Andrew Calisterio opened a package of fresh cod, eager to whip up some ceviche for dinner. But an uninvited guest quickly foiled those plans: a small, thin, wriggling worm found inside the packaging.

Calisterio, a popular bartender at a Sacramento, California, gastropub, filmed a few seconds of the writhing invertebrate on his iPhone and posted the video to his Facebook page. A slew of grossed-out comments followed, along the likes of:

"Yaaarrrggh!" … "OMG EWWWW!!!!" … "I think I may have to eliminate fish now. Forever."

But some of Calisterio’s colleagues in the restaurant industry made a counterpoint: Worms in fresh cod and other whitefish are actually fairly common, and the fish is fine if cooked thoroughly.

That’s to say, if you’ve ever taken down a basket of fish and chips, chances are you’ve ingested some deep-fried worm parts at some point.

"A lot of ‘Taco Tuesdays’ also use cod," Calisterio said. "It’s fun to be romantic and say, ‘I’m eating fresh,’ but there’s a little reality check when you see a worm in your food."

Similar instances of worms found in fresh fish have emerged on social media. One video taken of a worm found in a package of cod purchased at a South Carolina Costco was shared more than 349,000 times on Facebook. By comparison, Calisterio’s video was shared just seven times on Facebook but drew more than 40 comments, ranging from the snarky to the sickened and the sensible.

Calisterio purchased the fish at a Safeway, where he recalls the fish monger saying the fresh cod was an especially good deal and would be perfect for Calisterio’s ceviche.

"I got home, cracked open the freshly wrapped cod and started deboning," Calisterio said. "Then I see the worm. It’s not in the fish. It’s next to it in the packaging – and following my finger."

The worm found in Calisterio’s cod was most likely an anisakid nematode, a larval roundworm that’s associated with cod, halibut and other bottom feeders. According to the U.S. Food and Drug Administration, infections caused by ingesting these worms through raw or undercooked seafood are rare, fewer than 10 cases annually. However, the FDA reports that many more cases may go undetected.

In most cases, swallowing this worm won’t cause much more than temporary stomach discomfort. These worms are usually eliminated from the digestive tract within three weeks. In the most severe scenario, the parasite or its remnants would have to be removed via surgery.

The prevalence of these worms is why you never see cod sashimi offered at a sushi bar. Cod is meant to be cooked thoroughly to kill any critters that might still be clinging to the fish. The U.S. Department of Health & Human Services recommends an internal temperature of 145 degrees Fahrenheit when cooking such seafood.

Basically, the worm in the cod isn’t much different than the occasional bug found in that haul of farmers-market fruit. Many fish processors try to ferret out the worms by examining the seafood under lights, but sometimes the creatures still make it to market.

"This is a rare occurrence at Safeway," said Keith Turner, a spokesperson for Safeway, in a statement. "If a customer has a concern with fish or any other product, they should return the item for a full refund."

And that’s what happened to Calisterio once he contacted the midtown Safeway. Calisterio says they initially offered him a replacement of fresh cod, but he opted to just get his eight bucks back. Dinner plans for homemade ceviche were scrapped, and Calisterio chose frozen shrimp instead.

Even though Calisterio ultimately learned the worm was fairly benign, the whole experience was a buzz kill.

"I’m going to be a lot more cautious," Calisterio said. "It will take some convincing for me to buy cod any time soon."