La perche commune, Perca fluviatilis L. est un poisson maigre (moins de 2% de lipides dans le filet) mais dont les teneurs en acides gras polyinsaturés de la famille n-3 (AGPIn-3) et principalement en acide docosahexaènoque (DHA) sont très élevées (40% des AG totaux). L’objectif de ce travail est d’étudier les facteurs qui influent sur le métabolisme lipidique chez la perche et qui assurent ces taux élevés de DHA. Les hypothèses testées qui permettraient d’expliquer les fortes teneurs en DHA sont une incorporation préférentielle de cet AG ainsi qu’une capacité, typique des poissons d’eau douce, à bioconvertir le 18:3n-3 présent dans l’alimentation en AGPI n-3 supérieur, EPA et DHA. Pour tester ces hypothèses nous avons mis en place trois expérimentations. Dans un premier temps, nous avons caractérisé les lipides des différents tissus impliqués dans le métabolisme lipidique en observant leurs teneurs en lipides totaux, neutres et polaires et leur composition en acides gras. Dans un deuxième temps nous avons déterminé et hiérarchisé les facteurs ayant un effet sur la teneur en lipides et la composition en AG en utilisant un plan d’expérience multifactorielle. Enfin, nous avons étudié plus particulièrement l’effet de la composition en acides gras de la source alimentaire sur la composition en AGPI n-3 des tissus, l’activité enzymatique et l’expression des gènes codant pour les enzymes impliquées dans la bioconversion des AG. Le génome de la perche n’étant pas séquencé pour l’instant, le premier travail a été de mettre au point les protocoles de dosage d’activité enzymatique et d’expression génique chez cette espèce. La qualité nutritionnelle de la perche a été vérifiée, avec la mise en évidence de taux élevés de DHA dans tous les tissus. Dans le muscle la teneur en lipides est stable. La teneur en AGPI est élevée (40-60% des AG totaux), avec des teneurs élevées en DHA (35-45% des AG totaux) qui est l’AG majoritaire dans ce tissu. La teneur en lipides du foie et du tissu adipeux est variable en fonction de l’aliment. Le tissu adipeux est le lieu de stockage de l’énergie, il contient entre 85-90% de lipides dont 30-50% sont sous forme mono-insaturée, principalement représentés par le 18:1n-9. Le foie a une composition en AG intermédiaire entre celle du muscle et celle du tissu adipeux, le DHA étant là aussi l’AG majoritaire. Nos résultats ont complété ceux de la littérature en donnant des informations sur la répartition et la teneur en lipides neutres et polaires des tissus (Muscle LN/LP= 50/50 ; Foie LN/LP= 60/40 ; Tissu adipeux : LN/LP= 90/10), ainsi que sur leur profil en acides gras (les lipides polaires sont composés majoritairement d’AGPI alors que les lipides neutres sont plus riches en acides gras saturés). Ils ont permis de mettre en évidence une spécificité du profil en acides gras en fonction du tissu ou du type de lipides. L’hypothèse de bioconversion des AGPI a été vérifiée puisque la delta 6 désaturase a été détectée dans le foie, l’intestin, le cerveau. De plus, son activité a été mise en évidence dans le foie. L’hypothèse d’incorporation préférentielle de certains acides gras a également été vérifiée, avec une incorporation préférentielle d’AGMI dans le tissu adipeux et d’AGPI dans le filet et le foie. Concernant l’effet des facteurs étudiés, nos résultats ont montré qu’il existe un déterminisme différent en fonction de l’acide gras.. La nature des lipides alimentaires est le facteur le plus important, il a un effet direct ou en interaction avec d’autres facteurs sur le profil en AG des tissus. Nos résultats ont montré que si l’alimentation est le facteur principal de variation, dans des conditions de croissance limitée, sur un poisson de taille commerciale, une teneur de 3% de DHA et de 2% d’EPA dans l’aliment est suffisante chez la perche pour obtenir une composition en acides gras du filet de bonne qualité pour le consommateur avec une bioconversion des AGPI n-3 limitée / Perca fluviatilis L. (Eurasian perch) is characterized by a low intramuscular amount of lipids (<2%) and a high poly-unsatured fatty acid (PUFA) content. Docosahexaenoic acid (DHA, 22:6n-3) is present in a high proportion (40% of total fatty acid). The aims of this work are twofold: first to analyse the factors that could influence the lipid metabolism of Perca fluviatilis L. and second to identify factors that could explain the elevated contents of DHA in this fish. Assumptions, which have been tested to explain the high concentration of DHA, are a selective incorporation of this fatty acid and the ability of this fish to transform 18:3n-3 present in the diet into higher PUFA n-3, EPA and DHA; typical capacity of freshwater fish (bioconversion assumption). Three experiments have been conducted to test these assumptions. First, we described lipid composition of the different tissues, which play a role in lipid metabolism, by distinguishing total, neutral and polar lipids. Second, we identified and classified the factors influencing the lipid content and fatty acid composition by using a multifactorial approach. Third, we analysed the effect of diet fatty acid composition on PUFA n-3 tissues composition, enzymatic activity and genes expression, which code for enzymes implicated in fatty acid bioconversion. As Perca fluviatilis L. genome is not sequenced for the moment, the first work was to construct experiments for dosing enzymatic activity and gene expression in this species. Concentration of DHA was elevated in all the tissues we analysed, showing the good nutritional quality of Perca fluviatilis L. In the fillet, lipid content was stable. PUFA content was high (40-60% of total fatty acid), with elevated contents in DHA (35-45% of total fatty acid), which was the main fatty acid of this tissue. Lipid content in the liver and the fat tissue was variable according to the type of food. Adipose tissue, that is the lipid storage tissue in this species, was composed of 85-90% of lipid, of which 30-50% are mono-unsatured fatty acids (MUFA), mainly 18:1n-9. Liver fatty acid composition presented characteristics in an intermediate position between fatty acid composition of the fillet and the adipose tissue, but DHA was still the most abundant fatty acid. Our results were in accordance with literature. They added informations on the distribution and the concentration in neutral and polar lipids (NL and PL) of the tissues we studied (fillet NL/PL=50/50; Liver: NL/PL=60/40; adipose tissue: NL/PL=90/10), and on their composition in fatty acid (polar lipids are mainly composed of PUFA whereas neutral lipids are richer in saturated fat acids). Our results showed that the profile in fat acid depended on the tissue and the type of lipids. Our assumption of the ability of Perca fluviatilis L. to transform PUFA was verified because we were able to detect delta 6 desaturase in the liver, intestine, and brain. Moreover, the activity of this enzyme was put in evidence in the liver. Our assumption of selective incorporation of some fatty acids was also verified, MUFA being preferentially absorbed in the adipose tissue and PUFA in the fillet and the liver. Regarding the effect of factors we studied, our results showed that a differential determinism existed according to the type of fatty acid. The nature of lipids contained in the diet was the most important factor. This factor could influence the profile of fatty acid in the tissues through a direct effect or in interaction with other factors. Although the diet is the main factor of variation, our results showed that under condition of limited growth and for a fish with a commercial size, a content of 3% of DHA and 2% of EPA in the diet was sufficient to obtain, in the fillet, a composition in fatty acids of good quality for consumers with a limited bioconversion of PUFA

Zootechnical and behavioural traits can vary substantially among wild allopatric European perch populations. Choosing wild European perch population(s) showing higher growth rate, lower cannibalism and size heterogeneity with specific behavioural traits such as low aggressive interaction rate and homogeneous spatial distribution in rearing units are crucial for the establishment of the European perch broodstock and subsequent selective breeding programs. Therefore, knowledge of the zootechnical and behavioural traits relative to geographic origin supported by genetic analyses may ultimately help to overcome current challenges and bottlenecks of European perch aquaculture. Population differences in zootechnical and behavioural traits can be shaped by genetic differentiation, phenotypic plasticity, or by their combination. However, it is not clear whether the inter-population differences are genetically- or environmentally-induced. Therefore, we explored the zootechnical traits of geographically different European perch populations at larval- (two Finish, two Polish, two Slovakian, one Czech; Chapter II) and juvenile-stages (Polish, Czech, Slovakian; Chapter III) in the same standardized conditions reducing the environmental effect. Additionally, we provided a genetic-based assessment on four mitochondrial markers: cytochrome b, D-loop of control region, 16S rRNA, and cytochrome oxidase I (Chapters II, III). In Chapter IV, we observed behavioural traits of larvae and juveniles from two Finish and one French populations. According to obtained results, zootechnical and behavioural traits differed among allopatric populations of European perch. Moreover, the differences in zootechnical traits were mainly observed between most genetically differentiated populations (both Finish in Chapter II, and Polish in Chapter III). This could suggest a genetic basis of the observed growth differentiation and, consequently, a potential heritability of this pattern. Additionally, higher growth rate of northern populations could be partly attributed to behavioural traits as we found more cohesive and homogenous group structure in both Finish compared to French populations which, on the other hand, showed higher aggressive interactions. However, European perch larvae and juveniles from genetically lower- or un-differentiated populations (i.e. Polish, Slovakian and Czech in Chapter II and Slovakian and Czech in Chapter III) showed variations in zootechnical traits as well. The variation could be a consequence of different food intake, health status, pre-collection environment, transgenerational effect and usage of conservative mitochondrial markers, i.e. the lack of genetic differentiation among some populations should be further assessed by higher resolution analyses (e.g. microsatellites). Further studies are needed to assess the importance of these factors in geographic differentiation of aquaculture performance.

Lietuvos ežeruose siekiant praturtinti žuvų maistinius išteklius buvo introdukuota keletas Ponto-Kaspijos komplekso šoniplaukų bei mizidžių rūšių. Manyta, kad verslinės žuvys, tame tarpe ir ešeriai specializuosis maitintis šiais vertingais maisto objektais. Atlikti tyrimai parodė, kad ešeriai introdukuotomis rūšimis pradeda maitintis jau pirmaisiais gyvenimo metais. Ešeriams augant, minėtų vėžiagyvių reikšmė jų mityboje didėja. Ežeruose, kur introdukuotosios rūšys litoralėje suformavo gausias populiacijas, šių vėžiagyvių ešerių skrandžiuose pasitaiko daugiau lyginant su ežerais su negausiomis vietinių vėžiagyvių populiacijomis. Atliktos analizės parodė, kad vis tik invaziniai vėžiagyviai kryptingai nekaičia ešerių mitybinės nišos pločio, o ešeriai introdukuotais Ponto-Kaspijos komplekso vėžiagyviais selektyviai nesimaitina. Ešeriai yra „generalistai“ ir maitinasi tuo metu aplinkoje esančiais, lengvai prieinamais bei tinkamais pagal dydį maisto objektais. / SUMMARY The influence of the introduced Ponto-Caspian scuds and opossum shrimps on perch (Perca fluviatilis) diet and growth rate in the lakes of Lithuania The purpose of this study was to examine perch (Perca fluviatilis) feeding habits and diet differences between two types of lakes that differ in having and lacking abundant littoral populations of introduced Ponto-Caspian opossum shrimps and scuds. The growth of the perch has been performed in order to answer whether introduced crustaceans really improve fish food basis in lakes. 1104 individuals were used to perform their growth rate analysis. 861 individuals were used to clear their diet. Fish and littoral benthic animal’s samples were collected in 2004 – 2006 summer and fall seasons in 10 Lithuanian lakes (Dusia, Daugai, Asveja, Žeimenys, Šakarvų, Baluošai, Nedingis, Lavysas, Plateliai and Beržoras). Analyses show that perches consume introduced Ponto-Caspian crustaceans from their first year. Kruskal-Walis ANOVA test show significant general lake effect on consuming rate of both scuds and opossum shrimps when comparing between three types of lakes that differ in littoral scuds and opossum shrimps population size. There was bigger consuming rate in lakes with larger crustacean’s populations in four different age groups of perch. We found significant correlations between relative biomass of littoral scuds in the benthic communities and in the perch stomach in three different age groups of perch. However we failed to find... [to full text]

The aim of this study was investigate if increasing total organic carbon (TOC) affects the growth rate and biomass of perch (Perca fluviatilis) and biomass of roach (Rutilus rutilus). The ongoing climate change affects the climate by increasing annual mean temperature and precipitation. The runoff to surface waters will increase, which also has the consequence that the export of terrestrial organic matter (TOM) and nutrients to surface waters will increase. Increasing of TOM into the surface waters make it darker, i.e. brownification of the water. This brownification of surface water affects the amount of available light for benthic algae causing the benthic primary production to decrease. As the benthic primary production decreases also whole lake ecosystem productivity decreases. The impact on fish biomass and production of fish were studied in five small lakes in Sweden. Lake morphology, water chemistry and fish community characteristics were sampled. A subset of perch from the catch was selected to determine age and growth. Data from age determination was then used to calculate the size dependent growth and production of perch in each lake. Total fish biomass and biomass of perch and roach was negatively affected by TOC and yearly biomass production of perch was lower in lakes with higher TOC. Thus, climate change may at least in small forest lakes lead to lower production and biomass of fish in the future.

Phenotypic plasticity in Eurasian perch (Perca fluviatilis) can be driven by a trade-off for ecological specialisation to littoral and pelagic resources. Previous studies on perch have found that this specialisation can have different effects on linkage between the littoral and pelagic food web depending on water transparency. In this study I aimed to answer how foraging efficiency and prey preference of phenotypic divergent perch are affected by high and low water transparency, and the presence of a predator in a series of aquarium experiments. Two different phenotypes of perch were kept in littoral and pelagic environments in the lab. By presenting perch with Daphnia sp. and Ephemeroptera, either separately or combined. I found that in clear water the littoral and pelagic phenotypes were comparatively more efficient on resources that were representative of their habitats (Ephemeroptera and Daphnia, respectively) and that both phenotypes prefer Ephemeroptera over Daphnia. In low visibility the differences in foraging efficiency between phenotypes when feeding on Daphnia disappeared but remained similar to clear water when feeding on Ephemeroptera. When vision was constrained littoral and pelagic perch showed no sign of prey preferences. In the presence of a predator the difference in foraging efficiency between the phenotypes, and also prey preference disappeared. I found that littoral phenotypes interacted more with other group members than did pelagic phenotypes, when foraging on littoral prey. And for perch in general, when foraging for Daphnia the interaction among group members was markedly reduced compared to when foraging for Ephemeroptera. In this study I show that morphological adaptation and prey choice is affected by visibility and predation. I also give suggestions how and argue why this can affect linkage of food webs and the community composition in littoral and pelagic habitats.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2009. / Härtill 5 uppsatser.

L’amélioration des performances de reproduction des poissons d’élevage nécessite de déterminer les facteurs intrinsèques et extrinsèques influençant la qualité des gamètes d’une part, et de définir des paramètres fiables permettant de prédire les performances de reproduction d’autre part. Notre objectif est donc de comprendre le déterminisme multifactoriel de la reproduction chez la perche commune, Perca fluviatilis. Quatre facteurs nutritionnels (type d’aliment et taux de rationnement distribués lors des phases d’induction et de vernalisation) et 3 facteurs populationnels (poids initial, origine géographique, niveau de domestication) ont été testés. Une différence de réponse entre les sexes a été observée. Le type d’aliment distribué en vernalisation et le poids initial ont modifié l’état général des femelles. Les mâles ont plutôt été sensibles aux taux de rationnement et à l’origine géographique. L’étude des performances de reproduction a montré que le taux de ponte était sous l’influence de l’interaction entre le type d’aliment distribué en induction et en vernalisation, tandis que l’origine géographique a modulé la date de ponte. La régulation des performances de reproduction est donc un mécanisme complexe sous l’influence simultanée de plusieurs facteurs. La seconde partie de ce travail concerne la recherche de marqueurs prédictifs de la qualité des ovules. Nous avons d’abord montré que peu de paramètres morpho-anatomiques des pontes ou ovules sont des prédicateurs fiables. Cependant, l’analyse protéomique a permis de mettre en évidence plusieurs protéines exprimées différemment selon la qualité des pontes, pouvant jouer le rôle de biomarqueurs de qualité des ovules / Improving fish reproduction in breeding conditions implies to understand intrinsic and extrinsic factors influencing gametes quality on the one hand and to define relevant parameters allowing the prediction of fish reproductive performance on the other hand. Our goal was thus to understand the multifactorial determinism of the common perch (Perca fluviatilis) reproduction. Four nutritional factors (type of food and rate of rationing used either during the induction or vernalization phases) and 3 populational factors (initial weight, geographic origin and domestication level of breeders) have been tested. Data show different responses between females and males. type of food during wintering phase and initial broodstock weigh modified female condition. Males have been sensitive to rationing during wintering phase as well as geographical origin. Data show also that spawning rate was under the influence of interaction between kind of food during wintering phase and induction whereas geographical origin modulated the spawning date. The regulation of the performance reproduction is also a complex mechanism influenced by several factors. The second part of this work consisted on the research of parameters potentially predictive of ova quality. Firstly, our work shows that morphometric parameters measured before the fertilization are poorly relevant to predict reproductive performance. However, the proteomic analysis of several spawn allowed us to highlight proteins differently expressed according to the spawn quality, such proteins could be ova quality biomarkers

Top predators in aquatic ecosystems often have strong top-down effects on the ecosystem. Northern pike (Esox lucius) has been documented to cause whitefish (Coregonus lavaretus) populations to diverge into different ecomorphs. This can facilitate piscivory in other predators as a novel resource becomes available to them in the form of dwarf whitefish. The aim of this study is to examine whether the presence of pike causes Eurasian perch (Perca fluviatilis) to shift their diet from insectivory to piscivory, and whether this is directly driven by whitefish polymorphism. Stomach contents of 147 perch from lakes with and without pikes were analyzed. The results show that the presence of pike has a clear influence on the diet of the perch. In lakes without pike, perch are mostly insectivorous, and in lakes with pike, they are mostly piscivorous. This diet shift appears to be driven by whitefish availability, as a majority of the diet of perch in pike lakes consisted of whitefish, while none of the fish eaten by perch in non-pike lakes was whitefish. In addition, the results showed that perch undergo the diet shift from insectivory to piscivory at a smaller size when coexisting with pike. This study can be added to the growing body of evidence for the ecological significance of pike.

The Lower Karori Reservoir (LKR) is a small, monomictic lake of 2.34 ha situated in the Karori Wildlife Sanctuary (KWS), Wellington. Over the past decade cyanobacterial blooms have become a common occurrence in this water body. In 2005 Anabaena planktonica was detected for the first time in the LKR and this species now forms dense blooms during summer. These blooms are problematic as they reduce aesthetic appeal and have resulted in odour problems for visitors to this high profile wildlife sanctuary. The objectives of this study were to identify key physical, chemical and biological variables influencing phytoplankton dynamics in the LKR and to use ecological models to investigate plausible management options. The key parameters investigated, that may cause bloom formation were; summer stratification, high nutrient levels, and the food web effects of a large population of European perch (Perca fluviatilis). High resolution sampling was carried out every six hours over a 72 hour period during pre-bloom, bloom and post-bloom periods in 2006/7 to elucidate short term temporal and spatial variations in biological and physico-chemical parameters. Quantitative polymerase chain reaction (QPCR) was used to enumerate A. planktonica populations, allowing a large number of samples to be simultaneously evaluated. Algal densities were also estimated using conventional phytoplankton enumeration and chlorophyll a analysis. Water samples were collected for nutrient analysis at discrete depths and profiles were taken for temperature, dissolved oxygen and photosynthetic active radiation. Secchi depth and pH were also measured. Weekly or fortnightly phytoplankton and zooplankton samples and physical variables have been collected at LKR since September 2005 as part of an independent sampling program carried out by the KWS, Waikato University and Cawthron Institute. In this project the 2-year data set was used to assist with analysis of lake processes and for validation of the hydrodynamic-ecological model DYRESM-CAEDYM. Between 12 and 15 February, 2007, electric fishing was undertaken within the LKR. A total of 3,946 P. fluviatilis were removed and the effects on phytoplankton and zooplankton concentrations were investigated. To increase knowledge of the physiology of A. planktonica, laboratory experiments were undertaken using cultures subjected to a range of different light intensities and temperature regimes The phytoplankton assemblage of the LKR shows very distinct temporal variations. Summer stratification occurred in the LKR for ~4 months each summer. During these periods A. planktonica comprised up to 99.9% of the surface phytoplankton population. During isothermy chlorophytes, bacillariophytes and small flagellated dinophytes are co-dominant in the phytoplankton assemblage. The results of the QPCR showed distinct diurnal vertical movement of A. planktonica, with the highest cell concentrations occurring at 1900 hours at the surface. Ammonium (NH4-N) is the dominant species of inorganic nitrogen during periods of stratification, while nitrate (NO3-N) is generally dominant during times of isothermy. Phosphate concentrations at surface and depth remained at low levels throughout the sampling period. The large surface populations of A. planktonica, are probably responsible for the elevated total nitrogen concentrations in surface waters during stratified periods. There appeared to be some short term effects of the P. fluviatilis removal with an increase in large crustaceans (e.g., Daphnia sp.) and a reduction in A. planktonica densities observed in the months following the P. fluviatilis removal. Only a small proportion of the total P. fluviatilis population was removed and it is unlikely that the effects will be long-lasting without subsequent removal steps. However, it seems likely that P. fluviatilis is one of the factors contributing to cyanobacterial blooms and management of this fish species should be considered in future lake restoration plans. Growth experiments indicated A. planktonica grow over a wide range of light intensities and temperatures, although highest growth rates were generally associated with higher temperatures (25 C) and light intensities (60 - 140 μmol m-2 s-1). Ecological and hydrodynamic trends within the LKR over a two year period were simulated with adequate success using the model DYRESM-CAEDYM. Management scenarios simulated using DYRESM-CAEDYM suggest implementation of an artificial destratification system in the LKR may be the most practical and effective means of controlling A. planktonica blooms. The addition of an artificial aeration system emitting air at a rate of approximately 50 l-1 s-1 should result in an isothermal system. Without summer stratification some of the physiological features of A. planktonica (e.g., buoyancy regulation and nitrogen-fixation) that give it a competitive advantage over other phytoplankton species will be reduced.

Individuals within a single population can vary widely in their phenotype e.g. in their body shape. These differences are an important source of biodiversity and they can precede evolutionary divergence within a population. In this thesis we use the biological invasion of the zebra mussels into Swedish lakes to investigate which processes create or maintain phenotypic diversity within populations of the two native fish species perch and roach and the mussel itself. Both fishes have specially adapted body shapes that depend on whether they feed in the near-shore or open-water habitat of lakes. This habitat-specific divergence was more pronounced in lakes with zebra mussels, probably because resources in both habitats were in higher supply due to the mussels’ effects on the lakes. Divergence in perch body shapes between habitats was also higher in lakes with a higher water clarity, suggesting that visual conditions can affect the resource use and thus also the expression of a habitat-specific body shape. When investigating the diversity of body shapes in the mussel itself we found that mussels from one lake changed their shell shape when exposed to different predators: fish predators induced a more elongated shell shape while crayfish predators induced a rounder shell. These specific shell shapes probably serve as two alternative predator defenses protecting the mussel from predation. We conclude that the availability and use of distinct resources is an important source of diversity within populations. Abiotic conditions can play a previously underappreciated role by promoting or impairing the use of the distinct resources thus affecting the divergence. The diversity of shell shapes we found in the zebra mussels complements our study by demonstrating that not only consumer responses to resources but also resources’ responses to predators can generate phenotypic diversity.