Trotz der Schlüsselstellung heterotropher Protisten als Bindeglied zwischen dem mikrobiellen und dem klassischen Nahrungsnetz ist noch wenig über ihre biochemische Zusammensetzung und ihren Nährwert bekannt. In der vorliegenden Doktorarbeit wurde untersucht ob die biochemische Zusammensetzung von Protisten (1) von deren Nahrungsgrundlage (Alge oder Bakterien) und Ernährungsweise (Autotrophie, Mixotrophie oder Heterotrophie) abhängt und (2) ihre Nahrungsqualität für räuberisches Rotatorien (Keratella quadrata) bedingt. Die Fettsäure-, Sterol- und Aminosäurezusammensetzung vier heterotropher Protisten spiegelte generell die ihrer Nahrung wider. Es trat jedoch eine Akkumulation dieser biochemischen Substanzen in den Protisten auf. Auch die Ernährungsweise eines Flagellaten (Ochromonas sp.) beeinflusste stark dessen biochemische Zusammensetzung, insbesondere die Konzentrationen an mehrfach ungesättigten Fettsäuren (PUFAs). Bei der Untersuchung des Nährwertes vier heterotropher Protisten für K. quadrata wurden signifikante Korrelationen zwischen verschiedenen PUFAs, drei Sterolen und einer Aminosäure (Leucin) der Protisten und der Eiproduktion der Rotatorien festgestellt. Auch die experimentelle Supplementierung eines Flagellaten mit einer PUFA (Docosahexaensäure, DHA) erhöhte seinen Nährwert für die Rotatorien signifikant. Die Ergebnisse verdeutlichen die Fähigkeit heterotropher Protisten, die biochemische Zusammensetzung organischer Materie schon auf einer unteren Ebene des aquatischen Nahrungsnetzes zu verändern, nämlich beim Übergang zwischen Algen/Bakterien und dem Mesozooplankton. Hier können biochemische Änderungen weitreichende Folgen für den Stoff- und Energiefluß des gesamten Nahrungsnetzes nach sich ziehen. / Heterotrophic protists are an important link between the microbial and the classical food web. However, little is known about their biochemical composition and nutritional quality as prey. In this thesis, I analysed (1) whether the biochemical composition of the protists depends on their dietary resources (bacterial or algal food) or trophic mode (autotrophy, mixotrophy or heterotrophy), and (2) whether the biochemical composition of protists determines their nutritional quality as prey for a rotifer species (Keratella quadrata). The fatty acid, sterol, and amino acid composition of four heterotrophic protists generally resembled the dietary composition, but the protists accumulated these compounds. Moreover, the trophic mode strongly affected the composition of a flagellate (Ochromonas sp.), especially that of polyunsaturated fatty acids (PUFAs). When investigating the nutritional quality of four protist species for K. quadrata, several PUFAs, three sterols (desmosterol, ergosterol, stigmastanol), and one amino acid (leucine) of the protists were significantly correlated with the rotifer’s egg production. Moreover, the nutritional quality of a heterotrophic flagellate for the rotifer was significantly enhanced by artificially supplementing the flagellate with a PUFA (docosahexaenoic acid, DHA). The thesis highlights the ability of heterotrophic protists to modify the biochemical composition of organic matter at an early stage in aquatic food webs, i.e. at the interface between algae/bacteria and mesozooplankton. Biochemical modifications at this stage may profoundly affect matter and energy transfer through the entire food web.

Made available in DSpace on 2016-06-02T19:31:57Z (GMT). No. of bitstreams: 1 3764.pdf: 1429773 bytes, checksum: 4073170af6df253bf6cb50f4e03c4a19 (MD5) Previous issue date: 2011-07-01 / Universidade Federal de Sao Carlos / The hatchery is now the main obstacle of aquaculture. The live food, especially zooplankton, is essential in early life stages of fish. However, there are difficulties in obtaining enough biomass. The Anostraca Dendrocephalus brasiliensis, known as branconeta, has great potential of use in national aquaculture. In this study, it was performed experiments of food selectivity and secondary production with fingerlings of matrinxã (Brycon cephalus) and pintado-da-amazônia, a hybrid between Pseudoplatystoma corruscans and Leiarius marmoratus, using D. brasiliensis and other species of zooplankton as food. Food selectivity results were evaluated using the Ivlev selectivity index and the coefficient of food Paloheimo. For both species, the indexes of the juveniles indicated a preference by D. brasiliensis in comparison to zooplankton. Secondary production values were better when matrinxã was fed with Artemia plus artificial food; there was no significant difference to fish fed with branconeta. For pintado-da-amazônia, the highest production was obtained from branconeta treatment. So, the selectivity for D. brasiliensis is positive, once it was accepted by both species, without rejection. The results allow us to assert that the use of D. brasiliensis is suitable for the cultivation of both species. / A larvicultura é hoje o principal entrave da aqüicultura. O alimento vivo, em especial zooplanctônico, é essencial nas fases jovens de peixes. No entanto, há dificuldades em se obter biomassa suficiente. O Anostraca Dendrocephalus brasiliensis, conhecido como branconeta, tem grande potencial de utilização na aqüicultura nacional. No presente estudo, foram realizados estudos de seletividade alimentar e produção secundária com alevinos de matrinxã, Brycon cephalus, e pintado-da-amazônia, um híbrido entre Pseudoplatystoma corruscans e Leiarius marmoratus, utilizando-se D. brasiliensis e outras espécies zooplanctônicas como alimento. Os resultados de seletividade alimentar foram avaliados utilizando-se o índice de seletividade de Ivlev e o coeficiente alimentar de Paloheimo. Para as duas espécies, os índices apontaram preferência dos alevinos por D. brasiliensis frente ao zooplâncton. Os ensaios de produção secundária com matrinxã resultaram em melhor rendimento com ração e Artemia, sem diferença significativa com branconeta. Para o pintado-da-amazônia, a maior produção foi obtida com branconeta. Podemos dizer que a seletividade para D. brasiliensis é positiva, aceita por ambas as espécies, sem rejeição. Os resultados nos permitem afirmar que o uso de D. brasiliensis é apropriado no cultivo de ambas as espécies.