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The aim of this diploma thesis has been to establish and to verify functionality of a model biofloc system for Nile tilapia (Oreochromis niloticus) farming. The main criteria to be observed during the experiment were chemical characteristcs of the water, development of the biofloc microflora and the reaction of the system to technological interventions. The experiment has consisted of two phases. The first phase monitored an insufficiently functioning system. Due to unsatisfactory assurance of the oxygen concentration as well as the water column stirring, 4 different types of air-sourcing devices have been used in the experiment. For assuring of the perfect stirring and of the sufficient oxygen concentration ( 6 mg×l-1) an airlift fulfilling both the criteria has been constructed. The impact of the carbohydrates application on the decrease of the amonia nitrogen has been sucessfully verified during the experiment. The average value of the C/N ratio of 14 has been reached thanks to the quantity of flour being added as the carbohydrate source into the system. When the recommended amount of TSS (200 ml×l-1) with the corresponding biofloc microflora that has been transforming all the nitrogen in the experiment tank into the microbial protein, the system was evaluated as fully functional. During the biofloc analysis, the presence of N-substances at the amount of 223.6 g at all of the experiment tank (1300 l) has been detected. In the comparison with the applied feed material at the amount of 300 g containing 39% of the N-substances, only 67.1 g of the N-substances has been added into the system. The biofloc (bacterial flakes) serves as food for the tilapia during the entire period of the functional system.

(Oberflächen-) Gewässer weltweit sind mit geringen Mengen (ng/L bis wenige µg/L) humaner Pharmazeutika belastet. Diclofenac (DCF; nicht-steroidal, entzündungshemmend) und Metoprolol (MTP; ß-Blocker) gehören entsprechend ihres hohen Verbrauchs zu den am häufigsten gefundenen Substanzen. Deren biologische Aktivität ist nicht auf den Menschen beschränkt. Gut konservierte Enzyme innerhalb der Vertebraten legen Auswirkungen auf Nicht-Zielorganismen wie Fische nahe, die bisher in Langzeituntersuchungen mit umweltrelevanten Konzentrationen unzureichend untersucht wurden. In der vorliegenden Arbeit wurden die physiologischen Effekte von DCF und MTP auf die Nil-Tilapie (Oreochromis niloticus), einem der wichtigsten Aquakulturfische weltweit, untersucht. In vitro konnte anhand primärer Hepatozyten gezeigt werden, dass bereits umweltrelevante Konzentrationen von DCF zu einer erhöhten Genexpression verschiedener Schlüsselenzyme der Detoxifizierung führten. Nach MTP-Exposition waren die Veränderungen weniger eindeutig. Beide Substanzen induzierten die Vitellogenin Genexpression, nur DCF jedoch bereits in umweltrelevanter Konzentration. In vivo wurden in zwei Langzeit-Expositionsversuchen die physiologischen Effekte vom befruchteten Ei bis 80 Tage nach Schlupf in O. niloticus untersucht. Beide Substanzen hatte keinen Einfluss auf Schlupferfolg und Überleben, das Wachstum war nach 80 Tagen nach Schlupf leicht reduziert. Die deutlichsten Auswirkungen waren histopathologische Veränderungen der Kiemen, veränderte Genexpressionen der Gonadotropine und eine erhöhte Expression von Vitellogenin. Die Ergebnisse legen eine stärkere östrogene Aktivität von DCF im Vergleich zu MTP nahe. Zusammenfassend sind die Bedenken gegenüber den Einzelsubstanzen eher gering, negative Auswirkungen auf die Reproduktion und sich verstärkende Effekte bei zeitgleicher Exposition gegenüber DCF und MTP lassen sich jedoch nicht ausschließen und sollten im Weiteren untersucht werden. / Surface waters worldwide are contaminated with low levels (ng/L up to few µg/L) of human pharmaceuticals. Diclofenac (DCF; non-steroidal, anti-inflammatory) and metoprolol (MTP; ß-blocker) are highly consumed and therefore commonly detected. Their biological activity is not restricted to humans. Well conserved enzymes within the vertebrates suggest effects on non-target organisms such as fish, poorly studied in long-term exposure experiments using environmentally relevant concentrations. In the presented work, physiological effects of DCF and MTP on the Nile tilapia (Oreochromis niloticus), an important aquaculture fish species, were studied. Using primary hepatocytes, it was shown in vitro that environmentally relevant concentrations of DCF increased the gene expression of different key enzymes of the detoxification, while MTP exposure had a less clear effect. Both substances induced vitellogenin gene expression, but only after DCF exposure this was significantly elevated already at the environmentally relevant concentration. In vivo, two long-term exposure studies on the physiological effects from the fertilized egg until 80 days post-hatch were evaluated. Both substances did not affect hatching success and survival, while growth was slightly reduced after 80 days post-hatch. Histopathological alterations of the gills, changed gene expression patterns of the gonadotropins and induced vitellogenin gene expression were the most dominant findings. The results indicate a stronger estrogenic mode of action of DCF compared to MTP. Overall, the risk due to a single substance exposure seems to be relatively low but adverse effects on reproduction and additive effects during simultaneous exposure to DCF and MTP cannot be excluded and should be investigated further.