GLOUCESTER, England — The coronation of King Charles III and Camilla, the queen consort, on Saturday will involve many of the same ancient traditions that have been followed for nearly a thousand years. But some things will be new: The royal horse-drawn carriage will have air-conditioning. There will be an official coronation emoji issued by Buckingham Palace.

And, in a break with eight centuries of culinary tradition, a pie for the newly crowned monarch has been baked not with lampreys — slimy, jawless, eel-like fish with a single nostril — but with pork.

At a ceremony on Thursday in the city of Gloucester, about 100 miles northwest of London, Mayor Howard Hyman presented the pie to a representative for the king. Instead of actual lampreys, whose numbers in Britain have dwindled, the pie was decorated with two pastry lampreys. A third pastry lamprey had fallen off.

Charles’s representative, Lord-Lieutenant Edward Gillespie, accepted the pie on behalf of the king and donated it to a local charity focusing on hunger. He said that it was right that the tradition had been updated. “It would be inappropriate in these times to present lampreys to anybody,” Lord-Lieutenant Gillespie said after the ceremony. “He wouldn’t like it,” he said of the king.

While some in Gloucester lamented the change in tradition, many said it made sense to substitute pork for lamprey to reflect changing tastes.

“I’m not particularly fussed at what’s in the pie,” Alan Myatt, the town crier, said at the ceremony, which about 100 people attended at the Folk of Gloucester museum, a building constructed in the 1500s. “The most important thing is we’re commemorating and celebrating the coronation by presenting a pie.” He applauded Gloucester for coming together to carry on the tradition. “God save the king!” the crowd chanted.

The tradition of supplying the monarch with lampreys dates to at least the late 12th century, when lampreys, then plentiful in the local River Severn, were served at royal banquets and feasts, said Andrew Armstrong, an archaeologist for the Gloucester City Council. Even earlier, in 1135, King Henry I died after eating too many lampreys, according to “The History of the English People 1000-1154,” by Henry of Huntingdon, the 12th-century Anglo-Norman historian.

In 1200, King John fined the men of Gloucester 40 marks — a significant sum at the time — for failing to deliver a lamprey pie. John’s son, King Henry III, was also a big fan, and his household accounts show entries of payments for lamprey orders for him and for his wife, Eleanor, Queen of England, according to the short book “Royal Lamprey Pie of Gloucester,” published in 1953.

In the past, lampreys were marinated in red wine or salt and then roasted with spices, according to English Heritage, a charity that manages historic buildings in England. By the 18th century, the lamprey pie recipe included lemons, Mr. Armstrong said.

Queen Elizabeth II received several lamprey pies over her 70-year reign, though it was unclear whether she ever sampled any of them.

Robin Start, 96, who attended the ceremony in Gloucester on Thursday, was among a group of war veterans who delivered a 42-pound lamprey pie to Windsor Castle for Elizabeth’s coronation in 1953. Lampreys are “horrible, horrible things,” Mr. Start said, describing how they latch on to other fish and suck their blood. “Would you want to eat a fish like that?”

Charles most likely would not. A longtime environmentalist, he has spoken out against overfishing and said in a BBC interview in 2021 that he avoids meat and fish two days a week. The official dish for the coronation, according to a recipe released by Buckingham Palace, is a vegetarian quiche made of spinach, tarragon, cheese and fava beans. The king and queen are encouraging people to serve this dish at street and garden parties that will take place across Britain over the long coronation weekend, which begins on Saturday.

While lampreys have fallen out of fashion in Britain, they are still eaten in parts of Europe. The Portuguese town of Montemor-o-Velho holds an annual lamprey festival, in which gourmands descend on the city to sample lampreys, which are prepared by boiling them in their own blood.

Other culinary traditions long popular with European nobility persist today. One of the greatest delicacies in France is the ortolan, a tiny songbird whose dwindling numbers caused the government to forbid its sale. Diners consume the bird in a single mouthful while covering their heads with white napkins to hide their sin from God (and to savor the aroma). Former President François Mitterrand’s last meal before he died in 1996 included the rare and illegal ortolan.

Eating lamprey in Britain is not illegal, but catching one requires permission from the British government. The city of Gloucester used lampreys in pies for Elizabeth in 2012 and 2015, though the lampreys were imported from Canada, where they were considered pests and a threat to local trout populations.

While Gloucester officials said it was no longer appropriate to ship lampreys from Canada, given Charles’s focus on sustainability, the tradition could potentially be brought back if conservation efforts in England are successful.

“If we can restore them, they’ll no longer be an endangered species,” Mr. Armstrong said, “and we’ll be happier about putting them in pies.”