Das Vorkommen von über den Umgebungsdruck erhöhten Sauerstoffpartialdrucken in Geweben ist im Tierreich nur von der Schwimmblase und dem Auge von Knochenfischen bekannt. Die physiologischen Mechanismen dieser Sauerstoffkonzentrierung wurden an der Schwimmblase insbesondere des Aals intensiv untersucht, entsprechende Untersuchungen zu den Vorgängen im Auge der Knochenfische fehlen jedoch. In dieser Arbeit wurde daher eine Methode etabliert, mit der die Sauerstoffkonzentrierung im Auge der Knochenfische an isolierten Augen untersucht werden kann. 1. Das Gefäßsystem der Regenbogenforelle (Oncorhynchus mykiss, Walbaum 1792) wurde durch Gefäßausgüsse dargestellt. Das im Auge gelegene choroidale Rete mirabile wird über die Arteria ophthalmica, die gleichzeitig die efferente Pseudobranchienarterie darstellt, versorgt. Die Pseudobranchie selber empfängt das Blut aus der efferenten Arterie des ersten Kiemenbogens. Diese Gefäßtopologie, Versorgung der Pseudobranchie mit bereits im ersten Kiemenbogen oxygeniertem Blut und auschließliche Versorgung des choroidalen Rete mirabile mit Blut aus der Pseudobranchie, weist auf die Bedeutung der Pseudobranchie für die Prozesse im Auge hin. 2. Die Retina der Regenbogenforelle wurde mikroskopisch untersucht. Die einzelnen Schichten der Retina entsprechen denen anderer Wirbeltiere. Die Forellenretina ist mit 407 µm aber wesentlich dicker als z.B. die Retina von Mammaliern. Zusätzlich fehlt der Retina der Forelle die bei vielen Mammaliern vorhandene retinale Blutgefäßversorgung. Mit den der Retina am nächsten gelegenen Gefäßen in der Choroidea bestehen bei der Forelle wesentlich größere Diffusionsstrecken von den Blutgefäßen zum Ort des Sauerstoffverbrauchs in den Zellen der Retina als bei anderen Wirbeltieren. Dies wir durch den erhöhten Sauerstoffpartialdruck in den Choriokapillaren kompensiert. 3. Für die Messung des intraretinalen Sauerstoffpartialdrucks wurden im Rahmen dieser Arbeit Sauerstoffmikroelektroden inklusive der zur Betreibung der Elektroden notwendigen Elektronik entwickelt. Die Elektroden waren vom Recess-Typ: die reaktive Oberfläche schloss nicht mit dem Ende der Glaskapillare ab, sondern war unter Belassung eines Hohlraumes in der Elektrodenspitze (Recess) in das innere der Glaskapillare verlagert. Dadurch waren die Elektroden unempfindlich gegenüber Rühreffekten. Die Mikroelektroden hatten eine Spitzendurchmesser von < 10 µm und eine mittlere Empfindlichkeit von 172 fA Torr-1 O2. Die Linearität der Elektroden über eine Partialdruckbereich von 0 bis 760 Torr O2 war besser als r = 0,9998. 4. Zur Überprüfung des normale Sauerstoffpartialdrucks in der Retina wurden Regenbogenforellen betäubt und künstlich ventiliert. Die systemischen Parameter wie arterieller PO2-Wert, Blutdruck und Herzschlag entsprachen dabei im Mittel mit 99 Torr (arterieller PO2), 28 Torr (Blutdruck) und 1,23 Hz (Herzschlag) den Werten unbetäubter, freischwimmender Forellen. Lediglich der arterielle pH-Wert war mit 8,02 während der künstlichen Ventilation durch eine ungenügende Kompensation einer respiratorischen Alkalose leicht gegenüber dem normalen Wert von 7,9 erhöht. 5. Die Auswirkungen der Präparation des Auges zur Messung des intraretinalen Sauerstoffpartialdrucks auf den Augeninnendruck wurde überprüft. Der Augeninnendruck betrug 4,9 Torr. Die Einbringung der Sauerstoffmikroelektrode hatte keine Auswirkung auf den Augeninnendruck. Erst das Entfernen der Elektrode nach der Messung führte zu einer deutlichen Verringerung des Augeninnendrucks. 6. Zum ersten Mal wurde in der vorliegenden Arbeit die Durchblutungsrate des Auges eines Knochenfisches bestimmt. Aus präparatorischen Gründen wurde die Messung an der afferenten Pseudobranchienarterie durchgeführt. Der mittlere Blutfluss in dem Gefäß betrug 745 µl min-1 kg-1. Durch Verschluss des kontralateralen Gefäßes stieg der Fluss auf 135% des ursprünglichen Wertes, da jetzt durch das ipsilaterale Gefäß und über die zwischen den beiden Gefäßen bestehende Anastomose beide Augen durch das ipsilaterale Gefäß mit Blut versorgt wurden. 7. Die Funktion der Retina während der intraretinalen Sauerstoffmessung wurde durch Ableitung des Elektroretinogramms kontrolliert. Trotz der während der Versuche fortbestehenden Betäubung mit dem Betäubungsmittel MS222, welches sich negativ auf das Elektroretinogramm auswirken soll, konnten normale Elektroretinogramme aufgezeichnet werde. Die invasive Messung des intraretinalen PO2 wirkte sich nicht negativ auf die Funktionalität der Retina aus. 8. Der intraretinale Sauerstoffpartialdruck wurde an betäubten, künstlich ventilierten Forellen überprüft. Der mittlere maximale PO2 im Bereich der Bruch´schen Membran betrug 382 Torr. An der Innenseite der Retina wurde ein PO2 von 10 Torr gemessen. Der Bereich des O2-Partialdruckgradienten in der Retina, gemessen über den Vorschub der Sauerstoffmikroelektrode vom niedrigsten bis zum höchsten PO2, betrug 433 µm, ein Wert der gut mit der mikroskopisch bestimmten Dicke der Retina (407 µm) übereinstimmt. 9. Zur Untersuchung der Einflüsse von Blutparametern auf die Sauerstoffkonzentrierung im Auge der Forelle wurden isolierte Augen künstlich mit verschiedenen Erythrozytensuspensionen perfundiert. Dazu wurde zum einen eine Suspension von Forellenerythrozyten eingesetzt, bei der erst der Root-Effekt in Abhängigkeit vom pH-Wert der Suspension bestimmt wurde. Bei basischem pH-Werten war das Hämoglobin der Erythrozyten vollständig gesättigt. Bei einem pH-Wert von 7,68 war noch eine Sättigung von 90% vorhanden, die bis zu einem pH-Wert von 7,31 auf 50% abnahm. 10% Sättigung wurden bei einem pH-Wert von 6,94 erreicht. Für die Perfusion wurde die Suspension der Forellenerythrozyten mit einem pH-Wert von 7,48 eingesetzt. Bei diesem pH-Wert liegt die Sättigung bei ca. 82% und eine Änderung des pH hat in diesem Bereich eine deutliche Änderung der Sättigung zur Folge, was die Freisetzung von O2 von Hämoglobin erleichtert. Als alternative Perfusionslösung wurde eine Suspension von Humanerythrozyten eingesetzt. Humanhämoglobin weist keinen Root-Effekt auf, es kann also durch die im Auge der Knochenfische vorhandenen Mechanismen kein Sauerstoff freigesetzt werden. 10. Der mittlere intraretinale Sauerstoffpartialdruck isolierter Augen betrug bei Perfusion mit der Suspension von Forellenerythrozyten 99 Torr. Nach dem Wechsel auf die Suspension mit Humanerythrozyten fiel der intraretinale Sauerstoffpartialdruck sofort auf 30 Torr ab. Der Perfusionsdruck änderte sich bei dieser Umstellung nicht. Bei Perfusion mit Ringerlösung fiel der intraretinale PO2 auf 20 Torr, gleichzeitig fiel jetzt auch der Perfusionsdruck ab. 11. Eine Konzentrierung des Sauerstoffs konnte bei der künstlichen Perfusion isolierter Augen nicht nachgewiesen werden. Die Notwendigkeit des Root-Effekts für einen hohen Sauerstoffpartialdruck im Auge wird trotzdem deutlich, da bei Perfusion mit einer Suspension von Humanerythrozyten, die einen höheren Sauerstoffgehalt aufwies als die Suspension der Forellenerythrozyten, der intraretinale Sauerstoffpartialdruck deutlich geringer war. 12. Das Modell des isoliert perfundierten Auges ist zur physiologischen Untersuchung des choroidalen Rete mirabile und Sauerstoffkonzentrierung besser geeignet als in vivo - Experimente, da systemische Einflüsse vermieden und die Auswirkungen der Pseudobranchie auf die Blutchemie ausgeschaltet werden können. / Oxygen partial pressures (Po2) above ambient levels are found only in the swimbladder and the eye of teleost fish species. The mechanisms related to the involved oxygen concentration processes have been investigated to some detail in eel swimbladder, but little attention has been paid to analogous mechanisms of the teleost eye. This thesis has accordingly concentrated on developing a method promoting investigation of oxygen concentrating mechanisms in teleost eyes by application of an isolated perfused eye preparation. 1. The vascular supply of eye and pseudobranch in rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) was depicted by corrosion casts of the vascular system. The choroid rete mirabile is supplied with blood by the ophthalmic artery as the efferent blood vessel of the pseudobranch, with a small anastomosis to the contralateral vessel. The pseudobranch in turn is fed by the efferent artery of the first gill arch. This pattern of serial vascular connection suggests a role for the pseudobranch in the process of providing high oxygen tensions required for the high metabolic demand of the visual perception in the retina. 2. Eyes of various fish species were sectioned after paraffin embedding and examined microscopically. The organisation of teleost fish retinae is characterised by the same features and organisation well known from other vertebrates. However, the total thickness of 407 µm found for the retina of the rainbow is much larger than that observed in other animals such as mammals. The conditions of diffusive oxygen supply of retinal nerve cells is further hampered by the complete lack of intraretinal blood vessels commonly found in mammals. In trout, blood is supplied to only the choroid layer, leaving large diffusion distances to the retinal nerve cells to be spanned by oxygen partial pressures, elevated as compared to the bulk arterial system in the choroid capillaries. 3. Intraretinal oxygen partial pressure was determined in long-term anaesthetised specimens of Oncorhynchus mykiss, using specially developed oxygen microelectrodes and required electronic circuitry. Characteristic features of the electrodes include insensitivity of the signal to stirring, achieved by a recess of the reactive metal surface in a glass capillary, an average tip diameter of less than 10 µm and a characteristic sensitivity to oxygen of 172 fA Torr-1. The response of the electrodes to oxygen was linear over a range of partial pressures from 0 to 760 Torr O2 (r= 0,9998). 4. Normal oxygen partial pressures in trout retina were measured in long-term anaesthetised and artificially ventilated specimens of Oncorhynchus mykiss. In order to conduct the experiments under conditions as close as possible to normal homoiostasis, several systemic valuables were monitored continuously. During experimentation arterial Po2 averaged 99 Torr, mean blood pressure was 28 Torr and heart frequency was on the average 74 bpm, respectively, data in the range of values determined in unanesthetized, freely swimming trout. As the one exception, arterial pH (8,02) was slightly elevated during artificial ventilation as compared to control values (7,89), a shift induced by an inadequately high rate of artificial ventilation. 5. The impact of insertion of electrodes required for intraretinal Po2 measurement into the eye was found to have little effect. The intraocular pressure remained unaffected by opening the eye by puncture with leading cannula and inserted micro-Po2-electrode. The intraocular pressure fell only after removing the electrode after completion of the experiment. 6. Normal function of the retina during experimentation in vivo was checked by repeatedly measuring electroretinograms provoked by light flashes under dark ambient conditions. Although extended anaesthesia with MS222 is expected to affect the electroretinogram in fish, there was no indication of abnormal or reduced electroretinograms during experimentation. Also puncture of the eye with insertion of electrodes did not affect the electroretinogram. 7. Intraretinal Po2 was measured in anaesthetised and artificially ventilated trout. Oxygen profiles were recorded during advancement of the electrode tip though the retina, from the lowest Po2 at the inner surface with about 10 Torr to the highest Po2 in the region of Bruch´s membrane with about 382 Torr, travelling a total distance of 433 µm. This distance closely corresponds to the thickness of the retina measured by microscopic sectioning. 8. Blood flow to the eye as an important parameter for the establishment of an isolated eye preparation was measured in the afferent artery of the pseudobranch. Due to the anatomical situation this represents the closest possible approximation to measurement of flow in the ophthalmic artery. The blood flow was estimated by ultrasonic Doppler techniques with in situ calibration to be 216 µl min-1. Occlusion of the contralateral vessel resulted in an increase of the blood flow in the ipsilateral vessel to 135% of the original as a result of flow through the small anastomosis between the two ophthalmic arteries. This estimate is the first performed for blood flow to the eye of a fish. 9. An isolated eye preparation was used to investigate the influence of specific blood parameters on oxygen concentrating processes in the eye of Oncorhynchus mykiss. Eyes were perfused with suspensions of trout erythrocytes, human erythrocytes and Ringer´s solution. The Root Effect of trout haemoglobin was confirmed in suspension of erythrocytes. The haemoglobin was fully saturated at pH 8.45, still 90% saturated at 7.68, 50% at 7.31 and 10% at pH 6.94. In order to provide optimal starting conditions for the release of oxygen by relatively small changes in pH, pH 7.48 (resulting in 82 % saturation) was chosen for the perfusion of isolated eyes. As a control perfusion, suspensions of human erythrocytes provided a perfusate lacking any Root effect, thus not supporting the oxygen concentrating processes in fish eyes. 10. Perfusion of isolated trout eyes with pH 7.48 trout erythrocyte suspension resulted in an average intraretinal Po2 of 99 Torr, whereas perfusion with human erythrocytes resulted in an immediate decrease of Po2 to (of) 30 Torr, with a further drop to 20 Torr during perfusion with Ringer´s solution. Changes in perfusion between erythrocyte suspensions were performed without any changes in perfusion pressure, but the switch to control perfusion with Ringer´s solution exhibited a drop in perfusion pressure due to the reduced viscosity of the medium. 11. Although perfusion of isolated eyes did not exhibit Po2 above ambient values, the effect of oxygen concentrating processes were clearly indicated by comparison with Root effect-lacking human erythrocyte perfusate (Po2´s of 99 vs. 30 Torr, respectively). 12. It is concluded that studies of oxygen concentrating mechanisms are to be performed preferably on isolated eye preparations. For closer analysis of the involved mechanisms this preparation allows for isolated control of individual parameter of the perfusate. In particular, uncontrolled effects of the pseudobranch on the perfusate can be eliminated.

Cette thèse précise les conditions pour introduire une sélection sur apparentés de caractères de qualité assistée par empreintes génétiques dans un programme de sélection massale sur la croissance chez la truite arc-enciel. Ce travail confirme l’intérêt à maîtriser l’effet maternel avec une doublement de l’héritabilité du poids à 70 g (0,36 vs 0,16), des estimations d’héritabilités des caractères mesurés de valeurs intermédiaires (0,37-0,54), l’intérêt d’utiliser la résiduelle des parties mesurées régressées linéairement au poids vif pour une sélection indépendante du poids pour les rendements, l’intérêt à remplacer la mesure du rendement au filetage par celle du rendement en carcasse éviscérée-étêtée plus héritable et très corrélé au rendement au filetage (0,97),la corrélation génétique élevée entre les rendements avec le ratio échographique e8/e23 (0,72-0,85) permettant une sélection sur candidats plus efficace qu’une sélection sur apparenté sur le rendement lui-même, des précisions élevées des valeurs génétiques (0.63–0.82) malgré très peu d’individus par famille (3,5-4) et une efficacité surestimée d’une sélection sur apparentés pré-sélectionnés (de 14 % à 62 %). Les conclusions sont qu’il est possible d’introduire une sélection sur apparentés dans un programme de sélection massale avec des gains génétiques au moins équivalents à ceux attendus en sélection familiale classique avec familles élevées initialement de façon séparées / The thesis aims at describing conditions to improve mass selection on growth by sib-selection on quality traits assisted by DNA parentage assignment in rainbow trout. Main results are that the control and management of differences in egg size between dams doubles heritability of body weight at 70 g (0.36 vs 0.16), heritabilities of quality traits are intermediates (0.37-0.54), the opportunity to use the residual of the body part (e.g. fillet weight) regressed to the whole body weight to select independently of body weight for ratios, the higher efficiency to replace fillet yield by deheaded and gutted carcass weight more heritable and highly genetically correlated to fillet yield (0.97), the possibility to use e8/e23ultrasound measures to predict genetically yields (0.72-0.85) allowing a direct selection on breeding candidates more efficient than in using sib information, a surprising intermediate to high accuracy of EBV even with a very low mean number of sib per full-sib family (3.5-4) and the medium to high overestimation of EBV when using pre- selected sibs (14 % to 62 %). The general conclusion are that sib-selection on quality traits can be introduced in mass selection with at least similar expected genetic gains than in traditional breeding design based on families reared initially separated

La pression sur les quotas de pêche et l’augmentation de la production aquacole ont contribué à une substitution importante des farines et des huiles de poisson incorporées dans les aliments pour poissons carnivores, par des farines et des huiles végétales. La truite arc-en-ciel, qui est un poisson carnivore, est affectée par ce changement de régime. Ainsi un retard de croissance apparaît dès le plus jeune stade si certaines transformations et supplémentations ne sont pas apportées aux végétaux. L’objectif de ce travail a été d’évaluer, aux stades alevins et juvéniles, l’impact d’une substitution totale des huiles et farines de poisson sur le tractus digestif de la truite arc-en-ciel, et plus particulièrement sur ses capacités digestives et sur la composition de son microbiote intestinal. Le but in fine étant de déterminer si certaines enzymes de la digestion, transporteurs intestinaux, ou sous-communautés bactériennes sont impactés par le changement de régime et peuvent expliquer le retard de croissance observé. Chacun de ces facteurs ont été étudiés via une approche de métagénomique par séquençage de nouvelle génération NGS pour la caractérisation du microbiote, et via de la PCR quantitative et des mesures d’activités enzymatiques pour la comparaison des capacités digestives. Des lignées isogéniques de truites, identifiées comme divergentes dans leur réponse à l’alimentation végétale (capables d’adaptation ou réfractaires) ont permis de disposer d’un matériel biologique pertinent pour répondre à cette question. Une modification du microbiote intestinal associé à la muqueuse digestive pourrait également contribuer à la baisse de l’homéostasie intestinale. Le changement de régime conduit en effet à une équitabilité plus faible chez les truites ayant reçue un aliment végétal, ce qui reflète un changement dans la représentativité de certains OTUs. Ce changement de régime s’est également traduit par des communautés dissimilaires en moyenne à 70 %, d’après l’estimation de la β-diversité entre les communautés de truites nourries avec l’aliment marin et celles nourries avec l’aliment végétal. La sélection opérée par l’aliment a conduit à un remplacement des OTUs rencontrés au sein des Firmicutes, c’est-à-dire que différentes espèces bactériennes de Firmicutes sont rencontrées suivant le régime considéré. La comparaison de communautés bactériennes entre les différentes lignées isogéniques a montré que la sélection opérée par le génotype de l’hôte a davantage eu lieu sur le remplacement des β-Protéobactéries. Enfin, les comparaisons d’abondances en certaines espèces bactériennes particulières suggèrent que les bactéries Cetobacterium somerae, capables de synthétiser de la vitamine B12, et Shewanella, dont l’implication dans la stimulation des cellules β du pancréas endocrine a déjà été observée chez d’autres espèces, pourraient être impliquées dans la réponse métabolique des truites aux végétaux. Les modifications identifiées dans ce travail constituent des indicateurs biologiques qui pourront être mis à profit pour évaluer la réponse du tractus digestif des truites à de nouvelles formules alimentaires. / Over-fishing pressure and increasing aquaculture production led to an important substitution of fish oil and fish meal with oil and meal from plant origin in feed meant for farming fish. However this replacement has some deleterious incidence on fish. For rainbow trout, which are carnivorous fish, some growth delay often appears from the early life stages when they are fed with plant based diet. The aim of this work was to assess, at alevin and juvenile stages, the impact of a total replacement of fish meal and oil on rainbow trout gastrointestinal tract, and more particularly on the digestive capacity and the associate microbiota. The objective, in fine, being to determine if some digestive enzymes, intestinal transporters, or bacterial communities are impacted by the dietary replacement and if these biological factors can be related to the observed growth delay. Metagenomic approach using next generation sequencing was used to characterize the gut bacterial communities, while digestive capacity was assessed through quantitative PCR and enzymatic measurements in order to compare rainbow trout responses to a plant-based diet. In our investigations, rainbow trout isogenic lines that diverge in their response to this alternative diet (tolerant or rather reluctant) were adopted because they constitute a pertinent biological material for answering this question.In alevin rainbow trout, a plant-based diet led to an increase of pepsinogen, trypsinogen, and chymotrypsinogen genes which codes for proteolitic enzymes. Two main assumptions can explain this response, and their effectivness remains to investigate: wether this is a physiological response due to a lower weight of trout fed with the plant-based diet, or so it is due to an increase transcritpion of pancreatic enzymes to compensate for a reduction of protein digestibility. In the intestine, it appears that an increase transcription of IAP, SGLT1, CCK-t, and PEPT1 genes, and a decrease transcription of GLUT2 gene under a plant-based diet could reflect a disability to grow under a vegetable diet.In juvenile rainbow trout, a plant-based diet led to a decrease of lipid digestibility, and of triglycerides and total amino acid plasmatic levels. These perturbations could be explained in part by a decrease of the phosphatase alkaline activity, which suggest perturbancesof intestinal homeostasis, and by a decrease of phospholipase A2 activity. Transcriptional decrease of the triglycerides transporter MTP and of the prolidase, which is a peptidase from intestinal cell cytosol, has also been observed. Some modification of the microbiota associated to the intestinal mucosa could also contribute to the decrease of the intestinal homeostasis. The dietary replacement effectively led to reduce evenness of the bacterial communities in trout fed with a plant-based diet, which reflected a shift in the representativeness of some OTUs. Bacterial community from trout fed with a marine diet and trout fed with a plant-based diet were on average 70 % dissimilar. Dietary substitution led to the replacement of OTUs from the Firmicutes class, different bacterial species being observed according to the considered diet. The comparison of bacterial community between the isogenic lines showed that the genotype led to the replacement of β-Proteobacteria. Finally, abundance comparison suggested that Cetobacterium somerae, which is able to synthesise vitamin B12, and Shewanella, which has already been reported to stimulate pancreatic β cells, could be implicated in the trout response to vegetable.Modifications observed in this work constitute biological indicator that could be used to assess the response of the digestive tract to future feed formulations.

Juvenile rainbow trout (Oncorhynchus mykiss) fed L-tryptophan (TRP) supplemented feed for 7 days show a suppression of aggressive behaviour along with a reduction in post-stress plasma cortisol levels. However, 3 days of elevated dietary TRP does not have any effects on either aggressive behaviour or post-stress plasma cortisol levels. The effects of TRP on aggression and stress responsiveness could be related to elevated brain serotonergic activity, TRP being the precursor of serotonin (5-HT). However, 5-HT is, in turn, the precursor of melatonin (ME) and we found that elevated dietary intake of TRP results in an increase in daytime plasma levels of ME. Elevated plasma ME concentrations in rainbow trout fed TRP supplemented feed appear to be of gastrointestinal origin. ME has been suggested to have inhibitory effects on aggressive behaviour and to act as a glucocorticoid antisecretagogue. However, we found that exogenuos ME did not affect aggressive behaviour or post-stress plasma cortisol in rainbow trout. Instead, the effects of TRP on aggressive behaviour and plasma cortisol were mimicked by treatment with the selective serotonin re-uptake inhibitor, citalopram, suggesting that the effects of TRP are mediated by a stimulation of brain 5-HT activity and not by increased ME synthesis and secretion. However, the slow time-course of the effects of TRP on aggressive behaviour and plasma cortisol suggests that effects on 5-HT receptors mechanism are likely to be involved.

La truite arc-en-ciel a un déterminisme du sexe strictement génétique de type XX/XY. Pourtant des femelles génétiques se sont spontanément masculinisées après une gynogénèse endomitotique. Ce phénotype masculinisé à pénétrance incomplète serait dû à une mutation inconnue appelée " mal ". Afin d'identifier le gène causal porteur de cette mutation, une meilleure caractérisation de son phénotype est nécessaire. Pour cela, nous avons procédé à la caractérisation du phénotype gonadique en utilisant à la fois des approches histologiques et moléculaires. Tous les animaux XXmal présentent une différenciation sexuelle très perturbée autant sur le plan histologique que sur le plan de leurs profils d'expression géniques. Parmi ces perturbations, l'inhibition de l'expression du gène de l'aromatase gonadique (cyp19a1a), une enzyme de synthèse des œstrogènes, pourrait être un facteur explicatif de cette masculinisation. De plus des températures d'élevage élevées (18°C) augmentent fortement la masculinisation de ces animaux XXmal. Enfin, la croissance des animaux XXmal est affectée négativement selon le degré de perturbation. En conséquence, la masculinisation de ces animaux serait le résultat d'une dérégulation profonde en amont du gène cyp19a1a, avec comme conséquence une instabilité précoce de la différenciation ovarienne suivie par la masculinisation effective d'une partie des animaux XXmal. Cette instabilité serait amplifiée par des températures élevées qui affecteraient à la fois le développement global des animaux XXmal et la transcription de cyp19a1a. Nos résultats suggèrent fortement que le phénotype "mal" est plus complexe qu'un simple phénotype "femelle masculinisée".

Recovery from exhaustive exercise in the white muscle of rainbow trout (Oncorhynchus mykiss) was used to examine the role of the adenylates in the control of energy metabolism and to assess the validity of equilibrium models of the behaviour of the high energy phosphates. The difficulty of obtaining muscle samples from fish makes detailed analysis of the behaviour of the labile high energy phosphates complex. The use of a new sampling procedure, the infusion of a lethal dose of anaesthetic via an indwelling cannula, minimized this problem. At exhaustion [ATP] and [PCr] were depressed by 75 and 80% respectively relative to the resting values. [ATP] depletion was mirrored by a stoichiometric increase in [IMP]. During recovery [PCr] returned to the resting level within 2 hours, but [ATP] recovery was slow and not complete until 24 hours post exercise. In contrast, energy charge and RATP(the proportion of the free adenylate pool phosphorylated to ATP) were, if anything, higher than the resting values by 2 hours post exercise. Therefore, [ATP] and energy status can be dissociated in tissues like fish white muscle because of the action of the purine nucleotide cycle. At 2 hours post exercise the calculated free ADP concentration dropped to less than one tenth the value at rest. As a result the [ATP] / [ADP] free ratio increased by nearly 6 fold. This condition may be required for glycogen resynthesis from lactate in muscle. Several similar equilibrium models of the behaviour of the adenylates and PCr were applied to the fish white muscle system. In general, the models well describe the relationship between the high energy phosphates. However, the definition of the high energy phosphate pool introduces some complications since this includes the total [ATP]. Because of the action of AMP deaminase the [ATP] concentration can change without measurable changes in the energy status, which is not considered in any of the models. As long as the extent of IMP formation is known the models can be applied, but since the formation of IMP may vary from fish to fish or with exercise regime the models lose much of their predictive power. / Science, Faculty of / Zoology, Department of / Graduate

The effect of transferring fish from water at pH 7.0 to either more acid or more alkaline conditions was to reduce the maximum critical velocity of the fish. In water of pH 4.0, 5.0, and 10.0, the maximum critical velocity was only 54.5%, 66.5%, and 61% respectively of that recorded for fish in the water of pH 7.0. Thus, both acid and alkaline conditions in the water reduce the aerobic swimming capacity of trout. Exposure to acid conditions increased mucus secretion and this was associated with an increase in coughing and breathing frequency in resting fish. Coughing rate increased from 41/hr to 592/hr; and respiration frequency increased from 81/min to 104/min when fish were transferred from water at pH 7.0 to water at pH 4.0. In comparing fish exposed to acid and alkaline waters, the results indicates that fish have a greater capacity to regulate blood pH in acid than in alkaline conditions. The gill potential was strongly dependent on water pH, being negative in neutral water, but positive in acid water and more negative in alkaline solution. Catecholamine levels increased significantly during acid exposure, but were not altered during alkaline exposure. The increasing catecholamine levels appeared at different time periods in different fish during acid exposure and seemed to be associated with the death of the fish. Na⁺ and C1⁻ ion concentrations in plasma decreased significantly after 24hrs of acid exposure, but did not change significantly in alkaline water. This may indicate that ionoregulatory disturbance in plasma is one of the reasons for the decrease in the maximum critical velocity in acid water, but not in alkaline water. / Science, Faculty of / Zoology, Department of / Graduate

No description available.

Disease has been identified as a major problem in the aquaculture industry for the welfare of the fish stocked as well as for its economic impact. The number of diseases affecting cultured fish has increased significantly during recent years with the emergence of several conditions that have added to the overall impact of disease on the industry. Frequently, a lack of scientific knowledge about these diseases is compounded by an absence of effective treatment and control strategies. This has been the case with rainbow trout gastroenteritis (RTGE), an emerging disease of rainbow trout (Oncorhynchus mykiss Walbaum). This study investigated several aspects related to its aetiology and control. A retrospective survey of UK rainbow trout farmers was undertaken to ascertain the extent and severity of RTGE in the UK as well as to identify RTGE risk factors at the site level. Participants in this study accounted for over 85% of UK rainbow trout production in 2004. It was found that the total number of RTGE-affected sites had risen from 2 in the year 2000 to 7 in 2005. The disease was only reported from sites producing more than 200 tonnes of trout/year for the table market. Analysis of risk factors associated with RTGE at the site level showed that this syndrome was associated with large tonnage and rapid production of rainbow trout for the table market. The data collected during this study enabled the identification of those sites that were most likely to present with RTGE the following year and this information was used to study the epidemiology of RTGE at the unit level. A prospective longitudinal study was undertaken in 12 RTGE-affected UK sites. It described in detail the impact, presentation, current control strategies and spread pattern of RTGE within affected UK sites. The risk factors associated with RTGE presence and severity were also investigated. Data were collected for each productive unit (i.e. cage, pond, raceway or tank) on the mortalities, fish origin, site management and environmental factors. RTGE was identified using a case definition based on gross pathological lesions. Analysis of these data revealed that RTGE behaved in an infectious manner. This conclusion was supported by the presence of a pattern typical of a propagating epidemic within affected units. Also, the risk of an unaffected unit becoming RTGE positive was increased if it had received fish from or was contiguous to a RTGE-affected unit. The presentation also suggested an incubation period of 20-25 days. Risk factor analysis identified management and environmental risk factors for RTGE, including high feed input and stressful events, which could be used to generate a list of control strategies. A study of the histopathological and ultrastructural presentation of RTGE was conducted. The location of segmented filamentous bacteria (SFB) and pathological changes found in affected fish were examined. Pyloric caeca were the digestive organ where SFB were found more frequently and in higher numbers, suggesting that this was the best location to detect SFB in RTGE-affected trout. Scanning and transmission electron microscopy revealed a previously undescribed interaction of SFB with the mucosa of distal intestine and pyloric caeca and this included the presence of attachment sites and SFB engulfment by enterocytes, as previously described in other host species. The SFB were not always adjacent to the pathological changes observed in the digestive tract of RTGE-affected trout. Such changes included cytoskeletal damage and osmotic imbalance of enterocytes, with frequent detachment. These observations suggested that if SFB are indeed the cause of RTGE their pathogenesis must involve the production of extracellular products. Analysis of the gross presentation and blood biochemistry in RTGE-affected fish was used to examine the patho-physiologic mechanisms of RTGE. To enable identification of positive RTGE cases for this study, a case definition was created from the information available on RTGE gross presentation in the literature. This case definition was assessed in a sample including 152 fish cases and 152 fish controls from 11 RTGE-affected UK sites, matched by unit of origin. The analysis of these fish using bacteriology, packed cell volume (PCV) and histopathology revealed that RTGE occurred simultaneously with other parasitic and bacterial diseases in a percentage of fish identified with this case definition. With the information gained after analysing the gross presentation, RTGE-affected fish without concurrent disease were selected for the study of the pathogenesis, which included blood biochemical analyses. These analyses revealed a severe osmotic imbalance, and a reduced albumin/globulin ratio suggesting selective loss of albumin, typical for a protein losing enteropathy. The role of the SFB “Candidatus arthromitus” in the aetiology of RTGE was assessed using a newly developed “C. arthromitus”-specific polymerase chain reaction assay (PCR) in conjunction with histological detection. This technique was applied to eight different groups of trout, including an RTGE-affected group and seven negative control groups. This analysis was conducted on DNA extracted from paraffin wax-embedded tissues as well as fresh intestinal contents. The results revealed the presence of “C. arthromitus” DNA in apparently healthy fish from sites where RTGE had never been reported. Additionally, SFB were observed histologically in two trout from an RTGE-free hatchery. These findings do not permit the exclusion of “C. arthromitus” as the aetiological agent for RTGE, although they suggest that the presence of these organisms in the digestive system of healthy trout is not sufficient to cause clinical disease, and therefore other factors are necessary. In conclusion, this study has used a multidisciplinary approach to the study of RTGE which has generated scientific information related to the epidemiology, pathogenesis and aetiology of this syndrome. The results of this project have suggested priority areas where further work is required, including experimental transmission of RTGE, field assessment of the control strategies proposed and further investigation into the aetiology of RTGE.

Les téléostéens euryhalins peuvent vivre dans des milieux à salinité très différentes. L'objectif de mon travail est de décrire les processus d'acclimatation à l'eau salée chez la truite arc-en-ciel par une étude couplant approches de génomique fonctionnelle et génétique. A partir d'une première approche cinétique de transcriptomie différentielle menée sur la branchie, une liste de gènes candidats a été établie et la réponse physiologique des poissons étudiée. Les principaux résultats révèlent de bonnes capacités d'euryhalinité et une réponse transcriptomique maximum 24h après le transfert en eau de mer. Des processus biologiques impliqués dans les mécanismes d'acclimatation sont également proposés. Une seconde partie de ce travail consistait en la caractérisation d'un contrôle génétique des processus liés à l'acclimatation à l'eau de mer chez la truite. Utilisant comme caractères, les teneurs plasmatiques en sodium et en chlore mesurées 24h après un transfert d'eau douce en eau salée répété à 2 reprises, ainsi que le poids branchial, des analyses univariées et multivariées ont permis de détecter 18 QTL dont 9 sont qualifiés de robustes. Une dernière étape de détection de QTL d'expression a alors permis de proposer 69 gènes candidats de premier choix. C'est la première fois qu'une approche mêlant transcriptomie différentielle et approche QTL / eQTL est menée chez une espèce d'intérêt aquacole au génome non séquencé pour la capacité d'acclimatation à un milieu osmotique différent. Ces résultats pavent la route pour une investigation précise des bases génétiques des processus d'acclimatation à l'eau de mer chez les téléostéens.