A new joint study reveals that fish change their behavior when they consume microplastics. They become more active and courageous and wander into risky areas where they die in large numbers.
The survival hazard caused by microplastics is also intensified by degrading coral reefs. Dying corals trigger younger fish to become more desperate in their quest to find nutrition and shelter, causing them to explore dangerous areas of the sea where predators are likely to eat them.
The study, conducted by James Cook University and other institutions, including the University of Cambridge, involved marine ecologists’ pulse feeding groups of juvenile Ambon damselfish across several tanks.
To imitate the dietary choices fish encounter in the natural environment, the researchers fed the fish a diet of brine shrimp and fine microplastics, such as polystyrene spherical beads approximately 200 microns (0.2mm) thick. The hungry fish ate the majority of microplastics.
After feeding the fish tanks differently for four days, the team tagged the fish and released them into the ocean where they originally came from—the northern area of Australia’s Great Barrier Reef. Divers freed the fish in different zones, including healthy corals and degraded ones.
The results, detailed in the Proceedings of the Royal Society B journal, showed that the groups of fish that had consumed microplastics displayed more active, daring, and risky behavior. Predators killed all of the microplastic-eating fish released in the degraded corals within three days.
According to the study’s lead author, Prof. Mark McCormick, the behavioral change and succeeding impact on their chances of survival was caused because the fish feel full when they eat plastic, but their instincts know they haven’t received enough nutrition. “Their gut is saying ‘you’re full,’ but their brain is saying ‘you need nutrition,'” McCormick added.
McCormick explained, “Like humans, when we’re very hungry, we might run across the road … as opposed to walking across safely. And for the fish who are hungry, they are more willing to take risks, and this means straying further from a shelter for food, where they are eaten by predators.”
Most of the microplastic waste in Australian waterways comes from fast food-related items, including containers and bottles, which broke down into “millions of pieces” by agitation and weather events.
The study specifically looked at juvenile fish because they’re particularly vulnerable to larger fish and are at a phase of life “where they’ve got to learn who is a predator and who is not very quickly. Anything that influences their mortality at their baby stage has quite major influences on how many fishes survive and how many can reproduce,” said McCormick.
This isn’t the first study revealing that fish change their personality when consuming plastic. Marine ecologist Louise Tosetto, from Sydney’s Macquarie University, points out that previous studies had shown chemicals from hormones and pharmaceuticals that entered waterways could alter fish behavior.
The pattern extends beyond fish: a 2026 study found microplastics in 93% of Maya octopus sampled off Mexico’s Campeche coast.
