Three nutritional feeding trials were undertaken to investigate the nutritional role of zinc (Zn) and selenium (Se) in the promotion of health in rainbow trout (Oncorhynchus mykiss Walbaum). Organic and inorganic sources of both elements were assessed by determining bioavailability, effects on growth, feed utilisation, immuno-competence, oxidative status, fillet quality and interactions with other trace elements. A focus was made on the use of practical diets throughout the study. The first experiment assessed the bioavailability of residual Se and Zn from a white fishmeal based practical diet during a 10-week trial in comparison to diets containing either supplemental Se-yeast and Zn proteinate (Zn-pr) or sodium selenite (Na2Se03) and Zn sulphate (ZnS04). Se-yeast and Zn-pr were hypothesised to be more digestible and more effective in raising Se and Zn status than inorganic sources. Apparent digestibility of residual Zn and Se was 21.9% and 54.2% respectively. No conclusive difference in overall Zn bioavailability was observed between treatments. Se-yeast significantly increased Se digestibility to 63.7%, Se levels in all tissues, and the activities of hepatic thioredoxin reductase (Trx-R) and glutathione peroxidase (GSH-Px). Selenite supplementation only resulted in increased GSH-Px activity. Se-yeast was found to be a highly bioavailable Se source, effectively raising Se status. The second experiment determined the efficacy and effect on health of residual Zn in comparison to 125, 312 and 781 mg kg-1 supplemented Zn-pr or Zn sulphate in a practical diet. It was hypothesised that Zn-pr would be more efficacious in the promotion of health than Zn sulphate. The retention of both Zn sulphate and Zn-pr followed the same exponential decay (R2 = 0.978) with increasing dietary Zn loading. This was accompanied with a lack of effect of 12-weeks Zn supplementation on standard growth rate (SGR), feed conversion ratio (FCR) , Zn enzyme activity (CU/Zn-superoxide dismutase and alkaline phosphatase), oxidative status (hepatic and pyloric caeca malondialdehyde (MDA) , total plasma antioxidant capacity (TAC) and oxidative DNA damage), immuno-competence (superoxide generation, lysozyme and leukocyte counts), hematocrit, nuclear abnormalities (micronuclei, and notched and blebbed nuclei), and fillet quality (drip loss and astaxanthin). Both dietary Zn-pr (R2 = 0.573) and Zn sulphate (R2 = 0.453) interacted with hepatic manganese (Mn) but not with iron (Fe) or copper (Cu). No significant 3 differences were observed between sources and a strict homeostatic regulation of dietary Zn in rainbow trout was observed. Preliminary investigations were carried out to establish the effects of seven days chronic husbandry related stressors on immuno-competence and oxidative status. It was hypothesised that chronic husbandry related stressors would result in oxidative stress and impaired immuno-competence. Alternating between netting and confmement stressors resulted in oxidative stress as determined by decreased TAC, increased oxidative DNA damage and modulated superoxide generation by leukocytes in the whole blood. The final experiments investigated the efficacy and effects on health of residual Se in comparison to 2, 4, and 8 mg kg-l supplemental sodium selenite or Se-yeast in a commercial trout grower diet. It was hypothesised that supplemental Se would confer benefits to the health of both stressed and un-stressed fish, and Se-yeast would be more efficacious than selenite in its effects. Following a 10-week trial, the implication of seven days husbandry related stressors were also evaluated. Se retention was reduced in fish fed selenite up to 4 mg kg-l in comparison to fish fed the basal diet; in contrast Se-yeast increased Se retention. SGR, FCR, hepatic GSH-Px and Trx-R, plasma TAC, hepatic MDA, respiratory burst, lysozyme, nuclear abnormalities, and hematocrit were not affected by the supplemented dietary Se. However, in prestress fish fillet quality (drip loss) may be improved by Se-yeast supplementation; this was not observed with selenite. Stress decreased whole body Se in all treatments and increased GSH-Px to the greatest extent in Se supplemented diets suggestive of an increased Se utilisation during stress. Se had no protective effects on immuno-competence and oxidative status post stress. On the contrary, 8 mg kg- l Se from selenite increased hepatic MDA and resulted in the lowest GSH-Px increases amongst supplemented fish, which may be indicative of the sub-lethal effects of Se in fish fed a high level of inorganic Se; this was not observed with Se-yeast. Selenite (R2 = 0.6611), but not Se-yeast (R2 = 0.073), significantly interacted with whole body Cu. No interactions were found between dietary Se and Fe or Mn. Levels of whole body Fe, Mn, Cu and Zn were not affected by husbandry related stressors. The study concludes that Se-yeast supplemented in fishmeal based diets is more bioavailable and efficacious in the maintenance of health than selenite. The efficacy of Zn-pr was not distinguished from that of Zn sulphate in the supplementation of practical diets. No difference was observed between Zn-pr and Zn sulphate in terms of bioavailability or efficacy. This may be due to the tight homeostatic regulation of dietary Zn above marginal levels. Se utilisation may increase during chronic husbandry related stress. Due to the lack of any measurable toxic effects and increased retention, Se-yeast may be more suitable for the delivery of Se in fish exposed to husbandry related stress, which was shown to result in oxidative stress. Higher quality practical diets may meet requirements for Se in un-stressed fish, but in conditions of stress, maximal GSH-Px and Se status may only be achieved by diets containing supplemental Se. 4 All experimental work involving animals was carried out in accordance with the 1986 Animals Scientific Procedures Act under Home Office project license # 30/2135 and personal license # 30/7809 5

Globally, freshwater fisheries are faced with numerous impacts that compromise fish populations. A knowledge and understanding of riverine fish movements are crucial for effective management and conservation of populations. However, there is a paucity of information about the spatial behaviour and ecology of wild and stocked cyprinids in floodplain rivers, especially under the influence of elevated flows. This study examined the factors affecting the lateral and longitudinal dispersal of juvenile and adult (wild and stocked) coarse fish in three lowland river catchments, namely the River Trent, the Yorkshire Ouse and the River Roding.A literature review was carried out to review the influence of floods on riverine ecosystem function and structure, and fish assemblage patterns. In unmodified lowland rivers, floods are characterized by lateral expansion onto floodplains resulting in high levels of habitat heterogeneity, essential for fish refuge, spawning, nursery and feeding. However, anthropogenic alterations to the flow regime and floodplain connectivity have had considerable detrimental impacts on fish populations. The main conclusion of the review was the need to restore and rehabilitate lowland rivers in an attempt to recover natural features or functionality. The effects of flood timing and magnitude were examined by sampling 0+ fish populations before, during and after floods in the Yorkshire Ouse, a constrained lowland river. Large numbers of eurytopic 0+ fishes were stranded on isolated floodplains when artificial levees ‘over-topped’ in summer (August). By contrast, backwaters provided refuge for high densities of 0+ eurytopic and rheophilic fishes. During floods, small fish were displaced or had lower survival. The results highlight the influence of flood timing on 0+ fish populations, the use of refuge areas and their importance of lowland river rehabilitation.In the River Trent, 0+ fish populations were sampled in the margins of the main river channel and in ten man-made floodplain waterbodies to evaluate the importance of variable connectivity between these habitats for rehabilitating the riverine-floodplain ecosystem. Fish assemblages compared favourably with studies on unmodified river reaches, i.e. succession of lotic-to-lentic habitat corresponded to a sequence of rheophilic-to-eurytopic-to-limnophilic fish species. Consequently it was concluded that the connection of man-made floodplain waterbodies to the river should incorporate variable, not just high, levels of hydrological connectivity into holistic riverine ecosystem management plans.Dual-Frequency Identification Sonar (DIDSON) was used to determine the influence of elevated flow on the lateral movements of adult fish between the Yorkshire Ouse and a marina (refuge habitat). Fish activity in the entrance was predominantly during daylight hours. Increased river flow resulted in significantly reduced fish movements, both towards and away from the marina, and fish presence in the entrance, except for larger fish (more than 30 cm) during the night. This study emphasised the importance of artificial floodplain waterbodies for adult cyprinid fish during winter months.The influence of environmental variation (flow and temperature) on movements of wild and stocked adult cyprinids is poorly understood, partially because of experimental difficulties. A laboratory study on PIT tagging individual juvenile cyprinids, identified that the method would be suitable for such investigations. In the River Roding, a combination of PIT and radio telemetry was used to compare habitat use, longitudinal movement (timing and direction), site fidelity and survival between wild populations and hatchery-reared fish. Wild cyprinids had high levels of ‘site fidelity’ but highly mobile individuals were present within the population, with movements positively correlated with temperature and flow. During elevated winter flows, wild fish occupied areas of reduced flow to reduce energy expenditure, but some fish performed exploratory movements. Movements of stocked fish were more frequent and longer than for wild fish, particularly just after release, possibly for exploratory purposes. Subsequently, movements of stocked fish were minimal, did not correlate with flow or temperature and the final distributions were more widely dispersed than found in wild fish. Importantly from a stocking perspective, stocked cyprinids had the behavioural and physiological ability to cope with elevated flows. However, differences in movements and habitat use between wild and stocked chub probably had consequences on survival.

Dans le cadre de la production de nouvelles espèces aquacoles, le sandre, Sander lucioperca, est devenu, depuis plusieurs années, une espèce d’intérêt piscicole en raison de sa valeur économique potentielle. Pour développer et pérenniser sa production aquacole, il est nécessaire de comprendre et maîtriser son cycle de reproduction ainsi que les mécanismes physiologiques mis en jeu afin d’obtenir des œufs et des juvéniles viables tout au long de l’année. Dans cet optique d’optimisation du contrôle du cycle, la dopamine apparaît, chez de nombreux téléostéens dont certains perciformes, comme un inhibiteur de l’axe gonadotrope, via les récepteurs de la famille D2, en bloquant le pulse ovulatoire de LH et l’ovulation. Chez le sandre, le rôle de la dopamine et de ses récepteurs, notamment les récepteurs de la famille D1, est inconnu. L’objet de cette thèse est de déterminer le rôle du système dopaminergique lors des phases finales de l’ovogénèse chez le sandre à travers trois axes principaux : (1) déterminer l’effet du blocage des récepteurs de la dopamine, D1 ou D2, sur la régulation de l’axe gonadotrope et l’induction de l’ovulation en absence et en présence d’une molécule de sGnRHa, (2) définir le répertoire et le profil d’expression des récepteurs dopaminergiques par l’étude du transcriptome cérébral du sandre en période pré-ovulatoire et (3) établir le rôle de la dopamine et de ses différents récepteurs (familles D1 et D2) dans la régulation directe et locale de l’axe gonadotrope aux niveaux cérébral et ovarien. La première partie de ce travail a permis pour la première fois, par l’utilisation d’antagonistes spécifiques des familles de récepteurs D1 et D2, de mettre en évidence un rôle potentiel de la dopamine sur la sécrétion de certains stéroïdes sexuels en période pré-ovulatoire chez le sandre par l’intermédiaire des récepteurs de la famille D1. L’identification de l’ensemble des récepteurs de la dopamine existant chez le sandre nous a permis de confirmer leur expression à tous les niveaux de l’axe gonadotrope (cerveau, hypophyse et ovaires) étayant l’hypothèse d’un rôle de la dopamine dans la reproduction du sandre. Enfin, la dernière partie de ce projet a permis de montrer un rôle régulateur du système dopaminergique, directement au niveau ovarien, sur la production de testostérone par l’intermédiaire des deux familles de récepteurs de la dopamine. L’implication des deux familles de récepteurs a également été mise en évidence dans la production ovarienne de la 17β-estradiol. Au niveau cérébral, seule la famille des récepteurs D2 a été montrée impliquée dans la régulation de l’expression du gène de la GnRH-3. De façon générale, cette étude a permis de mettre en évidence l’implication des récepteurs de la dopamine dans la régulation de l’axe gonadotrope lors des phases finales de l’ovogenèse. Toutefois, des travaux ultérieurs devront être menés pour approfondir les mécanismes physiologiques mis en jeu. D’un point de vue aquacole, les traitements hormonaux à base d’antagonistes des récepteurs de la dopamine ont été inefficaces pour améliorer les performances de reproduction du sandre ce qui n’est pas en faveur de leur utilisation future pour induire l’ovulation chez cette espèce. Ainsi, la mise au point d’autres méthodes d’optimisation sera nécessaire pour continuer à développer la production aquacole du sandre / Pikeperch, Sander lucioperca, is a potential valuable economic fish, making it a species of interest for aquaculture diversification. In the domestication process, controlling and understanding the reproductive cycle is a crucial step in order to produce viable offspring in a synchronous and predictable way. In many teleosts including some perciforms, dopamine inhibits the ovulatory pulse of LH and the ovulation step through D2 dopamine receptors family. In pikeperch, the roles of dopamine and its receptors, especially those belonging to the D1 receptors family, are unknown. For the purpose of the optimization of pikeperch reproduction, we investigated the role of the dopaminergic system during the final stages of oogenesis in this species: (1) by determining the effects of D1 or D2 receptor antagonists alone or in association with sGnRHa on the regulation of the reproductive axis and on the induction of ovulation, (2) by determining the repertoire and the expression profile of the dopamine receptors using a brain transcriptome analysis during the pre-ovulatory period and (3) by evaluating the role of dopamine and its receptors (D1 and D2 families) in the direct and local regulation of the gonadotropic axis at the brain and ovarian levels. For the first time, we showed that the dopamine/D1 receptors complex regulates the sex-steroids release during the pre-ovulatory period, suggesting that dopamine is involved in pikeperch reproduction. Also, we support its involvement thanks to the identification of the dopamine receptors gene expression at the brain, pituitary and ovarian levels. Finally, we showed that the dopaminergic system directly regulates the ovarian testosterone production, through both D1 and D2 receptor families. The involvement of both dopamine receptor families was also highlighted on ovarian 17β-estradiol production. Only the D2 receptor family was shown to be involved on the brain GnRH-3 gene expression. In conclusion, we point out a dopamine receptors implication on the gonadotropic axis regulation during the final stages of oogenesis in pikeperch. However, further studies should be performed to pinpoint the physiological mechanisms behind this phenomenon. From an aquaculture point of view, hormonal treatments with dopamine receptor antagonists appear to be ineffective to improve pikeperch reproductive performances. Therefore, their use to induce pikeperch ovulation should be put into question and the development of alternative methods is necessary to further promote pikeperch production