In the hectic countdown to Christmas, it’s well-known that stores, shopping malls and groceries are going to be thronged with people doing their final rounds before the holiday.

A seafood market doesn’t immediately jump to mind as someplace that would have shoulder-to-shoulder crowds. But that’s exactly what greeted anyone walking through the front door of Harbor Fish Market on Custom House Wharf in Portland on Sunday morning.

The weeks leading up to Christmas and New Year’s are the busiest period of the year at the store, said owner Mike Alfiero.

“When this time of year comes, people go on a buying frenzy,” Alfiero said.

Some of the demand is linked to traditions such as like the multi-course fish feast his Italian-American family enjoyed when he was growing up, Alfiero said. For others, it is an excuse to indulge in some special holiday foods.

“It is the one time of year when people, as much as they can afford it, drop their guards on how much they are willing to spend,” he said.

The store was so busy Sunday morning that a policeman and employee dressed in a Santa costume were directing traffic into parking spaces on the narrow wharf.

Inside, customers crowded around glass cases lined with ice, succulent cuts of fish and piles of oysters, clams, mussels and shrimp. Employees scooped live lobsters from huge, gurgling saltwater tanks.

A line of about 20 people, plastic bags weighted down with their selections, waited to check out at the counter. The lengthy line barely changed, as a steady stream of customers jockeyed for standing space on the damp concrete floors. Workers hustled to weigh purchases and lugged ice and fish from the back warehouse into the front.

Monday, Christmas Eve, will likely be even busier, with customers lining up before the store opens at 7 a.m. The market brings on about 10 temporary employees to deal with the rush. Alfiero could not estimate how much fish the market sells during the holiday season, but the store does the same sales in the two weeks around Christmas and New Year’s as it does during a busy month in the summer.

Chris Anderson, 37, was picking out three dozen oysters and two dozen clams for a holiday dinner. His sister-in-law Chelsea Obourn was bringing some home with her to Rochester, New York.

Christmas seafood isn’t really a tradition in her family, but her grandfather has a soft spot for oysters, Obourn said. Most of the oyster selections were from Maine, but she made sure to get some from Wellfleet, Massachusetts, near where he owned a beach home.

“My grandpa loves it,” she said. “He has had some health problems, but it is one of the only things he has an appetite for anymore.”

It is not unusual to have a lot of out-of-state customers over the holidays, Alfiero said. Some people make the trip to Portland year after year, bringing generations to select the premium fresh seafood the market is known for.

“A lot of people see coming here and shopping in the store as a tradition,” he said.

The weathered row of buildings along Custom House Wharf has been a fish market since the late 1800s. The Alfiero family bought the business in 1966 and Mike Alfiero now runs it with his brother Nick.

Some customers are coming in to prepare for the Feast of the Seven Fishes, a holiday tradition for Italian-American families like his own, Alfiero said. The idea is to serve seven different seafood dishes, or seafood prepared seven different ways, for Christmas dinner. The precise origin of the tradition is unclear, but it likely developed among Italian immigrant families in the U.S. It is rooted in the Roman Catholic custom of not eating meat before important holidays.

For Alfiero’s family, Christmas meant dishes such as stuffed squid, fried eels, baccalà – salt cod – salad, fish cakes and anchovy pasta. These days, the menu for his big family dinner skews more to meat and less to the sea, Alfiero said.

Heritage aside, seafood keeps growing in popularity and around the winter holidays, demand reaches a fever pitch.

“For Christmas, it is high volume on everything – there isn’t anything we are not selling a lot of,” Alfiero said.