The availability of polyunsaturated fatty acids (PUFAs) in food items influences the fitness of organisms at higher trophic levels. Omega 3 and omega 6 fatty acids are essential compounds that cannot be synthesised de novo in these animals. PUFAS are needed to adjust membrane fluidity, used as building blocks for hormone synthesis and serve as sources for high energetic storage fuel reserves. Especially the omega 3 PUFA eicosapentaenoic acid (EPA) is an important molecule, as it is a limiting nutritional component for growth and reproduction in numerous marine and freshwater zooplankton species. With our transcriptomic study in Daphnia magna we address the transcriptomic network behind the metabolism and conversion that are connected to physiological EPA limitation.