The diel vertical migration (DVM) and feeding periodicity of myctophids (lanternfishes) were studied in the high-latitude Masfjorden, Norway, and the tropical Red Sea. In Masfjorden, a bottom-mounted echo sounder permitted continuous studies throughout the year, and revealed a diverse seasonal DVM behavior. During spring and summer, when zooplankton peaks in the epipelagic zone, migrating glacier lanternfish performed normal DVM (NDVM), ascending to the epipelagic zone during night and residing below ~200m during daytime. During autumn and winter, when Calanus overwinters between ~150–300 m, migrating glacier lanternfish mainly performed inverse DVM (IDVM), ascending to feed on Calanus in mid-waters during daytime. Non migrating (NoDVM) individuals were present all year below ~300 m in Masfjorden. In the Red Sea, where zooplankton has an epipelagic distribution, the whole population of skinnycheek lanternfish performed NDVM, feeding in the epipelagic zone at night, while residing at ~500–750 m during daytime. The warm waters of the Red Sea were hypothesized to limit the time individuals can stay in the mesopelagic zone without migrating to feed in the epipelagic layers. The DVM behavior of myctophids largely seemed to relate to the distribution of zooplankton, and it was hypothesized that NDVM will prevail with epipelagic distribution of prey, while IDVM and NoDVM are common in areas where zooplankton migrate seasonally to mesopelagic depths. Potential predators were continuously present, found to apparently attack glacier lanternfish, at mesopelagic depth in Masfjorden. Thus, myctophids are under threat of predation even at mesopelagic depth.

Made available in DSpace on 2014-12-17T15:36:55Z (GMT). No. of bitstreams: 1 BrunoJRC.pdf: 626236 bytes, checksum: fd4d631df050e2568c96cf38fd170017 (MD5) Previous issue date: 2008-12-15 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The analysis of the index of hierarchy and structural models of the formation of groups allowed to establish the hierarchical position of members of two groups of the genus Cebus. By the analyses of the hierarchical positions and the application of tests to obtain a food resource (TORA), we know the difference between these groups and groups in the wild. The results show a high ranking for both Cebus apella, as well as Cebus libidinosus. The results have enabled us to establish that the hierarchical structure in groups of Cebus in captivity: a) can be fixed and rigid different from highly flexible hierarchical structure studied in groups of wild b) even which similar hierarchy indices, there are differences in the hierarchical structure presents between C. apella and C. libidinosus in captivity c) hierarchy directly influence the behavioral patterns of obtaining food in Cebus / A an?lise do ?ndice de hierarquia e modelos estruturais de forma??o de grupos possibilitou estabelecer a posi??o hier?rquica dos membros de dois grupos do g?nero Cebus. Atrav?s da an?lise das posi??es hier?rquicas e tamb?m da aplica??o de testes de obten??o de recurso alimentar (TORA), pudemos perceber a diferen?a existente entre estes grupos e grupos estudados em vida livre. Os resultados mostram linearidade tanto para Cebus apella, quanto para Cebus libidinosus. Os resultados nos permitiram estabelecer que a estrutura hier?rquica em grupos de Cebus em cativeiro: a) pode ser r?gida e fixa diferente da estrutura hier?rquica altamente flex?vel estudada em grupos de vida livre; b) mesmo com ?ndices similares de hierarquia, existem diferen?as na estrutura hier?rquica apresenta entre C. apella e C. libidinosus em cativeiro; c) hierarquia influencia diretamente os padr?es comportamentais de obten??o de alimentos em Cebus

Thesis (MScEng (Process Engineering))--Stellenbosch University, 2008. / With the harvesting of fish and other aquatic organisms from natural waters having reached its upper limit, aquaculture is vital in providing for the ever increasing demand for fishery products (Boyd, 1999). Not surprisingly, aquaculture has seen considerable growth over the last decade or more. With the rising importance of aquaculture, there is an increased emphasis on cost and reducing of waste for environmental reasons. Therefore, attempts to automate or increase efficiency of feeding are constantly being explored. On an aquaculture unit approximately 60% of all costs are for feed; therefore high quality feeding management is essential for all fish farmers. The rainbow trout farm at Jonkershoek Aquaculture Research farm near Stellenbosch currently have a feeding management system which makes use of traditional hand feeding. Handfeeding is not considered optimal, as the feed intake or pellet loss is not closely monitored resulting in higher operating costs. Automation of aquaculture systems will allow the industry to produce closer to markets, improve environmental control, reduce catastrophic losses, minimize environmental regulation by reducing effluents, reduce production costs and improve product quality. The history of automated control in aquaculture has been brief; most of the systems have been custom-designed, personal computer systems. A very popular approach for an automated feeding system is to monitor waste pellets beneath the feeding zone of the fish, with a feedback loop that can switch off the feeder if this waste exceeds a predetermined threshold. Other approaches use hydroacoustics to monitor waste pellets or demand feeders have also been implemented. These approaches however are not considered optimal as automatic feeders do not necessarily ensure optimal feed intake. Social dominance using demand feeders does not allow even feeding distribution among all sizes of fish. In this project it was investigated whether an automated feeding system can be developed based on fish feeding behaviour. After facing problems with poor visibility at the Jonkershoek Aquaculture farm near Stellenbosch, video data were acquired from the Two Oceans Aquarium in Cape Town. Since it was a feasibility study, the focus was rather to investigate whether a predictive model could be generated for fish feeding behaviour in a more ideal environment which can form a foundation for further research. The well-established multivariate methods of principal components

With the different threats sea turtles are currently facing, such as habitat reduction and pollution, increase of fishing and harvesting of aquatic resources by Humans, or invasive species, it is important to learn as much as possible about their biology and behaviour in order to ensure the success of conservation programs. In this study, loggerhead sea turtles (Caretta caretta) feeding behaviour duration as well as energy expenditure approximation during a feeding event were tested and compared using two different types of food: green shore crabs (Carcinus maenas) or Japanese clam (Ruditapes phillipinarum) or Venus clams (Chamelea gallina). The data show that the turtles took longer to approach the crabs but took more time to eat the clams. However, comparison of energy expenditure values for the feeding phase showed no significant differences. The turtles were observed to eat the clams’ shell as well as their meat. These shells are rich in calcium, which is one possible explanation for this behaviour. This study shows that data loggers represent a viable tool for studying the behaviours of marine animals.

Serotonin (5-HT) nimmt eine wichtige Rolle in der Regulation von Nahrungsaufnahme ein. Erhöhte 5-HT-Freisetzung hemmt die Nahrungsaufnahme. Der 5-HT1A-Rezeptor liegt sowohl somatodendritisch als auch postsynaptisch vor. Seine Stimulation mit 8-OH-DPAT vermindert die 5-HT-Freisetzung. Die in-vivo-Mikrodialyse ermöglichte uns eine kontinuierliche Messung von extrazellulärem 5-HT im lateralen Hypothalamus an der frei beweglichen Ratte. Unsere Ergebnisse zeigen einen Abfall der 5-HT-Freisetzung bei satten Ratten, nicht jedoch wenn diesen nach Substanzgabe Futter angeboten wurde. Bei hungrigen Ratten war nach Substanzgabe keine signifikante Veränderung in der 5-HT-Freisetzung zu messen. Zusammenfassend wird mit der vorliegenden Studie erstmals die Wirkung von 8-OH-DPAT auf die 5-HT-Freisetzung im LHA in Abhängigkeit von unterschiedlichen Motivationszuständen in Verbindung mit Nahrungsaufnahme gezeigt. / Serotonin (5-HT) is an important mediator of satiety. Increase of 5-HT release inhibits food intake. 8-OH-DPAT, an agonist at the somatodendritic 5-HT1A autoreceptor, reduces serotonergic activity and induces food intake. With the technique of in vivo microdialysis we were able to measure continuously extracellular 5-HT in the lateral hypothalamic area (LHA) in freely moving rats under different feeding conditions. The present results show a decrease of 5-HT release in freely feeding rats after administration of 8-OH-DPAT. This effect was not obtained when offering food after drug application. In contrast, no significant effect in 5-HT release after application of 8-OH-DPAT in food deprived rats was measured. In summery this study demonstrates the effect of 8-OH-DPAT on the 5-HT release in LHA of freely moving rat depending on the different feeding conditions.

In nature, all organisms face the daily challenges created by a fluctuating environment. Circadian clocks synchronize behaviour and physiology allowing an organism to adapt to and predict daily changes to environmental conditions. In the fruit fly, Drosophila melanogaster, circadian clocks reside in a set of ~150 neurons in the brain, collectively referred to as the central clock, and in the cells of many peripheral tissues. The central clock regulates daily behavioural rhythms, whereas peripheral clocks are thought to regulate the local metabolic activities of the cells in which they reside. In this thesis, I demonstrate that a peripheral clock resides in the abdominal fat body, a tissue analogous to the mammalian liver and adipocytes. Moreover, I show that flies display a temporal feeding pattern that is partly regulated by a peripheral clock. I propose that the central clock and peripheral clocks coordinate to regulate the timing of fly feeding behaviour.

In nature, all organisms face the daily challenges created by a fluctuating environment. Circadian clocks synchronize behaviour and physiology allowing an organism to adapt to and predict daily changes to environmental conditions. In the fruit fly, Drosophila melanogaster, circadian clocks reside in a set of ~150 neurons in the brain, collectively referred to as the central clock, and in the cells of many peripheral tissues. The central clock regulates daily behavioural rhythms, whereas peripheral clocks are thought to regulate the local metabolic activities of the cells in which they reside. In this thesis, I demonstrate that a peripheral clock resides in the abdominal fat body, a tissue analogous to the mammalian liver and adipocytes. Moreover, I show that flies display a temporal feeding pattern that is partly regulated by a peripheral clock. I propose that the central clock and peripheral clocks coordinate to regulate the timing of fly feeding behaviour.

The obesity epidemic is a major health threat affecting one in four people in the affluent western world, where high-energy foods are easily available and there is little need for exercise. To identify novel therapeutic targets for the treatment of obesity, one important step is to further define the complex circuitry in the brainwhich is ultimately responsible for our appetite and body weight regulation. Although complex, appetite can be thought of as having two distinct, though none mutually exclusive, aspects: the need to eat (homeostatic) and the desire to eat(hedonistic).The need to eat, a product of energy homeostasis, is what drives the consumption offood for basic survival. In an attempt to further define the mainly “homeostatic” neuronal circuitry, we combined blood-oxygen-level-dependent (BOLD)pharmacological-challenge magnetic resonance imaging (phMRI) with c-Fosfunctional activity mapping to characterise “whole brain” responsiveness to anorexigenic dose of the glucose anti metabolite 2-deoxy-D-glucose (2-DG). Using thesecomplementary methods, we demonstrated functional brain activity in a number ofknown glucose-sensing brain regions, including parts of the hypothalamus andbrainstem, following administration of 2-DG when compared with vehicle treatment.The desire to eat is a result of a complex interplay between the reward andmotivational circuits implicated in addictive behaviours, and those which controlenergy homeostasis. Recent research has pointed to the endocannabinoid system,and specifically the central cannabinoid 1 (CB1) receptor, as a key target mediatingthe functional cross talk between the two appetitive systems. To define the sites ofaction of cannabinoids, we used an orexigenic dose of the full CB1 agonist, CP55940,to map responsive brain regions again using BOLD phMRI and whole-brain c-Fosfunctional activity mapping. Areas of interest demonstrated a drug interaction whenthe CB1 receptor inverse agonist, Rimonabant was co-administered. These complementary methods demonstrated functional activity in the cortico-striatalhypothalamicpathway, a key system in the motivational drive to eat.The appetitive actions of synthetic CB1 inverse agonists such as Rimonabant are welldocumented. We, however, described a putative novel endogenous CB1 inverseagonist, hemopressin, which is the first identified peptide ligand of CB1 receptors.We showed that hemopressin inhibits agonist-induced receptor internalisation in aheterologous cell model in vitro. When administered centrally or systemically in vivo,we found that hemopressin decreases nocturnal food intake in out-bred rats andmice, as well as in obese, leptin-deficient ob/obmice. Importantly, hemopressininduces hypophagia without causing any apparent adverse side effects. We have also shown that the anorectic effect is absent in CB1-/- mice, and that hemopressin canblock CB1 agonist-induced hyperphagia in male rats, providing strong evidence forantagonism of the CB1 receptor in vivo. We speculate that hemopressin may be one of a family of endogenous functional CB1 receptor ligands that modulate the activity of appetite pathways in the brain.

Background: Dopamine levels has been implicated in obesity, feeding behaviour, and hedonic control of appetite like olfactory cues and food palatability. Methylphenidate (MPH) is a dopamine reuptake inhibitor that increases brain dopamine levels and has been shown to reduce appetite and promote weight loss in patients with attention deficit hyperactivity disorder (ADHD). As such, the objectives of this study were to test the possible effect of MPH on appetite, olfaction, and food palatability as well as its effects on energy intake and body weight of healthy individuals with obesity. Methods: In a randomized, double-blind study, 12 participants (age 28.9±6.7 yrs) (BMI 36.1±4.5 kg/m2) were assigned to receive MPH (0.5mg/kg) (n=5) or placebo (n=7) twice daily for two months. Appetite and palatability (Visual Analog Scale (VAS)), odour threshold (Sniffin’ Sticks®), in-lab energy intake (ad libitum buffet), free-living energy intake (3-day food boxes) and body weight (DEXA scan) were measured at baseline (day 1) and final visit (day 60). Results: MPH intake caused significantly greater suppression of appetite sensations (desire to eat (p=0.001), hunger (p=0.008), and prospective food consumption (p=0.003)) and increase in fullness (p=0.028) over time compared to placebo. There was a significant increase in odour threshold scores in the MPH group (6.3±1.4 vs. 9.4±2.1) compared to placebo (7.9±2.3 vs. 7.8±1.9) (p=0.029). Both placebo and MPH groups showed decreases in their energy intake (p=0.021) and body weight (p=0.005) over time but with large effect sizes favouring greater reduction in the MPH group compared to placebo. Conclusions: Compared to placebo, MPH intake over 60 days suppressed appetite and improved olfactory sensitivity in individuals with obesity. These data provide novel findings into the possible efficacy of MPH to favourably impact appetite and therefore promoting weight loss in individuals living with obesity.

Biomanipulation im Sinne einer top-down Steuerung des Nahrungsnetzes wurde in Standgewässern intensiv erforscht und wird als Mittel zur Verbesserung der Wasserqualität bzw. Verringerung der Eutrophierungserscheinungen eingesetzt. Ebenso könnte die Idee der Biomanipulation genutzt werden, um die Eutrophierung in kleinen Fließgewässern zu verringern. Eine Förderung benthischer herbivorer Schlüsselorganismen (z.B. Eintagsfliegenlarven) durch die Reduzierung des Fischfraßdruckes könnte helfen, Algenmassenentwicklungen zu vermeiden. Studien zur Biomanipulation von Nahrungsnetzen in Standgewässern zeigten allerdings eine zunehmende Entwicklung von planktischen invertebraten Räubern bei Abwesenheit planktivorer Fische. Die Bedeutung des Fraßdruckes invertebrater Räuber in fischfreien Fließgewässernahrungsnetzen ist dagegen noch unbekannt. Aufgrund von letalen und subletalen Fischeffekten könnte die Konsumtion räuberischer Invertebraten bei Fischabwesenheit so stark gefördert werden, dass das Ziel der Biomanipulation verfehlt wird. Invertebrate Räuber haben insgesamt einen relativ hohen Anteil an der Biomasse der Benthosgemeinschaft in Fließgewässernahrungsnetzen. Sie könnten somit potentiell einen ähnlichen Fraßdruck wie vertebrate Räuber (z.B. benthivore Fische) auf die unteren trophischen Ebenen ausüben. Auch der Anteil der Omnivorie ist in Fließgewässernahrungsnetzen hoch. Ziel dieser Arbeit war es deshalb, die Bedeutung invertebrater Prädation im Nahrungsnetz eines kleinen Fließgewässers (Gauernitzbach) unter Berücksichtigung der obligaten Räuber sowie des räuberischen Potentials Omnivorer abzuschätzen. Außerdem wurde der Einfluss benthivorer Fische auf die Populationsentwicklung und das Ernährungsverhalten der wichtigsten invertebraten Räuber und Omnivoren untersucht. Dazu wurde ein Bachabschnitt, der mit benthivoren Fischen (Gobio gobio, Barbatula barbatula) besetzt war, mit einem fischfreien Abschnitt über zwei Jahre verglichen. Nach der Identifizierung wichtiger Räuber- und Omnivorenarten anhand ihrer Biomasse und ihrer trophischen Positionen mittels Isotopenanalyse wurde ihr Gesamtfraßdruck abgeschätzt. Invertebrate Prädatoren im Nahrungsnetz des Gauernitzbaches waren Rhyacophila fasciata und Plectrocnemia conspersa (Trichoptera), Isoperla grammatica (Plecoptera) sowie Dugesia gonocephala (Turbellaria). Wichtige Omnivore aufgrund ihrer hohen Biomassen waren Gammarus pulex (Amphipoda) und Hydropsyche spp. (Trichoptera). Anhand eines Mischungsmodells (ISOSOURCE), das auf der Basis der stabilen Isotopensignaturen d13C und d15N die einzelnen Ressourcenanteile einer gemischten Signatur berechnet, konnte das ausgeprägte räuberische Potential der Omnivoren gezeigt werden, da sie einen hohen tierischen Anteil in der Nahrung aufwiesen (20-90 %). Im Nahrungsnetz des Gauernitzbaches waren Omnivore als Räuber damit ebenso bedeutsam wie obligat räuberische Invertebrate. Der Gesamtfraßdruck der invertebraten Räuber und Omnivoren auf die Beuteorganismen (bis 16 g TM m-2 a-1) in der Fischstrecke war höher als der Fraßdruck der benthivoren Fische (~3 g TM m-2 a-1). Dieser Unterschied lag hauptsächlich in höheren täglichen Konsumtionsraten bei ähnlich hohen Biomassen der Invertebraten begründet. Durch die Analyse der stabilen Isotope von Kohlenstoff und Stickstoff konnten die trophischen Beziehungen im Nahrungsnetz des Gauernitzbaches identifiziert werden. Dabei stellten allochthone Kohlenstoffquellen im Frühjahr und Herbst die bedeutendste Ressource für die Primärkonsumenten dar, während autochthone Ressourcen nur im Frühjahr für wenige Herbivore relevant waren. Dies spiegelte sich ebenso in der Nahrung der Omnivoren wider, die neben Organismen hauptsächlich Detritus nutzten. Ebenso zeigten die invertebraten Räuber eine deutliche Abhängigkeit vom allochthonen Kohlenstoff über die Nutzung der Primärkonsumenten. Letale Effekte der Fische auf die räuberischen und omnivoren Populationen im Gauernitzbach fanden hauptsächlich in Abhängigkeit von den bewohnten Habitaten statt. Die Pool-Arten (P. conspersa, D. gonocephala, G. pulex) entwickelten geringere Biomassen in der Fischstrecke, während die Biomassen riffle-bewohnender Invertebraten (R. fasciata, I. grammatica, Hydropsyche spp.) nicht deutlich reduziert wurden. Dabei waren allerdings meist hohe Biomassen in der Fischstrecke weniger stark ausgeprägt als in der fischfreien Strecke. Die Adulten der untersuchten Arten wurden oft stärker letal beeinflusst als die Juvenilstadien. So war die Emergenzproduktion der räuberischen Köcherfliegen und die Abundanz großer und eiertragender Weibchen von G. pulex in der Fischstrecke deutlich verringert. Subletale Effekte der Fische traten im Gauernitzbach in Abhängigkeit von den Ernährungstypen auf. Während die adulten räuberischen Köcherfliegenarten R. fasciata und P. conspersa keine negative Beeinflussung der Fitness und Größe zeigten, emergierte die omnivore Köcherfliege H. instabilis in der Fischstrecke kleiner als in der fischfreien. Außerdem unterschieden sich die Antworten der omnivoren Arten vermutlich aufgrund ihrer unterschiedlichen Lebenszyklen. G. pulex zeigte als ausschließlich aquatisch lebende Art keine subletalen Kosten (unveränderte Fitness) bei Fischanwesenheit wie dies für die omnivore merolimnische Insektenart H. instabilis beobachtet wurde. Die mittlere Fitness der Populationen (gemessen an der Eiproduktion pro Zeit- und Flächeneinheit) war für alle untersuchten invertebraten Räuber und Omnivoren bei Fischanwesenheit deutlich geringer als in der fischfreien Strecke. Für die Räuber (R. fasciata, P. conspersa) und G. pulex waren vermutlich letale Fischeffekte für den geringen Reproduktionserfolg verantwortlich. Dagegen wurde die Fitness der Population von H. instabilis durch die Kombination aus der geringeren individuellen Körpergröße (subletal) und den schwachen letalen Effekten auf die Emergenz reduziert. Der Einfluss der Fische auf die räuberischen Larven von R. fasciata und P. conspersa resultierte in einem Wechsel der Beutezusammensetzung, nicht in der Reduzierung der täglichen Fraßaktivität. Dies war vermutlich auf eine Aktivitätsänderung des Räubers R. fasciata bzw. auf die veränderte Beuteverfügbarkeit für P. conspersa unter Fischeinfluss zurückzuführen. Eine grundsätzliche Verringerung der Fraßaktivität oder der tierischen Anteile in der Nahrung der omnivoren Arten unter dem Einfluss benthivorer Fische wurde nicht festgestellt. Dagegen änderten sich die Relationen der Ressourcen Omnivorer zueinander, so konnte in der fischfreien Strecke eine flexiblere Ressourcennutzung nachgewiesen werden. Die jährliche Gesamtkonsumtion der räuberischen und omnivoren Invertebraten wurde durch die Anwesenheit der benthivoren Fische um 20-50 % reduziert, wofür hauptsächlich fischinduzierte Biomasseänderungen verantwortlich waren. In der fischfreien Strecke konnte dagegen die erhöhte Konsumtion der Invertebraten den fehlenden Fischfraßdruck mehr als kompensieren. Allerdings änderte sich die beutespezifische Konsumtion der Räuber in der fischfreien Strecke durch den verhaltensinduzierten Wechsel in der Beutezusammensetzung. Damit fand ein erhöhter Fraßdruck auf detritusfressende Arten (z.B. Diptera) statt, während die vermuteten Schlüsselarten einer potentiellen Biomanipulation (grazende Eintagsfliegen) in der fischfreien Strecke relativ unbeeinflusst blieben. Da die invertebrate Prädation in Fließgewässern sehr bedeutend sein kann, ist Biomanipulation nur unter Berücksichtigung aller Populationen räuberischer Invertebraten möglich. Nur durch Einstellung einer optimalen (relativ hohen) Biomasse geeigneter benthivorer Fischarten kann eine ausreichende Hemmung der invertebraten Räuber erreicht werden, so dass grazende Arten indirekt profitieren. / Biomanipulation (top-down control of the food webs) in lakes was intensively studied and can today be regarded as an important tool for improvement of the water quality and eutrophication. Similarly, the idea of biomanipulation can be used to reduce eutrophication phenomena in streams. The enhancement of benthic herbivorous key species (e.g. mayflies) by reduction of fish predation pressure could prevent exploding benthic algae biomass. Studies dealing with trophic cascades in lakes suggested that biomass of planktic invertebrate predators is increasing in the absence of planktivorous fish. But until now the importance of invertebrate predation pressure in fishless stream food webs is hardly known. Due to lethal and sublethal fish effects the consumption of predatory invertebrates could be enhanced by the absence of fish to such an extent that biomanipulation could be off target. In general, the proportion of invertebrate predators to the biomass of the benthic community in stream food webs is relatively high. Therefore, invertebrate predation on benthic prey can be as important as vertebrate predation (e.g. by benthivorous fish). Furthermore, omnivory occurs frequently in streams. Therefore, the aim of this thesis was to assess the importance of invertebrate predation in a food web of a small stream (Gauernitzbach) including the obligatory predators as well as the predatory potential of omnivores. Furthermore, the impact of benthivorous fish on population dynamics and feeding behaviour of the most important predators and omnivores was studied. Therefore, a reach stocked with benthivorous fish (Gobio gobio, Barbatula barbatula) was compared with an upstream fishless reach over a two-year period. After identification of important predators and omnivores based on their biomass and trophic position by stable isotope analyses their total consumption was estimated. Rhyacophila fasciata and Plectrocnemia conspersa (Trichoptera), Isoperla grammatica (Plecoptera) as well as Dugesia gonocephala (Turbellaria) were the invertebrate predators in the food web of Gauernitzbach. Because of their high biomasses the most important omnivores were Gammarus pulex (Amphipoda) and Hydropsyche spp. (Trichoptera). Using a mixing model (ISOSOURCE) that estimates the proportions of single resources on a mixed signature on the basis of the stable 13C and 15N isotopes, the predatory potential of both omnivores was pronounced by a high animal food proportion (20-90%). In this stream food web the predation impact of omnivores was comparable to this of obligatory predacous invertebrates. The total invertebrate predation pressure (up to 16 g TM m-2 a-1) in the fish reach was higher than the vertebrate predation pressure (~3 g TM m-2 a-1) mainly caused by the higher daily consumption rates and similar biomass compared to fish. Using stable isotope analyses of carbon and nitrogen the trophic pathways in the food web of Gauernitzbach could be identified. The most important resources for primary consumers in spring and autumn were allochthonous carbon sources. Autochtnonous carbon sources were only utilized by a few herbivores in spring. This was also reflected in the food of omnivores which assimilated mainly detritus beside animal material. Similarly, the predators depended distinctly on the allochthonous pathway by feeding primary consumers. Lethal fish effects on the predatory and omnivorous invertebrate populations were mainly depended on their preferred habitats. Pool-dwelling species (P. conspersa, D. gonocephala, G. pulex) showed decreased biomass in the presence of fish. Contrary, the biomass of riffle-dwelling invertebrates (R. fasciata, I. grammatica, Hydropsyche spp.) was not significantly reduced in the fish reach. Thereby, the highest biomass values in the fish reach could not reach the same level as in the fishless reach. Adults of the investigated species were influenced more lethal than the young stages. Hence, the emergence production of the predatory caddisflies and the abundance of the biggest and gravid females of G. pulex were reduced in the fish reach. Sublethal fish effects existed in dependence on the feeding groups of the invertebrates in Gauernitzbach. Whereas the adult predatory caddisflies R. fasciata and P. conspersa did not show disadvantages in fitness and size, the omnivorous caddisfly H. instabilis emerged with smaller size in the fish reach than in the fishless reach. Different responses of both omnivorous species were observed because of their different life cycles. The exclusively aquatic living G. pulex was not influenced sublethal by fish as the merolimnic insect species H. instabilis. The average fitness of population (measured as egg production per unit time and space) of the studied invertebrate predators and omnivores was distinctly reduced in the fish reach compared to the fishless reach. Probably, lethal fish effects were mainly responsible for the low reproductive success of the predatory species (R. fasciata, P. conspersa) and G. pulex. In contrast, the reduction of population fitness of H. instabilis was caused by the reduced individual adult size (sublethal effect) in combination with the weak lethal effect on emergence. The impact of fish on the feeding behaviour of the predatory larvae of R. fasciata and P. conspersa resulted in a switched prey composition, whereas a reduction in the daily feeding activity was not observed. That was supposed because of changes in the activity pattern by the predator R. fasciata or the changed prey availability for P. conspersa in the fish reach. A general reduction in feeding activity or animal food proportion of the omnivores was not assessed in the presence of fish. In contrast, the relations between the resources switched to a more variable utilisation in the fishless reach. The annual total consumption of invertebrate predators and omnivores was decreased by 20-50% in the fish reach, mainly caused by fish induced biomass reduction. The missing fish consumption could be at least balanced by higher invertebrate consumption in the fishless reach. Contrary, the prey specific consumption of invertebrate predators changed by behavioural-induced switch in the prey composition between the stream reaches. Therefore, a higher predation pressure on detritus feeding species (e.g Diptera) was found in the fishless reach, but not on the supposed key species of the potential biomanipulation (e.g. grazing mayflies). Due to the high importance of invertebrate predation in stream food webs, the aim of biomanipulation can only be reached by considering the populations of predatory invertebrates. Controlling the biomass of suitable benthivorous fish to an optimum (relatively high) level could sufficiently reduce the impact of invertebrate predators leading to an indirect enhancement of grazing species.