Hypoxia refers to any condition in which the water is less than fully saturated with oxygen. Although it is generally accepted that adults are more tolerant of hypoxic conditions than larval stages, there is little information to support this assumption. To determine whether reduced concentrations of dissolved oxygen (DO) affect fishes differently during various early life stages, I examined the responses of two species of fish (fathead minnows (Pimephales promelas) and rainbow trout (Oncorhynchus mykiss)) exposed to low dissolved oxygen concentrations at different ages during the first 100 days post-hatch. The changes in oxygen requirements and respiratory patterns that occur during ontogeny and exposure to hypoxia were observed. The results of this study suggest that the early larval stages appear to be at least as tolerant of short-term exposure to low dissolved oxygen concentrations as the older, more developed stages. Fathead minnows underwent a gradual transition from being metabolic conformers to regulators during development. Hemoglobin appeared to be playing a larger role in oxygen supply in the early post-hatch trout than in the minnows. Fathead minnow larvae produced relatively low concentrations of lactate upon exposure to hypoxia. Conversely, rainbow trout larvae exhibited significant increases in lactate concentration under similar conditions. This implies that there is a threshold oxygen concentration below which trout larvae utilize anaerobic metabolism to provide additional energy. Lactate dehydrogenase activity increased as the rainbow trout larvae aged, suggesting that they develop an anaerobic capacity which could be used to provide additional energy during hypoxia. The minnows did not exhibit this increase in activity. The ability of larval fishes to detect and avoid hypoxic conditions was also examined. The overall trends suggest that throughout this period of development, both fish species gradually leave an area as the dissolved oxygen concentration decline. Both species appeared to leave the hypoxic areas with deliberate motions, indicating that a directed sensor system allowed them to detect oxygen gradients. The results suggest that a combination of physiological, biochemical, and behavioral mechanisms may allow fishes to cope with hypoxia. / Ph. D.

The heavy reliance on live feeds is currently restricting the growth and sustainability of the aquaculture industry, therefore, the overall goal of this research was to improve the utilization of formulated dry diets at first feeding of larval fish. This was done with a specific focus on the production and provision of the optimal dietary protein form and composition. Chapter 2 aimed to provide an efficient protein source for larval fish by using same-species muscle and endogenous enzymes to produce hydrolysates and by providing a series of diets with increasing molecular weight protein fragments through larval development. Largemouth Bass (Micropterus salmoides) (LMB) muscle was mixed with the digestive enzymes from adult LMB and hydrolyzed for 1.5, 3, and 6 h, respectively. Five diets were produced, an intact diet containing non-hydrolyzed muscle and four diets with 37% muscle hydrolysate inclusion. The molecular weight profile of those diets were formulated to vary based on the inclusion level of each hydrolysate. To account for gut development, one group of larval LMB was fed a weekly series of diets with an increasing molecular weight profile. The initial inclusion of the hydrolysates significantly improved the total length of the larval LMB; however, neither the hydrolysate inclusion nor the series of dietary molecular weight profiles improved the overall growth of larval LMB. The inclusion of hydrolysates significantly decreased the occurrence of skeletal deformities. The results from this study suggest that the inclusion of same-species hydrolysates can improve the initial growth of first-feeding LMB, but further research is necessary to determine the optimal molecular weight profile, hydrolysate inclusion level, and physical properties of feeds to improve the overall growth performance during the larval stage. Chapter 3 compared the effect of dietary inclusion of a fish muscle hydrolysate produced from species-specific muscle and enzymes to hydrolysates produced from those of a different species, in diets for larval Walleye (Sander vitreus). Four intact and hydrolyzed protein products were produced from each combination of Walleye muscle and endogenous enzymes, and muscle and endogenous enzymes from Nile Tilapia (Oreochromis niloticus). The hydrolyzed products were continuously mixed for 3 h during the hydrolysis, (at 22oC and 28oC for Walleye and Tilapia enzymes, respectively), and the pH was adjusted throughout the process to mimic gastric and intestinal digestion conditions. Four diets were produced with the dietary protein supplied as a 50/50 ratio of the intact and hydrolyzed muscle from the respective muscle/enzyme combination. There was a significant interaction effect between muscle and enzyme source on the growth of larval Walleye. At the conclusion of the study, the larval Walleye that received the diet with muscle hydrolysate produced with Walleye muscle and Walleye endogenous enzymes had a significantly higher average weight than all other groups, and significantly higher postprandial levels of total free amino acids and indispensable amino acids in the muscle. Each hydrolysate-based diet led to a significant reduction in skeletal deformities and survival, compared to a group fed with a commercial diet. The results from this study suggest that species-specific muscle and enzymes produce a more optimal dietary protein source for larval fish than non-species-specific products, but further research should focus on improving the physical properties of the formulated diets to improve survival of fish larvae. Chapter 4 proposed a practical controlled hydrolysis method to utilize the endogenous enzymes within the fish body for the breakdown of tissues proteins, and to produce a species-specific meal that is tailored to the nutritional requirements and absorptive capacity of fish larvae. Four Zebrafish (Danio rerio) meals were produced from whole-body adult Zebrafish, three hydrolysates that were hydrolyzed for 1, 2, and 3 h, respectively, and an unhydrolyzed meal. From these meals, three diets were produced, each defined by their supply of dietary protein. The Unhydro diet was solely based on the unhydrolyzed Zebrafish meal. The 50% Hydro diet was based on 50% Zebrafish hydrolysate mix and 50% unhydrolyzed Zebrafish meal. The 100% Hydro diet was 100% based on the Zebrafish meal hydrolysate. The hydrolysate mix contained equal parts of the 1, 2, and 3 h hydrolysates. Proteomic analysis showed that the proposed hydrolysis method was able to efficiently hydrolyze the protein within Zebrafish body. The feeding trial found no significant differences in the final weight, total length, or survival between the Unhydro, 50% Hydro, and 100% Hydro groups, but the 50% Hydro group did express a significant upregulation of PepT1 at 24 h after feeding, compared to the Unhydro group. The growth results paired with PepT1 gene expression potentially indicate Zebrafish larvae to be adapted to dry feeds at first feeding and able to utilize dietary protein in different molecular forms efficiently for growth. Overall, the proposed hydrolysis method provides a practical and cost-effective approach to producing species-specific fishmeal hydrolysates. Further research is necessary to determine whether the produced hydrolysates can improve the growth of larval fish in other fish models. Further insight into behavioral and physiological responses in fish to imbalanced dietary amino acid profiles was provided in Chapter 5. The objective of this study was to determine how stomachless fish respond to diets deficient in the main limiting IDAA (lysine, methionine, and threonine), using Zebrafish as a model species. Six semi-purified diets were formulated for this study. The CG diet contained casein and gelatin as its only protein sources, while FAA50 diet had 50% of is dietary protein supplied with crystalline amino acids. Both were formulated to contain identical, balanced amino acid profiles. The remaining diets were supplied with the same amino acid mix as the FAA50 diet, but with minor adjustments to create deficiencies of the selected IDAA. The (-) Lys, (-) Met, and (-) Thr diets had lysine, methionine, and threonine withheld from the free amino acid (FAA) mix, respectively, and the Def diet was deficient in all three. The fish were fed to apparent satiation three times a day, and each feeding was carefully observed to ensure all feed added to the tanks was consumed. The results showed that although the singular deficiency of the three main limiting amino acids did not induce significant changes in feed intake, the combined deficiency of the three IDAA significantly increased the feed intake of juvenile Zebrafish. This increased feed intake prevented the IDAA deficiencies from significantly reducing growth, however, the feeding efficiency was also reduced. There was also an observed upregulation of neuropeptide Y (NPY), an orexigenic hormone, in the Def group, compared to the FAA50 group. The outcomes of this study provide insight into the behavioral and physiological response to dietary amino acid imbalances of stomachless fish and suggests stomachless fish increase their feed intake when challenged with IDAA-deficient diets, and that the regulation of NPY might play a role in this response. Chapter 6 assessed the postprandial FAA dynamics in the plasma, liver, and muscle of three species; 1) Largemouth Bass – warm-water, stomach-possessing carnivorous species; 2) Walleye – cool-water, stomach-possessing carnivorous species; and 3) Zebrafish– tropical, stomachless omnivorous species. Two diets were formulated for this study, a diet based on intact casein and gelatin (CG), and a diet with 50% of its protein supplied in FAA form (FAA50). Forty-two fish from each species were utilized, with one group of 21 receiving the CG diet, and the other 21 receiving the FAA50 diet. All fish were starved for 24 hours prior to the final feeding before sampling. Three fish were sampled at each time point, with three samples (plasma, liver, and muscle) taken from each fish. Samples were taken prior to feeding (0 h) and then at 0.5, 1, 2, 3, 6, and 12 h after feeding, for all species. A significant three-way interaction was observed between the diet, species, and postprandial time on the total FAA, IDAA, and DAA levels in the plasma, liver, and muscle, indicating that the postprandial FAA patterns were significantly different between species and in response to the different diets. In stomach-possessing species, dietary amino acids from the FAA50 diet were absorbed more rapidly than those from the CG diet, resulting in fewer correlations with the dietary IDAA profiles. The absorption of FAA in cool-water Walleye was more gradual and prolonged than the warm-water LMB, leading to more significant correlations with the dietary IDAA and more sustained peaks. The postprandial peaks of FAA typically occurred at the same time in the stomachless Zebrafish fed with the CG or FAA50 diet. The levels of FAA were noticeably lower after feeding with the FAA50 diet in Zebrafish, compared to the CG diet. These results provide a reference for differences in the FAA dynamic patterns of three species with differing physiological characteristics, when fed diets with intact protein or supplemented with FAA. The findings presented in this dissertation provide support and novel methods for the production and inclusion of species-specific protein hydrolysates as an ideal protein source in formulated diets for first-feeding larval fish. This research contributes to the development of larval diets that can release the limitations of growth placed on the aquaculture industry by the reliance on live feeds, particularly within the hatchery sector. This research also provides further understanding of dietary protein utilization and delivers new fish nutrition knowledge that will benefit the aquaculture industry as a whole.

No / Larval biotherapy is a debridement tool used in wound management. The mechanism of action involves degradation of eschar by serine proteases including chymotrypsin within the alimentary fluids of first instar Lucilia sericata. With the rationale of obviating some limitations of biotherapy, including cost, complexity of use, and patient reticence, the present study describes a mobile hydrogel formulation containing freeze-dried recombinant L. sericata chymotrypsin designed for topical application. Neither freeze-drying nor formulation into the hydrogel significantly attenuated the measured activity of released enzyme compared to fresh-frozen enzyme in aqueous solution. Gel electrophoresis confirmed qualitatively that the chymotrypsin/hydrogel formulation both with and without supplementary urea at 10% w/v degraded human chronic wound eschar ex vivo. Mindful that the hallmark of intractability of chronic wounds is aberrant biochemistry, the pH activity profile for the enzyme/hydrogel formulation was compared with exudate pH in chronic wounds of mixed aetiology in a cohort of 48 hospital in-patients. Five patients' wounds were acidic, however, the remainder were predominantly alkaline and coincided with the pH optimum for the insect enzyme. Thus, a recombinant L. sericata chymotrypsin and hydrogel formulation could represent a pragmatic alternative to larval therapy for the management of chronic wounds.

Analysis of larval fish collected at four stations in a 330-ha cooling reservoir indicated Dorosoma spp. were most numerous at all stations, followed by Lepomis spp. and Percina Macrolepida. Largest numbers and greatest diversity of larval fish were found at the station least affected by thermal effluent; the mid-lake station provided the smallest numbers and least diversity. The two warmwater stations were intermediate, with similar numbers and diversity. Diversity and abundance of zooplankton between stations were similar to those of fish. The most abundant zooplankter (Bosmina) was generally selected against by Dorosoma, Lepomis and Micropterus spp. larvae except when the larvae were quite small ((10mm). Cyclopoid copepods were most often selected by all larvae.

Com o avanço da meliponicultura, a utilização das abelhas sem ferrão, assim como de seus subprodutos, tem abrangido novas áreas, como a polinização de culturas agrícolas. Assim, a demanda pelo aumento do número de colônias tem sido constante, porém devido ao pouco conhecimento sobre a biologia reprodutiva dessas abelhas, há dificuldade de produção de colônias em larga escala, acarretando uma séria limitação quanto à utilização comercial desses polinizadores. Buscamos com este trabalho, oferecer ferramentas que possibilitem a multiplicação de colônias de abelhas sem ferrão em grande quantidade em um curto período de tempo. Nas abelhas indígenas sem ferrão (exceto no gênero Melipona e nos casos onde ocorrem rainhas-miniatura) a quantidade de alimento ingerido pelas larvas fêmeas é o fator responsável pela diferenciação das castas, pois as larvas que se tornam rainhas ingerem mais alimento que as larvas de futuras operárias, não havendo diferença qualitativa entre o alimento fornecido às larvas que originarão ambas as castas. De acordo com este modelo de determinação de castas, buscamos estabelecer a produção in vitro de rainhas em Tetragonisca angustula oferecendo maior quantidade de alimento às larvas de operárias, induzindo seu desenvolvimento em rainhas, que após a emergência foram introduzidas em mini-colônias órfãs para verificação da sua viabilidade (fecundação natural e postura de ovos). Em condições naturais as larvas de T. angustula que se tornam rainhas e operárias recebem respectivamente 55 µL e 8 µL de alimento em média. Assim, para a produção in vitro de rainhas oferecemos 55 µL de alimento a larvas de operárias coletadas em estágio pré-alimentação de ninhos naturais e conseguimos uma taxa de sobrevivência de até 51% e de 19% na obtenção de rainhas fisiogástricas, configurando um avanço em relação à taxa natural de emergência de rainhas, que foi de 0,21%. Das mini-colônias onde foram introduzidas rainhas virgens, 41% tiveram sucesso e se tornaram colônias perenes. A utilização de larvas de operárias na produção in vitro de rainhas é possível devido ao fato de as larvas serem totipotentes, assim como a utilização de alimento coletado de células de cria de operárias/machos, pois os resultados das análises comparativas do conteúdo protéico e de aminoácidos totais e livres dos alimentos contidos em células de cria de operárias/machos e células reais mostraram não haver diferenças significativas. A utilização de alimento larval de Scaptotrigona aff. depilis na criação in vitro de rainhas de T. angustula mostrou a possibilidade de produção de rainhas viáveis com esta nova técnica embora os perfis protéicos dos alimentos larvais de ambas as espécies sejam diferentes. Os experimentos de produção in vitro de rainhas com diferentes quantidades de alimento oferecido às larvas mostraram a existência de uma quantidade limite de alimento entre 35 µL e 45 µL acima da qual todos os indivíduos se tornam rainhas e abaixo da qual todos se tornam operárias, não havendo a ocorrência de indivíduos intermediários (intercastas). Introduzindo as rainhas produzidas in vitro em mini-colônias órfãs, conseguimos o estabelecimento de 16 colônias perenes a partir de seis colônias doadoras de material no período de seis meses, o que configura um avanço de 33% em relação às técnicas tradicionais de multiplicação de colônias que conseguiriam formar, no máximo, 12 colônias no mesmo período. A verificação da freqüência de produção de sexuados nas colônias naturais ao longo do ano mostrou que os machos são produzidos sazonalmente com alta taxa no período de fevereiro a abril, e embora as rainhas possuam uma produção baixa e homogênea ao longo do ano, concluímos que aquelas produzidas no período onde ocorre maior disponibilidade de machos possuem maiores chances de serem fecundadas. Assim, foi extremamente importante sincronizar a produção in vitro de rainhas com o período de maior disponibilidade de machos, uma vez que a fecundação destas ocorreu naturalmente. A produção in vitro de rainhas e a multiplicação de colônias nas abelhas sem ferrão se tornam ferramentas importantes para as técnicas de manejo que visam obter colônias em larga escala, com emprego na polinização, meliponicultura e conservação. / With the improvement of meliponiculture, the use of stingless bees, as well as their byproducts, has comprised new areas, such as the pollination of crops. Thus, the requirement by increasing the number of colonies has been constant, but due to poor knowledge about reproductive biology of these bees, have been difficult produce colonies on a large scale, what causes serious limitations on the commercial use of these pollinators. Our goals were to offer tools that allowed the multiplication of stingless bees colonies in large quantities in a short time. In stingless bees (except in the genus Melipona and in cases where there are miniature-queens) the amount of food ingested by female larvae is the responsible feature for caste differentiation, because the larvae that will become queens must to ingest more food than the larvae of future workers, and there is no qualitative difference between the food provided to larvae of both castes. According to this model of caste determination, we aimed at to establish the in vitro production of queens in Tetragonisca angustula, offering a large quantity of larval food to the workers larvae, thus inducing their development into queens that after rearing were introduced in orphaned mini-colonies to verify their feasibility (natural mating and egg laying). Under natural conditions the larvae of T. angustula that become queens and workers receive respectively, 55 µL and 8 µL of food on average. Thus, for the in vitro production of queens we offered 55 µL of food to workers larvae collected in pre-feeding stage from natural nests and we were able to get a survival rate up to 51 % and 19% in obtaining viable queens, which is an improvement compared to 0,21% of rearing queens observed in natural hives. About 41% of mini-colonies, where viable queens were introduced were successful and have become perennial colonies. The use of workers larvae on in vitro production of queens is possible because the larvae are totipotent, as well as the use of food collected from workers/males brood cells, because the results of comparative analysis of protein content and total and free amino acids of food stored in worker/males brood cells and royal cells showed no significant differences. The use of larval food from Scaptotrigona aff. depilis on in vitro rearing of T. angustula queens showed the possibility of producing viable queens, with this new technique, although the protein profiles of larval food of both species were different. The experiments of in vitro production of queens with different amounts of food offered to the larvae showed the existence of a threshold quantity of food between 35 mL and 45 mL above which all individuals become queens and below which all individuals become workers, without the occurrence of intermediate individuals (intercaste). Inserting the queens produced in vitro in orphaned mini-colonies, we were able to establish 16 perennial colonies as from six colonies donors of material in six months, constituting an increase of 33% compared to traditional techniques of multiplication of colonies which would form up only 12 colonies in the same period. Verification of frequency of sexuals reared in natural colonies over the year showed that males are produced seasonally with high rate in the period from February to April, and although the queens have a low and homogeneous occurrence over the year, we concluded that the queens produced during the period where there is greater availability of males, have higher chances of being fertilized. Thus, was extremely important synchronize the in vitro production of queens with the period where there is greater availability of males, since fertilization of these queens occurred naturally. The in vitro production of queens and multiplication of colonies in stingless bees become important tools for handling techniques that aim to obtain colonies on a large scale, with employment in pollination, meliponiculture and conservation.

Nos estudos de populações pesqueiras é comum o uso de modelos hidrodinâmicos acoplados a modelos biológicos e, um tipo de modelo merece destaque: o baseado no indivíduo (IBM). A Plataforma Continental do Atlântico Sudoeste comporta uma importante atividade pesqueira e, a influência da circulação na distribuição de ovos/larvas nessa região é pouco entendida. Estudos anteriores sugerem que o transporte de Ekman em direção à costa e o deságue de água fluvial impedem a perda de ovos e larvas da área costeira. Este trabalho apresenta resultados de um estudo englobando os padrões de circulação e de transporte de larvas nessa área, realizado através do desenvolvimento de um IBM para os estágios iniciais da Engraulis anchoita e o acoplamento deste a dois campos de velocidade superficial: a de Ekman, e a saída de um modelo hidrodinâmico 3D. Os resultados mostram que somente a deriva de Ekman não é suficiente para explicar o padrão de retenção larval observado na região. Os valores de retenção encontrados com a utilização da saída do modelo estão próximos aos observados. Maiores concentrações larvais foram obtidas no outono/inverno e menores na primavera/verão. Estes resultados estão diretamente relacionados à combinação dos efeitos dos padrões de vento da área com a influência das Correntes do Brasil e das Malvinas e do deságue continental na circulação sobre a plataforma. / Recruitment of pelagic fishes is the net result a series of continuous events in their life cycle. Most of the variability in natural mortality is thought to occur during the early stages of development and is related to environmental factors. The use of coupled physical-biological modeling in the study of fisheries populations is very common and a particular type of model deserves special mention: the Individual Based Model (IBM). The Atlantic Southwestern Continental Shelf is one of the most productive fishing sites in the Western South Atlantic, but the processes involving the circulation in this area and its influence on eggs/larvae transport and retention are still poorly understood. Recent studies describe the spawning activity of anchovy and its relationship to oceanographic processes and suggest that predominant onshore Ekman transport, during the austral winter/spring, keeps the eggs and larvae in coastal areas. According to these studies, the river runoff contributes to the formation of a retention zone for planktonic organisms over the area. This work presents results of a study that considers both the circulation pattern and larval transport, throught the development of an IBM for the early stages of anchovy Engraulis anchoita. The model is coupled to two surface velocity fields: the Ekman drift, and the output of a 3D hydrographic model. The results show that just Ekman surface velocities are not able to explain the larval dispersion observed in this region. Retention values obtained with the model output are much closer to observed values. Autumn and winter seasons present the highest values of retention. These results are due to the combined effect of the wind patterns registered in the area with the influence of the river runoff and the Brazil-Malvinas shelf circulation.

Nos estudos de populações pesqueiras é comum o uso de modelos hidrodinâmicos acoplados a modelos biológicos e, um tipo de modelo merece destaque: o baseado no indivíduo (IBM). A Plataforma Continental do Atlântico Sudoeste comporta uma importante atividade pesqueira e, a influência da circulação na distribuição de ovos/larvas nessa região é pouco entendida. Estudos anteriores sugerem que o transporte de Ekman em direção à costa e o deságue de água fluvial impedem a perda de ovos e larvas da área costeira. Este trabalho apresenta resultados de um estudo englobando os padrões de circulação e de transporte de larvas nessa área, realizado através do desenvolvimento de um IBM para os estágios iniciais da Engraulis anchoita e o acoplamento deste a dois campos de velocidade superficial: a de Ekman, e a saída de um modelo hidrodinâmico 3D. Os resultados mostram que somente a deriva de Ekman não é suficiente para explicar o padrão de retenção larval observado na região. Os valores de retenção encontrados com a utilização da saída do modelo estão próximos aos observados. Maiores concentrações larvais foram obtidas no outono/inverno e menores na primavera/verão. Estes resultados estão diretamente relacionados à combinação dos efeitos dos padrões de vento da área com a influência das Correntes do Brasil e das Malvinas e do deságue continental na circulação sobre a plataforma. / Recruitment of pelagic fishes is the net result a series of continuous events in their life cycle. Most of the variability in natural mortality is thought to occur during the early stages of development and is related to environmental factors. The use of coupled physical-biological modeling in the study of fisheries populations is very common and a particular type of model deserves special mention: the Individual Based Model (IBM). The Atlantic Southwestern Continental Shelf is one of the most productive fishing sites in the Western South Atlantic, but the processes involving the circulation in this area and its influence on eggs/larvae transport and retention are still poorly understood. Recent studies describe the spawning activity of anchovy and its relationship to oceanographic processes and suggest that predominant onshore Ekman transport, during the austral winter/spring, keeps the eggs and larvae in coastal areas. According to these studies, the river runoff contributes to the formation of a retention zone for planktonic organisms over the area. This work presents results of a study that considers both the circulation pattern and larval transport, throught the development of an IBM for the early stages of anchovy Engraulis anchoita. The model is coupled to two surface velocity fields: the Ekman drift, and the output of a 3D hydrographic model. The results show that just Ekman surface velocities are not able to explain the larval dispersion observed in this region. Retention values obtained with the model output are much closer to observed values. Autumn and winter seasons present the highest values of retention. These results are due to the combined effect of the wind patterns registered in the area with the influence of the river runoff and the Brazil-Malvinas shelf circulation.

Dans de nombreux pays, l’aquaculture de pectinidés dépend aujourd’hui du succès de la production contrôlée de juvéniles. Néanmoins, les fortes variations des taux d’éclosion des oeufs et de la survie larvaire, enregistrées à ce jour, rendent cette production imprévisible. Les élevages larvaires en flux ouvert de coquilles Saint-Jacques (Pecten maximus) ont été développés en Norvège et présentent des résultats prometteurs. Malheureusement, les rendements de production encore faibles et l’impossibilité de travailler à fortes densités restent un frein majeur au développement de cette technique. En France, une technique en flux-ouvert, en petit volume (5 L), et à forte densité (≤ 300 larves mL-1) a été développée pour les ostréidés. Des expériences préliminaires visant à décliner ce système d’élevage aux larves de P. maximus se sont avérées infructueuses : retard de croissance et forte mortalité en quelques jours. Il est reconnu que les larves de pectinidés doivent faire face à des contraintes diverses en écloserie : bactériologiques, physiologiques et environnementales. Elles sont également plus sensibles que les larves des autres espèces de bivalves comme par exemple l’huître japonaise (Crassostrea gigas). Il apparait donc nécessaire aujourd’hui d’identifier plus clairement l’origine des phénomènes perturbant le bon développement des larves en flux ouvert afin d’améliorer la qualité des élevages et les rendements larvaires. Grâce à l’étude et à la compréhension des mécanismes physiologiques impliqués dans la lutte contre le stress des larves de P. maximus en flux ouvert, ce projet de doctorat donne des clés permettant d’améliorer cette technique d’élevage tout en limitant l’utilisation de produits chimiques en milieu contrôlé. / In many countries, aquaculture of pectinids depends on the success of artificial spat production in hatchery. This production is always unpredictable due to the variability of hatching rate and larval survival. Flow-through larval rearing systems were developed in Norway for the King scallop Pecten maximus and showed promising results. Unfortunately the system needs to be optimized since the larval yields and the densities used are still relatively low. In France, a small-scale (5 L) and high-density (≤ 300 larva mL-1) flow-through larval rearing system was successfully developed for oysters. First trials in such system and in similar conditions with P.maximus failed as we registered slower growth and high mortality rate in only a few days. It is known that pectinids larvae are more sensitive to environmental conditions than the oyster Crassostrea gigas, for example.Nowadays, it is important to identify and to understand the phenomena disturbing larval development in flowthrough system to improve larval quality and production yields. This doctoral project provided some indications how improving P. maximus flowthrough rearing system while limiting the use of antibiotic through a better understanding the physiological mechanisms involved in the larval response to a stressful environment

Processes during the meroplanktonic phase regulate population dynamics for many marine benthic invertebrates. I examined changes in vertical distribution of different meroplanktonic larvae in a coastal embayment during a stable period, at high temporal frequencies and spatial resolutions. Plankton samples were collected at 6 depths (3, 6, 9, 12, 18, 24 m) using a pump, every 2-h over a 36- and a 25-h period, during a spring and neap tide, respectively, concurrently with measures of temperature, salinity, fluorescence and current velocity. For 10 gastropod taxa, larval vertical distribution was mostly related to the thermal structure of the water column. Each of 7 taxonomic groups was found either exclusively near the surface, associated with the fluorescence maximum, or showed diel changes in distribution. These larvae that occupy different depths in the water column exhibit different dispersal potentials. / Biogeographical data contained in this thesis will be submitted to the Oceanographic Biogeographic Information System (OBIS) and may be accessed on-line at http://www.iobis.org

This project predominantly investigated the implications of spatial heterogeneity in the ecological processes of competition and infection. Empirical analysis of spatial heterogeneity was carried out using the lepidopteran species Plodia interpunctella. Using differently viscous food media, it was possible to alter the movement rate of larvae. Soft Foods allow the movement rate of larvae to be high, so that individuals can disperse through the environment and avoid physical encounters with conspecifics. Harder foods lower the movement rate of larvae, restricting the ability of individuals to disperse away from birth sites and avoid conspecifics encounters. Increasing food viscosity and lowering movement rate therefore has the effect of making uniform distributed larval populations more aggregated and patchy. Different spatial structures changed the nature of intraspecific competition, with patchy populations characterised by individuals experiencing lower growth rates and greater mortality because of the reduced food and space available within densely packed aggregations. At the population scale, the increased competition for food individuals experience in aggregations emerges as longer generational cycles and reduced population densities. Aggregating individuals also altered the outcome of interspecific competition between Plodia and Ephestia cautella. In food media that allowed high movement rates, Plodia had a greater survival rate than Ephestia because the larger movement rate of Plodia allowed it to more effectively avoid intraspecific competition. Also the faster growth rate, and so larger size, of Plodia allowed it to dominate interspecific encounters by either predating or interfering with the feeding of Ephestia. In food that restricts movement, the resulting aggregations cause Plodia to experience more intraspecific encounters relative to interspecific, reducing its competitive advantage and levelling the survival of the two species. Spatial structure also affected the dynamics of a Plodia-granulosis virus interaction and the evolution of virus infectivity. Larval aggregation forced transmission to become limited to within host patches, making the overall prevalence of the virus low. However potentially high rates of cannibalism and multiple infections within overcrowded host aggregations caused virus-induced mortality to be high, as indicated by the low host population density when virus is presented. Also aggregated host populations cause the evolution of lower virus infectivity, where less infective virus strains maintain more susceptible hosts within the aggregation and so possess a greater transmission rate. The pattern of variation in resistance of Plodia interpunctella towards its granulosis virus was found using two forms of graphical analysis. There was a bimodal pattern of variation, with most individuals exhibiting either low or high levels of resistance. This pattern was related to a resistance mechanism that is decreasingly costly to host fitness.