Anyone who has ever owned an aquarium knows the story: You pick out an expensive fish at the pet store, an employee scoops it out for you with a little net, and you carry it home in a plastic bag. The fish looks healthy, and you do everything right to keep it that way. It should live for years. But a few days after you get home, you find the fish floating on its side at the top of your tank.

Questions and doubt fill your brain. Did you feed it the wrong food? Was it too hot? Did it not get enough oxygen? Did you stress it out in some way?

Well, here’s a shocker: It probably wasn’t you. It just may have been that plastic bag you carried it home from the store in—or one just like it.

You see, almost every fish sold in the aquarium trade is wild-caught, usually from along coral reefs in countries such as Indonesia, Australia, or Fiji. After the fish are captured, they are placed in little plastic bags for transport to the U.S. or other markets.

According to new research published in the journal Chemosphere, those bags are miniature death traps. Even though the bags meet FDA food-grade specifications—they’re the same kind that you see in the supermarket bread aisle—they still leach a chemical called nonylphenol into the seawater inside the bag and then into the fish.

It doesn’t take much time for the water to turn toxic. The researchers found that the seawater contained in the bags ended up having nonylphenol concentrations of 163 parts per billion in less than 48 hours. That’s 25 times higher than the EPA considers dangerous to marine organisms.

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It definitely is dangerous. The study found that as many as 90 percent of all fish that go through the aquarium trade die, either before they make it to the store or within a few weeks of being purchased. The death rates, as well as the speed of mortality, varied according to which companies manufactured the bag. Sixty percent of the fish stored in one manufacturer’s bags routinely died in less than 48 hours.

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So Why Should You Care? “The aquarium trade really is a threat to coral reef conservation,” said Craig Downs, a coauthor of the paper and the executive director of Haereticus Environmental Laboratory, a nonprofit lab in Clifford, Virginia. “The more fish and coral that die from transport, the more that they have to take from the reef to meet demand.”

Downs said the new research also suggests that marine plastics pose previously unrecognized threats to fish and other organisms. Nonylphenol is an endocrine disruptor, and it may be leaching out of floating plastic bags or other plastic particles. That means it could be entering fish in the wild—or even the humans who eat the fish.

Downs said he hopes people will demand accountability from the aquarium trade to protect the decorative fish that they love. “The aquarium industry needs to either find alternatives to plastic bags or set criteria for the manufacturing of plastic bags so they have very low toxicity,” he said.

Until then, he encourages fish enthusiasts to ask for animals that are bred in captivity. “There is an effort within the industry to push ‘cultured’ organisms,” he said. The demand still far outstrips the supply, however, with many companies having six- to eight-month waiting lists.

Still, waiting six months for the perfect fish is a lot better than paying $300 for one you’ll end up flushing down the toilet in a week. It’s also a heck of a lot better than the risk of a species disappearing from the wild forever because of over-collection or plastic poisoning.