The bloom of toxic red tide that closed shellfish beds from Maine to Nantucket spared the Vineyard this week, fading off the eastern shore of Chappaquiddick into Nantucket Sound.

Shellfish samples taken on Monday in Oak Bluffs, Menemsha and Edgartown came back clean in two separate rounds of testing, so no ponds were closed on the Vineyard, despite vague reports in the mainland print press of closures in Edgartown.

The conch fishery in Nantucket Sound has been closed.

Believed to be the worst in the history of New England, the red tide bloom moved rapidly down from Maine last week, forcing state-mandated closures of shellfish beds in Chatham, all of Cape Cod Bay, parts of Buzzard's Bay and Nantucket. Scientists believe the bloom was caused by an unusually cold and wet winter and spring. Red tide only affects bivalves, including clams, oysters, quahaugs, mussels and conch, and is harmful to people who eat them. Lobster, shrimp and finfish are not affected by it.

Fish sellers on the Vineyard said yesterday that the demand for shellfish has plummeted as they now battle a perception problem in the market in the wake of the massive closures in the region.

"By now I should have sold a thousand oysters. In the last five days I have sold 300," said Jack Blake, an Edgartown oyster farmer.

Last weekend, Mr. Blake harvested 5,000 oysters from Katama Bay and placed them in a refrigerator truck, thinking that a closure was imminent. He said he will put his oysters back in the water today. "My oysters are safe to eat. God, they are delicious right now and yet I think people are afraid," said Mr. Blake, who sells his oysters to Vineyard and Nantucket markets.

Louis Larsen, owner of the Net Result fish market in Vineyard Haven, said his counter staff has been handing customers a computer printout from the state Division of Marine Fisheries web site showing the Vineyard is clear. "The impact has been huge," Mr. Larsen said. "People are still buying shellfish but we are not getting the volume," he added.

Mr. Larsen's sister Betsy Larsen, who runs Larsen's Fish Market in Menemsha, agreed.

Ms. Larsen said: "Every third or fourth customer asks about it. I am still eating them. I would say the raw bar has slowed down. Generally business has slowed this week," she said.

"I want to assure the public that if they go into a restaurant and a fish market and order shellfish, what they are getting is safe," said Jim Fair, a former assistant director of the state Division of Marine Fisheries.

Even in the areas where there are shellfish closures, Mr. Fair said there has been no illness associated with the tide. Infected shellfish are not making it to market.

Mr. Fair reiterated last night that shellfish in Martha's Vineyard coastal ponds and along the shoreline are safe and the prognosis is good. The only shellfish affected in this area are conch.

Rob Garrison, manager of the Wampanoag Tribe's solar shellfish hatchery, said yesterday so far his orders for Tomahawk oysters are at the same level as the week before. Mr. Garrison said he and many others thought that demand for shellfish would increase if the Vineyard stayed clean.

"Everyone was thinking that the demand for oysters would increase but I think the demand is going down because of the news and people are shying away from shellfish," Mr. Garrison said. "So we aren't seeing any increase, but neither are we seeing any decrease."

Mr. Garrison said he will ship out 14,000 oysters this week. Some were shipped on Wednesday and the rest will go out today. His customers are in Boston, New York city and Washington, D.C.

"I had restaurant people tell me they weren't going to sell shellfish from the Vineyard," Mr. Garrison said. "And it is all based on the wrong information."

Mike Syslo, director of the state lobster hatchery in Oak Bluffs, went out on Monday and collected samples for state testing. On Wednesday night Mr. Syslo said the results came back from the state lab in Gloucester. All the Vineyard samples came in well under the threshold of 80 micrograms of biotoxin per 100 milligrams of shellfish tissue, he said.

"Hopefully this is the line drawn in the sand," Mr. Syslo said. "Time will tell."

Warm weather and a prevailing southwest wind are expected to help push the red tide further offshore and away from the Vineyard.

Today the Woods Hole Oceanographic Institution's 60-foot research vessel Tioga will be out sampling the waters in Buzzards Bay and in Vineyard and Nantucket Sounds. High levels of red tide were recorded at the Cape Cod Canal entrance to Buzzards Bay.

"The good news is that we haven't seen the tide spreading yet," said Mr. Fair. "We don't know what it is doing offshore. There has been no sampling in federal waters."

On the north side of the Cape the tide appears to be getting stronger, he said. "The Western Cape Cod Bay area results are getting higher. The bloom is not subsiding there," Mr. Fair said. The algae Alexandrium fundyense does not thrive in water temperatures above 50 degrees.

"There is some evidence that the organism is starting to go into the next phase. That is good and bad news. The good news is that the bloom will end. The bad news is that it starts to form the cysts which then settle to the bottom, so it will establish a reservoir for forming again next year," Mr. Fair said.

The last time Alexandrium algae bloomed was in 1972. In the fall of that year the entire state was closed to shellfishing. Then the algae had a different name, and was called Gonyaulax tamarensis. "When it started we had no idea what was happening. We didn't have the monitoring program we have now. It was a very unusual circumstance and we weren't ready for it," Mr. Fair said. "We had a lot of sick people," he said. It is very different today. "We can see it coming before it becomes a problem."

Mr. Fair said his priority is to sample areas where there is concern about red tide spreading. He said there is no immediate plan to sample Vineyard waters soon, since it is clear. "Eventually we will go back to the areas that have been closed," Mr. Fair said.

"Ideally what will happen is that southwest wind that we usually get will push the entire mass out to sea," he added.

This week a state congressional delegation approached Gov. Mitt Romney to ask for economic relief for Cape Cod shellfishermen affected by the red tide closures. It is estimated that there are 1,700 shellfishermen out of work on the Cape.

Late yesterday the National Oceanic and Atmospheric Administration (NOAA) announced an award of $12,000 to WHOI to support the emergency response efforts to the red tide. Led by its red tide expert Donald M. Anderson, the marine institution in Woods Hole is the national research center for red tide.