Plastic pollution in our world’s oceans might carry more dire consequences than we initially realized. According to a new study published in the journal Science, some baby fish like to chow down on plastic microparticles instead of natural foods like free-swimming zooplankton. In turn, this unnatural diet leads to stunted growth, changed behavior, and, ultimately, increased mortality rates, the BBC reports.

Researchers from Uppsala University in Sweden collected fertilized European perch eggs and embryos from the Baltic Sea. They then exposed them to different concentrations of polystyrene plastic microparticles that were smaller than one-fifth of an inch, around the size of ones floating in the sea.

When the eggs weren’t exposed to microplastics, 96 percent of them hatched. But when they were exposed to high concentrations of the plastics, the amount dropped to 81 percent. Meanwhile, the surviving fish that had been exposed to the plastic were reportedly “smaller, slower, and more stupid,” the study’s lead author, Oona Lönnstedt, told the BBC.

The fish also didn’t fare well against predators as their olfactory responses were impaired. Within 24 hours, larger fish like pike had gobbled up all the fish that had been raised with high plastic concentrations. In comparison, half the fish from clean waters survived.

Perhaps most strikingly, fish larvae that had access to the plastic particles preferred to eat them instead of zooplankton. “This is the first time an animal has been found to preferentially feed on plastic particles and is cause for concern,” Peter Eklöv, the study’s co-author, said in a press statement.

Researchers plan to research the perch in their natural setting, and study how exposure to other plastic contaminants affects development. “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 told PBS NewsHour. “If we can target the chemical that is most harmful, at least this could hopefully be phased out of production.”

While President Obama signed a ban on plastic microbeads last year, some 13 million tons of plastic reportedly flows into the sea each year, and experts say that amount will only increase. Meanwhile, according to PBS NewsHour, up to 236,000 metric tons of microplastics enter the oceans each year thanks to larger pieces of plastic breaking down into little pieces.

[h/t BBC News]