Thesis (Ph.D.) - University of St Andrews, May 2008.

Glass eels of the European eel migrate from coastal waters inland to freshwater as part of the catadromous lifecycle. The osmotic challenge faced at this time is augmented by their large surface area to volume ratio, and by the fact that the migration may only be completed after several attempts, due to the effects of tide and river flow. Glass eels and elvers developed normally when maintained in waters of differing salinity over a six month period. Drinking rates increased with environmental acclimation salinity (from 0.072 +/- 0.023 mul/g/h to 0.698 +/- 0.099 mul/g/h in FW and SW respectively), and freshwater acclimated fish exhibited a rapid drinking response upon contact with seawater. These accounts of dipsogenic behaviour are similar to those previously reported for adult eels. Results obtained from determinations of branchial Na+K+ATPase activities were more equivocal. Only after nearly five months were activities higher in SW (508.52 +/- 99.76 nmoles/Spairs gills/h) as compared to FW fish (151.65 +/- 8.9 nmoles/5pairs gills/h). Following the transfer of FW acclimated fish to SW there was a trend towards increased Na+K+ATPase activity after seven days post-transfer, which reached a significant peak after two months post-transfer. A transient increase in whole body cortisol content was noted following the transfer of fish from freshwater (388.02 + 90.38 pg/g) to seawater (6268.44 +/- 773.14 pg/g). However, it was not possible to ascertain that this was due to a direct effect of environmental salinity change. There were no clear changes in interrenal cell morphology between salinity groups, although the cells did appear reduced in size with time, regardless of environmental salinity. Total body Na+ content increased with time, and was higher in SW (58.66 +/- 1.66 mumoles/g) as compared to FW reared fish (44.85 +/-1.01 mumoles/g).

1) Closed recirculating intensive aquaculture potentially offers major advantages over existing technologies including reduction in normal production time, reduced water input and output and beneficial environmental effects. 2) The major aim of this study was to produce a basic scientific understanding of the factors that affect intensive recirculating culture of the European eel Anguilla anguilla in order to increase efficiency and economic viability of eel aquaculture in the E.U. 3) Unlike some intensively farmed fish such as salmonids little is known of the stress factors affecting optimal growth rates in intensive eel culture. The primary effects of stress are mediated by corticosteroids and catecholamines which may have profound effects on growth, appetite and ion and water balance. 4) Growth rates of the eel Anguilla anguilla were investigated in closed water recirculating systems utilising fresh water or saline water (12 ppt)at 23°C. Eels were initially graded into two similar populations consisting of three categories, small (12g), medium (24g) and large (48g) based on initial growth rates. 5) During a 300 day period the medium and large group's growth rates were significantly greater in 12 ppt saline water than in fresh water, although for the small fish group there was no such difference. Stocking densities were maintained at commercial levels of approximately 30-100 kg/m3. 6) Plasma cortisol concentrations increased throughout the growth period in both fresh and saline water, although there were no significant differences between the two groups during the experiment. Metabolic clearance rates of cortisol were however consistently higher in saline water fish. 7) Both groups showed an increase in plasma glucose concentration throughout the experiment. However there were no significant differences between fresh water and saline water fish for plasma concentrations of glucose, free fatty acids or lactate. 8) Eels held at stocking densities of 130 kg/m3 continued to grow in the saline water whereas the control fish in fresh water ceased growing. The results suggest that maintaining water salinity at 12 ppt in closed recirculating aquaculture systems produces increased growth rates and possibly increased efficiency of food conversion. 9) In response to acute grading stress, plasma osmolality and glucose concentrations were elevated in both fresh and salt water groups 20 minutes after grading but returned to pre-grading values within 90 minutes. Plasma cortisol concentrations were elevated after 20 and 40 minutes in saline water but returned to control values after 90 minutes. In fresh water fish, plasma cortisol concentrations were elevated after 20 minutes and remained elevated throughout the experiment. 10) Acute netting stress (tank transfer) resulted in a transient increase in plasma osmolality within 20 minutes after net transfer. Plasma cortisol concentrations were significantly elevated after 20 minutes in saline water but returned to control values after 60'minutes. In fresh water fish, plasma cortisol concentrations were elevated throughout the 90 minute period monitored after net transfer. 11) In both cases of acute stress (netting and grading), plasma catecholamines were elevated within a five minute period after the stressor was applied. This study has developed techniques to assess both long-term and short-term stress in eels and has optimised the environmental conditions leading to improved growth rates. Improvements in the performance of recirculating aquaculture for on-growing eels have been demonstrated and suggestions for future possible improvements as a way forward in commercial aquaculture have been suggested. These factors will, hopefully, lead to increased economic efficiency and increased profits in eel aquaculture within the E.U.

1. Groups of eels, Anguilla anguilla, were adapted from freshwater (FW) to seawater, (SW) for periods of 90 - 300 mins. maximum (acute transfer), 0 - 7 days (chronic transfer), or for more than 14 days (longterm seawater transfer). 2. Acute SW transfer led to a decline in blood pressure, an elevation in plasma osmolality and chloride concentration, an immediate "reflex" drinking response and a non-significant increase in plasma angiotensin II (AH) concentration. 3. Administration of papaverine to FW adapted eel caused hypotension, with subsequent recovery of blood pressure, elevation in the drinking rate and plasma All concentration, and a decline in plasma osmolality. Captopril alone had no effect on blood pressure, drinking rate, osmolality or All concentration, but was successful in partially blocking the papaverine-induced blood pressure recovery and increase in AH concentration, with complete inhibition of the drinking. 4. Administration of papaverine to SW adapted eel caused hypotension, with partial recovery of blood pressure, increased drinking rate, plasma All concentration and plasma osmolality. Captopril alone caused a sustained decrease in blood pressure, inhibition of basal SW drinking and a reduction in plasma All concentration, with change in plasma osmolality. Administration of captopril prior to papaverine was successful in partially blocking the papaverine-induced recovery in blood pressure, increase in drinking, plasma All concentration, and plasma osmolality. 5. Chronic SW transfer led to a general decline in blood pressure, increase in plasma electrolyte concentration, elevation in drinking rate after 4-5 days, an increase in plasma All concentration, and a rise in Na+-K+-ATPase, all leading to long term SW values. 6. Plasma arginine vasotocin concentrations were unchanged in long term-FW and SW adapted fish, with a small transitory rise after 4 days in SW. 7. Cortisol plasma concentrations were similar in both long term- FW and SW- adapted fish, with a rise observed 1 day after transfer to SW. 8. Metabolic clearance rates (MCR) and blood production rates (BPR) were significantly elevated in long term SW adapted fish and during chronic SW adaptation, compared to the FW levels. Binding of 125I-AII to gill (filaments and lamellae), brain (cerebellum and medulla oblongata), kidney (head and caudal), and liver was observed in long term FW and SW adapted fish and 6 day SW transfer animals, with significant increase observed in binding in the caudal kidney and cerebellum and medulla oblongata between the FW group and 6 day SW transfer group.

Το απόθεμα του Ευρωπαϊκού χελιού (Anguilla anguilla), βρίσκεται σε ιστορικό ελάχιστο και η αλιεία του δεν είναι βιώσιμη, με τα δεδομένα να δείχνουν μείωση της στρατολόγησης της τάξης του 95%. Παρόμοιες πτωτικές τάσεις ισχύουν και στην Ελλάδα. Γι’ το λόγο αυτό ο κανονισμός της Ευρωπαϊκής Ένωσης 1100/2007 αναγκάζει όλα τα κράτη μέλη να προχωρήσουν στη σύνταξη διαχειριστικών σχεδίων για το χέλι προκειμένου να αυξηθούν οι διαφυγές αργυρόχελου στο 40% των διαφυγών που θα είχαμε αν δεν υπήρχαν οι ανθρωπογενείς παρεμβάσεις. Οι λόγοι μείωσης του αποθέματος του Anguilla anguilla είναι διάφοροι, με πιο σημαντικό για την παρούσα εργασία τις τεχνητές δομές που αποκλείουν κατάλληλους βιοτόπους για το χέλι. Στην παρούσα εργασία έγινε μια πρώτη τυπολογία των φραγμάτων, με ιδιαίτερη έμφαση στα φράγματα των Διαχειριστικών μονάδων 1 και 2 για το χέλι. Για το σκοπό αυτό, δημιουργήθηκε μια βάση δεδομένων, με στοιχεία από την Ελληνική Επιτροπή Μεγάλων Φραγμάτων και έρευνα στο google earth. Καταρχάς, τα αποτελέσματα της πρώτης τυπολογίας, έδειξαν ότι φράγματα σε ποσοστό 80% έχουν ύψος 0-50 m και από αυτά το 35% έχει ύψος 10-20m και το 25% 20-30m. Το 40% των μεγάλων φραγμάτων βρίσκεται σε απόσταση από τη θάλασσα έως 20km. Τα φράγματα που βρίσκονται πιο κοντά στην ακτή είναι τα Πουρνάρι ΙΙ (27km), Πουρνάρι Ι (30km), ο Λούρος (42km), το φράγμα του Φλόκα (17km), ο Στράτος (70km) και το φράγμα Αχυρών (11km). Το 35% των φραγμάτων χρησιμοποιείται αποκλειστικά για άρδευση και 10% αποκλειστικά για ύδρευση. Το 50% των φραγμάτων βρίσκεται σε υψόμετρο 0-200m και το 45% των φραγμάτων βρίσκεται σε υψόμετρο 200-900m. Η τυπολογία των φραγμάτων βάσει του όγκου του ταμιευτήρα έδειξε ότι τα περισσότερα φράγματα (60%) έχουν όγκο ταμιευτήρα έως 1.000.000m3 και ποσοστό 20% από 1.000.000 m3 έως 5.000.000m3. Στη συνέχεια, αξιολογήθηκαν τα παραπάνω φράγματα για την επίδραση τους τόσο στην ανάδρομη, όσο και στην κατάδρομη μετανάστευση. Ως προς την ανάδρομη μετανάστευση των χελιών, σύμφωνα με τα κριτήρια του Steinbach και με βάση τη σειρά του εμποδίου στην πορεία του χελιού, σημαντικά κρίθηκαν τα φράγματα του Στράτου, Πουρναρίου ΙΙ, Φλόκα, Μόρνου και Εύηνου. Ως προς την κατάδρομη μετανάστευση, σημαντικά κρίθηκαν τα φράγματα Καστράκι, Στράτος, Πουρνάρι Ι και ΙΙ, Λάδωνα, Φλόκα, Λούρου, καθώς είναι φράγματα που χρησιμοποιούνται -είτε αποκλειστικά είτε σε συνδυασμό με άλλες χρήσεις- για παραγωγή υδροηλεκτρικής ενέργειας. Παρ’ όλα αυτά, τα παραπάνω συμπεράσματα δεν είναι απόλυτα, καθώς πρέπει να αξιολογηθεί η αφθονία του χελιού στη συνολική μεταναστευτική του οδό. Στη Ευρώπη χρησιμοποιούνται τεχνικές παρεμβάσεις για τη διευκόλυνση της μετανάστευσης, όπως σκάλες χελιών ή διακοπή της λειτουργίας των τουρμπινών των υδροηλεκτρικών εργοστασίων. Στην Ελλάδα μεγάλο ποσοστό φράγματων έχουν μεγάλο ύψος (πάνω από 10m), όταν στην Ευρώπη ύψος πάνω από 2m θεωρείται σχεδόν απροσπέλαστο από τα χέλια, σύμφωνα με τα κριτήρια του Steibach. Τεχνικές λύσεις, όπως δημιουργία ειδικών χελιοδιαδρόμων, ίσως να μην ενδείκνυται λόγω αυτής της ιδιομορφίας. / The European eel (Anguilla anguilla) fishery is considered no more sustainable. In fact, present recruitment is about 1-5% of the maximum levels recorded in the past (early 70’s). Similar downward trends are observed in the Hellenic landings. For this reason, the EU regulation 1100/2007 obliges all Member States to propose management plans for the eel. The main objective is to increase silver eel escapement to the sea in order to participate in the reproduction of the population. The escapement should reach 40% of the escapement occurring without anthropogenic influence. The reasons reducing the stock of Anguilla anguilla are various, with the most important in this study, the artificial structures which exclude suitable habitat for eel. In the present a typology of dams was developed, with special emphasis on dams in Eel Management Units 1 and. For this purpose, we created a database with data from the Greek Dams Commission and from geographical elements about the position and altitude of the dams. The results revealed that 80% of the dams have heights varying between 0 and 50 m (35% have 10-20m height and 25% 20-30m). About 40% of large dams are located at less than 20km from the sea. The dams closest to the shore is Pournari II (27km), Pournari I (30km), Louros (42km), Stratos (70km), Floka (17km) and Axyron (11km). 35% of the dams are used for irrigation and only 10% exclusively for water supply. 50% of dams are in altitudes 0-200m and 45% of dams are in altitude 200-900m. The volume of 60% of the reservoirs was up to 1.000.000 m3 and 20% have reservoir volumes up to 5.000.000m3. The dams were evaluated for their effect both on upstream, and downstream eel migration. For the upstream migration of eels, according to the criteria of Steinbach and based on their sequential position from the sea, the major dams were Stratos, Floka, Pournari II, Mornos and Evinos. As for the downstream migration, significantly important dams are Kastraki, Stratos, Floka, Pournari I and II, Ladon, Louros, because these dams are used, either alone or in combination with other uses, for hydro-energy production. Nevertheless, these hierarchy is only based on geographical and technical elements and it have to be completed by the abundance of eel in the related ecosystems.. In Europe technical measures to facilitate the migration of eels comprise fish-laddes or shutting down the turbines of hydroelectric plants. In Greece, a large percentage of the dams have great height (over 10m), when in Europe height over 2m is considered almost impassable by the eel. In these cases, technical solutions, such as creating special eel passes, may be expensive, difficult and of reduced efficiency.

Den europeiska ålen (Anguilla anguilla) har en katadrom livscykel som innebär att den under sin livstid kommer att ned- och uppströmsmigrera genom älvar till sina tillväxt- och reproduktionsområden. I samband med att människan bygger vattenkraftverk för utvinning av energi skapas migrationshinder för den rödlistade ålen. Åtgärder har gjorts till att lösa det växande problemet som inkluderar, till exempel utsättning av klättringsramper vid vandringshinder. För att undersöka om den europeiska ålens val påverkas av vilket substrat den klättrar på byggdes sex testramper som vardera var indelade i 3 banor innehållandes vandringssubstraten EF16, Fishpass samt Enkamat. EF16 används vid anläggning av gröna tak som hjälper till att hålla kvar växtlighet, vatten och jordmassor på lutande underlag. Fishpass kan liknas en konstgjord gräsmatta som återskapar en våt gräsig vandringsmiljö för ålen. Enkamat har en hård trådstruktur och används i huvudsak som erosionsmattor. Studien visade att större delen av individerna i ålgrupperna föredrog substratet EF16 att klättra på, samt att importerade individer vandrar i större utsträckning än vad de vilda individerna gör. Att fastslå varför ålen föredrar vandringssubstratet EF16 samt varför de importerade individerna vandrar i större utsträckning är svårt. Faktorer som substratskillnader, eventuell exponering för vandringssubstraten innan undersökningen och olika tillväxtförhållanden innan studien kan påverka substratvalet. Dock tycks det substrat med både nedåt- och uppåtgående knoppar vara den mest effektiva åtgärden till det ökande vandringsproblemet, då 40,5 % av det totala individantalet valde att klättra på banor beklädda med substratet EF16.

Européenne, (Anguilla anguilla) a conduit à une diminution du nombre d’anguille jaune dans les bassins versants. En 2007, le règlement (CE) instaure que 60% des civelles pêchées (<12 cm de long) doivent être dédiés à des opérations de repeuplement. Cependant, pour migrer et coloniser un nouvel environnement, les civelles doivent avoir une bonne condition énergétique. Or, les civelles ne s’alimentent pas ou peu durant leur migration estuarienne et la vitesse d’utilisation de leurs réserves dépend de divers facteurs (température, contaminants etc.). Dans l’estuaire de l’Adour, différents travaux ont mis en évidence de fortes concentrations en methylmercure (MeHg) dans les sédiments et une bioaccumulation de ce composé chez l’anguille jaune. L’exposition au MeHg entraîne la mise en place de processus de détoxication qui pourraient être couteux en énergie ce qui, chez des organismes jeûnant comme les civelles, conduirait à une perte de poids pouvant affecter leurs capacités de migration. Pour étudier l’impact du méthylmercure sur le potentiel de migration des civelles, nous avons tout d’abord (1) effectuer un état des lieux des concentrations en MeHg des civelles de l’estuaire de l’Adour, (2) évaluer l’effet du MeHg sur deux synchroniseurs de la migration estuarienne: le signal crépusculaire et l’alternance des marées chez les civelles grâce à l’utilisation de traceurs isotopiques et (3) étudier dans le milieu naturel (Adour) le comportement de migration, les taux de contamination au mercure et les mécanismes de détoxication des civelles. Nos résultats montrent des fluctuations temporelles et saisonnières de la concentration en MeHg des civelles prélevées en entrée et en milieu de l’estuaire. Par ailleurs, l’exposition au MeHg, en milieu contrôlé, a augmenté l'activité des civelles mais pas leur comportement de migration. Cependant, suite à la contamination, la structure mitochondriale et le métabolisme ont été modifiés suggérant un plus fort stress oxydant et une activation des défenses antioxydantes notamment des civelles ayant un faible potentiel de migration (non migrantes).En complément, l’étude en milieu naturel a mis en évidence une plus forte demande énergétique pour les civelles non migrantes entrainant une augmentation du fonctionnement des mitochondries et pouvant conduire à un plus fort stress oxydant. / Over the last three decades, the arrival of Anguilla anguilla glass eels has markedly declined which has lead to a decrease in the number of yellow eels in the watersheds. In 2007, the Regulation (EC) indicated that 60% of glass eels (<12cm long) caught by fisheries should be used for restocking. To migrate and colonize a new environment, glass eels must have a good energetic condition. However, during their estuarine migration, glass eels either feed very little or more likely not at all. The speed at which they expend their energy stores depends on various factors (temperature, contaminants etc.). In the Adour estuary, many studies have reported relatively high methylmercury (MeHg) concentrations in the sediments, and bioaccumulation in yellow eels. Exposure to MeHg requires energy for detoxification which, in starving organisms such as glass eels, might lead to weight loss, decreasing their ability to migrate up the estuary. To study the impact of MeHg on migratory behaviour in glass eels, we first conducted an inventory of MeHg concentrations of glass eels in the estuary of the Adour, (2) evaluate the effect of MeHg on two synchronizers of estuarine migration: dusk and tide on glass eels through the use of isotopic tracers and (3) to study the natural environment (Adour) migratory behavior, mercury contamination levels and detoxification mechanisms of glass eels. Our results show temporal and seasonal fluctuations in the concentration of MeHg glass eels collected input and middle of the estuary. Moreover, MeHg exposure, in a controlled environment, increased the activity of glass eels but not in response to migratory behavior. However, due to contamination, mitochondrial structure and metabolism have been modified suggesting a stronger oxidative stress and activation of antioxidant defences of glass eels, particularly those with low migration potential (non-migrant). In addition, the wild study showed a higher energy demand for non-migrating glass eels causing an increase in mitochondrial function which may lead to higher oxidative stress.

La anguila europea es una especie de gran importancia comercial en la acuicultura europea, pero el dramático descenso de las poblaciones naturales ha provocado la inclusión de esta especie en la lista CITES (convención del comercio internacional de especies en peligro de la fauna y flora salvaje). Considerando esta situación, se hace necesaria más investigación en el control reproductivo. El presente documento contiene 5 estudios que se pueden dividir en dos partes principales: la primera, una descripción del proceso de la maduración artificial de la anguila, seguida por una segunda parte centrada en el de desarrollo de técnicas para la evaluación de la calidad espermática, y la conservación del esperma. Una vez fijado el tratamiento hormonal en anteriores estudios, nosotros hemos estudiado la evolución de la calidad espermática a lo largo del periodo de espermiación, tratando de determinar las semanas con mayor porcentaje de muestras con alta calidad espermática. Para la evaluación de la calidad espermática los parámetros analizados fueron los siguientes: porcentaje de células vivas, motilidad, y morfometría de la cabeza del espermatozoide. El porcentaje de células vivas fue medido poniendo a punto técnicas de tinción fluorescentes, mientras que la medida del tamaño de la cabeza fue llevado a cabo por un programa informático (sistema ASMA), pero este análisis presentó problemas debido a la especial forma de la cabeza del espermatozoide de esta especie. Para validar esta técnica fue necesario comparar los resultados obtenidos por el sistema ASMA con los obtenidos por el microscopio electrónico de barrido. Distintos machos que recibieron el mismo tratamiento hormonal mostraron diferentes respuestas en cuanto al nivel de desarrollo gonadal y calidad espermática. Para entender qué factores podían influir en en estos factores, se realizó por primera vez la descripción de la maduración de machos de anguila europea, analizando la expresión de GnRHs y gonadotropinas, los n / Sánchez Peñaranda, D. (2008). Study of male reproductive physiology and sperm conservation in the european EEL ( Anguilla anguilla, L.) [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/3063 / Palancia

Im Jahr 2006 wurden insgesamt 767 Aale des Bodensee-Obersees auf den Befall mit dem Schwimmblasenwurm A. crassus und dessen Folgen untersucht. Zusätzlich wurden die Befallsdaten von weiteren 2.326 Aalen aus den Jahren 1988 bis 2005 und 2007 bis 2009 ausgewertet. Weiterhin wurden in den Jahren 2006 bis 2008 eine Anzahl von 383 Kaulbarschen und zahlreiche Copepoden auf den Befall mit dem Larvenstadium von A. crassus untersucht. Auf der Ebene der echten Zwischenwirte ließ sich A. crassus im Bodensee-Obersee im Freiwasserplankton nicht nachweisen. Jedoch konnten Copepoden der Gattung C. abyssorum experimentell mit A. crassus infiziert werden. Der Kaulbarsch ist für A. crassus der wichtigste Stapelwirt im Bodensee-Obersee. Die untersuchten Kaulbarsche waren zwischen 18,8% und 52,1% mit A. crassus infiziert, wobei die Infektion einen deutlichen Frühjahrespeak aufwies. Im Jahr 2006 lag die Prävalenz befallener Aale im Bodensee bei 55,6%, die durchschnittliche Befallsintensität lag bei 4,4 adulter Parasiten je Aal. Durch die Datenauswertung von insgesamt 3.425 Aalen konnte der Verlauf der Anguilli­coloidose im Zeitraum von 1989 bis 2009 rekonstruiert werden. Der Höhepunkt der Infektion lag demnach im Jahr 1993 mit einer durchschnittlichen Prävalenz des Erregers von 58,3% und einer durchschnittlichen Befallsintensität von 16,6. Seit 1996 werden die Schadwirkungen von A. crassus auf die Schwimmblase aufgezeichnet und wurden nun in dieser Arbeit ausgewertet. In diesem Zeitraum nahm die Anzahl der Aale mit schweren Schwimmblasenschäden deutlich zu. Im Jahr 2006 besaßen 89,9% der Aale eine Schwimmblase mit geringer bis sehr starker Schädigung. Bei den abwanderungswilligen Blankaalen besaßen insgesamt 10% eine Schwimmblase mit sehr starken Schäden. Es bestand eine positive Korrelation zwischen der Größe der Aale und der Ausprägung der Schwimmblasenschäden. Weiterhin wurde ein negativer Einfluss durch den Befall mit Larven von A. crassus auf das Milzgewicht beobachtet. Der Befall mit abgestorbenen Adulten war mit Anämie korreliert. Durch den kumulativen Effekt der Schwimmblasenschäden, die durch die Infektion mit A. crassus hervorgerufen werden, werden vor allen Dingen größere Aale im Bodensee-Obersee beeinträchtigt. Eine parasiteninduzierte Mortalität von A. crassus liegt jedoch nicht vor.

Depuis plusieurs dizaines d’années, la population des anguilles européennes a souffert d’un dramatique déclin et est classée parmi les espèces hors de leurs limites biologiques depuis 1998. Différents phénomènes, tels que la pêche, les obstacles aux migrations, ou le réchauffement climatique, en sont à l’origine. Cependant, les perturbations environnementales, telles que les contaminations métalliques et organiques ou les épisodes d’hypoxie, participent probablement à la vulnérabilité de cette espèce. Or, l’estuaire de la Gironde est soumis à des contaminations poly-métalliques historiques, ainsi qu’à des contaminations organiques de différentes origines, et à des épisodes hypoxiques réguliers. Les travaux menés au cours de cette thèse, se sont donc composés d’études de terrain visant à identifier les contaminants majeurs chez les anguilles jaunes de l’estuaire de la Gironde, ainsi que leur voie de bio-accumulation et leurs impacts au niveau physiologique, biochimique et moléculaire. Ces études ont nécessité la mise en place d’expériences préliminaires ayant pour objectifs de vérifier les impacts de certaines procédures, telles que l’anesthésie et la mise en cage des anguilles jaunes. D’autre part, les impacts des deux principaux contaminants métalliques et organiques des anguilles européennes de l’estuaire de la Gironde, ont été testés, de façon individuelle et combinée, ainsi que ceux de l'hypoxie sur des anguilles pré-contaminées ou non, lors d’une étude expérimentale.Ainsi, ces travaux ont mis en évidence que les anguilles européennes installées dans la zone avale de l’estuaire, étaient susceptibles d’être soumises à des contaminations poly-métalliques plus importantes, essentiellement d’origine trophique, responsables d’une croissance pondérale moins élevée et de perturbations transcriptionnelles hépatiques et cérébrales. De plus, bien que les contaminations métalliques de ces anguilles ne mettent pas ne danger la santé humaine, les contaminations en PCB sont, en revanche, supérieures aux normes de consommation. D’autre part, ces travaux ont également mis en évidence des dérèglements mitochondriaux ainsi qu’un stress oxydant, au niveau branchial et cérébral chez des anguilles contaminées au Cd, et au niveau cérébral, branchial, hépatique et rénal chez les anguilles contaminées aux PCB. Enfin, la concomitance de ces deux contaminants et/ou d’un épisode d’hypoxie, réduit et/ou retarde les capacités de réponses transcriptionnelles de ces anguilles. Il semble donc que les différentes perturbations chimiques subies par les anguilles européennes au stade jaune au sein de l’estuaire de la Gironde participent de façon non négligeable à la vulnérabilité de cette espèce. / For several decades, the European eel has been suffering from a dramatic decline and has been classified among species beyond their biological limit since 1998. Different phenomena, as fishing, migration barriers, or global warming, are to blame. Environmental perturbations, as metallic and organic contaminations, or hypoxic episodes, probably take part to the vulnerability of this species. The Gironde estuary has been submitted to historic poly-metallic contaminations, to organic contaminations from different origins, and to regular hypoxic episodes. This thesis work is composed of field studies aimed to identify the main contaminants in yellow eel living in the Gironde estuary, their major bioaccumulation way and impacts on physiological, biochemical and molecular parameters. These studies needed preliminary experiments aimed to verify whether some field and handling procedures are consistent with ecotoxicological analyses. Moreover, impacts of the two main contaminants in European eels from the Gironde estuary have been assessed individually or combined, with those of hypoxia on pre-contaminated eels.Thus, these studies have demonstrated that European eels installed in the downstream area of the estuary, were likely to be subject to largest poly-metallic contaminations, mostly by food web, and responsible for a less weight gain and high liver and brain transcriptional disturbances. Furthermore, although the metal contamination of eels does not endanger human health, PCB contaminations are higher than consumption standards. On the other hand, these studies have also revealed oxidative stress and mitochondrial disorders in gills and brain of Cd-contaminated eels, and in brain, gills, liver and kidneys of PCB-contaminated eels. The combination of these two contaminants and/or an episode of hypoxia, reduces and/or delays the transcriptional responses ability of these eels. It seems that the different chemical disturbances, suffered by the yellow eels in the estuary of the Gironde, participate significantly to this species vulnerability.