Monitoring studies have revealed the presence of large numbers of natural as well as anthropogenic microfibers, plastic and non-plastic, in environmental samples. However, the interaction of organisms with microfibers is largely understudied. This is the first ecotoxicological study that compares short-term feeding of anthropogenic plastic and non-plastic microfibers on a consumer (leaf-shredding detritivores) species. The freshwater amphipod Gammarus duebeni was selected for this study as it is a model ecotoxicological species. After a 96-hour exposure, 58.3% and 41.7% of the amphipods contained cellulose or polyester fibers in their digestive tracts, respectively. Microfiber ingestion was analysed per polymers in presence or absence of food. The G. duebeni group exposed to 'polyester fibers in presence of food' accumulated highest numbers of microfibers in their digestive tracts (5.2 ± 3.4 MFs/amphipod) followed by those exposed to 'cellulose in presence of food' (2.5 ± 0.9 MFs/amphipod). A significantly (Three-way ANOVA, p-value <0.05) higher number of microfibers was found in the midgut-hindgut (posterior) sections, compared to the foregut (anterior) section. Microfiber uptake had no apparent short-term negative effect on amphipod survival at 96 h. Yet, as amphipods are both predators and prey, and therefore are key species in the aquatic food web, the rapid accumulation of anthropogenic microfibers in their digestive system has potentially further ecological implications. Future studies need to consider the possible transfer of ingested anthropogenic microfibers to higher trophic levels in freshwater communities. Copyright © 2020 Elsevier B.V. All rights reserved.