SEOUL (REUTERS) - Ms Lee Gui Ja, a South Korean housewife, will not be preparing traditional pollack pancakes for Thanksgiving celebrations this week due to worries the fish may be contaminated by radiation from Japan's leaking Fukushima nuclear reactor.

Japan has sought to reassure the international community that the facility is under control but South Korea has banned fishery imports from the affected region.

Even though the vast majority of frozen pollack comes to South Korea from Russian waters, sales of fish have plunged before South Koreans mark the main annual holiday this week.

Japanese officials have been lobbying - without success - to have the ban lifted.

"I watched the news and will not put frozen pollack pancakes on the table this year, although they have always been there," Ms Lee said at a fish market in central Seoul.

"Maybe I will prepare mung bean or beef pancakes instead."

Pancakes are one of the dishes traditionally placed on the table to honour ancestors and then shared by the family once the ritual is complete.

"Sales are more than 60 percent down and stocks are all piled up," said Park Sun Young, who sells frozen pollack. "We keep telling people that these are not Japanese fish but people don't believe it."

Kim Heon Tae, an official at the Korea Overseas Fisheries Association, told Reuters that 98 percent of imported frozen pollack comes from Russian waters.

Even so, Hansung Enterprise, a South Korean fisheries company, said sales of frozen pollack fell 42.5 percent between January and August from a year earlier.

"This is the toughest time I have ever seen," said Ms Park as she sliced pollack that no one appeared to want. Ms Park runs her parents' shop, which has been in business for 20 years.

Scientists have played down the risk of contamination, to no avail.

"Frozen pollack comes from different waters so we don't have to worry about it at all," said Kune Suh, a nuclear engineering professor at Seoul National University. "But public sentiment has already swung."