The deleterious effects of plastic ingestion are widely reported, but we are still understanding the factors that make organisms more susceptible to plastic ingestion. Understanding the causes of plastic ingestion is fundamental if we are to assess the risk of populations and species to this global threat. In this context, our aim is to assess which factors influence the ingestion of plastic by animals. Through an experimental approach (using zebrafish (Danio rerio) as a model species) we will test three hypotheses about the causes of plastic ingestion: i) the greater the availability of plastic in the environment, the greater its ingestion; ii) organisms that are experiencing nutritional stress will be more prone to ingesting plastic; and, iii) the greater similarity in a characteristic of plastic to a food item will cause greater ingestion of this plastic.