LimnoPlast ITN (Marie Skłodowska-Curie Actions, Horizon2020) addresses the issue of microplastic pollution in the environment from an interdisciplinary environmental, technical and social point of view to find new innovative solutions together. Whereas most research on microplastics is conducted on marine ecosystems, LimnoPlast focuses on freshwater systems. This contribution to the holistic project is the investigation of acute and chronic toxicity of microplastics in freshwater fish species. We will design studies that differentiate between polymer microparticles and the chemicals inherent to these materials. Freshwater fish species (perch, stickleback, and brown or rainbow trout) are selected by their ecological relevance and establishment as model organisms with available knowledge on their physiology and genetics. Different life stages, from larvae to adult, and fish cell cultures will be studied. In addition, we will address impacts in fish species exhibiting different feeding strategies. Both aspects are supposed to give a broader spectrum of real life conditions. The toxicity of microplastic polymers will be assessed with several endpoints on life cycle parameters (e.g. growth, reproduction), metabolism (including proteomics), general stress response and behavior. The toxicity of conventional and biodegradable microplastic polymers and their leachates will be tested in comparison.