Body shape affects the capacity and efficiency of swimming in fishes, and places constraints on foraging and reproductive performance. Hence, fitness components, such as aerobic swimming capacity and efficiency, can be determined from analysis of swimming energetics using active respirometry. In particular, body shape adaptations, such as streamlining, aim at reducing hydrodynamic drag (resistance), thereby increasing swimming efficiency in the presence of water flow, which is a principal contributor to resistance for fish inhabiting rivers. For two populations of bluegill sunfish, one from the Brazos River and the other from Moelman’s Slough (a Brazos River oxbow lake), the metabolic transport rate (MTR) was determined to evaluate differences in swimming efficiency. The standard cost of swimming (SCOS) was also determined to evaluate differences in swimming capacity, which represents the overall capacity of the skeletal muscles to generate mechanical power to overcome hydrodynamic resistance. The MTR and the SCOS describe holistic swimming performance, where the MTR specifies the hydrodynamic response due to swimming, and the SCOS specifies the physiologic response due to swimming. The differences in swimming performance are mainly attributed to factors affecting hydrodynamic resistance and could be predicted by morphology; because body shape, like water flow, is also a principal contributor to resistance. Multivariate body shape, from generalized Procrustes analysis, was used to assess the influence of multiple shape traits on swimming costs. This measure of shape related to swimming performance using partial least-squares analysis showed the two bluegill populations to be significantly different. The results were as follows: the shallow-bodied condition in bluegills was highly correlated with efficient swimming and low swimming capacities; whereas, deep-bodied bluegills were highly correlated with inefficient swimming and high swimming capacities. This is an empirical case of divergent natural selection. For convergence, however, the position of the caudal peduncle is consistent with optimal swimming speed (Um), which depends on standard metabolic rate (SMR), or metabolic maintenance. Bluegills with erect caudal peduncles have a high range of swimming speeds without suffering much cost of swimming ability compared to bluegills with prone caudal peduncles. The adaptive physiological response to high Um is due to a low SCOS because swimming efficiency is low and metabolic maintenance is high. In other words, bluegills that are inefficient swimmers and require a high energy intake cannot survive unless they gain the ability to increase their foraging capacity by thrust or metabolic power reduction. This is perhaps one of the most remarkable adaptive physiological responses due to the joint effects of shape and SMR.

<p> </p><p>ABSTRACT</p><p> </p><p>Migration is common among populations of brown trout (Salmo trutta) and Atlantic salmon (Salmo salar). However, not all individuals in the same population migrate, a phenomenon referred to as partial migration. The aim of this thesis was to investigate if an individual’s behaviour and metabolic rate influences its decision to migrate and how such knowledge may be used when trying to produce hatchery-raised smolts with as high a proportion of migrating individuals as possible. In paper I the influence of reduced food ration on the proportion and swimming speed of migrating brown trout and Atlantic salmon smolts was investigated. Furthermore, the standard metabolic rate (SMR) of migrating and non-migrating individuals was compared. In paper II, a laboratory experiment, SMR was correlated to the behaviour of individual brown trout and Atlantic salmon. Dominant fish of both species had a higher SMR than subordinates (paper II). In addition, migrant brown trout had a higher SMR than non-migrant trout when given a normal food ration, whereas no difference in SMR between migrating and non-migrating salmon could be seen (paper I). When administered low food rations, smolts of both species migrated faster than smolts given a normal food ration, and the proportion of migrating smolts was higher for salmon given less food when the size difference for smolts from the two feeding regimes was large (paper I). Other factors that influenced migration speed were the degree of smolt development and water temperature (paper I). SMR was not correlated with aggressiveness, or with different measurements of boldness. Moreover, aggression and boldness were not correlated with each other (paper II). Trout showed a higher level of aggressiveness and acclimated more rapidly to laboratory conditions than salmon (paper II). In summary, there was no support for the existence of coping styles in migratory Atlantic salmon and brown trout. Instead, metabolic rates were related to both migratory behaviour and social status. Furthermore, an individual’s decision to migrate was influenced by ration size.</p>

ABSTRACT   Migration is common among populations of brown trout (Salmo trutta) and Atlantic salmon (Salmo salar). However, not all individuals in the same population migrate, a phenomenon referred to as partial migration. The aim of this thesis was to investigate if an individual’s behaviour and metabolic rate influences its decision to migrate and how such knowledge may be used when trying to produce hatchery-raised smolts with as high a proportion of migrating individuals as possible. In paper I the influence of reduced food ration on the proportion and swimming speed of migrating brown trout and Atlantic salmon smolts was investigated. Furthermore, the standard metabolic rate (SMR) of migrating and non-migrating individuals was compared. In paper II, a laboratory experiment, SMR was correlated to the behaviour of individual brown trout and Atlantic salmon. Dominant fish of both species had a higher SMR than subordinates (paper II). In addition, migrant brown trout had a higher SMR than non-migrant trout when given a normal food ration, whereas no difference in SMR between migrating and non-migrating salmon could be seen (paper I). When administered low food rations, smolts of both species migrated faster than smolts given a normal food ration, and the proportion of migrating smolts was higher for salmon given less food when the size difference for smolts from the two feeding regimes was large (paper I). Other factors that influenced migration speed were the degree of smolt development and water temperature (paper I). SMR was not correlated with aggressiveness, or with different measurements of boldness. Moreover, aggression and boldness were not correlated with each other (paper II). Trout showed a higher level of aggressiveness and acclimated more rapidly to laboratory conditions than salmon (paper II). In summary, there was no support for the existence of coping styles in migratory Atlantic salmon and brown trout. Instead, metabolic rates were related to both migratory behaviour and social status. Furthermore, an individual’s decision to migrate was influenced by ration size.

En général, le métabolisme des poissons est estimé à des valeurs de température constantes, mais les effets de fluctuations journalières de température similaires à celles retrouvées en milieu naturel semblent peu connus. Les objectifs du présent mémoire sont de quantifier les effets de la température moyenne d’acclimatation et d’évaluer les effets de l’historique thermique des individus, sur les réponses métaboliques de tacons de saumon Atlantique (Salmo salar) aux fluctuations journalières de la température. Des tacons provenant de deux rivières, une fraîche et une chaude, ont été acclimatés à un maximum de quatre régimes thermiques (constant 15 °C ou 20 °C, fluctuant 15 °C ± 2.5 °C ou 20 °C ± 2.5 °C) et leur taux métabolique standard estimés par respirométrie par débit-intermittent. Les fluctuations journalières de température (15 °C ± 2.5 °C) près de l’optimum thermique pour cette espèce (16 °C) n’affectent pas le taux métabolique standard. À l’opposé, les fluctuations journalières de température plus chaudes (20 °C ± 2.5 °C) augmentent de 35.4% le taux métabolique standard des tacons de la rivière plus chaude, mais pas ceux des poissons de la rivière fraîche. Ainsi, la température moyenne à laquelle sont acclimatés les poissons peut affecter leur réponse métabolique aux fluctuations journalières de température, mais cette réponse peut varier entre populations provenant de rivières présentant des régimes thermiques différents. Enfin, grâce aux données de métabolisme précédemment estimées, un modèle de métabolisme standard a été développé pour des tacons de saumon Atlantique soumis à des fluctuations journalières de température. / Usually, fish metabolism is evaluated under constant values of temperature, but the effects of daily temperature fluctuations similar to those found in natural environment on metabolism seems to be much less understood. The goals of this study are to quantify the effects of the mean acclimation temperature and to assess the effects of the thermal history on the metabolic response of Atlantic salmon (Salmo salar) parr to daily fluctuations of water temperature. Atlantic salmon parr originating from two rivers, one cool and one relatively warm, were acclimated to up to four thermal regimes (constant 15 °C or 20 °C, daily fluctuating 15 °C ± 2.5 °C or 20 °C ± 2.5 °C) and their standard metabolic rate was estimated using intermittent-flow respirometry. Daily temperature fluctuations (15 °C ± 2.5 °C) near this species’ thermal optimum (16 °C) do not influence standard metabolic rate. In contrast, daily fluctuations of higher temperature (20 °C ± 2.5 °C) do increase standard metabolic rate by 35.4% for fish from the warmer river, but not for fish from the cooler river. Therefore, the mean temperature to which fish are acclimated may affect their responses to daily fluctuations of water temperature, but this response may vary between populations originating from rivers having different thermal regimes. Using standard metabolic rates previously estimated, a standard metabolic rate model was developed for Atlantic salmon parr exposed to daily fluctuations of temperature.

Le réchauffement climatique cause plusieurs modifications abiotiques et biotiques dans les milieux naturels. La hausse de la température de l’eau cause une diminution de l’oxygène dissous dans les lacs et augmente la quantité de zone hypoxique observée. Une autre conséquence de la hausse de la température est l’augmentation du métabolisme et de la consommation d’oxygène des espèces ectothermes dont les poissons et les parasites. Le parasitisme est omniprésent dans les réseaux trophiques et a un effet néfaste sur l’hôte affecté. Les parasites et l’hypoxie peuvent limiter la portée aérobie (AS) des poissons pour la réalisation d’activités journalières. Ainsi, cette étude analyse l’effet dans le temps d’une infection de trématodes causant la maladie du point sur le métabolisme et sur la tolérance hypoxique de l’hôte puisque le développement de ces parasites suggère un effet sur le poisson qui varie selon le temps de résidence des parasites. Nous avons utilisé des crapets-soleil (Lepomis gibbosus) infectés par ces trématodes comme système modèle. Nous avons émis l'hypothèse que l'infection parasitaire réduirait la portée aérobie et la tolérance à l'hypoxie des poissons en fonction du temps du développement de l’infection. Afin d’étudier cette relation hôte-parasite, des tests de respirométrie et d’hypoxie critique ont été performés à cinq moments lors des deux premiers mois suivant l’infection. Les traits métaboliques aérobies (taux métabolique standard et maximal, AS), des indices de la tolérance hypoxique et du métabolisme anaérobiques (tension critique d’oxygène, pression partielle d’oxygène entraînant la perte d’équilibre, la concentration de lactate) et le taux d’hématocrite sont les variables analysées à l’aide de la respirométrie et de prélèvements sanguins. Nous démontrons ici que l’infection expérimental de ces trématodes n’affecte ni la portée aérobie ni la tolérance hypoxique et ce indépendamment du temps de développement du parasite. Un faible effet temporel, mais significatif, est observé entre les premiers jours d’expérimentations et les derniers, des différences principalement dues aux faibles différences non significatives des taux métaboliques standards et maximaux. Le stress induit par captivité et l’effet des changements saisonniers sur les taux métaboliques sont possiblement en cause. Pour l’instant, selon les conditions environnementales actuelles, le crapet-soleil démontre une résilience à l’infection parasitaire ainsi qu’à l’hypoxie. / Global warming is causing several abiotic and biotic changes in natural environments. The rise in water temperature causes a reduction in dissolved oxygen in lakes and increases the amount of hypoxic zone observed. Another consequence of rising temperatures is the increased metabolism and oxygen consumption of ectothermic species, including fish and parasites. Parasitism is ubiquitous in food webs and has a detrimental effect on the affected host. Parasites and hypoxia can limit the aerobic range (AS) of fish for daily activities. Thus, this study analyzes the effect over time of a trematode infection causing the blackspot disease on the metabolism and hypoxic tolerance of the host since the development of these parasites suggests an effect on the fish that varies according to the residence time of the parasites. We used sunfish (Lepomis gibbosus) infected with these trematodes as a model system. We hypothesized that parasite infection would reduce the aerobic range and hypoxia tolerance of fish as a function of the time of infection development. Respirometry and critical hypoxia tests were performed at five time points during the first two months post-infection to investigate this host-parasite relationship and its impact over time. Aerobic metabolic traits (standard and maximum metabolic rate, aerobic range), indices of hypoxic tolerance and anaerobic metabolism (critical oxygen tension, partial pressure of oxygen leading to loss of equilibrium, lactate concentration) and hematocrit levels were analyzed using respirometry and blood sampling. We demonstrate here that experimental infection with trematodes affects neither aerobic range nor hypoxic tolerance independently of parasite development time. A small but significant temporal effect is observed between the first and last days of experimentation, differences mainly due to small non-significant differences in standard and maximum metabolic rates. This may be due to stress induced by captivity and seasonal changes affecting metabolic rates. For now, considering actual environmental conditions, sunfish show high resiliency to parasitic infection and to hypoxia.