As you bite down into a delicious piece of fish, you probably don’t think about what the fish itself ate — but perhaps you should. More than 50 species of fish have been found to consume plastic trash at sea. This is bad news, not only for fish but potentially also for humans who rely on fish for sustenance.

Fish don’t usually die as a direct result of feeding on the enormous quantities of plastic trashfloating in the oceans. But that doesn’t mean it’s not harmful for them. Some negative effects that scientists have discovered when fish consume plastic include reduced activity rates and weakened schooling behavior, as well as compromised liver function.

Most distressingly for people, toxic compounds that are associated with plastic transfer to and bioaccumulate in fish tissues. This is troubling because these substances could further bio­accumulate in people who consume fish that have eaten plastic. Numerous species sold for human consumption, including mackerel, striped bass and Pacific oysters, have been found with these toxic plastics in their stomachs.

It is well known that plastic trash poses a serious threat to marine animals, but we are still trying to understand why animals eat it. Typically, research has concluded that marine animals visually mistake plastic for food.

While this may be true, the full story is probably more complex. For example, colleagues at the University of California at Davis and I showed in a recent study that plastic debris may smell attractive to marine organisms. That study focused on seabirds, but now my co-authors and I have found that plastic trash has a similar effect on anchovies — a critical part of ocean food chains.

Olfaction (smell) is a very important sense for marine animals, including fish. Sharks can smell minute quantities of blood over long distances, which helps them find prey. And scientists believe that salmon’s sense of smell helps them navigate up rivers to spawn in the specific tributaries where they were born. Fish may use their sense of smell in behavioral contexts including mating, homing, migrating and foraging.