“One possibility is that it could just move through the digestive system and come out the other end without causing any harm," Hoellein said. "But we don’t know how long particles stay in their gut. So I had a student do a project where she fed round gobies these acrylic fibers in fish food. She tracked how long it took to go in to out. It was pretty fast — faster than I thought. Within a couple days, plastics moved through. Not much was retained in their stomachs permanently.”