The chronic toxicity of MP in fish will be investigated with a focus on metabolism and general stress in laboratory experiments. Several ecologically relevant fish species will be used, all of which have well-known physiology and genetics. ESR12 will assess the toxicity of biodegradable and conventional MP polymers. The endpoints will focus on life cycle parameters, metabolism, stress, and behaviour endpoints. Proteomics will be considered to gain further insights into altered metabolism or mechanisms. Fish species with different feeding strategies and also different life-stages will be considered for the study of MP uptake to obtain a picture of species sensitivities and vulnerabilities under real conditions. Biodegradable and conventional MP polymers will be compared. In addition, the toxicity of leachates from conventional and biodegradable polymers will be tested.