WHILE THE affluent wailed about the cost of caviar, Saufong Chen was getting churlish about the cost of shark's fin in Boston's Chinatown. Her family had an insatiable appetite for shark's fin soup, but a package of the dried needles yielding only a large bowl-and-a-half cost $32.

Deciding to trace the fin to its source, Chen passed the word around to her friends who fished off the New Hampshire coast to save any sharks they caught for her. Then one sunny afternoon, she came home to find a 150-pound monster lying on the garage floor.

That was the first of many. Now she has within easy reach plenty of shark's fin in various stages of preparation. A pint container ready for soup defrosts on the kitchen counter, a mass of near-transparent threads, some thicker and longer than the others. The overall color is faintly golden, like water with a trace of tea in it.

A whole fin dried by Chen waits in the base cabinet beneath the countertop range. It is a rigid triangle of battleship gray, about 12 by 16 inches, that had previously hung on the clothesline in the Chens' back yard. More previously it was attached to a 300-pound shark not far off Rye Harbor.

Chen held it up and traced with her finger the faint spokes that radiated from the base of the fin. "These are what you process out for the needles. Some dishes call for the connective tissue, too, but there are the strands that are dried and packaged. Last time I checked, they had gone up to $50 a pound.

Even American cooks who are devoted to Chinese food can go forever without buying shark's fin, especially when they discover how long it takes to prepare.

Chen prodded a mass of prepared needles with chopsticks to show how firm the broth is when cold. The needles moved sluggishly in the thick liquid; the firmness dissolves when heated.

"They don't taste, you know, but their special chewiness is very appealing to the Chinese. And they absorb the flavors of the other ingredients."

A shark's skin is like leather, and Chen dulled every knife in the kitchen on the shark's six fins before she discovered it was only the dorsal fin -- the big one -- that she wanted. "I seldom deal with the whole fish any more. When the commercial fishermen come in at the end of day, I meet them at the dock to see if they've caught a shark. They cut off the dorsal fin for me because the fish cooperative would only throw it away."

One retired fisherman has become interested in Chen's quest and acts as a spotter. One day he arrived at her house with all the fins and a huge tail from one shark. "Without a pot big enough, I had to cook one end [of the tail] and reverse it to cook the other," she said. The tail has some of the needles, but not enough to make the tail worthwhile. "All the fins of one pretty big shark will fill four of the pint freezer containers, and each one is just enough for my husband and me," she added.

Wearing jeans and a quilted Chinese jacket reproduced in yellow gingham, Chen, who is barely five feet tall, moves through her kitchen with crisp efficiency. She has a small batch of bean curd under way, the whey draining through the filter system of her automatic coffee maker. A Cantonese cook in New England learns to be resourceful.

Shortly after the Chinese revolution, Chen and her husband, Chien-Min, came to San Francisco to finish their medical degrees. Ultimately, they both practiced on the East Coast, but Saufong Chen retired after the birth of their third child. She transferred her surplus energies to tennis, scuba diving and food foraging that included an intensive bout of wild-mushroom identification.

"Of course, people think I'm strange with my sharks, maybe a little less now that the meat is more common in fish markets. I remember my grandmother in China cooking a slice of fresh shark. When it was done, she took her chopsticks and carefully lifted off the skin to prevent any of the tiny scales from dropping back onto the fish."

One drawer in the Chen kitchen is jammed with menus from Chinese restaurants. "I look at them when I can't decide what to have for dinner," she says. Selecting a colorful menu from Hong Kong, she opens it to the shark's fin dishes. "It's expensive there, too. The last time a cousin came for a visit, I sent her back to Hong Kong with a dried shark's fin for my mother."

Shark's fin with crabmeat, a dish sometimes seen in American Chinese restaurants, was $120 in Hong Kong, compared with an average of $26 for the other dishes. Most American restaurants list shark's fin without prices to reduce the shock.

Beneath the shark's fin section of the menu are fish lips and chicken wings with five dish descriptions, and beneath them a section for beche-de-mer.

Sea cucumber, Chen translated. "I found some when we were diving in the Caribbean, but my husband wouldn't let me bring it home. It smells terrible." Chen's family has a long history of her fishy collections: bags of sea urchins she picks while diving and the remainder of that 150-pound shark that provided the first fin. "It was delicious. First I marinated it with fresh ginger and scallion and then invented a creamed dish with parmesan cheese and white wine. But I served everyone too generously. If I'd been stingy and told them it was $5 a pound, they would have eaten it all up." Finally she made pet food to freeze and then had to get into a wet suit and tanks and escort the head out to deep water. "You can't put a thing like that in the garbage can."

None of her neighbors has caught her enthusiasm for this particular venture. Chanterelles from the surrounding meadows, yes. Shark's fin, no.Its charm is hard to translate into New England fish chowder. SHARK'S FIN NEEDLES FROM FRESH SHARK'S FIN Fins from one shark 8 thin slices ginger (about the size of a quarter), peeled 4 scallions, cut in 1-inch lengths

Cover the fins of one shark with plenty of water, bring to a boil, and simmer gently for 1 to 2 minutes, depending on the size. Drain, and when the fins are cool enough to handle, scrape off the tiny scales and as much skin as you can easily. (The Chinese, who never throw anything away, also make a soup out of the skin.)

Return the fins to the pot, cover with fresh water and simmer for 15 minutes, or just long enough to loosen the structure. The needles should be simple to extract; if they aren't, return to the boiling water until they are. The bottoms of the fins are useless. Watch very carefully and test the fins often to make sure that you don't cook them too long, or the cartilage, skin and connective tissue will collapse together and the needles will be all but impossible to get out.

Place the needles in cold water with 2 slices of ginger and 1 scallion. Bring to a boil, drain and repeat with more ginger and scallion. Continue to simmer gently for 2 or 3 hours, changing the water 2 more times. Watch carefully toward the end. Too much cooking will dissolve them, but a needle should be easy to cut. Drain, cover with fresh cold water and store in the refrigerator or freezer until ready to use. SAUFONG CHEN'S SHARK'S FIN SOUP (Serves 2 Chens, 3 or 4 others)

"When I was little in China, we were very poor. Our maid (somebody was always poorer) would buy the chickens from the restaurants after they had made their broth, Chinese-style. The meat was still good. I save chicken necks and pork bones in the freezer until I have enough for a rich broth." 3 cups rich chicken broth 1 pint prepared shark's fin, prepared at home or bought from a Chinese grocery 2 tablespoons dry sherry Ground pepper to taste 1 tablespoon cornstarch, dissolved in 2 tablespoons cold broth 2 eggs, slightly beaten (optional) 2 tablespoons shredded Virginia ham 1 scallion, shredded 1/2 teaspoon sesame oil

In a saucepan, bring broth to a boil. Rinse prepared shark's fin and add to the broth with dry sherry and pepper. Simmer 10 minutes. Add cornstarch and bring back to a boil, stirring constantly. (Sometimes in China so much shark's fin is used that the extra thickening is unnecessary.) If you are including the eggs, pour them in a thin stream into the soup and stir for 30 seconds. Transfer soup to a warm serving bowl and sprinkle with ham, scallion and sesame oil. STEAMED FISH SLICE (6 to 8 servings) 2 thin slices fresh ginger, peeled 1 scallion, shredded 2 tablespoons dry sherry 3 tablespoons peanut oil 1 slice large fish, halibut or shark (about 2 to 2 1/1 pounds) 2 scallions cut in 1/2-inch pieces 1/2 teaspoon sesame oil

Shread ginger, bruising it with the back of the cleaver to release its fragrance. Combine with shredded scallion, sherry and 1 tablespoon of oil in a shallow bowl. Turn the fish slice in this mixture to coat both sides. Marinate 30 minutes, turning once or twice. Transfer to a heat-proof plate and set in a Chinese steamer, or a steamer you have fashioned from a large covered casserole with 1 or 2 inches of boiling water and a trivet to hold the dish above it. Cook the fish slice briskly for 8 to 10 minutes, or just until the fish is opaque. Remove the skin carefully and pour off the liquid that has collected in the dish. Sprinkle fish with scallion. Have ready 2 tablespoons peanut oil and the sesame-oil that have been heated in a small saucepan. Just before the oils smoke, pour over the fish and serve immediately.