Climate change is expected to have a profound impact on freshwater fish communities, especially at higher latitudes. In this study I investigated potential effects of climate change on the niche structure of Eurasian perch (Perca fluviatilis) by looking at their diet across a latitudinal gradient and at varying light climate. Dietary niche width of Eurasian perch did not differ significantly between boreal and temperate latitudes. Additionally, no significant difference in the prevalence of specialist individuals was found along the latitudinal gradient and water transparency levels. Habitat was the main factor that significantly affected niche width and level of specialization with both being significantly higher in the littoral habitat. Taken together my results suggest that climate change might indirectly affect niche patterns by altering fish densities through changes in productivity resulting in niche and specialization variation among habitats.

Cette thèse a déterminé les rôles respectifs de la photopériode et de la température lors des différentes et successives étapes du cycle de reproduction (induction du cycle, vernalisation, ponte) chez la perche commune Perca fluviatilis femelle. La photopériode est le facteur environnemental principal qui synchronise l’induction du cycle de reproduction chez la perche commune, la température joue uniquement un rôle modulateur. Une baisse importante de la durée de la photophase de 4-8 heures est recommandée. Le maintien d'une photopériode constante basée sur une photophase longue et constante (17L : 7D) inhibe l’induction, alors que le maintien d’une température élevée et constante (22-23°C) ne le permet pas. Pour la phase de vernalisation, une photopériode de type jour court (8L : 16D) est nécessaire. Concernant les effets de la température, une forte et progressive baisse de la température (de 22 à 6°C sur 16 semaines) est recommandée pour assurer un développement gonadique complet (ovocytes aux stades de vitellogenèse avancée en fin de phase d’induction et de la maturation finale avant la période de ponte). Des baisses de température plus modérées (de 22 à 14-18°C) altèrent la reproduction, notamment pendant la phase de vernalisation. L’augmentation finale de la température après la vernalisation est le facteur principal de synchronisation de la ponte. Cette étude a permis la mise au point d’un protocole photo-thermopériodique fiable garantissant des taux d’induction et de ponte très élevés, proches de 100%, chez les femelles / This PhD thesis has determined the respective roles of photoperiod and temperature at the different and successive steps of the reproductive cycle (induction of the cycle, wintering period, spawning) in female Eurasian perch Perca fluviatilis. Photoperiod is the main environmental factor which synchronizes the onset of the reproduction cycle in Eurasian perch female, temperature plays only a modulating role. A high photoperiod decrease of 4 or 8 hours is recommended. The maintenance of constant photoperiod based on a long photophase (17L: 7D) delays the onset of the reproductive cycle, whereas the maintenance of a warm and constant temperature (22-23°C) does not delay it. For the wintering period, a photoperiod with a short daylight period (8L : 16D) is required. Concerning the effect of temperature variations, a high and progressive temperature decrease (from 22 to 6°C over 16 weeks) is recommended to ensure a complete ovarian development (all oocytes achieved the advanced vitellogenesis stage at the end of the induction phase and and final maturation stage just before spawning). Slight temperature decreases (from 22 to 14-18°C) alter the reproduction, especially during the chilling period (wintering period). The final increase of temperature (up to 14°C) after the wintering period is the main factor for spawning synchronization. This study allowed the development of a reliable photo-thermal protocol for out-of-season spawning with very high rates (close to 100%) of female response and spawning

The eurasian perch (Perca fluviatilis Linnaeus, 1758) is considered as very perspective species for breeding at intensive aquaculture, where was successful domesticated. Consumption of eurasian perch is increased at present. The greatest grow of consumption is mainly in countries of alpine region and in Scandinavian countries. The aim of experiment was monitor and character spawning of domesticated eurasian perch in controlled conditions of breed. It was determinated fertility and then fertilization of eggs. The next aim was make incubation of fertilization eggs and determinate hatching. After hatch was determinated total length of larvae and its quality by the help of osmotic shock. Domesticated eurasian perch is spawned without problems in controlled conditions of breed. The resulting data of domesticated perch are worse than date of non-domesticated perch in some spawning characteristic. This problem will resolve with gaining knowledge about spawning of eurasian perch. The greatest problem is hatching of eggs, which is very low during spawning of domesticated perch.

Global warming leads to an increased browning of lakes across the northern hemisphere. This browning can due to benthic light-limitation cause hypoxic bottom conditions which can have negative impact on the fish production in the northern lakes. In this study, I obtained data from a large-scale experiment to test if the removal of anoxic bottom conditions in the hypolimnion affects Eurasian perch (Perca fluviatilis) populations. This was done with a Before-After, Control-Impact design in two adjacent lakes by altering the oxygen conditions in the hypolimnion in one lake while the other remained as control. To analyse if experimental oxygenation of an anoxic hypolimnion altered perch performance, I analysed samples of individual growth (based on back-calculated growth from operculum bone readings), condition, diets and stomach fullness in perch before and after oxygenation from the control and impact lake. The results showed that growth, condition, and stomach fullness increased in the treatment lake but not in the control lake, suggesting that resource availability increased for perch with the removal of anoxic hypolimnion conditions. However, a decline in population abundances was also observed over time within both lakes, which may provide at least an alternative explanation of the observed responses. Still, I hypothesize that the oxygenation at least partially increased the resource abundance in brown lakes, thus increasing fish growth and size.

Movement increases the probability for an individual to find food resources, but also increase the metabolic costs and exposure to predators. Hence, swimming behavior of fish is strongly coupled to fitness. Even though swimming activity has been studied in numerous laboratory settings, less is known about in situ activity and its dependence on abiotic factors (temperature, light conditions and barometric pressure). In this study I hypothesized that the activity increases with 1) increasing temperature and decrease with 2) barometric pressure variability and 3) average light conditions (h/day). In order to test the universality of the three hypotheses I also searched for size dependent effects. Fish activity (km/day) was measured in three lakes on individual fish (N=14-21 per lake) using acoustic telemetry providing tracking of fish at a time resolution from seconds to hours. A positive correlation between temperature and swimming activity in line with my first hypothesis was only observed in one of the lakes. The activity decreased with increased variability in barometric pressure in two of the lakes, a finding supporting my second hypothesis. Meanwhile increased light conditions (h/day) decreased activity in one of the lakes, as predicted by my third hypothesis. Nevertheless, none of my hypotheses were valid in all three of the lakes and perch reacted differently to the abiotic factors. One of the possible explanations for this is the importance of size differences as I noticed that the swimming activity differed between bigger and smaller individuals. My findings suggest that not only the temperature, barometric pressure and light conditions alone predict the activity in perch, but also the fish individual size, predation and the metabolic costs linked to thermoregulation.

Aujourd’hui, la durabilité du modèle de développement de l’aquaculture est de plus en plus questionnée et une des solutions proposées consisterait à diversifier la production piscicole via la domestication de nouvelles espèces comme la perche commune, Perca fluviatilis, une espèce d’eau douce tempérée très intéressante pour la diversification de l’aquaculture continentale européenne. De nombreux aspects de la biologie de sa reproduction sont connus cependant, peu d’informations sont disponibles sur son développement. Or, des défauts de développement précoce, dont les causes sont encore mal définies, impactent actuellement la qualité de la production piscicole. C’est dans ce contexte que cette thèse vise à caractériser les succès et défauts de développement embryonnaire chez la perche commune à travers trois axes principaux : (i) déterminer une table de référence de l’embryogenèse normale permettant (ii) définir les défauts de développement tels que les malformations dans des conditions d’élevage différentes et (iii) identifier les liens entre différents paramètres de développement embryonnaire afin de déterminer des profils de développement variables. La première partie de ce travail a permis d’identifier la séquence précise de l’ontogenèse normale de cette espèce à travers la définition d’une table de développement embryonnaire alternative et flexible pour des espèces non-modèles, facilitant les comparaisons intra- et inter-espèces. Dans un second temps, l’identification la plus exhaustive possible de phénotypes anormaux a révélé 10 grandes catégories de malformations associées à des organes ou fonctions spécifiques. De plus, certains de ces défauts semblent fortement dépendants des conditions d’élevage des géniteurs ce qui permet d’identifier l’effet de potentiels facteurs extrinsèques sur le développement et d’améliorer les techniques de gestion des animaux. Enfin, l’ensemble de ces résultats et des paramètres mesurés durant l’embryogenèse ont permis d’effectuer une classification approfondie des pontes obtenues présentant des profils de développement similaires pour mettre en évidence des liens éventuels entre les divers phénotypes et paramètres utilisés. Les analyses de données effectuées ont montré que seulement 3 paramètres étaient nécessaires à la caractérisation de 4 profils de succès de développement variables : les taux de survie au début de l’organogenèse, d’éclosion et de malformations. A l’avenir, ces paramètres pourraient être généralisés permettant d’homogénéiser les critères d’évaluation du succès de développement chez d’autres espèces d’intérêt de poisson. L’ensemble de ces résultats constituent une base solide pour étudier l’effet des facteurs extrinsèques et/ou intrinsèques sur la qualité et le succès de développement embryonnaire / Currently, the durability of the aquaculture developmental model is clearly challenged and one solution consists to diversify the fish production by the domestication of new species such as the Eurasian perch (P. fluviatilis), a freshwater species promising and valuable for the diversification of European aquaculture. Several aspects of its reproductive biology are well known, nevertheless, only little information is available on its development. However, early developmental impairments, whose causes are unclear, actually impact the fish production quality. In this context, the present work aimed to characterize the developmental success and impairments in Eurasian perch on three main issues: (i) determine a model of normal embryogenesis table helping to (ii) define developmental impairments, in diverse rearing conditions and (iii) identify the relationships between various parameters of embryonic ontogenesis to characterize different patterns of developmental success. The first part of this study allowed identifying the accurate timing of normal ontogenesis of this species through the definition of an alternative and flexible developmental table to describe non-model fish species, allowing the intra- and inter-specific comparisons. In the second part, the exhaustive characterization of abnormal phenotypes revealed 10 categories of deformities linked to specific organs or functions. Moreover, some of these categories seemed to be related to rearing-conditions of the breeders allowing identifying the potential effects of extrinsic factors on the development and improving the management of fish. Finally, the previous results and the parameters measured during embryogenesis help to classify the several spawns obtained with the same developmental pattern and to highlight the potential relationships between diverse phenotypes and parameters. In addition, the data analyses showed that only 3 parameters are reliable to assess the developmental success: survival rate at the onset of the organogenesis, hatching and deformities rates. Henceforth, these parameters and this classification could be generalized as a new strategy to assess the developmental success in other fish species. All of these results provide a good basic knowledge to study the potential effects of various extrinsic and/or intrinsic factors on the developmental success and the embryonic quality

La diversification de la production, par la domestication de nouvelles espèces de poissons, constitue l’une des solutions pour une aquaculture durable. Dans ce contexte, l’élevage de la perche Eurasienne, Perca fluviatilis, s’est bien développé ces dernières années permettant aujourd’hui une production stable et croissante. Le progrès de la filière requiert, la mise en œuvre de programmes de sélection génétique pour améliorer, entre-autres, la croissance, la reproduction, et la résistance aux maladies. Pour ce faire, la caractérisation génétique des stocks de poisson actuellement en élevage est un pré-requis indispensable afin d’évaluer si la variabilité génétique est suffisante. Au cours de ce travail, nous avons analysé la variabilité génétique entre les populations sauvages de deux lacs alpins (lacs Léman et Neuchâtel) dont les populations sont utilisées comme fondatrices par les perciculteurs et les stocks de deux fermes d’élevage. Nous avons trouvé une seule population panmictique dans le lac Léman, alors que deux sous-populations ont été identifiées dans le lac Neuchâtel et dont la variabilité génétique est plus forte. Par contre, ces populations sauvages ne sont pas représentées dans les stocks d’élevage bien qu’elles étaient utilisées pour fonder les stocks de géniteurs. De plus, la variabilité génétique est plus forte dans les populations captives. Entre les géniteurs et leurs descendances, la diversité génétique n’a pas diminué malgré une faible augmentation de la consanguinité. Ainsi, ce travail permettra aux perciculteurs de mettre en place une réelle gestion génétique de leurs cheptels et par la suite de développer des programmes de sélection. De plus, il a permis de mieux comprendre les liens possibles entre le processus de domestication et l’évolution de la variabilité génétique / The diversification of production, by the domestication of new fish species, is one of the possible solutions for sustainable aquaculture. In this context, the farming of the Eurasian perch, Perca fluviatilis, has developed well in recent years allowing today a stable and increasing production. The progress of the sector requires, among others, the establishment of breeding programs to improve, growth, reproduction and disease resistance. For this, the genetic characterization of currently farmed fish stocks is an essential prerequisite to assess whether genetic variation is sufficient. In this work, we analyzed the genetic variability among wild populations of two alpine lakes (lakes Geneva and Neuchâtel) whose populations are used by fish farmers to establish their stocks. We found one panmictic population in Lake Geneva, while two sub-populations were identified in Lake Neuchâtel, whose genetic variability is higher. However, those wild populations are not found in captive stocks. In addition, the genetic variability is higher in captive populations. Between parents and their offspring, the genetic diversity has not decreased despite a small increase in inbreeding. Thus, this work will allow fish farmers to set up a real genetic management of their stocks and subsequently to develop breeding programs. Moreover, it provides a better understanding of the possible links between the process of domestication and the evolution of genetic variability

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.