Since this article was published, the journal Science has retracted the study on which Smithsonian.com’s reporting was based. The retraction followed an investigation by the Central Ethical Review Board in Sweden, which found serious ethical issues surrounding the study’s data and methods. A report on the investigation and the concerns by Science Magazine can be found here . We will update this post when new information is available.

Plastic pollution in the world’s oceans is a problem that has recently gained a lot of attention. Earlier this year a report from the World Economic Forum claimed there could be more plastic in the ocean than fish by 2050 and president Obama signed a ban on plastic microbeads into law late last year. Now, a new study shows that the problem may be more urgent than first thought—some baby fish choose plastic microparticles over natural food, leading to stunted growth and changes in behavior.

In a new study published in Science, researchers reared Eurasian perch eggs collected from the Baltic Sea in water with polystyrene plastic microparticles—bits smaller than 1/5 inches—similar to those found around the world. Researchers found that when the fish larvae had access to the plastic particles, they chose them over zooplankton, their natural food source.

“This is the first time an animal has been found to preferentially feed on plastic particles and is cause for concern,” Peter Eklöv, co-author of the study, says in a press release.

Matt McGrath at the BBC writes that when perch eggs were put in plastic-free water, about 96 percent of them hatched. That number decreased as the levels of plastic microparticles increased, with only 81 percent hatching in the presence of large amounts of plastic.

The fish that did hatch displayed stunted growth and were less active, especially in the presence of predators. “Fish exposed to microplastic particles ignored the smell of predators which usually evoke innate anti-predator behaviors in naïve fish,” study leader Oona Lönnstedt of Uppsala University says in the press release. In fact, the fish exposed to plastic were eaten by pike, their natural predator, four times faster than non-exposed fish.

The most worrying aspect of the study is that the fish larvae will choose to eat the plastic bits over natural foods. “They all had access to zooplankton and yet they decided to just eat plastic…It seems to be a chemical or physical cue that the plastic has, that triggers a feeding response in fish,” Lönnstedt tells McGrath. “They are basically fooled into thinking it’s a high-energy resource that they need to eat a lot of. I think of it as unhealthy fast food for teenagers, and they are just stuffing themselves.”

Eight trillion microbeads enter U.S. waters every day, writes oceanographer Carl Safina for National Geographic. But they aren’t the only problem. Up to 236,000 metric tons of microplastics enter the oceans each year, much of it created when larger pieces of plastic break down into smaller bits, reports Nsikan Akpan at PBS Newshour. The contamination can even come from washing synthetic clothing.

The next step in the study is to research the perch in their natural setting and to look at the impact of other plastic contaminants. “Now we know that polystyrene is harmful, but we also need to compare it to the other common polymers such as polyethylene and PVC,” Lönnstedt tells Akpan. “If we can target the chemical that is most harmful, at least this could hopefully be phased out of production.”