Fish Now Think Plastic Is Food

Pollution is so prevalent in water bodies now that fish can't help but eat it.

Photo: Adult perch in the Baltic Sea. Credit: Peter Eklöv Tiny bits of plastic are so prevalent in oceans and other bodies of water that fish now see them as food, reports a new study. Ingesting the particles can lead to odd-behaving mutant fish that often die young.

The findings, published in the journal Science, strengthen prior research calling for a reduction of plastic waste and a ban of microbeads in personal care products. Microbeads can be found in everything from toothpaste to facial cleansers, and are so small that they pass unfiltered through sewage treatment plants.

"Microplastic beads have a chemical or visual cue that triggers a feeding response in fish," Marine biologist Oona Lönnstedt of Uppsala University told Discovery News. "Naïve larvae that come across these plastic particles believe that they are a resource that they need to ingest large amounts of."

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She added, "If microplastic particles give off a chemical signature resembling the smell of a food resource that normally triggers an evolutionary response to feed, then plastic is circumventing (any possible) protective mechanism" that could deter fish from eating literal garbage.

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For the study, Lönnstedt and her team collected fertilized European perch eggs and embryos from the Baltic Sea. They exposed the specimens to varying concentrations of polystyrene microplastics, including very high concentrations comparable to those found in nature. Such bits measure about .2 inches or less.

Many perch larvae preferred eating the tiny plastic pieces, and those that did often exhibited stunted growth and very sluggish behavior.

When the perch were placed with a natural predator, pike, they ignored the smell of these predators and were caught and eaten more than four times quicker than perch that did not consume the plastic. By eating perch that previously consumed plastics, the pike also wound up ingesting plastic. This can go on up the food chain in the wild. All of the perch exposed to microplastic particles were dead within 48 hours.

Lönnstedt and her team suspect that ingestion of plastic could chemically affect the fish in one of two ways.

"Either the plastic particles exude toxic chemicals that interfere with the central nervous system of fish during development -- effectively altering their behaviors -- or the fish are lacking so much energy, since they have filled their stomachs only with plastic, that they simply have no energy to be active and to swim around," she said.

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Prior research found more than 100,000 small plastic bits can occur in about 264 gallons of water in nature. In the Northeast Pacific Ocean, approximately 30,400 plastic particles are found in just over a third of a gallon of water.

The waste particles reach oceans via waterways and lakes. In smaller bodies of water, such as shallow coastal areas critical to many animal populations, the plastics can accumulate in much higher concentrations.

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Boris Worm, a marine research ecologist at Dalhousie University, has also studied how plastics impact wildlife.

"Birds ingest a wide variety of plastic items, including disposable lighters, toothbrushes, tampon applicators, light sticks used in longline fishing, and broken shards of larger plastic debris," he told Discovery News. "They mistake them for food when skimming surface waters, searching for visible particles."

It would be next to impossible to fully remove the tiniest plastic pieces from oceans and more, so the scientists believe that prevention strategies are vital to at least stop the spread of more waste material.

"What we are doing now," Lönnstedt said, "is testing different types of microplastic polymers to see which ones are the most toxic. If we can identify the microplastic polymers that have the most harmful effects on wildlife than these hopefully can be phased out of production."