A Winnipeg woman got more than she bargained for on a recent shopping trip.

Dana Todd planned on making cod for dinner.

But that wasn't the only item in the package.

There was a something on the fish. And it was still alive!

"I realized it was a worm," said Todd. "Gross is a good word!"

University of Winnipeg biology professor Scott Forbes says the worm is a parasite called a nematode.

"They're fairly common in fish, and cod in particular," said Forbes.

The cod acquire them from the small crustaceans they eat. According to Forbes, the parasites then hatch inside the fish and start to move.

"It's kind of like Sigourney Weaver in Alien," said Forbes. "They burst out of the copepod, and then they burrow their way through the gut, and make their way into the flesh of the fish."

The worms don't kill the cod and according to food safety expert Rick Holley, they're unlikely to cause problems in people.

"Part of the reason for that is that they're killed by normal cooking," said Holley.

The Canadian Food Inspection Agency says nematodes in fish is a natural phenomenon not indicative of mishandling or spoilage and cannot be prevented.

The CFIA has inspection procedures and rules for fish.

It allows one parasite per kilo of fish.

Any more and the sample will be rejected.