Pharmaceutical contamination is increasing in the environment and the consequences this will bring are of growing concern. The highest contamination of pharmaceuticals can be found in aquatic ecosystems and the organisms of these systems are therefore of utmost importance to research in order to understand the ecological consequences of pharmaceutical contamination. This report will reveal the effect contamination can have on an important apex predator often found in temperate aquatic systems, the Northern pike (Esox lucius) when exposed to the psychiatric pharmaceutical Oxazepam. The predatory performance of pike was studied before and after Oxazepam exposure by monitoring how fast each pike caught three prey of roach (Rutilus rutilus), as well as observing the amount of failed predation attempts when hunting the roach. The exposed pike displayed more failed predation attempts after exposure as opposed to the control group. Furthermore it took the exposed pike longer to catch all three roach after exposure while the mean for the control group decreased. Hence, Oxazepam exposure seem to have an effect on predation performance of pike but no definite conclusion could be drawn about to which extent this affects the foraging success and thereby the survival of the pike considering the complex nature of aquatic systems. More studies are therefore needed in order to determine the full effect pharmaceutical contamination can have on complex aquatic ecosystems and more specifically on an apex predator.

Antalet ryggkotor varierar kraftigt mellan olika taxa, men också inom arter eller populationer. Omfattande forskning har visat att antalet ryggkotor hos fisk är resultatet av interaktioner mellan genetisk struktur och plastiska svar på miljöbetingelser under individens ontogeni. Ett vanligt mönster är tendensen för antalet ryggkotor att variera med kroppsform och/eller kroppslängd hos fisken. Gäddan (Esox lucius) i Östersjön har en komplex populationsstruktur, bestående av flera genetiskt distinkta subpopulationer, vilka utgörs av anadroma individer som uppvisar ett homing-beteende. Individer som tillhör dessa subpopulationer är sympatriska större delen av året och blir allopatriska endast kortvarigt under tiden för lek. Den här studien undersökte fördelningen av antalet ryggkotor hos tre anadroma sympatriska subpopulationer av gädda iÖstersjön. Signifikanta skillnader i fördelningen av antalet ryggkotor hittades både inom och mellan alla undersökta subpopulationer och åldersklasser. Resultaten från ett ”common-garden” experiment antydde att skillnader i antalet ryggkotor mellan olika subpopulationer delvis hade en genetisk basis, vilket indikerar möjligheten för selektion att verka på denna egenskap, och en potentiellt evolutionär förändring. En kvadratisk regression visade på ett kurvilinjärt samband mellan antalet ryggkotor och kroppslängd hos juveniler. Tillsammans tyfrt dessa resultat på att de kombinerade effekterna av stabiliserande och divergent selektion kan ha spelat en roll i fördelningen av antalet ryggkotor hos gäddan i Östersjön. Fördelningen av antalet ryggkotor inom subpopulationer verkar vara under inflytande av stabiliserande selektion. Skillnader mellan subpopulationer kan istället reflektera lokala anpassningar som drivs av divergent selektion. Dessa fynd signalerar behovet av att betrakta varje subpopulation som en egen enhet i bevarandebiologiska sammanhang. / Vertebral number (VN) is known to vary greatly across different taxa, but also within species orpopulations. Extensive research has shown that VN in fish is the result of interactions between geneticstructure and plastic responses to environmental cues during ontogeny. A frequently reported pattern is the tendency for VN to vary with body shape and/or length of the fish. The pike (Esox lucius) of the Baltic Sea has a complex population structure, with genetically distinct subpopulations consisting of homing anadromous individuals. Individuals belonging to these subpopulations are sympatric for most of their lives and become allopatric briefly during spawning each year. This study examined the distribution of VN in three anadromous sympatric subpopulations of pike in the Baltic. Significant differences in VN were found between juveniles and adults belonging to different subpopulations, but also across life-stageswithin all three subpopulations. Results from a common-garden experiment indicated that differences in VN among subpopulations were in part the result of genetic differences, indicative of evolutionary change. Furthermore, a quadratic regression revealed a curvilinear relationship between VN and bodylength of juveniles. Taken together, these results suggest that the combined effects of stabilizing and divergent selection might have played a role in shaping the distribution of VN in pike of the Baltic. The distribution of VN within subpopulations seems to be under the influence of stabilizing selection. Differences among subpopulations might instead reflect local adaptations driven by divergent selection. These findings signal the need for conservationists to view these subpopulations as unique units of management.

Northern Pike (Esox lucius) is an economically and ecologically valuable species with a circumpolar distribution across the Northern Hemisphere. Northern Pike have been shown to have low levels of genetic variation despite their great capacity to colonize new environments. Here, high-resolution resequencing data from 47 Northern Pike from across North America was used for SNP discovery and population analysis. Our analysis reveals an extraordinary lack of genetic variation among Northern Pike with observed heterozygosity (Ho) of just 0.0835. Our analyses suggest that two major groups of Northern Pike exist in North America that are separated by the North American Continental Divide. Genetic variation associated with the stratification of these two groups resides across the genome particularly in gene regions with multiple copy number variants and functions related to immunity, tissue permeability, and development. Northern Pike from Alaska and the Yukon River harbour about two times more heterozygosity than Northern Pike east of the Continental Divide with an average of one heterozygous SNP every 6,250 bases. Populations east of the Continental Divide possess a remarkable level of genetic homogenization with an average of just one heterozygous SNP every 16,500 bases. For comparison, an average of one heterozygous SNP per 309 bases was reported in herring (Martinez Barrio et al., 2016), one per 500 in Atlantic cod (Star et al., 2011), and one per 750 bases in Coho and chinook salmon (Koop, 2018). This is at least 5 – 10 fold less variation than is seen in humans (the 1000 Genomes Project Consortium, 2015). We observed a recently described master sex-determining gene, amhby, in three western North American populations but not in populations east of the Continental Divide. We could not resolve any signals indicating a genetic sex determination system was present in populations from southern Manitoba or the St. Lawrence River. This may indicate that environmental sex determination is at play in these populations. We found evidence of a possible female-heterozygous, male homozygous ZW-ZZ genetic sex-determination system in New Jersey Northern Pike. With the highest average of 181,268 heterozygous SNPs genome wide and the greatest Ho (0.3228) of all populations, as well as the presence of the sex-determining gene amhby indicate that Northern Pike from our Alaskan population are the oldest in North America. Fewer numbers of heterozygous SNPs (61,073), low Ho (0.0922), and the absence of amhby in Northern Pike east of the Continental Divide suggests that these are relatively young populations and are descended from a small founding population. These results imply that Northern Pike first came to North America through Beringia and colonized its North American range from there, possibly via pro-glacial lake formation and drainage. However, from the data herein it was not possible to trace how re-colonization occurred after the final retreat of glaciers at the end of the last ice age. This thesis provides a genetically high-resolution snapshot of Northern Pike population structure in North America. It demonstrates that organisms with largely homogenous genomes can be incredibly successful and resilient. Finally, it adds to the complex subject of sex determination in fish and provides insight into a sex determination system in transition. / Graduate / 2020-10-15

The main objective of this thesis is to describe and experimentally evaluate the possibility of adaptation of pike (Esox lucius L.) in controlled housing conditions and income artificial pelleted feed. The thesis is mainly based on the effect of an initial larval density of pike for adaptation and survival and the growth of larvae reared in the rearing tanks. The experiment consisted of four different densities of larvae (10, 20, 40, 80 pc of the larvae l??, which were always repeated three times. Two experiments were performed (M, H), with a length of rearing of five days. Rearing itself was conducted in twelve circular tanks with a capacity of 180 l??, the recirculation system connected to the experimental rearing facility in Vodňany FROV JU. The temperature during rearing was constant. For the first experiment the temperature was 22.3 ? 03 °C. For the second one, the average temperature was 21.5 ? 0.6 °C. The frequency of feeding was continuous (24 h) with a combination of hand feeding and feeders with a timer (at night). The illumination of the aquarium tanks was provided by fluorescent lamps, for each tank individually. The light intensity was high (210 lux) and constant during the rearing. Both experiments showed the optimal density at the initial feeding from 20 to 40 units . l??. Also, we have implemented made out performed- the basic biometric analysis of W (g) and TL (mm), the body length, size of eyes, head, jaw length, prenatal length.

Top predators in aquatic ecosystems often have strong top-down effects on the ecosystem. Northern pike (Esox lucius) has been documented to cause whitefish (Coregonus lavaretus) populations to diverge into different ecomorphs. This can facilitate piscivory in other predators as a novel resource becomes available to them in the form of dwarf whitefish. The aim of this study is to examine whether the presence of pike causes Eurasian perch (Perca fluviatilis) to shift their diet from insectivory to piscivory, and whether this is directly driven by whitefish polymorphism. Stomach contents of 147 perch from lakes with and without pikes were analyzed. The results show that the presence of pike has a clear influence on the diet of the perch. In lakes without pike, perch are mostly insectivorous, and in lakes with pike, they are mostly piscivorous. This diet shift appears to be driven by whitefish availability, as a majority of the diet of perch in pike lakes consisted of whitefish, while none of the fish eaten by perch in non-pike lakes was whitefish. In addition, the results showed that perch undergo the diet shift from insectivory to piscivory at a smaller size when coexisting with pike. This study can be added to the growing body of evidence for the ecological significance of pike.

Genetic variation is a prerequisite for the viability and evolution of species. Information on population genetic patterns on spatial and temporal scales is therefore important for effective management and for protection of biodiversity. However, incorporation of genetics into management has been difficult, even though the need has been stressed for decades. In this thesis population genetic patterns in continuous environments are described, compared among species, and related to conservation management. The model systems are moose (Alces alces) in Sweden and multiple species in the Baltic Sea, with particular focus on the Northern pike (Esox lucius). The spatial scope of the studies is large, and much focus is dedicated towards comprehensive sampling over large geographic areas. The moose population in Sweden is shown to be divided into two major subpopulations, a northern and a southern one. Both subpopulations show genetic signals of major population bottlenecks, which coincide with known population reductions due to high hunting pressure (Paper I). The Northern pike in the Baltic Sea shows relatively weak, but temporally stable population genetic structure. An isolation by distance pattern suggests that gene flow primarily takes place among neighboring populations, either over shortest waterway distance or along the mainland coast, with island populations acting as stepping stones (Paper III). In a comparative study of seven Baltic Sea species no shared genetic patterns were found, either in terms of genetic divergence among or genetic diversity within geographic regions. These results complicate the incorporation of genetic data into management, because it suggests that no generalization can be made among species in the Baltic Sea, but that species-specific management is needed (Paper II). Over the last 50 years, 61 species in the Baltic Sea have been studied with respect to spatial genetic patterns. For over 20 of these species information of direct relevance for management is available. Relevant information is synthesized into management recommendations (Paper IV). This thesis provides vital information on spatial and temporal genetic structure for a number of ecologically and socio-economically important species. It shows that such information is important to consider species by species and that both local and metapopulation approaches are needed to effectively manage genetic diversity in e.g. moose and pike. Further, it identifies for which organisms in the Baltic Sea genetic information exists, how it can be used, and where important information is lacking. In order to successfully make use of genetic data in management, effective communication channels between academia and policy-makers are needed. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

Northern pike or pike Esox lucius is total piscivorous fish species found in the brackish and freshwater ecosystems of the Northern hemisphere. It is a top predator and keystone species that causes cascading effects in these ecosystems. Otoliths have been used to estimate age and growth rates in most fishes. Cleithra have generally have been used in Pike due to opaque nature of the otoliths. The aim of this study was to develop a method for age and growth estimation of pike using sagittal otoliths and carry out age and growth rates estimation of four sub populations; Dunöbäcken, Kårehamn, Oknebäcken and Väderön that represent freshwater and brackish water spawning sites. Determination of growth rates differences between sub populations was done for the first 2 years of their life. The methods included burning of the otoliths, fixing the otoliths in the epoxy resin, polishing of otoliths and staining with Alizarin red, Silver nitrate solution, Tetracycline and alkaline Lugol's solution with observation under light, dissecting and epifluorescence microscopes. Four methods tested based on staining with Alizarin red, Silver nitrate, alkaline Lugol's solution and burning otoliths. Provided useful results and not the method with Tetracycline. Alkaline Lugol's solution staining method was chosen and further developed. There was a significant difference in the relative growth rates between the sub population from brackish water spawning site of Väderön and the sub population from freshwater spawning site of Kårehamn in the first year (One-way ANOVA:F value 3.18, p value 0.0356) and after Tukey post hoc test (p value 0.0362). No difference among sub populations from the freshwater spawning sites. There was no difference in growth rates between any other sub populations in the second year. The importance of the study is successful application of Lugol's solution staining method for age and relative growth estimation studies with otoliths in pike. / EcoChange

Northern pike (Esox lucius L) populations have been declining along the east coast of Sweden, including the Gävleborg coast. This negative trend is believed to be caused by factors related to pike recruitment including loss of suitable spawning habitats. The purpose of this study is to gain a deeper understanding for the recruitment process of pike by investigating their preferences when selecting spawning habitats. Data from a rod fishing inventory targeting adult pike was used to estimate pike densities in 20 assumed spawning bays along the coast of Gävleborg. By using the number of pike caught per hour as a measure of pike density I examined how the morphological characteristics of bays and fish communities influenced pike densities during the spawning period in the studied bays. The results suggest that the density of pike (# caught per hour) tend to increase in bays with deeper average depths, larger surface area, and higher densities of sticklebacks. These results contradict the hypothesis in the study and somewhat previous research. Possible explanations for these unexpected findings are discussed, and one theory suggest that the rod fishing method used may have influenced the results. Probably improvements can be made to make the density estimates from the fishing inventory more accurately, especially when comparing bays of varying sizes. Suggestions for enhancing density estimation include adjusting the fishing duration based on bay size or using a specific number of throws per casting rod and defined surface area and then move to next surface area.

The population of northern pike in the Baltic sea has seen a drasticdecrease in numbers in the last couple of decades. The reasons for this are believed to be many, but the majority of them are most likely anthropogenic. Today, many measures are being taken to prevent further decline of pike populations, ranging from nutrient runoff control to habitat restoration. This inevitably gives rise to the problem addressed in this project, namely: how can we best monitor pike populations so that it is possible to accurately assess and verify the effects of these measures over the coming decades? Pike is currently monitored in Sweden by employing expensive and ineffective manual methods of individual marking of pike by a handful of experts. This project provides evidence that such methods could be replaced by a Convolutional Neural Network (CNN), an automatic artificial intelligence system, which can be taught how to identify pike individuals based on their unique patterns. A neural net simulates the functions of neurons in the human brain, which allows it to perform a range of tasks, while a CNN is a neural net specialized for this type of visual recognition task. The results show that the CNN trained in this project can identify pike individuals in the provided data set with upwards of 90% accuracy, with much potential for improvement.

Le débit joue un rôle de première importance dans la modulation des caractéristiques physico-chimiques des rivières. Les poissons, à travers leur habitat, dépendent directement de cet ensemble de caractéristiques riveraines. De nombreuses études ont démontré qu’une altération du débit naturel des rivières, telle que par des installations hydro-électriques, a un effet négatif à l’échelle des populations et communautés de poissons. Par contre, les mécanismes qui sous-tendent ces relations sont toujours méconnus. Les processus physiologiques des poissons déterminent la façon dont ils sélectionnent leur habitat. La réponse au stress a été proposée comme étant un mécanisme qui les guide à travers les changements qui surviennent dans leur environnement. Le comportement, le cortisol plasmatique, le glucose et le lactate sanguin sont des indicateurs de la réponse au stress chez les poissons. Dans un premier temps, le mouvement de grands brochets Esox lucius L. a été observé dans deux rivières: l’une est régulée par éclusées, l’autre est non régulée et donc libre de barrage. Les résultats démontrent que le taux de mouvement chez des poissons qui habitent la rivière régulée est plus élevé que celui des poissons qui habitent dans la rivière non régulée. De plus, la direction de relation entre la distance parcourue par les poissons et le débit diffère entre rivières, et ce pour une même espèce. Dans un deuxième temps, l’effet d’une élévation de vitesse d’eau sur le cortisol, glucose et lactate de brochets qui proviennent de deux rivières qui présentent des types de gestion de débit contrastés est évalué. Ce chapitre conclut que les poissons de la rivière régulée 1) relâchent moins de glucose dans leur sang, et 2) ont des mécanismes qui permettent une accumulation moindre de lactate dans leur sang, que les poissons de la rivière non régulée lorsqu’ils sont soumis à une augmentation de vitesse d’eau. Dans un troisième temps, une approche analytique a été développée permettant de quantifier l’effet du débit sur la façon dont les brochets sélectionnent les conditions physiques de leur habitat, telle que la vitesse de l’eau. Les résultats des chapitres précédents suggèrent que les poissons de la rivière régulée sont soumis à des vitesses d’eau plus grandes que les poissons de la rivière non régulée. Ce nouvel outil permet de valider cette hypothèse. En dernier lieu, les taux de base et maximaux de cortisol plasmatique, ainsi que de glucose et lactate sanguin ont été mesurés chez des brochets qui vivent dans les deux types de rivière. Ces indicateurs témoignent de la qualité de l’habitat dans lequel les poissons vivent. Nos résultats suggèrent que les poissons qui vivent dans la rivière régulée peuvent moduler leurs niveaux de base et maximaux en cortisol plasmatique dans le but d’éviter le stress chronique. Cette thèse évalue les effets des changements de débit sur les poissons par des approches innovantes, situées à la frontière entre les domaines physiologiques et écologiques. Elle contribue à approfondir nos connaissances en ce qui a trait aux mécanismes par lesquels les poissons se distribuent à travers les différents habitats de rivière. / Flow is an important determinant of physicochemical characteristics of rivers. Fish communities in rivers are strongly dependant of their habitat, which is directly dictated by this set of characteristics. The loss of the natural flow regime, through regulation by hydroelectric facilities, for example, has the potential to directly affect the fish communities. Numerous studies have shown that the loss of natural flow regimes negatively impact fish populations and communities, but not much is known about the mechanisms that underlie such a relationship. Physiological processes determine the way that fish select their habitat. The stress response has been proposed as a mechanism that guides fish throughout the environmental changes happening in their habitat. Indicators of the fish stress response comprise behaviour, plasma cortisol, and blood glucose and lactate. First, northern pike Esox lucius L. movements were assessed in two rivers with contrasting flow regimes: a hydropeaking regulated river and an unregulated free-flowing river. Using manual tracking by radio-telemetry, we found that pike moved at a higher rate in the regulated river than in the unregulated river. Results also show that the direction of the relationship between movement of pike and flow can vary between rivers. Second, the effect of a water velocity increase on plasma cortisol, blood glucose and blood lactate levels in wild pike originating from the two rivers with contrasting flow regimes were assessed. Our results show that blood glucose and lactate concentrations are significantly diminished for fish originating from the regulated river, in comparison to fish originating from the unregulated river, following an increase in water velocity. Third, a novel analytical framework was developed that allow one to quantify the effect of the flow on fish selection of the physical conditions of their habitat (e.g. water velocity). Results obtained in the previous chapters suggest that pike living in the regulated river might be subjected to higher water velocities than fish living in the unregulated river. This novel tool will allow us to validate this hypothesis. Lastly, basal and maximum acute stress-induced concentrations in plasma cortisol, and blood glucose and lactate were quantified in pike living in both the regulated and the unregulated rivers. These physiological parameters can give an indication of the fish habitat quality. Our results suggest that fish from the regulated river are able to modulate their plasma cortisol to dampen their HPI-axis responsiveness and avoid chronic stress. This thesis assesses the effects of flow fluctuations on fish using novel approaches, situated at the intersection between the fields of physiology and ecology. It significantly contributes to broaden our knowledge of the mechanisms underlying fish habitat selection in rivers.