. The wild trout stayed in the northern part of the lake and the hatchery trout were more evenly distributed over the lake, but with a preference for the southern part of the lake. During spawning migration a larger proportion of the wild trout (44 %) moved to potential spawning habitats as compared to hatchery trout (16 %). The wild fish migrated more or less direct to the potential spawning grounds in River Österdal as compared to the hatchery fish, which showed an erratic behavior and preferred to migrate to the tributaries in Lake Siljan. Differences in movement patterns and preferred habitats in the lake can be caused by differences in behavior between the groups. This should motivate more studies of behavior of wild and hatchery trout. The time for spawning and potential spawning habitats are also important to study for future management and restoration of the wild population of brown trout in Lake Siljan. / Många salmonider är idag hotade av habitatfragmentering och brist på lekplatser. För att främja kvarvarande bestånd är vanliga åtgärder habitatrestaurering och utsättning av odlad fisk. Många bestånd av sjövandrande öring i Sverige är idag försvunna. I sjön Siljan har man under årtionden satt ut odlad fisk då den vilda stammen av siljansöringen är starkt hotad. En minskning av återvändande uppströmsvandrande odlad lekfisk har uppmärksammats. Vild och odlad öring märktes med sändare och data samlades in med akustisk telemetri under maj till oktober, 2018. Eventuella skillnader i rörelsemönster mellan fisk av olika ursprung har studerats under tillväxtperiod och lekmigration. Resultatet visade att det finns skillnader i var fiskarna uppehåller sig i sjön beroende på ursprung. Den vilda öringen föredrog den norra delen av Siljan, den odlade var mer spridd i hela sjön men föredrog den södra delen av sjön. Under tid för lekmigration rörde sig en större andel av den vilda fisken (44 %) mot potentiella lekhabitat jämfört med den odlade (16 %). Den vilda fisken var mer fokuserad i sin vandring mot Österdalälven än den odlade som uppvisade ett erratiskt beteende och som i större utsträckning besökte biflöden som mynnar i Siljan. Skillnader i rörelsemönster och placering i sjön kan bero på beteendeskillnader och interaktioner mellan grupperna. Detta borde öka intresset för att studera detta vidare hos den vilda och odlade öringen. Önskvärt är också att öka kunskapen om lekperiod och potentiella lekhabitat för att kunna upprätta ett effektivt åtgärdsprogram som ger ökade möjligheter för en återhämtning av den vilda populationen.

Les recherches menées sur les populations de truite à l'aval des barrages ont mis en évidence l'influence de nombreuses contraintes naturelles. Dans un premier temps, une analyse de la dynamique de 3 populations de truite (Salmo trutta), combinée à une analyse multi-sites (53 sites) des relations entre les populations et leur cadre d'habitat physique en TCC, ont mis en évidence différents éléments structurants. Le premier filtre est la largeur du cours d'eau. A cela se surimpose un forçage par les crues naturelles. En outre, le niveau de fragmentation du réseau hydrographique lié à la taille du barrage influence la variabilité du stade juvénile, tandis que le degré de reconstitution du débit le long du TCC détermine en partie l'abondance de truite. Dans un second temps, le travail a consisté à caractériser pour l'ensemble du parc hydroélectrique EDF le cadre géophysique général dans lequel s'inscrivent les différents types de tronçons de cours d'eau salmonicoles soumis à l'influence d'ouvrages hydroélectriques. 15 types ont ainsi été définis sur la base de leur appartenance à l'un des trois massifs Alpes, Pyrénées et Massif Central, de la combinaison de 2 caractéristiques hydromorphologiques majeures (pente et module), et du régime hydrosédimentaire. Finalement, le croisement des connaissances générales issues de la littérature sur les impacts des ouvrages sur les populations de truite, des connaissances spécifiques acquises via l'analyse multi-sites avec les types de situation ouvrages/milieu permet de tirer des enseignements généraux sur les sensibilités a priori des habitats des cours d'eau d'une région.

<p>The hydropower industry has altered connectivity in many rivers during the last century. Many fish species depend on both an intact longitudinal connectivity to be able to migrate between spawning, feeding and winter habitats, and vertical connectivity for development and survival of incubating embryos and larvae in the gravel. The objective of this thesis was to examine problems and remedial measures associated with disrupted longitudinal and vertical connectivity in regulated rivers. The issue of longitudinal connectivity was studied in the River Emån by evaluating the efficiency of two nature-like fishways for anadromous brown trout. Telemetry studies showed that the combined efficiency for the two fishways in 2001-2004 was 60.5%. The passage efficiencies of both fishways were high for trout (89-100%), but also for other species such as chub, perch, tench, burbot and roach (74%). The attraction efficiencies were largely dependent on power plant operation, and generally high for the fishway situated next to the tail-race and low for the fishway situated inside the former channel. More than half of the trout spawners were also observed using the fishways for downstream passage. The densities of brown trout yearlings upstream of the fishways were higher after the fishways were built than during pre-fishway years. Smolts produced upstream of the fishways were observed migrating downstream in 2003-2005. The percentage of smolts that passed both power plants in was 51%, with losses being attributed to predation (15%), turbine-induced mortality (16%) and other reasons (18%). Turbine-induced mortality was higher (40%) at the power plant with four small Francis runners, than at the power plant with one large Kaplan runner (12%). The issue of vertical connectivity was studied in three rivers in Värmland, one unregulated, and two regulated, one of which had no minimum flow requirements. In the unregulated river, temporal patterns in hyporheic water chemistry correlated to variation in surface water chemistry and discharge as expected. In the regulated rivers, the hyporheic water chemistry showed little correlation to discharge or surface water chemistry. The intra-gravel water chemistry conditions for brown trout eggs were more favourable in the unregulated river, characterised by high oxygen levels, than in the two regulated rivers. The regulated river with no minimum flow requirements had critically low oxygen levels at the end of the incubation period.</p>

The hydropower industry has altered connectivity in many rivers during the last century. Many fish species depend on both an intact longitudinal connectivity to be able to migrate between spawning, feeding and winter habitats, and vertical connectivity for development and survival of incubating embryos and larvae in the gravel. The objective of this thesis was to examine problems and remedial measures associated with disrupted longitudinal and vertical connectivity in regulated rivers. The issue of longitudinal connectivity was studied in the River Emån by evaluating the efficiency of two nature-like fishways for anadromous brown trout. Telemetry studies showed that the combined efficiency for the two fishways in 2001-2004 was 60.5%. The passage efficiencies of both fishways were high for trout (89-100%), but also for other species such as chub, perch, tench, burbot and roach (74%). The attraction efficiencies were largely dependent on power plant operation, and generally high for the fishway situated next to the tail-race and low for the fishway situated inside the former channel. More than half of the trout spawners were also observed using the fishways for downstream passage. The densities of brown trout yearlings upstream of the fishways were higher after the fishways were built than during pre-fishway years. Smolts produced upstream of the fishways were observed migrating downstream in 2003-2005. The percentage of smolts that passed both power plants in was 51%, with losses being attributed to predation (15%), turbine-induced mortality (16%) and other reasons (18%). Turbine-induced mortality was higher (40%) at the power plant with four small Francis runners, than at the power plant with one large Kaplan runner (12%). The issue of vertical connectivity was studied in three rivers in Värmland, one unregulated, and two regulated, one of which had no minimum flow requirements. In the unregulated river, temporal patterns in hyporheic water chemistry correlated to variation in surface water chemistry and discharge as expected. In the regulated rivers, the hyporheic water chemistry showed little correlation to discharge or surface water chemistry. The intra-gravel water chemistry conditions for brown trout eggs were more favourable in the unregulated river, characterised by high oxygen levels, than in the two regulated rivers. The regulated river with no minimum flow requirements had critically low oxygen levels at the end of the incubation period.

Two distinct stress coping strategies, proactive and reactive, have been stated in various animal studies, each associated with a set of behavioural and physiological characteristics. In a given challenging situation, proactive animals show more aggression, a higher general activity and a predominant sympathetic reaction. In contrast, the reactive copers respond more with immobility and avoidance, and a predominant parasympathetic/hypothalamic activation. This divergence in coping has also been indicated in salmonid fish. Interestingly, many of the differences reported between sea-ranched and wild fish resembles characteristics that differentiate proactive and reactive copers. In the present thesis it is shown that individuals with divergent stress coping styles are identifiable in several brown trout (Salmo trutta) populations. Further, the results show that the distribution of individuals displaying these distinct stress coping strategies differs between populations. This strongly indicates that these traits are heritable and that the variation in selection regime in the native rivers influences these traits. In addition, the results show that populations with hatchery origin are biased towards having higher frequencies of trout displaying a proactive style than populations having wild origin. Also, even though the frequency of early sexual maturation, known as a viable alternative life history in salmonids, differs between populations of brown trout, no link between stress coping strategy and early sexual maturation were found. However, this thesis show that maternal contribution, in the form of egg size, is of major importance whether the progeny will sexually mature early and that it also might be of importance for stress coping strategy. Further, correlations of traits commonly associated with stress coping strategies and behavioural syndromes across context and over time is investigated. The results show that individuals with a strong sympathetic reactivity are more prone to change their behaviour than others.